Photochromic Materials E-Book
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- Herausgeber: Wiley-VCH
- Kategorie: Fachliteratur
- Sprache: Englisch
Summarizing all the latest trends and recent topics in one handy volume, this book covers everything needed for a solid understanding of photochromic materials. Following a general introduction to organic photochromic materials, the authors move on to discuss not only the underlying theory but also the properties of such materials. After a selection of pplications, they look at the latest achievements in traditional solution-phase applications, including photochromic-based molecular logic operations and memory, optically modulated supramolecular system and sensors, as well as light-tunable chemical reactions. The book then describes the hotspot areas of photo-switchable surfaces and nanomaterials, photochromic-based luminescence/electronic devices and bulk materials together with light-regulated biological and bio-chemical systems. The authors conclude with a focus on current industrial applications and the future outlook for these materials.
Written with both senior researchers and entrants to the field in mind.
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Table of Contents
Title Page
Copyright
List of Contributors
Chapter 1: Introduction: Organic Photochromic Molecules
1.1 Photochromic Systems
1.2 Organic Photochromic Molecules: Main Families
1.3 Molecular Design to Improve the Performance
1.4 Conclusion
Irradiation at a Specific Wavelength: Isosbestic Point
Case A: When the Thermal Back-Reaction is Negligible Compared to the Photochemical Reaction (Typically P-type)
Case B: When the Thermal Back-Reaction is More Efficient than the Photochemical
B → A
Reaction (Typically T ype)
References
Chapter 2: Photochromic Transitional Metal Complexes for Photosensitization
2.1 Introduction
2.2 Photosensitization of Stilbene- and Azo-Containing Ligands
2.3 Photosensitization of Spirooxazine-Containing Ligands
2.4 Photosensitization of Diarylethene-Containing Ligands
2.5 Photosensitization of Photochromic N^C-Chelate Organoboranes
2.6 Conclusion
References
Chapter 3: Multi-addressable Photochromic Materials
3.1 Molecular Logic Gates
3.2 Data Storage and Molecular Memory
3.3 Gated Photochromores
References
Chapter 4: Photoswitchable Supramolecular Systems
4.1 Introduction
4.2 Photoreversible Amphiphilic Systems
4.3 Photoswitchable Host–Guest Systems
4.4 Photochromic Metal Complexes and Sensors
4.5 Other Light-Modulated Supramolecular Interactions
4.6 Conclusions and Outlook
References
Chapter 5: Light-Gated Chemical Reactions and Catalytic Processes
5.1 Introduction
5.2 General Design Considerations
5.3 Photoswitchable Stoichiometric Processes
5.4 Photoswitchable Catalytic Processes
5.5 Outlook
References
Chapter 6: Surface and Interfacial Photoswitches
6.1 Photochromic SAMs
6.2 Photoregulated Nanoparticles
6.3 Photocontrolled Surface Conductance
References
Chapter 7: Hybrid Organic/Photochromic Approaches to Generate Multifunctional Materials, Interfaces, and Devices
7.1 Introduction
7.2 Tuning the Polaronic Transport in Organic Semiconductors by Means of Photochromic Molecules
7.3 Photoresponsive Dielectric Interfaces and Bulk
7.4 Conclusions and Future Outlooks
Acknowledgments
References
Chapter 8: Photochromic Bulk Materials
8.1 Photochromic Polymers
8.2 Single-Crystalline Photoswitches
8.3 Photochromic Liquid Crystals
8.4 Photochromic Gels
References
Chapter 9: Photochromic Materials in Biochemistry
9.1 Introduction
9.2 Reversible Photochemical Switching of Biomaterial Function
9.3 General Design Strategies and Considerations
9.4 Selected Examples
9.5 Summary
References
Chapter 10: Industrial Applications and Perspectives
10.1 Industrialization and Commercialization of Organic Photochromic Materials
10.2 Perspectives for Organic Photochromic Materials
References
Index
End User License Agreement
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Guide
Table of Contents
Begin Reading
List of Illustrations
Chapter 1: Introduction: Organic Photochromic Molecules
Figure 1.1 Photochromic lenses and clothes: contributions to comfort and to fashion [4].
Figure 1.2 Rewritable optical memory medium based on photochromic compounds: (a) general structure of the recording medium [6d] and (b) alphabet letters recorded on the different layers [6b].
Figure 1.3 Super-resolution image of HeLa cells expressing keratin19 rsCherryRev1.4 by wide-field conventional microscopy (a) and by RESOLFT microscopy (b) (scale bar = 5 µm) and the corresponding magnifications of the highlighted area (c and d, scale bar = 500 nm). Line profiles (e) across the region between the arrows marked in (c) (full line) and (d) (dashed line) [7].
Figure 1.4 (a) Concomitant color and solubility changes of a photochromic solution [13a] and (b) color and shape changes of a photochromic crystal [14c].
Figure 1.5 Photochromism: a two-way light-induced reaction between two molecules A and B. (a) Potential energy diagram and (b) the related schematic absorption spectra.
Figure 1.6 Photochromic reaction of tetracene.
Figure 1.7 Examples of photochromic compounds deriving from phenylhydrazine, phenylosazone, and naphthalenone.
Figure 1.8 Solid-state photochromic reaction of 2,3,4,4-tetrachloronaphthalen-1-(4
H
)-one.
Figure 1.9 Photochromic reactions of semicarbazones, bianthrone, and spiropyrans.
Figure 1.10 General formula and reaction schemes for azines and thioindigoides.
Figure 1.11 Number of publications on photochromism.
Figure 1.12 Photoreaction (phototautomerism) of anils: the enol to keto reaction.
Figure 1.13 Photochromism of anils: schematic diagram illustrating the UV and visible light-induced reactions, and the excited-state intramolecular proton transfer (ESIPT).
Figure 1.14 Synthesis of anils: basic method by condensation of salicylaldehyde and aniline derivatives.
Figure 1.15 Photochromism of dinitrobenzylpyridine (DNBP) between the CH and NH forms, involving the OH species.
Figure 1.16
Trans–cis
isomerization of stilbene and azobenzene.
Figure 1.17 Crossed surface relief grating obtained by 2D photopatterning on a thin film of azobenzene derivative: (a) atomic force microscope (AFM) topographic image, (b, c) one- and two-photon transmission images with dark areas corresponding to hills [54b].
Figure 1.18 Synthesis scheme of the Mills reaction used to obtain azobenzenes.
Figure 1.19 Photochromism of hexaarylbiimidazole (HABI) between the triphenylimidazolyl dimer (TPID) and the triphenylimidazolyl radical (TPIR) pair.
Figure 1.20 Basic synthesis scheme of HABI.
Figure 1.21 Photoisomerization of spiropyrans between the closed and open merocyanine (MC) forms. Resonant zwitterionic and quinonic forms of MC.
Figure 1.22 Orbital interactions depicting the interactions between the nonbonding and the antibonding orbitals in spiropyrans around the spiro carbon, leading to the weakening of the C–O bond.
Figure 1.23 Common synthesis scheme for indoline-based spiropyrans and spirooxazines, involving the Fischer's base.
Figure 1.24 Photochromism of chromenes.
Figure 1.25 General structure of fulgides and fulgimides. The photochromic reaction is written for an example of furylfulgide, Aberchrome 540.
Figure 1.26 Typical reaction scheme of the photochromism of diarylethene when the aryl group is a heterocycle (e.g., X = O, N, S).
Figure 1.27 Photocyclization reaction of
cis
-stilbene and the subsequent oxidation to phenanthrene.
Figure 1.28 Typical examples of rings including the ethene bridge in diarylethenes (more specifically, dithienylethenes).
Figure 1.29 Synthesis of diarylethenes: typical reaction binding the ethane bridge with the aryl cycles (here thienyl).
Figure 1.30 Effect of the substitution by methyl groups on thiophene rings on fatigue resistance.
Figure 1.31 Substituted dithienylethenes (X = CH) and dithiazolylethenes (X = N).
Figure 1.32 Correlation diagram showing the influence of the ground-state energy difference between B and A forms on the potential barrier for the B form.
Figure 1.33 Comparison between hexafluorocyclopentene- and phenylthiazole-bridged diarylethenes: effect of the bridge on the thermal stability of the B form.
Figure 1.34 Substituent effect on the thermal stability of the B form in diarylethenes.
Figure 1.35 Example of fast HABI: naphthalene moiety avoids the separation in two molecules upon bond cleavage, leading to a fast thermal back-reaction [57].
Figure 1.36 Antiparallel (ap) and parallel (p) conformations of the open form of diarylethenes. Only the ap conformer is reactive.
Figure 1.37 Antiparallel conformation (ap) favored by introducing bulkiness in the bridging ring (a) [116] or constraint with an additional bridge (b) [117b].
Figure 1.38 Intramolecular interactions favoring the ap conformation and solvent effect on the
φ
A→B
value [118b].
Figure 1.39 Solvent–solute hydrogen bond favoring the ap conformation and increasing the
φ
A→B
value [119].
Figure 1.40 Enantiospecific photochromism resulting from a high-energy barrier between the open form conformations [121].
Figure 1.41 Stereospecific photochromism resulting from the control of the conformation of the open form by intramolecular hydrogen bonds [122].
Figure 1.A.1 Definition of the system under irradiation and its variables.
Chapter 2: Photochromic Transitional Metal Complexes for Photosensitization
Figure 2.1 Schematic representation of photosensitization via triplet–triplet energy transfer process (ISC: intersystem crossing).
Figure 2.2 Schematic drawing of (a) STPY and (b) the tris(bipyridyl)ruthenium(II) complex with styryl-bridged bipyridine ligand.
Figure 2.3 (a) Schematic drawing of stilbene and azo-containing pyridine ligands. (b) Excited-state dynamics of [Re(CO)
3
(bpy)(STPY)]
+
. (From [12]. Reproduced with the permission from American Chemical Society.) (c) Emission spectral traces of [Re(CO)
3
(phen)(NSP)]
+
upon irradiation at
λ
= 330 nm in degassed CH
2
Cl
2
.
Figure 2.4 Visible light-induced
cis
-to-
trans
isomerization of substituted [Fe(STPPY)
2
].
Figure 2.5 Dithiolato-bipyridine platinum(II) complexes with (a) azo-containing bipyridine ligand, (b) azo-containing benzene-1,2-dithiolato ligand, and (c) photocontrollable ternary photochromic platinum(II) complex with two different azo-containing ligands.
Figure 2.6 Photosensitized photochromism of [Re(CO)
3
(N–N)(
SOPY
)]
+
(N–N =
t
Bu
2
bpy, Me
2
bpy, phen).
Figure 2.7 (a) Rhenium(I) tricarbonyl complexes with spirooxazine-containing bipyridine ligands. (b) Qualitative energy state diagram for the quenching of the photochromic reaction with the lower lying MLCT excited state. (From [20]. Reproduced with the permission from Wiley-VCH.)(c) Fulgimide-containing tris(bipyridyl) osmium(II) and tris(bipyridyl) ruthenium(II) complexes.
Figure 2.8 (a) Schematic diagram for [Pt(
L2
)(C≡CR
2
)
2
]. (b) Photochromic gel formed by the cholesteryl platinum(II) bipyridine complex.
Figure 2.9 Triplet photocyclization of (a) diarylethene-containing phenanthroline ligand in the tricarbonyl rhenium(I) complex and (b) diarylethene-containing bridging bipyridine ligand in the dinuclear tris(bipyridyl)ruthenium(II) complex.
Figure 2.10 (a) Dithienylethene-bridged dinuclear tris(bipyridyl)ruthenium(II) and osmium(II) complexes. (b) UV–vis spectral changes accompanying the photocyclization of the dinuclear ruthenium complex. Inset: the corresponding decrease in emission intensity of the dinuclear ruthenium complex. Conditions: MeCN, 293 K. (From [26b]. Reproduced with the permission from American Chemical Society.) (c) Tris(bipyridyl) iron(II) and ruthenium(II) complexes with three dithienylcyclopentenes.
Figure 2.11 (a) Bis(2-methylbenzothien-3-yl)maleimide-coupled polypyridine ligands. (b) Qualitative energy-level diagram and photocyclization mechanism for [Ru(bpy)
2
(
L5
)]
2+
.
Figure 2.12 Percent conversion to the photostationary states as a function of time for CH
3
CN solutions of the diarylethene-containing platinum(II) terpyridine complexes upon irradiation into their MLCT absorption band.
Figure 2.13 Synthetic routes to photochromic 5,6-dithienyl-1,10-phenanthroline ligand.
Figure 2.14 (a) Proposed qualitative energy-level diagram for the photosensitized photochromism of [Re(CO)
3
(
L7
)Cl] by MLCT excitation. (b) UV–vis absorption spectral changes of [Re(CO)
3
(
L7
)Cl] in benzene (7.16 × 10
−5
M) upon MLCT excitation at 440 nm. (c) Overlaid normalized corrected emission spectra of the open form (——) and the closed form (– – –) of [Re(CO)
3
(
L7
)Cl] in EtOH–MeOH glass (4 : 1 v/v) at 77 K. (d) Photochromism of different complexes of
L7
.
Figure 2.15 (a) Photochromism of the tricarbonylrhenium(I) and the tetracyanoruthenate(II) complexes with different dithienyl-substituted 2-pyridylimidazole ligands. (b) Absorption maxima of the closed forms of the dithienyl-substituted 2-(2-pyridyl)imidazole ligands and their metal complexes.
Figure 2.16 (a) Diarylethene-containing cyclometalated iridium(III) and platinum(II) complexes. (b) Effect of the substituent on the diarylethene-containing ligand and the ancillary ligand on the closed-form absorption.
Figure 2.17 Selected examples of different types of diarylethene-containing ligands.
Figure 2.18 (a) UV–vis absorption spectral change of phosphino gold(I) complexes with photochromic N^C chelate of BMes
2
(10 μM) in toluene upon excitation at 365 nm. (b) Inhibited photochromic reaction in the rhenium complex with the same N^C chelate of BMes
2
.
Chapter 3: Multi-addressable Photochromic Materials
Figure 3.1 (a) Photochromic reaction between dual-fluorescent donor–acceptor dyad
1o
and
1c
, (b) truth table, and (c) symbol of two-input AND logic gate.
Figure 3.2 (a) Photochromic reaction between
2o
and
2c
, (b) NOR and (c) INHIBIT gate function, and truth table of (d) NOR and (e) INHIBIT.
Figure 3.3 (a) Photochromism and photographic images between
3o
and
3c
under the alternative irradiation with UV and visible light in THF, (b) ORTEP representation of the crystal structure of
3o
with displacement ellipsoids shown at the 50% probability level, and (c) color changes of
3o
in the crystalline state.
Figure 3.4 Performance of
3o
working as a half-adder or half-subtractor.
Figure 3.5 (a) Chemical structure of
4
(FGo-DTEo) and (b) photochemical interconversions among four photoisomeric structures.
Figure 3.6 (a) Chemical structure of
5
, (b) fluorescence emission intensities (
λ
= 650 nm upon excitation at
λ
= 470 nm) following various input sequences, and (c) photocycling of
5
.
Figure 3.7 Proposed sensing processes of compounds
6o
with Cu
2+
and then CN
−
, and the photochromic processes responding to light stimuli.
Figure 3.8 Proposed sensing processes of compounds
7
with H
+
and Ag
+
and the photochromic processes responding to light stimuli.
Figure 3.9 Proposed sensing processes of compounds
8
with Cu
2+
and Hg
2+
and the photochromic processes responding to light stimuli.
Figure 3.10 Proposed sensing processes of compounds
9
with Zn
2+
and H
+
and the photochromic processes responding to light stimuli.
Figure Scheme 3.1 Illustration of photoisomerization.
Figure 3.11 (a) Schematic diagrams of fluorescent diarylethene
10
, (b) involved FRET mechanism, (c) fluorescence images, (d) time trace, and (e) histogram of the time of single photoswitching molecules (
10
) upon alternate irradiation with 488 and 325 nm light.
Figure 3.12 (a) Chemical structure and photochromic reaction of diarylethene
11
and (b) four-level photochemical and photophysical ESIPT process of dye
12
.
Figure 3.13 (a) Photochromic reaction between
13o
and
13c
and (b) schematic energy diagram for the fluorescent open form (dashed line) and the nonfluorescent closed form (dotted line) of a diarylethene (DAE) and CT states of the DAE–dye conjugate.
Figure 3.14 (a) Molecular structure of diarylethene
14o
and (b) absorption and fluorescence spectra of each component in 1,4-dioxane. Absorption spectra of the open-ring isomer of diarylethene unit, the closed-ring isomer of diarylethene unit, and the PBI unit, and the fluorescence spectrum of the PBI unit.
Figure 3.15 (a) Molecular structures of photochromic complexes
15
and (b) schematic representation of transitions of the diarylethene (black line) and the Eu(III) complex (red line).
Figure 3.16 (a) Molecular structure of the open and closed forms of diarylethene
16
, (b) IR spectra of open form (solid line) and closed form (broken line) of diarylethene
16
, and (c) IR images of the recorded film containing 4 wt% diarylethene
16
.
Figure 3.17 (a) Molecular structure of the open and closed forms of diarylethene
17
,
18
, and
11
and (b) visible and IR images of the recorded film containing the three diarylethenes. IR image detected at 1549 cm
−1
(c), 1655 cm
−1
(d), 1527 cm
−1
(e), both 1655 and 1527 cm
−1
(f), both 1549 and 1527 cm
−1
(g), both 1655 and 1549 cm
−1
(h), and all three wavelengths (i).
Figure Scheme 3.2 Illustration of the photochromic reaction in diarylethene.
Figure 3.18 Enantiospecific photochromic reaction between
19o
and
19c
.
Figure 3.19 Diastereoselective photochromic reaction between
20o
and
20c
.
Figure 3.20 Diastereoselective photochromic reaction between
21o
and
21c
.
Figure 3.21 Diastereoselective photochromic reaction between
22o
and
22c
.
Figure 3.22 Antiparallel and parallel conformations of compounds
23
and
24
and the corresponding photochemical reaction from the antiparallel conformation.
Figure 3.23 Intramolecular hydrogen bond between the COOH and COO
−
in monoanionic form of
25o
.
Figure 3.24 “Lock and key” process of diarylethene
26o
by selected oxidization/reduction.
Figure 3.25 Gated photochromism of 1,8-naphthalimide-piperazine-tethered dithienylethene
27o
by the coordination of Cu
2+
.
Figure 3.26 Photochromic reactions of compound
28o
and “lock and key” gated process controlled by complexation/dissociation with BF
3
.
Figure 3.27 Diels–Alder reaction of diene
29
and photochromism of hexatriene
30o
.
Figure 3.28 Principle of the stepwise two-photon process for the cycloreversion reaction.
Figure 3.29 Gated photochromic process by the intramolecular proton transfer as a result of the formation of the intramolecular hydrogen bonding.
Figure 3.30 Principle of the lock and unlock process of compound
33o
containing conjugated (4-pyridyl)ethynyl group.
Figure 3.31 Protection reactions of
34o
, deprotection reactions of
35o
, and photochromism of
36o
.
Figure 3.32 Gated photochromism of
37o
and
38o
.
Chapter 4: Photoswitchable Supramolecular Systems
Figure 4.1 (a) Structure and photochromic process of
1
; (b) SEM and (c) CLSM images of
1O
in water (1.0 × 10
−5
M,
λ
ex
= 405 nm,
λ
em
= 480–580 nm); and (d) the schematic illustration of the aggregation formed by
1O
.
Figure 4.2 CLSM image (a–d) and the overlay image (e–h) of KB living cells incubated with
1O
for 20 min at 25 °C (a) in original state, (b) irradiated by 405 nm light (2 mW) for a single cell, (c) all cells, and (d) recovered by 633 nm light.
Figure 4.3 (a) The structure and (b) schematic diagram of
2
response to DNA with gated photochromism.
Figure 4.4 CLSM images of fixed Hela cell incubated with
2
(10 μM) for 10 min and followed with Hoechst33258 (10 μM) for 30 min at 37 °C; (a) Hoechst33258 in blue channel (420–480 nm), (b)
2
in red channel (520–620 nm), (c) overlay of Hoechst33258 and
2
, and (d) overlay image of (b) and the bright field image. (e) A selected cell and (f) cross-sectional analysis along the red line in image (e). (g) Cell viability value (%) by MTT 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide method. (h) Fluorescent images of selected cells in red circle bleached with 405 nm and recovered by 633 nm laser.
Figure 4.5 Chemical structure and photochromism of compounds
3
and
4
.
Figure 4.6 CD spectra of (
S
,
S
)-
4
(a) in water (2.6 × 10
−5
) and (b) in ethyl acetate (1.6 × 10
−5
). Red line, the open-ring isomer; blue line, the closed-ring isomer; and green line, the sample in the photostationary state under irradiation with 313-nm light.
Figure 4.7 Chemical structure of compounds
5–8
.
Figure 4.8 Chemical structure and photochromism of compound
9
.
Figure 4.9 Chemical structure of compound HPHEEP-Azo.
Figure 4.10 Photoisomerization of AzoC10 in the block ionomer complex vesicles (
Z
= 1). [PEG43-PAA153] = 0.06 mg ml
−1
; [AzoC10] = 8 × 10
−5
M.
Figure 4.11 Preparation scheme for the reversibly photoswitchable amphiphilic Pdots and their FRET-mediated photoswitching property.
Figure 4.12 Schematic illustration of novel amphiphilic reversible photoswitchable fluorescent nanoparticles via covalently incorporating fluorescent dye (FBP) and photochromic derivative (SPMA).
Figure 4.13 Photoresponsive self-assemblies established by Shinkai
et al.
(a) One-component system achieved by self-complementary azobenzene
10
functionalized on one end by an ω-ammonium alkyl and on the other by a crown ether. (b) Two-component system achieved by the mixture of symmetrical azocrown
11
and α,ω-diammoniumalkane
12
.
Figure 4.14 (a) Supramolecular rosettes I–III formed by mixing azobenzene-appended melamines AzoMel1 or AzoMel2 and barbiturates BAR or BAR-TDP or dodecyl cyanurate dCA. (b,c) The corresponding schematic representation of the phototriggered formation of rosettes.
Figure 4.15 Cartoon representation of photoresponsive PPR gel–sol–gel transitions driven by competitive inclusion complexation.
Figure 4.16 (a) Chemical structures of the host polymer and guest polymer. (b) Schematic representation of the interactions of the α-CD unit (cylindrical shapes) with azobenzene moieties (yellow shapes) upon irradiation with UV (365 nm) and visible light (430 nm) or heating at 60 °C.
Figure 4.17 (a) The chemical structures of the host gel (α- and β-CD-gels) and the guest gel (Azo-gel). (b) Gel assembly of α-CD-gel (blue) with the
trans
-Azo-gel (orange) and gel dissociation with irradiation of UV light. The scale bar corresponds to 1.0 cm.
Figure 4.18 (a) Light-induced
trans–cis
isomerization of DPDP. (b) UV–vis spectra of MB in solution in 10% methanol/acetone. As MB was released from
cis
-srMOP-1, the absorbance of MB in the solution increased. (c) Schematic illustration of the capture of MB by
trans
-srMOP-1 and its release from
cis
-srMOP-1.
Figure 4.19 Schematic of azobenzene-modified DNA-controlled reversible release system. Visible irradiation at 450 nm (azobenzene
trans
) leads to hybridization of the linker and the complementary DNA arm. Irradiation with UV (365 nm) converts azobenzene to the
cis
form, leading to dehybridization and pore opening.
Figure 4.20 (a) Schematic illustration of the “nanoimpeller's” action. Irradiation of azobenzene with light of wavelength at which both isomers absorb results in a continuous “wagging” motion of the untethered terminus of the switch. (b) Release profile for MS silica nanoparticles functionalized with bulky azobenzene groups at the pore orifices. (c) Release profile for MS silica NPs functionalized with unsubstituted azobenzene groups inside pore interiors.
Figure 4.21 Synthesis of TSUA- and BPDB-modified MCM-41. Two approaches to the operation and function of the azobenzene-modified MCM-41 NPs carrying nanovalves.
Figure 4.22 The process of the self-assemblies between
BTEPy
and carboxylic acid.
Figure 4.23 (a) Fluorescent spectra of
BTEPy·TDBA
in THF solution and the nanoparticles suspended in THF–water; (b) absorption (red line) and fluorescent (black line) spectral changes of solid film of
BTEPy·TDBA
upon irradiation of 365 nm light (inset: fluorescence switch cycles upon alternating irradiation of UV and visible light); (c) individual absorption and emission spectra of
BTEPy·BF
2
,
BTEPy
, and
BF
2
in solid film; and (d) fluorescent changes of
BTEPy·BF
2
during photochromism process (Ex: 365 nm); inset: excitation under 480 nm and switched under 365 nm.
Figure 4.24 (a) Principle of the upconversion luminescent switch consisting of
13
/LaF
3
:Yb,Ho-loaded PMMA film before (left), and after (right) irradiation with 365 nm light for 30 min (
λ
ex
= 980 nm). (b) UV–visible absorption spectra of loaded PMMA film before (dash line) and after (solid line) irradiation with 365 nm light for 30 min, and the normalized upconversion luminescence spectra of the prepared film (dotted line,
λ
ex
= 980 nm). Inset shows the image of the upconversion emission. (c) nondestructive readout capability of the film in the open state () and PSS state (),
λ
ex
= 980 nm. Inset shows the modulated upconversion luminescence intensity at 540 nm of the film during alternating UV and visible light irradiation.
Figure 4.25 (a) Chemical structure and photochromic process of
14
+ DTE and (b) SEM images of gels of
14
and
14
+ DTE from ethyl acetate before and after 365 nm light irradiation (scale bar: 5, 10, and 2 µm, respectively, from left to right); insets in (b) are water contact angle of
14
+ DTE before and after 365 nm light irradiation.
Figure 4.26 (a) Chemical structures and properties of the two monomers (
A11AB6
and
A9Bz9
) and crosslinker (
C9A
). (b) Preparation of an oriented CLCP/CNT nanocomposite film in four steps: (1) growth of a CNT array by chemical vapor deposition; (2) formation and stabilization of the CNT sheet on a glass substrate; (3) preparation of the LC (Liquid-Crystalline) cell by using two CNT-sheet-covered glass slides; and (4) injection of the molten mixture including the monomers, crosslinker, and photoinitiator into the LC cell. (c) SEM images of a CNT array (inset, high magnification). (d) Photographs of a CLCP/CNT composite film during one bending and unbending cycle after alternate irradiation by UV and visible light at room temperature. The intensities of the UV light at 365 nm and visible light at 530 nm were 100 and 35 mW cm
−2
, respectively.
Figure 4.27 (a) Structural formula of
trans
-azobenzene-terminated thiol (
trans
-MUA). (b) Schematic illustration of the light-induced NP self-assembly in a polymer gel. TEM (transmission electron microscope) images show dispersed NPs before (left) and aggregated NPs after (right) UV irradiation. (c) Local irradiation of the sample (here, through a transparency mask) can be used to record and store graphical information. (d) Aggregate size (and color of the film) depends on the duration of UV irradiation. (e) Examples of images/messages written in Au (top) and Ag (bottom) NP-based films and their self-erasure (slow in the dark, top; rapid upon intense visible-light irradiation, bottom).
Figure 4.28 Chemical structure and photochromic process of
15
.
Figure 4.29 Chemical structure and photochromic process of
16
with existing of Ag ion.
Figure 4.30 Chemical structure and photochromic process of
17
and
18
with existing of Cu and Zn ions, respectively.
Figure 4.31 Chemical structure and photochromic process of
19
with existing of Cs ion.
Figure 4.32 Chemical structure and photochromic process of
20
with existing of Cu ion.
Figure 4.33 Chemical structure changes of compound
21
in different states.
Figure 4.34 CLSM images of KB cells incubated with
21o
for 20 min at 25 °C (1 × 10
−5
M in PBS/DMSO, 100 : 2, v/v). (a,f) Brightfield transmission image of KB cells. (b) Overlay image of A and C. Confocal fluorescence image of (c) original state, (d) irradiated by 405 nm light (2 mW, 3 min) for one selected cell, and (e) recovered by 633 nm light (0.7 mW, 40 min). Confocal fluorescence image of (g) original state of F, and incubation by Zn
2+
solution with the concentrations of (h) 5 × 10
−5
M and (i) 1 × 10
−4
M. (j) Recovered by 5 × 10
−4
M EDTA solution. Panels (k–n) were the distribution of fluorescence intensity of (g–j), respectively.
Figure 4.35 Chemical structures of
22
and
23
.
Figure 4.36 Chemical structure and photochromic process of
L24
and
24
.
Figure 4.37 Chemical structure and multi responses of
25
and
26
.
Figure 4.38 Chemical structure and multi responses of
27
.
Figure 4.39 Chemical structure and photochromic process of
28
.
Figure 4.40 The graphical representation of the degenerate [2]rotaxane molecular shuttle gated by light irradiation and thermal energy.
Figure 4.41 Structure of the ring and axle components, showing the atom numbering system.
Figure 4.42 (a) Structural formula of
trans
-(4,40-bis (11-mercaptoundecanoxy)azobenzene) (
trans
-ADT). (b) Light-induced self-assembly of NPs. UV irradiation of a stable solution of
trans
-ADT-coated NPs induces AP isomerization and attractive interactions between NPs. When in close proximity, covalent crosslinks between the NPs form. (c) Phase diagram of NP suprastructures. Morphology of the resulting aggregate is dictated by the ADT surface concentration and the polarity of the solvent.
Figure 4.43 The structures of compounds
29
and
30
.
Figure 4.44 Chemical formula of
31
Figure 4.45 Chemical structures of
LC10
(a) and
G18
(b). Images of the sol–gel transition for the sole G18 (c) and the mixture of
LC10/G18
(1 : 19 w/w) (d) with a total concentration of 40 mg ml
−1
. SEM images of the corresponding xerogels of
G18
from ethanol (e); 1,4-dioxane (f, main body of the fiber and g, end of fiber); 1 : 19 w/w
LC10/G18
(h). 3 : 17 w/w
LC10/G18
(i) and 1 : 9 w/w
LC4/G18
(j). The total concentration of all of the gels is 40 mg ml
−1
.
Chapter 5: Light-Gated Chemical Reactions and Catalytic Processes
Figure 5.1 General approaches toward photocontrol of reactivity: (a) excited-state reactivity, where after photoexcitation reactions are performed in the excited state; (b) photocaged reactivity, where in the course of an irreversible photochemical transformation a reactive ground-state species is generated (“uncaged”); and (c) photoswitchable reactivity, where a reversible photochemical reaction (photochromism) allows for switching between unreactive and reactive ground-state species. In the last approach, which is the focus of this review, the photoswitchable system can be exploited either using stoichiometric processes (serving as substrate, product, or template) or substoichiometric processes (serving as the catalyst).
Figure 5.2 Molecular structure changes upon either
E
/
Z
-isomerization of azobenzene and stilbene or 6π-electrocyclization of dithienylethene and dithiazolylethene photoswitches, typically used as photochromic gates (see examples).
Figure 5.3 Concept of starting material control: photoswitching a substrate between inactive and active forms allows for controlled feeding or removal of a starting material to or from a dynamic covalent equilibrium. Reproduced from Ref. [5] with permission from The Royal Society of Chemistry.
Figure Scheme 5.1 Photocontrolled allyl transfer reaction of silyl azobenzenes with fluoride yielding hydrazine rearrangement products [11].
Figure Scheme 5.2 Photocontrolled addition of methanol to imidazol(in)ium ions embedded in a diarylethene framework [14].
Figure Scheme 5.3 Photomodulation of nucleophilicity by switchable coupling to an acceptor moiety through a diarylethene bridge [17].
Figure Scheme 5.4 Photoswitching of the nucleophilic properties of an acetylene moiety by coupling to an electron-donating residue through a diarylethene bridge [18].
Figure 5.4 Concept of product control: photoswitching a product to an inactive “locked” form removes it from a dynamic covalent equilibrium, while switching it back into its active “unleashed” form and re-introduces it to the system. Reproduced from Ref. [5] with permission from The Royal Society of Chemistry.
Figure Scheme 5.5 Photoswitching locks the Diels–Alder adduct (
11o
→
11c
) and removes it from the dynamic equilibrium (
10
→
11o
) [20].
Figure Scheme 5.6 Photoswitching locks the Diels–Alder adduct (
13o
→
13c
) and removes it from the dynamic equilibrium (
12
→
13o
) [21].
Figure 5.5 Concept of starting material and product control: photoswitching starting material as well as product to an inactive “locked” form removes them from a dynamic covalent equilibrium, while switching them back into their active “unleashed” forms re-introduces them to the system.
Figure Scheme 5.7 Photoswitching locks either the unreacted switch (
14o
→
14c
) or the Diels–Alder adduct (
15o
→
15c
) and thus removes the respective component from the dynamic equilibrium (
14o
→
15o
) allowing for amplification or inhibition of the Diels–Alder reaction [23].
Figure 5.6 Concept of template control: photoswitching a template between inactive and active forms allows for control of conversion of starting materials to products. Reproduced from Ref. [5] with permission from The Royal Society of Chemistry.
Figure Scheme 5.8 Photoswitchable template
16
, which in its
Z
-isomer enabling the coupling of amine
17
and activated acid
18
to amide
19
[24].
Figure Scheme 5.9 In a molecular walker–track conjugate, a photoswitchable stilbene moiety in the track guides the walker along the track by biasing the individual dynamic covalent equilibria for disulfide and hydrazone formation [26].
Figure 5.7 Concept of dynamic template control: photoswitching a building block of a dynamic constitutional library between reactive and nonreactive forms allows for the assembly of an active template, which facilitates the conversion of starting materials to products. Reproduced from Ref. [5] with permission from The Royal Society of Chemistry.
Figure Scheme 5.10 Photoswitching the composition of a dynamic constitutional library by incorporating a photochromic building block leads to a change of the host distribution in the presence of an oligoproline guest [27].
Figure 5.8 Concept of photoswitching the activity of a catalyst: photoswitching converts a catalyst from an inactive to an active form, which turns substrate over to product, while the inactive form shows no conversion (turnover). Thereby, one switching event can lead to the formation of many product molecules (amplification). Reproduced from Ref. [5] with permission from The Royal Society of Chemistry.
Figure Scheme 5.11 In the photoswitchable cooperative catalyst
24
,
E
→
Z
photoisomerization brings both barium centers and hence the two coordinated starting materials into close proximity to catalyze the ethanolysis of tertiary anilides [28].
Figure Scheme 5.12
E/Z
-photoisomerization of an azobenzene moiety controls the accessibility of a piperidine base, which can be used to catalyze a nitroaldol (Henry) reaction [30].
Figure Scheme 5.13 Ring-open
N
-heterocyclic carbene (NHC)
26o
catalyzes transesterification, amidation, and ring-opening polymerization reactions, yet upon irradiation its corresponding ring-closed isomer
26c
exhibits significantly reduced catalytic activity [32, 33].
Figure Scheme 5.14 Photoswitching of a dithienylethene-based
N
-heterocyclic carbene (NHC) ligand modulates the activity of the derived Rh(I)-complex in the hydroboration of styrene [34].
Figure 5.9 Concept of photoswitching the selectivity of a catalyst: photoswitching interconverts a catalyst between two forms exhibiting different selectivity in a given transformation. Again, one switching event can lead to the formation of many product molecules (amplification). Reproduced from Ref. [5] with permission from The Royal Society of Chemistry.
Figure Scheme 5.15 Photoswitching of a dithienylethene-based bisoxazoline ligand leads to modulation of its chelation ability and hence chirality of the corresponding copper complexes, which display different degrees of stereoselectivity for the cyclopropanation of styrene [35].
Figure Scheme 5.16 Modulation of the relative orientation of a pyridine basic and a thiourea hydrogen-bonding site embedded in a molecular motor leads to photoswitchable bifunctional organocatalyst, which allows for control over the activity and stereoselectivity of a Michael reaction [36].
Chapter 6: Surface and Interfacial Photoswitches
Figure 6.1 Spiropyran-modified electrode with photoreversible interactions with (a) cytochrome
C
, (b) glucose oxidase, and (c) Pt nanoparticles.
Figure 6.2 Dithienylethene-based electrochemical/photoelectrochemical switchable wired glucose oxidase electrode and the structure of amino-FAD.
Figure 6.3 Photoinduced wettability changes of perfluoroalkyl attached (a) azobenzene and (b) molecular rotor modified functional surfaces.
Figure 6.4 (a) Molecular structure of per-azobenzene-modified macrocyclic amphiphile. (b) Lateral photographs of light-driven motion of an olive oil droplet on a silica plate modified with macrocyclic amphiphile.
Figure 6.5 (left) A photoswitchable fluorinated molecular shuttles modified surface. (right) Lateral photographs of light-driven transport of a 1.25 µl diiodomethane drop on an
E
-1,11-MUA (11-mercaptoundecanoic acid). Au(111) substrate on mica up a 12° incline.
Figure 6.6 Photochemical (a) and electrochemical (b) uptake and release of DTE into and from the imprinted AuNPs matrix.
Figure 6.7 (a) Photoreversible azobenzene shuttles on the surface. (Adapted with permission [27]. Copyright 2008, Royal Society of Chemistry.) (b) Light/pH dual-responsive capture and release surface system based on azobenzene-CD shuttles. (Adapted with permission [28]. Copyright 2009, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.) (c) Light-switchable catalysis on photocontrolled host–guest functionalized surface.
Figure 6.8 (a) The flip-flop set/reset memory device based on DTE-modified gold electrode. (b) Photo “write/erase,” electronic “read” system based on DTE-modified ITO electrode.
Figure 6.9 Spiropyran/Co-functionalized erasable magnetic patterning surfaces for photo/electrochemical encoding system.
Figure 6.10 (a) Molecular rotor immobilized on AuNPs via two thiol anchors. (b) α-CD “makes room” for immobilized azobenzene to perform photoswitching on AuNPs. (c) Immobilized DTE on the AuNPs via arylthiol linkers (Ar = benzene, thiophene).
Figure 6.11 (a) Molecular structures of the photoresponsive azobenzene–thiol ligand. (b) Photoswitching of AuNPs aggregation. Dispersed NPs are catalytically active; aggregated NPs are catalytically inactive. (c) Hydrosilylation of 4-methoxybenzaldehyde catalyzed by AuNPs.
Figure 6.12 Rewritable and flexible films. (a) Sequential writing into and erasing from the same AuNP film. (b) Reversible spectral changes of an AuNP film upon alternating exposures to UV and visible light. (c) Patterned films can be mechanically distorted without disrupting the imprinted image.
Figure 6.13 Photoswitchable DNA-functionalized gold nanoparticle conjugates.
Figure 6.14 (a) Spiropyran-AuNPs based logic gates. (b) Photoinduced aggregation of AuNPs with spirothiopyran.
Figure 6.15 (a) Photoswitching QDs coated with an amphiphilic photochromic polymer. (Adapted with permission [76]. Copyright 2011, American Chemical Society.) (b) Dual-color photoswitching QDs coated with an amphiphilic photochromic polymer and Alexa 647. (Adapted with permission [77]. Copyright 2012, American Chemical Society.) (c) Dual-color photoswitching QDs coated with an amphiphilic photochromic polymer and Lucifer Yellow.
Figure 6.16 Single wavelength near-infrared-induced photochromism based on upconversion nanoparticles by changing the light intensity.
Figure 6.17 (a) Mesoporous silica nanoparticle (MSN) carriers with azobenzene as the photovalve. (b) Multistimulated MSN with light/α-CD/DTT as triggers. (Adapted with permission [92, 93]. Copyright 2009, American Chemical Society.) (c) MSN carriers with azobenzene-tethered DNA hairpin as gate keeper.
Figure 6.18 (a) Phototriggered release of cargo from MCM-41 modified with spiropyran. (Adapted with permission [95]. Copyright 2007, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.) (b) Releasing cargo from MSN by photoswitchable wettability.
Figure 6.19 Truth table for an AND logic gate based on azobenzene-modified MSN.
Figure 6.20 (a) Upconversion and (b) two-photon-based photorelease of drugs loaded in MSN.
Figure 6.21 (a) Schematic cross section of the device layout of a large-area molecular junction in which the diarylethene is sandwiched between Au and poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS)/Au. (b) Schematic picture of a photoswitchable nanoparticle network modified with diarylethenes. (c) Current changes of the open and closed DTE junctions by UV and visible light.
Figure 6.22 Structures of four molecules used in the difurylethene single-molecule conductance study.
Chapter 7: Hybrid Organic/Photochromic Approaches to Generate Multifunctional Materials, Interfaces, and Devices
Figure 7.1 Photochromic molecules encompassed in this review, featuring two independently addressable states that lead to reversible structural changes such as geometry/steric hindrance and electronic changes such as dipole moments, π-conjugation, HOMO–LUMO gap, and redox potential. All these changes occurring on the molecular level affect macroscopic properties such as shape, aggregation behavior, conductance of the resulting materials, or interface containing these photoswitches. In particular, the sketch depicts (a) azobenzenes, (b) diarylethenes, and (c) spiropyrans.
Figure 7.2 (a) Representation of the working principle of the AZO-SAM Field-Effect Transistor (FET) device. The semiconductor is a perylene diimide derivative, namely PDIF-CN2. The AZO-SAM chemisorbed on gold source and drain injecting electrodes undergoes reversible isomerization upon exposure to UV light (
trans
-to-
cis
) and switches back (
cis
-to-
trans
) after thermal recovery. As a result, the charge injection and ultimately the drain current are photomodulated. (
W
= 10 mm,
L
= 10 µm, film thickness 8–10 nm). (b) Transfer (right) and output (left) curves acquired after an
in situ
switching from of the AZO-SAM from
trans
to
cis
. The semiconductor is a spin-coated PDIF-CN2 film.
Figure 7.3 (a) Different device structures tested in Zacharias
et al
. The
y
-axis indicates the energy of the HOMO and LUMO levels of each single component of the multilayered structures encompassed in this study. In particular, (left) XDTE was blended with the emitting material, device of type “blend.” (center) XDTE was employed as an interlayer, device of type “bilayered.” (right) Various hole-injecting materials 2–8 and their combinations were used as an interlayer between XDTE and the ITO/PEDOT electrode, device of type “trilayered.” (b) Comparative plot of an optimized device comprising the following layers: PEDOT (35 nm)/2 (8 nm)/3 (8 nm)/1 (40 nm)/blue emitting polyspirofluorene (70 nm)/Ba(4 nm)/Al (150 nm), in which absorption and current density are simultaneously recorded under irradiation with UV (312 nm, left) and orange (590 nm, right) light sources.
Figure 7.4 (a) Schematic sketch of the molecular triad consisting of two perylene bisimide (PBI) units that are covalently linked to a dithienylcyclopentene (DCP). Top: closed form and bottom: open form. (b) Absorption spectra of the PBI–DCP–PBI triad dissolved in toluene at a concentration of 1.5 × 10
−6
mol l
−1
for the open (red) and the closed (blue) form of the DCP unit. For comparison, the dashed line shows the absorption spectrum of pure PBI in the same solvent at a concentration of 1.5 × 10
−6
mol l
−1
. (c) Contrast of the modulation of the fluorescence intensity as a function of the number of switching cycles that each consists of 2 × 5 conversion/probe sequences. Each data point corresponds to the average over 50 switching cycles. The illumination intensities (exposure times) were 96 mW cm
−2
(250 ms) at 514 nm, 130 mW cm
−2
(250 ms) at 300 nm, and 43 W cm
−2
(250 ms) at 635 nm. The kinks after about 1000 and 2500 switching cycles reflect slight readjustments of the fourth-harmonic generation due to drifts during the long-term experiment. The line serves as a guide for the eye. Insets bottom: modulation of the fluorescence intensity at the beginning and the end of the experiment. Inset top: transistor analogy identifying the S
1
and S
0
state of PBI as source and drain, the conversion beams as gate voltage of different polarity and the optical pumping as external circuit, respectively.
Figure 7.5 (a) The cross-linkable dithienylethene (XDTE) used in Ref. [56]. (b) Comparison of the current density (at 8 V) measured as a function of closed isomer fraction in the XDTE interlayer with electrical or optical stimuli. The “electrical closing” transport relies on the formation of electrically induced conductive filaments within the film, while in the “optical closing” case the closed isomers are quasi-isotropically distributed in the XDTE layer.
Figure 7.6 (a) Device layout employed by Li
et al.
: a top-contact bottom-gate transistor with HMDS-functionalized silicon oxide as the dielectric layer and gold source and drain electrodes as the injecting electrodes. The bicomponent film is a blend of P3HT and SP. The SP molecules are thought of being randomly dispersed within the interdigitated P3HT side chains and close to the polythiophene backbone. (b) An example of a switching cycle: the drain current versus time plot highlights how the device is able to respond with a different output upon irradiation with a different wavelength.
Figure 7.7 (a) General scheme of the tested organic thin-film transistors including chemical formulae of the molecules employed in the bicomponent film, namely the photochromic molecules DAE_1 and DAE_2 in their two isomeric states and the P3HT semiconducting polymer. (b) Energy diagram shows the HOMO levels of the employed components and depicts the photomodulation mechanism occurring in the device (UV, ultraviolet; Vis, visible). (c) Dynamic switching of an OTFT made from DAE_1o (20 wt% in P3HT) under several irradiation cycles with ultraviolet (
λ
irr
= 365 nm,
P
i
= 62 mW cm
2
) and white light (
λ
irr
> 400 nm,
P
i
= 5.06 mW cm
2
).
Figure 7.8 (Top panel) Device scheme employed in the study: gold nanoparticles with various coatings are blended with P3HT, which acts as the semiconductor layer for the bottom-contact bottom-gate transistor. (Bottom panel) Photoresponse cycles versus time of s-AZONPs/P3HT (in black), OPE-NPs/P3HT (in red), and P3HT (in blue). For the latter, the
I
D
/
I
D,min
was multiplied by a factor of 100 for a better comparison. (a) 4 Cycles and (b) 10 cycles. (
V
G
−
V
TH
= −4 V,
V
D
= −10 V,
L
= 5 µm).
Figure 7.9 (a) Plot of
I
D
versus time for a pentacene-based FET with SP-SAM-functionalized silicon oxide. The switching experiment lasted for about 3 h (first three cycles expanded for clarity) revealing a reversible photoswitching upon irradiation with UV and visible light.
V
D
= −30 V;
V
G
= −15 V. (b) Responsivity (
R
) and photosensitivity (
P
) as a function of the gate voltage (effective irradiance power = 7.4 μW cm
−2
) for the previously mentioned device (drain voltage was kept at −100 V).
Figure 7.10 (a) (left) Chemical structures of several substituted azobenzene derivatives indicated with AZO-Sil-R (with R = CF
3
, H, C
12
H
25
, CH
3
) chemisorbed in SAM form onto silicon oxide layers. Each type of SAM features a different dipole moment depending on the head group attached. In addition, (right) discrete clusters of multiple layers of azobenzene-carrying acid molecules, indicated as compound AZO-acid-R (with R = CF
3
, CH
3
), could also lead to bistability when acting within the bulk of the semiconductor (pentacene). (b) Schematics of the switching principle presented in the work by Tseng
et al.
When the azobenzene SAM undergoes isomerization, the dipole of the molecular backbone is changed leading to a different dipolar interaction with the pentacene upper layer.
Figure 7.11 Sketch of the bottom-gate top-contact FET structure employed in Lutzyk
et al
. [217]. The active layer is an n-type semiconductor (PTCDI-C
13
H
27
). The gate is either PMMA or PMMA blended with spiropyrans.
Chapter 8: Photochromic Bulk Materials
Figure 8.1 A schematic diagram of the potential energy surface of diarylethene (a) in the gas phase and (b) in the polymer matrix.
Figure 8.2 Fine metal patterning process on 5% diarylethene-doped polystyrene film. (a) Fine colored patterns on the surface was prepared by violet laser spot scanning. (b) Mg vapor was evaporated to the surface without a shadow mask. (c) The fine metal patterns were obtained with 15 µm widths and 50 µm pitches corresponding to the photoirradiated colored pattern.
Figure Scheme 8.1 Typical synthetic methods of fluorescent photochromic polymers: (a) the Wittig polycondensation reaction [16], (b) the Knoevenagel polycondensation reaction [17], (c) the Still polycondensation reaction [18], and (d) Pd-catalyzed Suzuki coupling reaction [19].
Figure Scheme 8.2 The structure of (a) photochromic chromophores and (b) conjugated polymers.
Figure 8.3 Schematic illustration of photoswitchable polymer nanoparticles embedded with an Ir(III) complex and a diarylethene derivative.
Figure 8.4 Schematic illustration of the preparation of the surface-attached, photoswitchable polymer networks.
Figure Scheme 8.3 The structure of diarylethene polymers.
Figure 8.5 Schematic illustration of photoresponsive polymeric vesicles.
Figure Scheme 8.4 Synthetic route of gold nanoparticle covered with a photochromic diarylethene polymer.
Figure Scheme 8.5 Schematic illustration for photoswitching and thermoswitching of gold nanoparticle covered with poly(
N
-isopropylacrylamide) attached with a diarylethene chromophore at the end group.
Figure Scheme 8.6 Photoresponsive polymers having azobenzene residues in the main chain.
Figure Scheme 8.7 Chemical structure of elastomer having azobenzene chromophore synthesized from poly(oxy(methylsilylene)).
Figure 8.6 Photographs of photochromic diarylethene single crystals.
Figure 8.7 (a) Geometrical change of
6
upon photocyclizaiton revealed by
in situ
X-ray crystallographic analysis. Black and red molecules indicate open-ring and photogenerated closed-ring isomers, respectively. Hydrogen atoms are omitted for clarity. (b) Top and side views of geometrical structures of the open- and closed-ring isomers.
Figure Scheme 8.8 Conformational change and photoisomerization reaction of diarylethene.
Figure 8.8 Relationship between photocyclization quantum yield and distance between reacting carbon atoms for 14 diarylethene single crystals.
Figure 8.9 Photograph of partially colored three-component crystal of
6
·
7
·
8
.
Figure 8.10 Color changes of three-component crystal of
9
·
10
·
11
.
Figure 8.11 Molecular packing diagrams of co-crystals of
12
·
13
(a) and
12
·
14
(b). Red, green, and blue molecules indicate
12–14
, respectively.
Figure 8.12 Schematic illustrations of photochromic reactions in co-crystals
12
·
13
(a) and
12
·
14
(b). Red, green, and blue areas indicate
12–14
, respectively.
Figure 8.13 Deformation of diarylethene crystals of (a)
14
and (b)
10
upon UV (365 nm) and visible (
λ
> 500 nm) light irradiation.
Figure 8.14 (a) Molecular packing of single crystal of
14
. The red arrows indicate the direction of contraction and blue arrows indicate the direction of expansion of the crystal upon UV irradiation. (b) Geometrical structures of the open- and closed-ring isomers of
14
in crystals.
Figure 8.15 Photoreversible crystal shape change of a mixed crystal of
15
and
16
.
Figure 8.16 Photomechanical work of a molecular crystal cantilever made of a co-crystal of
13
and
Np
F
.
Figure 8.17 Photoreversible twisting of a single crystal of
17
.
Figure 8.18 Molecular organization in crystal, LC, and liquid states of matter. In the solid crystal phase, the molecules possess both long-range positional order and orientational order; in the LC phase, the molecules possess long-range orientational order but short-range positional order; and in the liquid phase, there is no orientational or positional order of the molecules. In the figure, the molecular organization in the nematic phase of an LC is depicted.
Figure 8.19 Typical molecular shapes of thermotropic LCs of rodlike, bent-core, and discotics.
Figure 8.20 Commonly observed LC phase structures of rodlike, disklike, and bent-core molecules.
Figure 8.21 Molecular structures and photoisomerization of commonly studied photochromic molecular switches. In the figure,
λ
1
is the wavelength responsible for driving the molecule from state 1 (initial) to state 2 (photoisomer) while
λ
2
drives the system from state 2 to state 1. Δ represents thermal relaxation.
Figure Scheme 8.9 Spiropyran- and spirooxazine-based photochromic LC polymers and oligomers.
Figure Scheme 8.10 Polymerizable spirooxazine-based LCs.
Figure Scheme 8.11 Photochromic spiropyran-based LCs.
Figure Scheme 8.12 Spirooxazine-based molecular switches for induction of photoresponsive cholesteric LCs.
Figure Scheme 8.13 Mesogen-functionalized LC diarylethenes.
Figure Scheme 8.14 Liquid crystalline photochromic diarylethene derivatives.
Figure Scheme 8.15 Diarylethene-based photochromic glassy LCs.
Figure Scheme 8.16 Cholesterol-substituted LC diarylethene derivatives.
Figure Scheme 8.17 Axially chiral photochromic diarylethene derivatives.
Figure Scheme 8.18 Chemical structures of axially chiral photochromic diarylethene dopants.
Figure 8.22 Thermally stable red, green, and blue reflection colors in cholesteric films containing
47
.
Figure 8.23 Polarizing optical microscopic demonstration of handedness inversion in cholesteric films containing
50
.
Figure Scheme 8.19 Photoresponsive diarylethenes used in ferroelectric LCs.
Figure 8.24 Modulation of spontaneous polarization in ferroelectric LCs enabled by photochromic materials.
Figure Scheme 8.20 Azobenzene-based polymerizable photochromic LC monomers.
Figure 8.25 Precise control of the bending direction of a polydomain cross-linked LC polymer film by linearly polarized light. White arrows indicate directions of linearly polarized light.
Figure Scheme 8.21 Azobenzene-based photochromic LC polymers.
Figure Scheme 8.22 Azobenzene-based discotic photochromic LCs.
Figure Scheme 8.23 Azobenzene-based photochromic LC bent-core molecules.
Figure Scheme 8.24 Visible light-driven photochromic azobenzene-based chiral switch.
Figure 8.26 Full-range reflection color obtained by doping the mesogenic photochromic material
71
in a nematic LC host.
Figure Scheme 8.25 Cholesterol containing photochromic azobenzene LCs.
Figure Scheme 8.26 Chemical structures of axially chiral photochromic azoarenes.
Figure 8.27 Dynamic and photostationary red, green, and blue reflection colors achieved in cholesteric LCs using compound
74
.
Figure Scheme 8.27 Azoarenes with tetrahedral and axial chirality.
Figure Scheme 8.28 Chemical structures of photochromic LCs
78
and
79
.
Figure Scheme 8.29 Molecular structures of different types of photoluminescent LCs.
Figure 8.28 Chemical structures of photochromic gels based on azobenzene with teroid skeletons.
Figure 8.29 Chemical structures of photochromic gels based on azobenzene with sugar skeletons.
Figure 8.30 Illustration of a phase-selective gelation for the removal of small amounts of toxic solvents from water under light irradiation.
Figure 8.31 POM pictures and the respective schematic illustration of photoinduced structural changes in LC physical gels consisting of 4-cyano-4′-pentyl-biphenyl containing 3 wt% of
94
: (a) isotropic liquid state at 120 °C; (b) nematic gel state at room temperature; (c) cholesteric LC phase (LC sol state) at room temperature after UV irradiation of the nematic gel for 15 min; and (d) cholesteric gel state at room temperature after keeping the cholesteric LC phase.
Figure 8.32 Schematic representation showing aggregation of the melamine
–
azobenzene conjugate (
95
) with barbiturate (
A
) and cyanurate (
B
) derivatives. Rosette
95
3
·
B
3
can hierarchically organize into intertwined fibers (red arrows). The fiber formation can be regulated by light (blue arrows).
Figure 8.33 Illustration of the multichannel supramolecular chiroptical switches composed by
96
.
Figure 8.34 Chemical structures of photochromic gels based on spiropyran derivatives.
Figure 8.35 Chemical structures of photochromic gels based on spirooxazine derivatives.
Figure 8.36 Chemical structures of photochromic diarylethene gels with photoresponsive and chiroptical properties.
Figure 8.37 Chemical structures of photochromic fluorescent dithienylethene gels.
Figure 8.38 Multiple switching images of compound
105
in the cooperative effect of light, thermal, fluoride anions, proton. (a) Gel(open); (b) gel(closed); (c) sol(open); (d) sol(closed); (e) sol(open) + F
−
; and (f) sol(closed) + F
−
.
Figure 8.39 Chemical structures of functional photochromic diarylethene gels.
Figure 8.40 Chemical structures of photochromic naphthopyran gels.
Figure 8.41 Chemical structures of photochromic [2.2]paracyclophane-bridged imidazole dimmer and Schiff base gels.
Figure 8.42 Photoinduced gel-to-sol transition of
120
–N
,
N
′-dimethyldodecylamine organogel in toluene-
d
8
: (a) initial gel state, (b) after irradiation, and (c) after irradiation through a mask.
Figure 8.43 Photoisomerization profiles of helicenes (
M
)-
121
and (
P
)-
121′
and photographs of the gel at ambient temperature after irradiation of the original (
M
)-
121
-containing gel at 318 nm (middle) and then at 280 nm (right) or 343 nm (left).
Chapter 9: Photochromic Materials in Biochemistry
Figure 9.1 (a) A photochromic group is introduced to one or more sites within the biological target. The reversible structural changes that occur with isomerization influence the conformation and function of the macromolecule, either through alteration to the native structure (shown) or by changing the orientation of the photochromic group so that it can physically block or bind to a critical site (not shown). (b) The photochromic group is introduced into an external ligand. The structure and properties of the ligand are altered with isomerization and each isomer has a different affinity for the target.
Figure 9.2 General classes of photochromic species that can be used to prepare reversibly light-controlled biological molecules.
Figure 9.3 (a) Multiple myeloma drug bortezomib bound in a linear orientation in the active site of the 20s proteasome, PDB ID: 2F16 [48]. (b) Photochromic azobenzene-modified proteasome inhibitor, UV light converts the more active trans
-
isomer into the cis
-
isomer, and the isomerization can be reversed with white light [42].
Figure 9.4 (a) Hydrolysis of acetylcholine catalyzed by acetylcholinesterase. (b) Tacrine inhibitor bound to acetylcholinesterase (PDB ID: 1ACJ) hinders acetylcholine binding. (c) Structure of tacrine. (d) Photochromic acetylcholinesterase inhibitors [49].
Figure 9.5 Changes in the distance between pendant
meta
-substituted phosphate groups on dithienylethene-modified PriA enzyme inhibitor. The distance between the phosphate groups on the ring-open isomer is ideal for inhibition, resulting in an eightfold higher inhibitor potency compared to the ring-closed isomer [44].
Figure 9.6 (a) Azobenzene-modified maleimide of varying alkyl chain linkage length [52]. (b) Histone deacetylase-like aminohydrolase (HDAH) enzyme, active site, and external loop of enzyme mutation site. Image is of wild-type PDB ID: 2VCG.
Figure 9.7 (a) Tetra-
ortho
-substituted azobenzene photoswitches that can be isomerized using red light. (b) Red light converts the trans-isomer to the cis-isomer, and this process can be reversed with blue light [58].
Figure 9.8 Antimicrobial peptide gramicidin S [67].
Figure 9.9 Photochromic dithienylethene-based cyclic peptide with light-dependent antimicrobial activity [67].
Figure 9.10 (a) Traditionally used azobenzene-modified amino acid azo-phenylalanine and novel azo-phenylalanine with an additional reactive benzyl chloride, alkene, and keto site. (b) Reaction with a nucleophile is possible to prepare cross-linked photochromic amino acids [70].
Figure 9.11 Structures of attached photochromic groups: (
1
) trityl-substituted azobenzene, (
2
) maleimide-substituted azobenzene, and (
3
) spiropyran [71].
Figure 9.12 Diabetic drug Glimepiride and a photochromic version that show increased binding affinity for the K
ATP
channel in the cis-isomer [87].
Figure 9.13 Structure of azobenzene-modified glutamate ligand [88].
Figure 9.14 (a) Tetra-
ortho
-substituted azobenzene-derived glutamate tether for linkage to an ionotropic glutamate receptor, irradiation of the trans-isomer with 630 nm light produces the cis-isomer, and the reverse process is achieved with 450 nm light. (b) The tethered glutamate-azobenzene derivative allows for photocontrol of glutamate binding and channel activation by isomerization of azobenzene from the trans
-
to the cis
-
isomer [89].
Figure 9.15 Oligonucleotide modified with a spiropyran group. The planar charged merocyanine allows for more efficient intercalation into the base pairs than the bulkier spiropyran form [99].
Figure 9.16 Structures of D-threoninol linker,
meta-
and
para-
substituted azobenzene ribose [100].
Figure 9.17 Structures of photochromic diarylethene-derived deoxyuridine (
a
), deoxycytidine (
b
), and the photoswitch-modified nucleotide sequence based on deoxyuridine (
c
) [101].
Chapter 10: Industrial Applications and Perspectives
Figure 10.1 T-type photochromes: azobenzene, spiropyran, spirooxazine, and naphthopyran (from top to bottom).
Figure 10.2 P-type photochromes: fulgide and diarylethene (from top to bottom).
Figure 10.3 (a) Photochromism of 2
H
-indeno(2,3-
f
)naphtha(1,2-
b
)pyran. (b) Effect of electron-donating groups on C6 and C4′ of a phenyl group on C3 on resonance structures. (c) Effect of methoxy groups on C6, C11, and C4′ of a phenyl group on C3 on the resonance structures.
Figure 10.4 Possible therapeutic scenarios using photoswitchable bioactive compounds with a controlled half-life that show their activity in the thermodynamically unstable (A–C) or stable (D,E) state. (A) Irradiation prior to administration. (B) Irradiation at the point of action. (C) Multiple irradiation cycles of a drug with a short half-life for the on-state. (D) Irradiation prior to administration. (E) Irradiation prior to administration and while the drug is being cleared.
Figure 10.5 (a) Proposed sensing processes of compounds S1 and S3 with Hg
2+
and the photochromic processes responding to light stimuli. (b) The fluorescence change upon detecting Hg
2+
with open isomer (top) and the absorption change upon irradiation with UV and adding Hg
2+
sequentially (bottom).
List of Tables
Chapter 1: Introduction: Organic Photochromic Molecules
Table 1.1 Quantum yield (
φ
B→A
): effect of substituents on 1- and 5-positions of 1,2-bis(2,6-dimethyl-3-thienyl)perfluorocyclopentene (Figure 1.26, –R
2
= –R
6
= –CH
3
)
Table 1.2 Quantum yield (
φ
B→A
): effect of substituents on 3- and 4-positions of 1,2-bis(1,5-diphenyl-3-thienyl)perfluorocyclopentene (Figure 1.26, –R
1
= –R
5
= –Ph)
Table 1.A.1 Values of
α
B
(
λ
irr
) as a function of the thermal back-reaction rate
k
B → A
Chapter 6: Surface and Interfacial Photoswitches
Table 6.1 Length of the molecules in their open and closed forms, conductance values, and conductance switching ratios [111a]
