Molecular Technology, Volume 1 E-Book

• Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 587

Veröffentlichungsjahr: 2018

Beschreibung

Edited by foremost leaders in chemical research together with a number of distinguished international authors, this first of four volumes summarizes the most important and promising recent chemical developments in energy science all in one book.

Interdisciplinary and application-oriented, this ready reference focuses on chemical methods that deliver practical solutions for energy problems, covering new developments in advanced materials for energy conversion, semiconductors and much more besides.

Of great interest to chemists as well as researchers in the fields of energy science in academia and industry.

Leseprobe

Table of Contents

Cover

Foreword by Dr Hamaguchi

Foreword by Dr Noyori

Preface

Chapter 1: Charge Transport Simulations for Organic Semiconductors

1.1 Introduction

1.2 Theoretical Description of Charge Transport in Organic Semiconductors

1.3 Charge Transport Properties of Organic Semiconductors

1.4 Summary

Acknowledgments

References

Chapter 2: Liquid‐Phase Interfacial Synthesis of Highly Oriented Crystalline Molecular Nanosheets

2.1 Introduction

2.2 Molecular Nanosheet Formation with Traditional Surfactants at Air/Liquid Interfaces

2.3 Application of Functional Organic Molecules for Nanosheet Formation at Air/Liquid Interfaces

2.4 Porphyrin‐Based Metal–Organic Framework (MOF) Nanosheet Crystals Assembled at Air/Liquid Interfaces

References

Chapter 3: Molecular Technology for Organic Semiconductors Toward Printed and Flexible Electronics

3.1 Introduction

3.2 Molecular Design and Favorable Aggregated Structure for Effective Charge Transport of Organic Semiconductors

3.3 Molecular Design of Linearly Fused Acene‐Type Molecules

3.4 Molecular Technology of π‐Conjugated Cores for p-Type Organic Semiconductors

3.5 Molecular Technology of Substituents for Organic Semiconductors

3.6 Molecular Technology of Conceptually‐new Bent‐shaped π‐Conjugated Cores for p‐Type Organic Semiconductors

3.7 Molecular Technology for n‐Type Organic Semiconductors

References

Chapter 4: Design of Multiproton‐Responsive Metal Complexes as Molecular Technology for Transformation of Small Molecules

4.1 Introduction

4.2 Cooperation of Metal and Functional Groups in Metalloenzymes

4.3 Proton‐Responsive Metal Complexes with Two Appended Protic Groups

4.4 Proton‐Responsive Metal Complexes with Three Appended Protic Groups on Tripodal Scaffolds

4.5 Summary and Outlook

Acknowledgments

References

Chapter 5: Photo‐Control of Molecular Alignment for Photonic and Mechanical Applications

5.1 Introduction

5.2 Photo‐Chemical Alignment

5.3 Photo‐Physical Alignment

5.4 Photo‐Physico‐Chemical Alignment

5.5 Application as Photo‐Actuators

5.6 Conclusions and Perspectives

References

Chapter 6: Molecular Technology for Chirality Control: From Structure to Circular Polarization

6.1 Chiral Lanthanide(III) Complexes as Circularly Polarized Luminescence Materials

6.2 Magnetic Circular Dichroism and Magnetic Circularly Polarized Luminescence

6.3 Molecular Self‐assembled Helical Structures as Source of Circularly Polarized Light

6.4 Optical Activity Caused by Mesoscopic Chiral Structures and Microscopic Analysis of the Chiroptical Properties

6.5 Conclusions

References

Chapter 7: Molecular Technology of Excited Triplet State

7.1 Properties of the Triplet Exciton and Associated Phenomena for Molecular Technology

7.2 Near‐infrared‐to‐visible Photon Upconversion: Chromophore Development and Triplet Energy Migration

7.3 Singlet Exciton Fission Molecules and Their Application to Organic Photovoltaics

References

Chapter 8: Material Transfer and Spontaneous Motion in Mesoscopic Scale with Molecular Technology

8.1 Introduction

8.2 Mechanism to Originate Mesoscale Motion

8.3 Generation of “Molecular Power” by a Stimuli‐Responsive Molecule

8.4 Mesoscale Motion Generated by Cooperation of “Molecular Power”

8.5 Summary and Outlook

References

Chapter 9: Molecular Technologies for Photocatalytic CO

2

Reduction

9.1 Introduction

9.2 Photocatalytic Systems Consisting of Mononuclear Metal Complexes

9.3 Supramolecular Photocatalysts: Multinuclear Complexes

9.4 Photocatalytic Reduction of Low Concentration of CO

2

9.5 Hybrid Systems Consisting of the Supramolecular Photocatalyst and Semiconductor Photocatalysts

9.6 Conclusion

Acknowledgements

References

Chapter 10: Molecular Design of Photocathode Materials for Hydrogen Evolution and Carbon Dioxide Reduction

10.1 Introduction

10.2 Photocathode Materials for H

2

Evolution

10.3 Photocathodes for CO

2

Reduction Based on Molecular Catalysts

Acknowledgements

References

Chapter 11: Molecular Design of Glucose Biofuel Cell Electrodes

11.1 Introduction

11.2 Molecular Approaches for Enzymatic Electrocatalytic Oxidation of Glucose

11.3 Molecular Designs for Enhanced Electron Transfers with Oxygen‐Reducing Enzymes

11.4 Conclusion and Future Perspectives

References

Index

End User License Agreement

List of Tables

Chapter 7

Table 7.1 Comparison of the diffusion coefficient (

D

) and length (

L

) between singlet and triplet exciton diffusions.

Table 7.2 Comparison of the vertical excitation energies and reorganization energies obtained by DFT and ab initio theories for the low‐lying states of the pentacene molecule (eV).

Chapter 8

Table 8.1 Examples of translational motion induced by “molecular power.”

Chapter 9

Table 9.1 Photocatalytic CO

2

reduction using rhenium(I) bipyridine complexes.

Table 9.2 Reaction rates of OERS of

fac‐

[Re(4,4′‐X

2

bpy)(CO)

3

(PR′

3

)]

+

and quantum yields of the photocatalytic CO

2

reduction.

a

Table 9.3 Photocatalytic CO

2

reduction using

fac

‐[Re(bpy)(CO)

3

(L)] with an anionic ligand L (L = Cl

−

, NCS

−

, CN

−

) and their photophysical and electrochemical properties.

Table 9.4 Photocatalytic properties of Ru(II)−Re(I) systems.

Table 9.5 The relationship between the photocatalyses of

fac

‐[Re(N

∧

N)(CO)

3

(PR

3

)]

+

and their first reduction potentials.

a

Table 9.6 Photocatalytic properties of Ru(II)−Ru(II) systems.

Table 9.7 Photocatalytic properties of Ir(III)−Re(I) and Os(II)−Re(I) systems.

Chapter 10

Table 10.1 Comparison of the studies involving molecular photocathodes coated with [Fe

2

S

2

(CO)

6

] catalyst at pH = 0.3 under illumination with an Abet solar simulator.

Table 10.2 The reports by Moore and coworkers based on GaP‐modified cobaloxime photocathodes.

List of Illustrations

Chapter 1

Figure 1 Molecular structures of (a) pentacene, (b) rubrene, (c) DNTT, (d) C

‐BTBT, and (e) DNT‐V. (f) Annual change of the highest hole mobilities of different organic single‐crystal field‐effect transistors in the literature, and (g) the distribution of the reported mobilities for naphthalene [24], DNT‐V [25], pentacene [26–35], DNTT [36–41], C

‐BTBT [42–49], and rubrene [29, 31], [50–62].

Figure 2 (a) Structure of a single crystal of pentacene. (b) HOMOs of the molecules labeled A and B in (a). The transfer integral between molecules

is defined as the off‐diagonal elements of the Hamiltonian matrix

on the molecular orbital basis set.

Figure 3 (a) Schematic picture ofthe hopping transport. Charge carrier localized at a molecule moves to the neighboring molecules by the thermally activated hopping process. (b) Potential energy surface for the neutral state and the charged state of the single molecule.

Figure 4 Temperature‐dependent behavior of the hopping and band mobilities of pentacene single crystal with the transfer integrals between adjacent molecules are 43.6, 71.5, and

111.3 meV [73]. The reorganization energy of a pentacene molecule is

92 meV and the calculated hopping mobility is shown by the black triangles. For the reference, the hopping mobilities are calculated for the several reorganization energies from 1 to 400 meV. The calculated band mobility is represented by the white squares.

Figure 5 (a) Schematic picture of the band transport. Extended charge carriers are described by the Bloch states with the wave‐vector

and scattered by the molecular vibrations (phonons). (b) HOMO bands obtained from DFT using the plane‐wave basis set with symmetry points of

(0, 0, 0), X(1/2, 0, 0), Y(0, 1/2, 0), and S(1/2, 1/2, 0). The Fermi energy is located at

eV.

Figure 6 (a) HOMO band dispersion of bare electron of the pentacene single crystal. (b) Schematic picture of band narrowing by polaron formation.

Figure 7 Schematic picture of various extrinsic disorders and the depth of trap potential.

Figure 8 Schematic picture of an electron wave‐packet propagation in the organic semiconductor (a). Flowchart of numerical calculations for evaluating the mobility using the wave‐packet dynamics combined with the molecular dynamics (b).

Figure 9 Computing time and memory usage per one wave‐packet as a function of number of molecules on the TD‐WPD method. The number of molecule of two‐dimensional monolayer pentacene single crystal with each side length of 1

m is shown as an example. The number of time step is set to 1000.

Figure 10 (a) Schematic picture of a polaron state in an isolated pentacene molecule and in a pentacene single crystal. The calculated binding energies of polaron state and their size are also shown. (b) Fluctuation of some transfer integrals between molecules induced by the intermolecular vibrations.

Figure 11 (a) Temperature dependence of mobility of pentacene single crystals for several magnitudes of trap potential

. (b) Mean free path normalized by the intermolecular distance

vs temperature characteristics for several

. (c) Schematic picture of electron (hole) transport of organic semiconductor on the gate dielectric. Randomly oriented dipoles in gate dielectric are possible origin of trap potentials. If the transfer integral

is larger than the trap potential

, the electron–phonon scattering is dominated, thus the mobility decreases as increasing temperature. On the other hand, if

, the charge carrier is trapped tightly by the potential

; Therefore, the transport properties are close to typical thermally activated behaviors.

Figure 12 (a) Band and hopping mobilities at 300 K are plotted by squares and triangles, respectively, for naphthalene, DNT‐V, pentacene, DNTT, C

‐BTBT, and rubrene. (b) Mobilities at 300 K calculated by TD‐WPD method for naphthalene, DNT‐V, pentacene, DNTT, C

‐BTBT, and rubrene. Note that the mobility divided by 10 for the results of TD‐WPD method was plotted. Here, same material parameters, such as the transfer integrals, are employed even in above different theories. For comparison, the distributions of mobilities observed at room temperature are drawn by vertical bars.

Chapter 2

Figure 2.1 Schematic illustration of the assembly of crystalline metal–organic framework (MOF) nanosheets at the air/liquid interface.

Figure 2.2 Formation of NAFS‐13 (PdTCPP‐Cu nanosheet) was monitored by in situ grazing incident XRD measurements. The solution of PdTCPP molecular building units is spread onto the copper ion aqueous solution in a Langmuir trough. The surface pressure,

π

, is controlled by the movement of a single barrier and is kept constant during the collection of each GIXRD profile at the air/liquid interface. The right top figure shows surface pressure – mean molecular area (

π

 − 

A

) isotherms for NAFS‐13 (red) and for PdTCPP solution spread onto pure water subphase (black).

Figure 2.3 Proposed molecular arrangements of PdTCPP nanosheets in two different subphases as deduced by concentration of the molecular areas derived by the

π

 − 

A

isotherms.

Figure 2.4 UV–Vis absorption spectra for PdTCPP nanosheets (monolayer) fabricated on copper ion solution (NAFS‐13, red solid line) or pure water (black solid line) subphase.

Figure 2.5 In situ grazing incidence in‐plane synchrotron X‐ray diffraction patterns collected at the air/liquid interface for NAFS‐13 nanosheets. (a) Observed GIXRD (λ = 1.549 Å, incidence angle,

α

 = 0.12°) profiles at surface pressures,

π

 = 0, 1, 5, 10, 20, and 30 mN m

−1

. (b) Basal plane projection of the crystalline structure of NAFS‐13, which consists of a 2D “checkerboard” motif of PdTCPP units linked by binuclear Cu

2

(COO)

4

paddle wheels. (c) Schematic diagram of the crystalline structure of NAFS‐13, which consists of 2D sheets of thickness ∼3 Å viewed along the

b

axis. (d–g) Evolution of the crystalline structure and morphology of the molecularly thin NAFS‐13 nanofilms with change in surface compression. (d) Surface pressure – mean molecular area (

π

 − 

A

) isotherm. (e) Unit cell basal plane dimension,

a

. (f) Average crystalline sheet domain size estimated from the full width at half maximum of the intense (110) Bragg reflection. (g) Relative intensity of the (110) reflection normalized to the value at the highest surface compression versus mean molecular area.

Figure 2.6 UV–Vis absorption spectra for NAFS‐13 nanosheets. The films formed at a surface pressure of 1, 10, and 20 mN m

−1

were deposited onto quartz substrates and the spectra were measured after a rinsing/solvent immersion/drying process.

Figure 2.7 Schematic illustration of the assembling processes of the NAFS‐13 nanosheets at the air/liquid interface. Spreading molecular components PdTCPP on the copper ion aqueous solution subphase (a) drives immediate formation of 2D arrays where PdTCPP molecules are highly ordered because of the coordinative interaction between their carboxylic parts and copper ions. (b) The 2D domain arrays are distributed inhomogeneously when the surface area is relatively large in comparison with the number of spread molecules – the low surface pressure condition. (c) Further pressing of the surface gathers the 2D arrays to a smaller area, resulting in the high coverage of the sheets after deposition onto the solid substrates and the size of the crystalline domains becomes smaller by squeezing neighboring domains each other.

Figure 2.8 Brewster angle microscopy (BAM) images of the NAFS‐13 nanosheet at the air/water interface captured during compression. (a) Surface of the aqueous Cu

2+

ion aqueous solution subphase before spreading PdTCPP molecules, (b) at 0 mN m

−1

, after spreading PdTCPP molecules, (c) at 1 mN m

−1

, (d) at 5 mN m

−1

, (e) at 10 mN m

−1

, (f) at 20 mN m

−1

, (g) at 33 mN m

−1

, and (h) at 40 mN m

−1

.

Figure 2.9 Schematic illustration of the postinjection methodology employed in the fabrication of NAFS‐13 nanosheets. A PdTCPP solution is first spread directly on the pure water subphase. A concentrated copper ion aqueous solution is then slowly injected into the water subphase from the side surface, which is separated from the Langmuir trough by the compression barrier.

Figure 2.10 Observed grazing incidence in‐plane synchrotron GIXRD profiles (

λ

 = 1.549 Å, incidence angle,

α

 = 0.12°) for PdTCPP spread on the pure water subphase before (black line) and after (red line) injection of the copper ion aqueous solution in the absence of barrier compression. The

inset

shows a comparison of the in‐plane GIXRD profiles for the NAFS‐13 nanosheets formed by the conventional method of Figure 2.2 (blue line) and the postinjection method (red line) at

π

 = 0 mN m

−1

.

Figure 2.11 Brewster angle microscopy (BAM) images taken during the formation of the NAFS‐13 nanofilms fabricated by the postinjection (a and b) and the conventional (c and d) methods at compressions,

π

 = 0 and 20 mN m

−1

.

Figure 2.12 Schematic illustration of the assembly of the ZnTPyP‐Cu nanosheets (NAFS‐21) at the air/liquid interface.

Figure 2.13 Schematic illustration of the assembly process of the H

2

TCPP‐Cu nanosheets (NAFS‐2) at the air/liquid interface and their layer‐by‐layer (LbL) growth.

Figure 2.14 (a and b) Evolution of the UV–Vis absorption spectra (a) and IR absorption spectra (b) of NAFS‐2 on a SiO

2

/Cr/Au substrate with successive cycles of sheet deposition, rinsing, and drying. (c and d) Maximum absorbance of the H

2

TCPP Soret band (c) and the COO symmetric stretch band (d) of NAFS‐2 as a function of the number of film growth cycles.

Figure 2.15 Schematic illustration of possible structural variations of MOF nanosheets by LbL growth.

Figure 2.16 Schematic illustration of the MOF nanosheet fabrication protocol at the air/liquid interface and the molecular structures of the building units used. The combination of H

2

TCPP and copper ion leads to the formation of the nonpillar type of sheet described in Figure 2.15a, whereas the combination of CoTCPP, pyridine (py), and copper ion provides the sheet that includes the monodentate pillar projecting from the sheet plane, as shown in Figure 2.15b.

Figure 2.17 Grazing incidence synchrotron X‐ray diffraction profiles for NAFS films. (a, b) Observed wide‐range in‐plane XRD profiles for NAFS‐2 (a) and NAFS‐1 (b). The inset shows a schematic diagram of the proposed in‐plane crystalline structures and basal plane dimensions by using a pseudo‐2D tetragonal unit cell. The left image shows the combination of the molecular components and metal ion linkers – H

2

TCPP‐Cu for NAFS‐2 (top) and CoTCPP‐py‐Cu for NAFS‐1 (bottom).

Figure 2.18 Out‐of‐plane synchrotron X‐ray diffraction profiles for NAFS films and schematic images of the sheet stacking motifs. (a and b) Observed wide‐range out‐of‐plane XRD profiles for NAFS‐2 (a) and NAFS‐1 (b). (c and d) Schematic images of the layering manner in NAFS‐2 (c) and NAFS‐1 (d).

Figure 2.19 Rocking curve

θ

scan at the (001) reflection position in the out‐of‐plane orientation. (a) Rocking curves provide information on the degree of crystallinity. Full width at the half maximum (FWHM) of a peak observed in the rocking curve of a layer‐structured material represents the average tilting angle of the stacking layers. (b and c) Rocking curves observed for the NAFS‐2 (b) and NAFS‐1 (c) films. (d and e) Schematic images of the layer stacking motif for NAFS‐2 (d) and NAFS‐1 (e).

Figure 2.20 Molecular structures of the porphyrin building units, 5,10,15,20‐tetrakis(4‐carboxyphenyl)‐porphyrin (H

2

TCPP),

trans

‐5,15‐diphenyl‐10,20‐di(4‐carboxyphenyl)porphine (

trans

‐H

2

DCPP), and 5,10,15,20‐tetrakis[4‐(4‐carboxyphenylethynyl)phenyl]porphine (H

2

TCPEPP).

Figure 2.21 Grazing incidence (GI) in‐plane synchrotron X‐ray diffraction (XRD) patterns (green dots) for NAFS‐31 (a) and NAFS‐41 (b) nanosheets (left panels). In‐plane lattice parameters and indexing of the Bragg peaks are shown in the plots. Derived structural models for NAFS‐31 (a) and NAFS‐41 (b) are shown in the right panels. Calculated GIXRD patterns (black lines) and reflection positions (black bars) using the structural models are also shown.

Figure 2.22 Summary of the in‐plane structural arrangements in porphyrin‐based MOF nanosheets assembled at the air/liquid interface. Molecular building units (top) and corresponding in‐plane crystalline structures (bottom) are shown together with the unit cells obtained from synchrotron GIXRD measurements and calculated Connolly surfaces.

Chapter 3

Figure 3.1 Requirements of the next‐generation organic semiconductor.

Figure 3.2 Herringbone packing (2D), brick‐work packing (2D), and π‐stacking (1D).

Figure 3.3 HOMO and LUMO levels of a series of acenes (HOMO and LUMO levels are calculated at B3LYP/6‐31Gd and B3LYP/6‐31Gd

+

 levels, respectively).

Figure 3.4 (a) Chemical structures of benzene, naphthalene, anthracene, tetracene, and pentacene. (b) Packing structures of these acenes along with their space group in single‐crystal structures. (c) Electrostatic potential maps of all acenes in the property range from −100 to +100 kJ mol

−1

(calculated by SPARTAN 16 program).

Figure 3.5 Historical molecular design of p‐type semiconductors: Chemical structures and HOMO of a series of acenes and heteroacenes.

Figure 3.6 (a) Chemical structures of [5]TAc, DBTDT, BTBT, and DNTT. (b) Packing structures of [5]TAc, DBTDT, BTBT, and DNTT along with the absolute transfer integral values in the direction of column and transverse and their space group in single‐crystal structures. (c) Electrostatic potential maps of [5]TAc, DBTDT, BTBT, and DNTT in the property range from −100 to +150 kJ mol

−1

(calculated by SPARTAN 16 program).

Figure 3.7 Chemical structures and packing structure of TIPS‐Pen. (Triisopropylsilylethynyl groups are omitted for clarify.)

Figure 3.8 (a) Chemical structures of C

8

–BTBT and C

10

–DNTT and (b) packing structures of C

8

–BTBT and C

10

–DNTT along with the absolute transfer integral values (

t

c

and

t

t

) in the direction of column and transverse and their space group in single‐crystal structures.

n‐

Octyl and

n

‐decyl groups are omitted for clarify.

Figure 3.9 Molecular technology of bent‐shaped π‐electron cores.

Figure 3.10 Reaction scheme of DNT–V, C

n

–DNT–VW, DNBDT–N, and C

n

–DNBDT–NW.

Figure 3.11 Molecular structures of DNT–V, C

10

–DNT–VW, and C

10

–DNBDT–NW compared with those of BTBT and DNTT in single crystals.

Figure 3.12 (a) Chemical structures of DNT–V, C

10

–DNT–VW, and C

10

–DNBDT–NW, and HOMO of DNT–V and DNBDT–N (R = H). (b) Packing structures of DNT–V, C

10

–DNT–VW, and C

10

–DNBDT–NW along with the absolute transfer integral values (

t

c

,

t

t

,

t

t1

, and

t

t2

) in the direction of column and transverse (transfer integrals were calculated at PBEPBE/6‐31Gd level) and their space group in single‐crystal structures.

n

‐Decyl groups are omitted for clarify. (c) Electrostatic potential maps of DNT–V and DNBDT–N in the property range from −100 to +150 kJ mol

−1

(calculated by SPARTAN 16 program).

Figure 3.13 (a) Solution‐process image of edge‐casting method. (b) Solution‐crystallized films of C

10

–DNBDT–NW together with source and drain electrodes. (c and d) Transfer and output characteristics of the representative C

10

–DNBDT–NW solution‐crystallized transistor. (e) Thermal stress durability test of C

10

–DNBDT–NW solution‐crystallized transistor along with its molecular alignment and the device structure for the test.

Figure 3.14 Molecular design of n‐type semiconductors: chemical structures and LUMO.

Figure 3.15 Chemical structures of representative n‐type semiconductors.

Figure 3.16 (a) Chemical structures, molecular structure (space filling model), and packing structures of F

15

C

7

CH

2

–NDI, PDIF–CN

2

, and

m‐

OCF

3

–Ph–Th–BBT. F

15

C

7

CH

2

, F

7

C

3

CH

2

, and

m

‐OCF

3

groups for each molecule are omitted for clarity, respectively.

Figure 3.17 Hole and electron mobilities vs market size. Representative solution‐processable organic semiconductors along with high performance and high chemical stability.

Chapter 4

Scheme 4.1 Catalytic cycle proposed for [FeFe] hydrogenases.

Scheme 4.2 Mechanism of peroxidases.

Scheme 4.3 (a) Enzymatic nitrogen fixation. (b) Structure of FeMo‐co in molybdenum‐dependent nitrogenases. (c) Proposed mechanism for reduction of N

2

on FeMo‐co. E

n

denotes the FeMo‐co, where

n

gives the number of electrons transferred.

Scheme 4.4 Reversible deprotonation of pyrazole and hydroxypyridine ligands.

Scheme 4.5 (a) Synthesis of ruthenium complexes

4

and

5

bearing protic NNN pincer‐type ligands

3

. (b) Hydrogen bond interactions in protic pincer‐type complexes

4

.

P

 = PPh

3

.

Scheme 4.6 Reversible deprotonation and subsequent transformations of protic pincer‐type complex

4b

.

Ru

 = Ru(PPh

3

)

2

.

Scheme 4.7 Catalytic disproportionation of hydrazine with protic pincer‐type iron complex

10a

.

Scheme 4.8 Proposed mechanism for catalytic disproportionation of hydrazine with protic pincer‐type complex

10a

.

Fe

 = Fe(PMe

3

)

2

2+

. The

tert

‐butyl groups in the pincer ligand have been omitted in the mechanistic scheme.

Scheme 4.9 Synthesis and reactivities of unsymmetric, multiproton‐responsive pincer‐type complexes.

Scheme 4.10 Synthesis of protic NCN pincer‐type complexes.

Scheme 4.11 Synthesis of

N

,

N

‐chelate bis(hydroxypyridine) complexes

29

and

31

.

Scheme 4.12 Proposed mechanism for catalytic dehydrogenative oxidation of benzyl alcohol with bis(pyridonato) complex

32

.

Scheme 4.13 Dehydrogenation of formic acid and hydrogenation of CO

2

catalyzed by tetrahydroxybipyrimidine complexes

39

and

40

.

Scheme 4.14 Proposed mechanism for catalytic dehydrogenation of formic acid with bis(hydroxypyridine) complex

31

.

Scheme 4.15 Electrochemical water oxidation catalyzed by bis(hydroxypyridine)copper complexes.

Scheme 4.16 Synthesis of ruthenium complex

42

bearing hydroxypyridine‐based protic pincer‐type ligand.

Scheme 4.17 Proposed mechanism for catalytic transfer hydrogenation of ketone with protic pincer‐type complex

43

.

Scheme 4.18 Reactions of tris(pyrazolylmethyl)amine ruthenium complex

46

.

Scheme 4.19 Reactions of tris(hydroxylpyridylmethyl)amine copper complexes

52

.

Scheme 4.20 Dioxygen reduction catalyzed by protic tripodal manganese complex

46

. Protons and electrons required in each step are provided by 1,2‐diphenylhydrazine.

Scheme 4.21 Reactions of iron complex

61

bearing protic tripodal ligand.

Chapter 5

Figure 5.1 Schematic illustration of reversible photo‐alignment by a “command surface.”

Figure 5.2 (a) Schematic illustration of a photo‐alignment system using a photo‐responsive layer at the free surface. (b) Illustration of the inkjet printing procedure of a free‐surface command layer on a homeotropically aligned, non‐photo‐responsive LC polymer. (c and d) Examples of birefringence patterning by this inkjet alignment method. Scale bar, 200 μm.

Figure 5.3 Polarized optical micrographs of phototropic phase transitions. Illustrations of the photo‐induced phase transitions from isotropic to nematic (a–c), nematic to smectic (d–f), and isotropic to nematic (g–i).

Figure 5.4 (a) Schematic diagram of the optical setup for the observation of laser‐pointer‐driven nonlinear optical effects in a hybrid‐aligned cell. (b) Photograph of a ring pattern generated from a hybrid‐aligned cell with a common 1 mW handheld laser pointer.

Figure 5.5 (a) Unidirectional molecular alignment behavior of the polymer film photo‐polymerized with a line‐space photomask. Illustration of the photo‐polymerization process and a micrograph of the line‐space photomask (left). Polarized optical micrographs of the polymerized film (right). (b) Two‐dimensional (2D) molecular alignment by photo‐polymerization with a pinhole photomask. Micrographs of the pinhole (left) and 2D aligned film (center). Illustration of the alignment direction of the fabricated polymer film (right).

Figure 5.6 Photo‐actuation modes of azobenzene‐containing cross‐linked LC polymer ribbons, exhibiting a complex twisting photo‐mechanical response.

Figure 5.7 Actuation behavior of cross‐linked LC polymer films with the azimuthal and radial alignment upon heating with an IR lamp. The arrows along the radius and the azimuth indicate the direction of deformation.

Figure 5.8 (a) Photograph of LCE film with nine +1 topological defects between crossed polarizers and illustration of the alignment direction around the defect. (b) Actuation behavior of the LCE film. Nine cones arise from the LCE film upon heating, and the film becomes reversibly flat upon cooling.

Figure 5.9 (a) Illustrations showing a light‐driven motion of liquid “slugs” inside a tubular microactuator driven by photo‐deformation. (b) Photographs of the reversible motion of a silicone oil slug inside a microtube actuated by 470 nm light.

Chapter 6

Figure 1 Circularly polarized light obtained from vertically and horizontally polarized light.

Figure 2 Electric and magnetic dipole transition moment vectors. Antiparallel, perpendicular, and parallel transition moments are shown.

Figure 3 A series of chiral europium(III) camphorate complexes and their g

lum

values at the

5

D

0

 → 

7

F

1

transition [32–38].

Figure 4 Schematics of magnetic circular dichroism spectra. (a) When a material is put in the applied magnetic field along the direction of light propagation, the absorption spectrum of LCP is different from that of RCP; both peak wavelength and intensity are different between them. (b) When the direction of the magnetic field is reversed, the absorption spectra of LCP and RCP are replaced with each other.

Figure 5 Schematic diagram of propagation of circularly polarized light in helical superstructure and photonic bandgap arising from the helical superstructure.

Figure 6 This is the first report on the chirality of molecular assemblies and spiral nanostructures formed through the air/water interface by achiral molecules. An amphiphilic barbituric acid derivative was found to form stable monolayers showing a clear phase transition at the air/water interface. It is interesting to find that the deposited Langmuir–Blodgett (LB) films of the compound showed CD although the molecule itself was achiral. Atomic force microscope (AFM) measurements on the transferred one‐layer LB film revealed that spiral nanoarchitectures were formed.

Figure 7 CD micrograph of a thin (<50 mm) DHA crystal showing the (110) and (100) twin planes between enantiomorphous domains. The wavelength of observation was 530 nm.

Figure 8 Magnified transmission (a, c) and CD (b, d) images of the two‐dimensional array of chiral (swirl‐shaped) gold nanostructures. The wavelength of observation both for the transmission and CD images was 700 nm.

Figure 9 Macroscopic and local CD of gold nanostructures. (a) CD spectra macroscopically measured with the use of arrayed nanostructures (b) Distributions of local CD signals in the individual nanostructures observed with a near‐field CD imaging technique. The CD signal was defined as

as described above.

Chapter 7

Figure 7.1 Electronic couplings associated with the various transition processes against the distance of two anthracene molecules, which are placed in face‐to‐face orientation with slip parallel to the long‐axis and short‐axis by 1.0 and 0.5 Å, respectively.

Figure 7.2 Schematic diagrams for various transition processes in the materials.

Figure 7.3 Scheme for the common mechanism of TTA‐based UC. The system includes triplet sensitizer and emitter molecules (S = singlet, T = triplet).

Figure 7.4 Chemical structures of sensitizers having NIR (>700 nm) absorption.

Figure 7.5 Chemical structures of emitters that show fluorescence in the visible range (<700 nm).

Figure 7.6 Upconverted emission spectra of the

12

–

15

pair in deaerated 1,2‐dichlorobenzene under excitation of the 856 nm laser ([

12

] = 0.05 mM, [

15

] = 0.6 mM, 810 nm short‐pass filter).

Figure 7.7 (a) Common TTA‐based UC mechanism via sensitizer ISC that involves energy loss. (b) TTA‐based UC mechanism utilizing S–T absorption of sensitizer. The absence of energy loss due to ISC allows the large anti‐Stokes shift from NIR to visible range. (c) Chemical structures of sensitizer

16

and emitter rubrene. (d) Scanning electron microscopy image of the

16

‐doped rubrene nanoparticles. (e) Photograph of upconverted yellow emission of

16

‐rubrene in PVA film in air under 938 nm NIR excitation. (f) In‐air upconverted emission spectrum of the

16

‐doped rubrene nanoparticles dispersed in PVA film (λ

ex

 = 938, 780 nm short‐pass filter).

Figure 7.8 Chemical structure of the acene‐type SF compounds.

Figure 7.9 (a) Schematic of the SF process in the pentacene/C

60

photodetector and (b) energy diagram of the pentacene/C

60

photodetector.

Figure 7.10 EQE under background light (a) amorphous and (b) crystalline rubrene/C

60

OPVs, absorption spectra of (a) amorphous and (b) crystalline rubrene.

Figure 7.11 Chemical structure of the rylene‐type SF compounds.

Figure 7.12 Chemical structure of the nonpolycyclic SF compounds.

Figure 7.13 Chemical structure of the polymer‐type SF compounds.

Chapter 8

Figure 8.1 Schematic image of a flashing ratchet system. (a) An object is trapped. (b) External energy is injected, resulting in Brownian motion. (c) The injection of energy is stopped. (d) The object is trapped again.

Figure 8.2 Interaction between a substrate and an object. (a) Bare surfaces. (b) Modified surfaces with molecules. (c) Modified surfaces with molecules of various lengths.

Figure 8.3 Representative molecular machines. (a) Pirouette [27]. (b) Shuttle [28]. (c) Rotor [29].

Figure 8.4 Isomerization of photochromic compounds. (a) Azobenzene. (b) Spiropyran. (c) Diarylethene.

Figure 8.5 Illustrations of translational motions of a rod and beads. (a) Self‐propelled motion of Au/Pt Janus rod with consumption of hydrogen peroxide. (b) Passive motion of polystyrene beads in liquid crystal by photothermal conversion at polyimide film. (c) Passive motion of quantum dots by repetitive photoisomerization of DBAB.

Figure 8.6 (a) Light‐controlled locomotion of azobenzene elastomer. (b) Clustering of polystyrene beads by morphological change of self‐assembly composed of

1c

and

1o

.

Figure 8.7 Sequential micrographs of autonomous mesoscopic motion under continuous light irradiation. (a) Rotation of a glass rod. (b) Swimming of a self‐assembly.

Chapter 9

Figure 9.1 Use of oil in Japan (2014) [1].

Figure 9.2 Purpose of artificial photosynthesis.

Figure 9.3 Requirements for constructing artificial photosynthesis.

Figure 9.4 Photochemical electron transfer.

Figure 9.5 Two types of initiation mechanism in photocatalytic reactions.

Scheme 9.1 Photocatalytic CO

2

reduction using [Re(4,4′‐X

2

‐bpy)(CO)

2

LL′]

n

+

.

Scheme 9.2 Reaction mechanism of the OERS of

2

and CO

2

in the dark.

Scheme 9.3 Efficient multicomponent system with

4b

as PS and

8

as CAT.

Scheme 9.4 Mixed system of [Ru(dmb)

3

]

2+

and

13

functions under visible‐light irradiation.

Scheme 9.5 Structures of

Re‐ring

and BIH.

Scheme 9.6 Photocatalytic CO

2

reduction using a dye PS and a Co macrocyclam.

Scheme 9.7 Structure of Fe porphyrins as CATs for CO

2

reduction.

Scheme 9.8 Cu

I

complexes used as PSs in the photocatalytic reduction of CO

2

.

Scheme 9.9 Mixed system of [Ru(dmb)

3

]

2+

and

17

functions under visible‐light irradiation.

Scheme 9.10 Conceptual image of supramolecular photocatalysts for the reduction of CO

2

.

Scheme 9.11 Conceptual images of the hybrid systems of (a) the supramolecular photocatalyst and (b) the mixed system of mononuclear complexes on the surfaces of heterogeneous materials.

Chart 9.1 Structures and abbreviations of Ru(II)−Re(I) complexes.

Scheme 9.12 Reaction mechanisms of the photocatalysis using

Ru−Re1

.

Scheme 9.13 Reaction mechanisms using

Ru−Re14

.

Chart 9.2 Structures and abbreviations of Ru(II)−Ru(II) complexes.

Chart 9.3 Structures and abbreviations of Os(II)−Re(I) and Ir(III)−Re(I) complexes.

Figure 9.6 IR spectra of a DMF–TEOA (5 : 1 v/v) solution containing the equilibrated mixture of

Re−DMF

and

Re−OC

2

H

4

NR

2

before (blue) and after (red) CO

2

bubbling.

Figure 9.7

13

C NMR spectrum of

Re−OC(O)OC

2

H

4

NR

2

without

1

H decoupling under a

13

CO

2

atmosphere.

Figure 9.8 Ligand substitution of the dinuclear

Ru−Re−DMF

complex and the CO

2

capture behaviour in a mixed solvent system of DMF and TEOA (5 : 1 v/v). Three complexes,

Ru−Re−DMF

,

Ru−Re−OC

2

H

4

NR

2

and

Ru−Re−OC(O)OC

2

H

4

NR

2

, observed in the mixed solvent system under a CO

2

atmosphere. Composition ratios of the complexes depending on CO

2

concentration in a solution.

Figure 9.9 Photocatalytic reaction using

Ru−Re−DMF

and

Ru−Re−OC

2

H

4

NR

2

under a 100% or 10% CO

2

atmosphere, where blue, green, red and orange dots denote the turnover numbers of CO formation under 100% CO

2

, CO formation under 10% CO

2

, H

2

formation under 100% and H

2

formation under 10%, respectively.

Figure 9.10 Photocatalytic CO formation under various concentrations of CO

2

(0.5–100%).

Figure 9.11 Profound influence on photocatalytic CO

2

reduction by triethanolamine: (a) photocatalytic reactions under 100% and 1% CO

2

atmosphere with and without TEOA. (b) Linear relationship between the initial rate of CO formation and the concentration of

Ru−Re−OC(O)OC

2

H

4

NR

2

.

Scheme 9.14 Hybrid photocatalysts consisting of a supramolecular photocatalyst and semiconductors.

Figure 9.12

1

H NMR spectra of the photocatalytic reaction solutions:

(P)−Ru−Ru(CO)

2

Cl

2

−Ag/TaON

was irradiated at

λ

ex

 > 400 nm for 15 h in (a) CH

3

OH under

13

CO

2

and (b) CH

3

OH saturated with unlabelled CO

2

. Mass spectra of formaldehyde peaks in the GC/MS analysis of the photocatalytic reaction solutions:

(P)−Ru−Ru(CO)

2

Cl

2

−Ag/TaON

(1 mg) was irradiated at

λ

ex

 > 400 nm for 24 h in (c) unlabelled CO

2

‐saturated

13

CH

3

OH and (d) unlabelled CH

3

OH. Adapted with permission from ref. [36]. Copyright 2012 American Chemical Society.

Chapter 10

Figure 10.1 Schematic representation of the photosynthetic chain.

Figure 10.2 Schematic representation of photoelectrochemical cells (PECs) for water splitting or CO

2

reduction coupled with water oxidation.

Figure 10.3 Structure of the InP‐based electrode with physisorbed diiron catalyst.

Figure 10.4 Structure of the bioinspired sulfide clusters of molybdenum and tungsten used as hydrogen‐evolving catalysts by Chorkendorff and coworkers [18] to decorate silicon‐based photocathodes.

Figure 10.5 Structures of molecular‐based electrodes based on p‐Si [23] or p‐GaP [24] semiconductor materials.

Figure 10.6 Structure of photoelectrodes based on H

2

‐evolving catalysts attached onto TiO

2

via phosphonate [25] and carboxylate linkages [26].

Figure 10.7 Structure of various photoelectrodes based on ferrocenophane [28] and cobaloxime [29] catalysts embedded or grafted in polymeric frameworks.

Figure 10.8 Mechanism of light‐driven H

2

evolution in the ITO/H

2

Pc/C

60

‐Pt system. H

2

evolves at Pt‐loaded C

60

, after a 20‐min induction period during which C

60

2−

is formed.

Figure 10.9 Schematic illustration of a two‐compartment cell for unassisted solar water splitting using a TiO

2

photoanode and an OSC‐based photocathode.

Figure 10.10 Architectures of (a) the P3HT:PCBM/a‐MoS

x

[57] and (b) SubPc:C60/a‐MoS

x

[58] H

2

‐evolving photocathodes.

Figure 10.11 Schematic presentation of the electron transfers taking place upon irradiation of a dye‐sensitised photocathode (top) and the three different H

2

‐evolving photocathode architectures (bottom): physisorbed or diffusing catalyst (a); covalent or supramolecular dye–catalyst assembly (b); co‐grafted dye and catalyst (c).

Figure 10.12 Structure of photocathodes based on dye‐sensitised NiO with a physisorbed (a) [80] or a diffusing (b) [81] H

2

‐evolving catalyst.

Figure 10.13 Structures of photocathodes based on supramolecular (a) [84] or covalent (b) [85] dye–catalyst assemblies.

Figure 10.14 Structure of H

2

‐evolving dye‐sensitised photocathodes based on layer‐by‐layer fabricated supramolecular dye–catalyst assemblies [75, 86].

Figure 10.15 Dyes and catalysts employed for the construction of co‐grafted H

2

‐evolving photocathodes.

Figure 10.16 Schematic of CO

2

reduction using a combination of a molecular catalyst and a semiconductor photoelectrode.

Figure 10.17 Structures of Re molecular catalyst (a) utilised in Ref. [103] and Ru catalysts with pyrrole (b) and phosphonate groups (c) used in Refs [104, 105].

Figure 10.18 Protected Cu

2

O photoelectrode with covalently bound Re(I) CO

2

reduction catalyst.

Figure 10.19 Schematic of the photoelectrochemical cell for tandem CO

2

reduction and water oxidation comprising a RCP/InP–Zn photocathode and metal‐oxide photoanodes.

Figure 10.20 Schematic of CO

2

reduction using a molecular photocatalyst immobilised on a semiconductor electrode.

Figure 10.21 Structures of the supramolecular photocatalysts comprising a zinc porphyrin (a, [115]) or Ru(II) (b, [7, 116]) sensitiser and a Re(I) catalyst unit with carboxylic or methylphosphonate groups as anchors.

Figure 10.22 Schematic of hybrid photoelectrochemical cell comprising the NiO–

RuRe

photocathode and CoO

x

/TaON photoanode [118].

Chapter 11

Figure 11.1 Schematic presentation of the influence of the electron transfer type to the cell voltage of EBFCs related to the standard redox potential of glucose and oxygen vs NHE. FAD‐dependent glucose‐oxidizing enzymes and oxygen‐reducing multicopper enzymes are chosen as examples.

Figure 11.2 Illustrations of the different glucose‐oxidizing enzymes, their cofactors, and the two categories of most efficient molecular mediators.

Figure 11.3 Sketch of the mostly used oxygen‐reducing enzymes (laccase and BOD) for biofuel cell applications and appropriate molecular functions for oriented immobilization and promoted DET. In the center, the structure of ABTS used for MET modes is displayed.

Figure 11.4 Potential application of enzymatic biofuel cell.

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Related Titles

Yamamoto, H., Kato, T. (eds.)

Molecular Technology

Volume 2: Life Innovation

2018

ISBN: 978-3-527-34162-7

Yamamoto, H., Kato, T. (eds.)

Molecular Technology

Volume 3: Materials Innovation

2019

ISBN: 978-3-527-34161-0

Yamamoto, H., Kato, T. (eds.)

Molecular Technology

Volume 4: Synthesis Innovation

2019

ISBN: 978-3-527-34588-5

Molecular Technology

Energy Innovation

Edited by Hisashi Yamamoto and Takashi Kato

Volume 1

Copyright

Editors

Professor Hisashi Yamamoto

Chubu University

Molecular Catalyst Research Center

1200 Matsumoto

Kasugai

487-501 Aichi

Japan

Professor Takashi Kato

University of Tokyo

Department of Chemistry & Biotechnology

7-3-1 Hongo, Bunkyo-ku

113-8656 Tokyo

Japan

Cover

fotolia\_VAlex and fotolia\_Slanapotam

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Cover Design Adam-Design, Weinheim, Germany

Foreword by Dr Hamaguchi

Molecular Technology is a newly developed research field supported through Japan Science and Technology Agency (JST) research funding programs. These programs aim to establish an innovative research field that harnesses the characteristics of molecules to enable new scientific and commercial applications. It is our great pleasure to publish this book, with the ambition that it will develop both an understanding of and further support for this new research field within the research and student community.

Molecular Technology as introduced in this book began in 2012 as a research area within JST's Strategic Basic Research Programs. JST is an advanced network‐based research institution that promotes state‐of‐the‐art R&D projects and leads the way in the cocreation of future innovation in tandem with wider society. JST develops a wide range of funding programs related to the promotion of scientific and technological innovation, which include strategy planning, target‐driven basic research, and promotion of research and development.

Various research projects focused on Molecular Technology are currently underway within JST's Strategic Basic Research Programs:

The team‐based research program “CREST (Core Research for Evolutionary Science and Technology)”

The individual research program “PRESTO (Precursory Research for Embryonic Science and Technology).”

Dr Yamamoto (CREST) and Dr Kato (PREST) manage the Molecular Technology Research Area as research supervisors.

In addition, JST's Strategic International Collaborative Research Program promotes research projects in the area of Molecular Technology, including ongoing cooperation with L'Agence nationale de la recherche (The French National Research Agency, ANR).

A wide range of researchers from young to senior across the fields from green science, life science, and energy are participating in successful research aimed at establishing the new field of Molecular Technology. They are already producing excellent research results, and it is our hope that these will develop into technologies capable of initiating a new era in energy, green, and life sciences.

I encourage you to read not only researchers in related fields but also look more broadly to researchers working in other fields. Inspired by this book, I look forward to emerging new research fields and seeds toward future innovation.

Michinari Hamaguchi

President, Japan Science and Technology Agency

Foreword by Dr Noyori

As an affiliated institution of the Japan Science and Technology Agency (JST), the Center for Research and Development Strategy (CRDS) navigates the latest global trends in science, technology, and innovation to aid the Japanese government in formulating its national strategies. Molecular Technology is the outcome of a research project born of a CRDS Strategic Proposal realized under the excellent editorial supervision of Hisashi Yamamoto and Takashi Kato. To them and to the scientists who have made major advances in molecular technology through their uninhibited research, I extend my heartfelt congratulations and respect.

The significance of molecular science in all areas of scientific endeavor is certain to increase. Accurate understanding of molecular assemblies and molecular complexes is essential for comprehending the elaborate workings of natural phenomena and of the genesis and mechanisms of materials and life functions. Now, more than ever, science must be seen as a single entity, a comprehensive whole. Mathematical science and the most advanced technologies of observation and information help us to explore the essence of materials and substances in a way that brings together all fields of science. It is the nature of molecular science to continually advance and expand. Using the metaphor of light, we can say that molecules behave in the manner of both “waves and particles.”

The traditional separation of science into physics, chemistry, and biology no longer applies. Neither does it make any sense to maintain those seemingly self‐contained subdivisions of organic chemistry, inorganic chemistry, physical chemistry, or polymer chemistry. So long as specialized groups and rigid educational systems cling to outdated perceptions, the more important it is to encourage an “antidisciplinary” type of science in which diverse fields converge rather than conventional interdisciplinary or transdisciplinary attempts to link diverse fields.

Molecular Technology, while firmly grounded in fundamental scientific knowledge, aims for practical applications within contemporary society. Johann Wolfgang von Goethe once said, “Knowing is not enough; we must apply. Willing is not enough; we must do.” Technology with no practical application is meaningless to society. Researchers should not hesitate to set their own themes and topics of exploration in academia where self‐determination holds strong and creativity wins the highest respect. Researchers must show ingenuity in the pursuit of their chosen mission even as they fulfill their duty to pursue science‐based technology for society. Never forget that it is by no means advisable to function purely as a support for activities that industry should actually undertake on its own.

The creative outcomes of the Molecular Technology Project launched in 2013 in conjunction with new collaborations are certain to lead to a wide range of innovations and to make significant contribution to achieving the Sustainable Development Goals (SDGs) of the United Nations' 2030 Agenda.

Science is one; and the world is one. Those who will follow us have a responsibility to the world after 2030, and it is my hope that new generations will pioneer revolutionary molecular technology that will bring science and humanity ever closer together. Brain circulation and international collaboration are essential to achieve these goals. V. S. Naipaul, winner of the 2001 Nobel Prize in Literature, once noted that knowing what you wanted to write was three‐quarters of the task of writing. Humanity's future is to be found in the unbounded imagination of the young and in its ability to support the challenges they undertake.

December 2017

Ryoji Noyori

Tokyo, Japan

Preface

Chemical science enables us to qualitatively change exiting science and technology by purposefully designing and synthesizing molecules and creating the desired physical, chemical, and biological functions of materials and drugs at molecular level. In 2012, we started the big funding project in Japan, “Molecular Technology” (Establishment of Molecular Technology toward the Creation of New Functions (CREST) and Molecular Technology and New Functions (PRESTO)), and numerous research groups in Japan join the project of diverse research areas. All of these are typical transdisciplinary research projects between chemistry and various research areas of science and technology. In other words, Molecular Technology is the brand new scientific discipline. In principle, most of the proposed projects try to create the big bridge between chemistry and other basic science and technology. We thus propose a nice model for this bridge that is able to make valuable contribution for human welfares.

Between Japan Science and Technology Agency (JST) and French National Research Agency (ANR), we initiated a number of international collaboration projects of Molecular Technology in 2014. Since then 12 new collaboration projects started. The project provides quite unique collaboration opportunities between Japan and France, and quite active research groups involved in very close discussions of molecular technology between two countries. We are sure this project gave us close contacts between research groups of Japan and France for numerous discoveries. Overall, this international collaboration will be new entry for even more important discoveries in the future.

In 2016, we started the discussion for making a new and comprehensive book of molecular technology for the benefit of all researchers in the world to provide typical and leading examples of molecular technology. Overall, researchers of 15 CREST, 50 PRESTO, and 12 INTERNATIONAL groups have contributed to this book. Because of the wide areas of molecular technology, this book covers extremely diverse areas of science and technology from material to pharmaceuticals.

Hisashi Yamamoto

Chubu University, Supervisor of CREST

Takashi Kato

The University of Tokyo, Supervisor of PRESTO

1Charge Transport Simulations for Organic Semiconductors

Hiroyuki Ishii

University of Tsukuba, Division of Applied Physics, 1‐1‐1 Tennodai, Tsukuba, Ibaraki, 305‐8573, Japan

1.1 Introduction

1.1.1 Historical Approach to Organic Semiconductors

Organic semiconductors have the potential to be used in future electronic devices requiring structural flexibility and large‐area coverage that can be fabricated by low‐cost printing processes. Ordinary organic materials such as plastics (polyethylene) have primarily been regarded as typical electrical insulators. However, graphite exhibits the high electrical conductivity [1], which has been attributed to their molecular structures, which are made of network planes of the conjugated double bonds of carbon atoms with the ‐electrons. There exist some organic molecules that have similar molecular structures, for example, aromatic compounds. Around 1950, Eley [2], Akamatu and Inokuchi [3], and Vartanyan [4] have reported that the phthalocyanines, violanthrones, and cyanine dyes have semiconductive characters, respectively. These characters are attributed to the intermolecular overlapping of the electron clouds of ‐electrons in the condensed aromatic rings. These materials were named as organic semiconductors [5]. However, in general, these organic semiconductors were still recognized as the insulating materials because resistivity of these organic semiconductors is much higher than that of inorganic semiconductors such as silicon and gallium arsenide. The resistivity is given as

(1.1)

where , , and represent the carrier concentration, elementary charge of a carrier, and the electron (hole) mobility, respectively. The high resistivity of the organic materials originates from the low carrier concentration and the low mobility.

The carriers can be chemically doped by using the electron–donor–acceptor complexes. In 1954, Akamatu et al. found that the electron–donor–acceptor complex between perylene and bromine is relatively stable and has very good electrical conductance [6]. In 1973, Ferraris et al. have reported that the complex between the electron donor tetrathiafulvalene (TTF) and the electron acceptor tetracyano‐‐quinodimethane (TCNQ) has the very high conductivity comparable with the conductivities of metals such as copper [7]. Shirakawa et al. also showed that the organic polymer, polyacetylene, has a remarkably high conductivity at room temperature by chemical doping with iodine in 1977 [8]. These complexes are called organic conductors. The high electrical conductivity accelerated interest in organic conductors, not only because of their huge electrical conductivity but also by the possibility of superconductivity [9].

The multicomponent systems as mentioned above have some disadvantageous properties such as air and thermal instability in general. Therefore, semiconducting single‐component organic compounds are likely to be much more suitable for use as molecular devices. From a viewpoint of the electronic device applications, mobility is very important to evaluate the device performance because it characterizes how quickly an electron can move in a semiconductor when an external electric field is applied. In 1960, Kepler [10] and LeBlanc [11] measured the mobility of an organic semiconductor by the time‐of‐flight (TOF) technique, where the flight time of carriers in a given electric field is determined by observing an arrival time kink in the current that is caused by a pulse‐generated unipolar “charge carrier sheet” moving across a plane‐parallel slice of a sample. They reported that the anthracenes have the mobility of 0.1–2.0 cm V s at room temperature and their mobilities increase as the temperature decreases. Friedman theoretically investigated the electrical transport properties of organic crystals using the Boltzmann equation treatment of narrow‐band limit in the case of small polaron band motion [12]. Sumi also discussed the change from the band‐type mobility of large polarons to the hopping type of small polarons, using the Kubo formula with the adiabatic treatment of lattice vibrations in the single‐site approximation [13]. However, the mobility obtained by TOF technique is different from the mobility of actual devices such as field‐effect transistors(FETs) because the charge carriers are induced at the interface between the organic semiconductor and the dielectric film by an applied gate voltage. Kudo et al. reported the field‐effect phenomena of merocyanine dye films and their field‐effect mobilities of – cm V s estimated from the measurements in 1984 [14]. Then, Koezuka et al. fabricated the actual FET utilizing polythiophene as a semiconducting material and reported the mobility of cm V s [15].

A major industrial breakthrough occurred in the application to electroluminescent (EL) devices. Tang and VanSlyke reported the first organic EL device based on a ‐conjugated molecular material in 1987 [16]. After that, typical industrial applications spread to light‐emitting diodes (LEDs) [17, 18] and solar cells [19–21]. Recently, organic semiconductors are expected as the future electronic device semiconducting materials requiring structural flexibility and large‐area coverage that can be fabricated by low‐cost printing processes [22, 23]. However, we have a massive task for the realization of the “printed electronics,” for example, increasing the mobility, improvement of the solubility, and thermal durability, suppressing the variations of device characteristics, decreasing the threshold voltage, and so on.

Although ‐conjugated polymers with aromatic backbones have been widely investigated as soluble organic semiconductors, further improvement of mobility of polymer semiconductors has disadvantages owing to the statistical distribution of molecular size and structural defects caused by mislinkage of monomers, which act as carrier traps in the semiconducting channel. Therefore, small molecular materials, such as pentacene (see Figure 1.1a), have advantages in terms of their well‐defined crystal structure and ease of purification. At first, the organic transistors were fabricated utilizing the organic polycrystals. For example, the field‐effect mobility of polycrystal thin‐film transistors (TFTs) increases in proportion to the grain size [63, 64]. The mobility in the polycrystals is mainly limited by the grain boundaries, and the typical highest value is generally below 1.0 cm V s at room temperature. The temperature dependence with a thermally activated behavior indicates that the incoherent hopping process of spatially localized carriers between trap sites is dominated in the polycrystals [26]. In such a low‐mobility regime, the charge transport mechanism has been investigated theoretically using the Marcus theory [65, 66] based on the small polaron model [67].

Figure 1 Molecular structures of (a) pentacene, (b) rubrene, (c) DNTT, (d) C‐BTBT, and (e) DNT‐V. (f) Annual change of the highest hole mobilities of different organic single‐crystal field‐effect transistors in the literature, and (g) the distribution of the reported mobilities for naphthalene [24], DNT‐V [25], pentacene [26–35], DNTT [36–41], C‐BTBT [42–49], and rubrene [29, 31], [50–62].

1.1.2 Recent Progress and Requirements to Computational “Molecular Technology”

Recent rapid progress in technology enables us to fabricate the very pure rubrene single‐crystal FETs (see Figure 1.1b) with the high carrier mobility up to 40 cm2 V−1 s−1 at room temperature [60], which exceeds the mobility of amorphous silicon [68]. The high mobility attributes the exclusion of trap sites such as grain boundary in organic semiconductors. The mobility monotonically decreases with increasing temperature, [54]. The power‐law temperature dependence is a typical characteristic of coherent band transport by spatially extended carriers, which is scattered by the molecular vibrations (phonons). The rubrene single crystals obtained by the physical vapor deposition method show the excellent high mobilities at room temperature, but their poor solubility is a serious problem for the printed electronics. In 2006, Takimiya et al. reported solution‐processable organic semiconductors based on [1]benzothieno[3,2‐][1]benzothiophene (BTBT) core [69] and dinaphtho[2,3‐:2,3‐]thieno[3,2‐]thiophene (DNTT) core [36] with high mobility and stability, as shown in Figure 1.1c,d. Moreover, Okamoto et al. reported a new candidate semiconducting material based on V‐shaped dinaphtho[2,3‐:2,3‐]thiophene (DNT‐V) core (Figure 1.1e), with high mobility, solubility, and thermal durability [25]. Figure 1.1f,g shows annual change of the highest hole mobilities of different organic single‐crystal FETs in the literature, and the distribution of the reported mobilities for naphthalene [24], DNT‐V [25], pentacene [26–35], DNTT [36–41], C‐BTBT [42–49], and rubrene [29, 31, 50–62].

As shown above, new organic semiconductors with higher mobilities have been required. It is a very important and an urgent issue for us to establish the method and system for finding new organic semiconductors with high mobility from among various kinds of the candidate materials. Computer simulation to predict the mobility of candidate organic semiconductors becomes a powerful tool to accelerate the material development.

1.2 Theoretical Description of Charge Transport in Organic Semiconductors

As shown in Figure 1.2a, different from covalent crystals such as silicon, organic semiconductors are formed with van der Waals interactions between molecules [70]. The very weak interactions give the organic semiconductors the property of mechanical flexibility and the solubility. Charge carriers in organic semiconductors strongly couple with the molecular vibrations, namely, phonons. The total Hamiltonian consists of that for the electron , the phonon , and the interaction ,

(1.2)

The general expression can be given on the basis of molecular orbitals and the eigenfunctions of phonon as follows:

(1.3)