Molecular Materials E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Inorganic Materials Series
• Sprache: Englisch

Seitenzahl: 615

Veröffentlichungsjahr: 2011

Beschreibung

“… the book does an excellent job of putting together several different classes of materials. Many common points emerge, and the book may facilitate the development of hybrids in which the qualities of the “parents” are enhanced.” –Angew. Chem. Int. Ed. 2011

With applications in optoelectronics and photonics, quantum information processing, nanotechnology and data storage, molecular materials enrich our daily lives in countless ways. These materials have properties that depend on their exact structure, the degree of order in the way the molecules are aligned and their crystalline nature. Small, delicate changes in molecular structure can totally alter the properties of the material in bulk.

There has been increasing emphasis on functional metal complexes that demonstrate a wide range of physical phenomena. Molecular Materials represents the diversity of the area, encapsulating magnetic, optical and electrical properties, with chapters on:

• Metal-Based Quadratic Nonlinear Optical Materials
• Physical Properties of Metallomesogens
• Molecular Magnetic Materials
• Molecular Inorganic Conductors and Superconductors
• Molecular Nanomagnets

Structured to include a clear introduction, a discussion of the basic concepts and up-to-date coverage of key aspects, each chapter provides a detailed review which conveys the excitement of work in that field.

Additional volumes in the Inorganic Materials Series:

Low-Dimensional Solids | Molecular Materials | Porous Materials | Energy Materials

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Inorganic Materials Series Preface

Preface

List of Contributors

Chapter 1: Metal-Based Quadratic Nonlinear Optical Materials

1.1 Introduction

1.2 Basic Concepts of Second-Order Nonlinear Optics

1.3 Dipolar Metal Complexes

1.4 Octupolar Metal Complexes

1.5 Switching Optical Nonlinearities of Metal Complexes

1.6 Towards the Design of Pre-Organised Materials

1.7 Conclusions

References

Chapter 2: Physical Properties of Metallomesogens

2.1 Introduction

2.2 Overview of Mesophases

2.3 Optical Properties

2.4 Electrical Properties

2.5 Magnetic Properties

2.6 Conclusions

References

Chapter 3: Molecular Magnetic Materials

3.1 Introduction

3.2 Basic Concepts

3.3 The Van Vleck Equation

3.4 Dimensionality of Magnetic Systems

3.5 Switchable and Hybrid Systems and Future Perspectives

3.6 Conclusions

References

Chapter 4: Molecular Inorganic Conductors and Superconductors

4.1 Introduction

4.2 Families of Molecular Conductors Families of Molecular Conductors and Superconductors

4.3 Systems Based on Metal Bis-Dithiolene Complexes

4.4 Towards The Application of Molecular Inorganic Conductors and Superconductors

4.5 Conclusions

Acknowledgements

References

Chapter 5: Molecular Nanomagnets

5.1 Introduction

5.2 A Very Brief Introduction to Magnetochemistry

5.3 Techniques

5.4 Single Molecule Magnets

5.5 Emerging Trends

References

Index

Molecular Materials

Inorganic Materials Series

Editors:

Professor Duncan W. Bruce,Department of Chemistry, University of York, UK

Professor Dermot O’Hare,Chemistry Research Laboratory, University of Oxford, UK

Dr Richard I. Walton,Department of Chemistry, University of Warwick, UK

Series Titles

Functional Oxides

Molecular Materials

Porous Materials

Low-Dimensional Solids

Energy Materials

This edition first published 2010

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Library of Congress Cataloging-in-Publication Data

Molecular materials/edited by Duncan W. Bruce, Dermot O’Hare, Richard I. Walton.p. cm.Includes bibliographical references and index.ISBN 978-0-470-98677-61. Superconductors. 2. Organic conductors. 3. Magnetic materials—Optical properties.4. Inorganic compounds—Optical peoperties. 5. Molecular dynamics.6. Nonlinear optics. I. Bruce, Duncan W. II. O’Hare, Dermot. III. Walton, Richard I.QC611.95.M65 2010620.1′129—dc222009041767

A catalogue record for this book is available from the British Library.

ISBN: 978-0-470-98677-6 (Cloth)

Inorganic Materials Series Preface

Back in 1992, two of us (DWB and DO’H) edited the first edition of Inorganic Materials in response to the growing emphasis and interest in materials chemistry. The second edition, which contained updated chapters, appeared in 1996 and was reprinted in paperback. The aim had always been to provide the reader with chapters that while not necessarily comprehensive, nonetheless gave a first-rate and well-referenced introduction to the subject for the first-time reader. As such, the target audience was from first-year postgraduate student upwards. Authors were carefully selected who were experts in their field and actively researching their topic, so were able to provide an up-to-date review of key aspects of a particular subject, whilst providing some historical perspective. In these two editions, we believe our authors achieved this admirably.

In the intervening years, materials chemistry has grown hugely and now finds itself central to many of the major challenges that face global society. We felt, therefore, that there was a need for more extensive coverage of the area and so Richard Walton joined the team and, with Wiley, we set about a new and larger project. The Inorganic Materials Series is the result and our aim is to provide chapters with a similar pedagogical flavour but now with much wider subject coverage. As such, the work will be contained in several themed volumes. Many of the early volumes concentrate on materials derived from continuous inorganic solids, but later volumes will also emphasise molecular and soft matter systems as we aim for a much more comprehensive coverage of the area than was possible with Inorganic Materials.

We approached a completely new set of authors for the new project with the same philiosophy in choosing actively researching experts, but also with the aim of providing an international perspective, so to reflect the diversity and interdisciplinarity of the now very broad area of inorganic materials chemistry. We are delighted with the calibre of authors who have agreed to write for us and we thank them all for their efforts and cooperation. We believe they have done a splendid job and that their work will make these volumes a valuable reference and teaching resource.

DWB, YorkDO’H, OxfordRIW, WarwickJanuary 2010

Preface

One of the great attractions of working with molecular materials is the way in which the bulk macroscopic response of a material that can be held in the hand can be influenced by changes at the Ångström level. Thus molecular materials represent a class of substances where seemingly small, delicate changes in molecular structure can change totally the properties of the material in bulk.

Many molecular materials have been studied for a long period of time, but in the years since the 1980s there has been increasing emphasis on functional metal complexes able to demonstrate a wide range of physical phenomena. The scope is vast and it is simply not possible to encapsulate all in a single volume, hence we have chosen subjects that represent something of the diversity of the area, encapsulating magnetic, optical and electrical properties.

Once more, we have sought out active and expert practitioners from across the globe to distill the essence of their subject, providing well-referenced chapters with suitably pedagogical introductions and conveying the excitement of work in that field. We believe that they have done an excellent job and trust that you will agree.

DWB, YorkDO’H, OxfordRIW, WarwickJanuary 2010

List of Contributors

Koen Binnemans Department of Chemistry, Katholieke Universiteit Leuven, Leuven, Belgium

Hubert Le Bozec Laboratoire de Sciences Chimiques de Rennes, Université de Rennes, Rennes, France

Olivier Maury Laboratoire de Chimie, CNRS – Ecole Normale Supérieure de Lyon, Université de Lyon, Lyon, France

Eric J. L. McInnes School of Chemistry, The University of Manchester, Manchester, UK

Neil Robertson School of Chemistry, University of Edinburgh, Edinburgh, UK

Hisashi Tanaka Molecular Nanophysics Group, AIST, NRI, Tsukuba, Japan

Lydie Valade Laboratoire de Chimie de Coordination, CNRS, Toulouse, France

Richard E. P. Winpenny School of Chemistry, The University of Manchester, Manchester, UK

Gordon T. Yee Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA

Chapter 1

Metal-Based Quadratic Nonlinear Optical Materials

Olivier Maurya and Hubert Le Bozecb

a Laboratoire de Chimie, CNRS - Ecole Normale Supérieure de Lyon,Université de Lyon, France

b Laboratoire de Sciences Chimiques de Rennes, Université de Rennes, France

1.1 INTRODUCTION

Nonlinear optical (NLO) materials have been the focus of intensive investigations for several decades from both the fundamental and practical points of view for their possible applications in the domain of optoelectronics and photonics.[1–4] NLO materials can be used to manipulate optical signals, and when light interacts with such materials the incident light can be changed and new electromagnetic field components generated. NLO materials have potential applications in optical signal processing, frequency generation such as second and third harmonic generation (SHG and THG, respectively), and can also contribute to optical data storage and image processing. NLO activity can be found in inorganic crystals, such as LiNbO3, and also in organic materials. The latter have attracted great interest owing to their fast and large nonlinearities, their inherent tailorability, which allows fine tuning of the NLO properties, and to their compatibility with polymer matrices. About twenty years ago, the field of NLO was extended to molecular materials featuring organometallic and coordination complexes.[5–11] Compared with organics, metal-based chromophores offer additional advantages due to their structural, electronic and optical properties. Greater design flexibility can be achieved by varying the metal, its oxidation state, the ligand environment and the geometry.

The subject of this chapter is to review some developments, made in the last fifteen years, in quadratic NLO materials based on organometallic and coordination compounds. After a brief introduction about the principles of nonlinear optics, the two main classes of second-order metal-based NLO chromophores are described, i.e. the dipoles and octupoles: the most widely investigated NLO metal complexes belong to the class of dipolar molecules constituted by a D-π-A system, in which the donor (D) and/or the acceptor (A), or the bridge (π) moieties are constituted by an organometallic or coordination group. Octupoles are nondipolar two-dimensional (2D) or three-dimensional (3D) chromophores, and coordination chemistry is particularly useful to design original octupolar architectures of octahedral or tetrahedral geometry. Recent advances in metal complexes as NLO switches and as precursors of supramolecular organised NLO materials are presented in the last two parts of the chapter.

1.2 BASIC CONCEPTS OF SECOND-ORDER NONLINEAR OPTICS

1.2.1 Introduction to Nonlinear Molecular Materials

NLO phenomena result from the interaction between light and matter and, more precisely, between the polarisable electron density and the strong electric field associated with a very intense laser beam. They were experimentally observed firstly in 1961 just after the development of intense laser sources in particular by Kaiser and Garett for two-photon absorption[12] and by Franken for SHG.[13] They can be divided in two main classes depending on the incident laser wavelength (Figure 1.1):

FIGURE 1.1 Jablonski diagram and spectral representations of NLO phenomena

(i) the nonresonant NLO phenomena, such as SHG or THG, but also Pockel or Kerr effects, can be described as resulting from an electronic perturbation of the molecular ground state;

(ii) the resonant NLO phenomena, like two(multi)-photon absorption, are due to the quantic nature of molecule and occur only when the laser energy is a multiple of the energy gap between the ground and excited states. In this latter case, an electron is promoted from the fundamental to the excited state by nonlinear absorption, which is in marked contrast with nonresonant phenomena.

All these phenomena can occur simultaneously within the same material, as illustrated by the spectral response of an oriented polymer doped with DCM dye (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran) under 1.06 μm laser irradiation (Figure 1.1). The two sharp signals at 532 and 354 nm are coherent emission induced by SHG and THG, whereas the broad band is incoherent emission of two-photon excited fluorescence (TPEF).

The principles of nonlinear optics and the main techniques used to evaluate the second-order NLO properties are briefly presented here. Major details can be found in more specialised reviews and books.[1–11] At the molecular level, the interaction between polarisable electron density and the alternating electric field of the laser light beam (E) induces a polarisation response (Δμ) that can be expressed following Equation 1.1:

(1.1)

where α, β and γ represent the first, second and third hyperpolarisability tensors, respectively. With normal values of E, the quadratic and cubic terms in Equation 1.1 can be neglected and only linear optical behaviour is observed. However, when E approaches the magnitude of atomic field strengths (like a laser beam), the quadratic β·E2 and cubic γ·E3 terms become important. The equivalent form of Equation 1.1 at the macroscopic level is given in Equation 1.2, where ΔP is the induced macroscopic polarisation, and χ(1), χ(2) and χ(3) are the first, second and third susceptibility tensors, respectively. For molecular systems, β and χ2 are related if it is understood that polarisation is dipole moment/unit volume.

(1.2)

χ(2) quantifies all second-order NLO effects such as SHG, electro-optic effect (Pockel) and frequency mixing. χ(3) is representative of third-order NLO effects such as THG, optical Kerr effect and two-photon absorption (TPA). The real part of γ describes the nonlinear refractive index and its imaginary part the two-photon cross section (σ2).

Due to parity considerations, nonzero β are restricted to noncentrosymmetric molecules and materials, while no symmetry restrictions are required for third-order NLO activity. Molecular engineering rules for the optimisation of second (β)- or third (γ, σ2)- order NLO properties have been carefully established in the case of organic molecules or conjugated polymers; basically NLO chromophores possessing quadratic or cubic NLO activities can be divided into three main classes depending on the molecular symmetry (): (i) the dipoles (D-π-A), (ii) the quadrupoles (D-π-D, A-π-A, D-π-A-π-D, -A-π-D-π-A…) or (iii) the octupoles of (A–D or D–A) or / (A–D or D–A) symmetry (where D and A represent electron-donating and-withdrawing groups respectively, and π a conjugated skeleton). It is worth noting that only dipoles and octupoles are noncentrosymmetric; therefore, only these two approaches are discussed in this review.