Bridging the gap between the multitude of advanced research articles and the knowledge newcomers to the field are looking for, this is a timely and comprehensive monograph covering the interdisciplinary topic of intramolecular charge transfer (ICT).
The book not only covers the fundamentals and physico-chemical background of the ICT process, but also places a special emphasis on the latest experimental and theoretical studies that have been undertaken to understand this process and discusses key technological applications. After outlining the discovery of ICT molecules, the authors go on to discuss several important substance classes. They present the latest techniques for studying the underlying processes and show the interplay between charge transfer and the surrounding medium. Examples taken from nonlinear optics, viscosity and polarity sensors, and organic electronics testify to the vast range of applications.
The result is a unique information source for experimentalists as well as theoreticians, from postgraduate students to researchers.

Ramprasad Misra did his doctoral studies in the Department of Physical Chemistry, Indian Association for the Cultivation of Science (IACS) in Kolkata, India. His research interests encompass physical organic chemistry and molecular spectroscopy. He was an integrated PhD fellow of IACS, visiting postgraduate research student at the University of Warwick, UK, and postdoctoral fellow at the University of Pittsburgh, USA. He has authored/co-authored several research articles in peer-reviewed journals and a book for undergraduate students. Presently, he is a postdoctoral fellow at the Weizmann Institute of Science, Israel. He is a member of the Royal Society of Chemistry (RSC).

S. P. Bhattacharyya, a fellow of the Indian Academy of Sciences, joined the Department of Physical Chemistry, Indian Association for the Cultivation of Science (IACS), Kolkata, India in 1979 as a lecturer after receiving his PhD degree from the University of Kolkata. He has been professor of physical chemistry at the IACS from 1991 until his retirement in 2012. He was in the Department of Chemistry, Indian Institute of Technology Bombay on Raja Ramanna Fellowship awarded by the Department of Atomic Energy, Government of India, between 2012-15. His research interests are in quantum chemistry, soft-computation and chemical dynamics. He has served as the Editor-in-Chief of the Indian Journal of Physics. Till date, he has mentored 21 doctoral students and has more than 200 research publications to his credit.

Preface vii

1 Introduction 1

1.1 An Overview of the ICT Process 1

1.2 Experimental and Theoretical Studies of the ICT Process 4

1.3 Applications of ICT Molecules 19

References 24

2 Brief History of ICT Molecules 29

2.1 Introduction 29

2.2 Background of Studies on Charge Transfer 32

2.3 A Brief Review of ICT Process in Commonly Studied Organic Molecules 34

2.3.1 ICT in 4-N,N-Dimethylaminobenzonitrile and Related Molecules 34

2.3.2 ICT in Some Commonly Studied Organic Molecules 44

2.4 Structure of the ICT State: Twisted or Not? 52

2.5 Through-Space Charge Transfer 55

2.6 Charge Transfer in Inorganic Complexes 55

2.7 Electron Transfer in Biomolecules 62

References 63

3 New Theoretical and Experimental Techniques for Studying the ICT Process 71

3.1 Introduction 71

3.2 Computational Studies on ICT 73

3.3 Theoretical Treatment of ICT Rates 92

3.4 ExperimentalMethods for Studying ICT Process 99

3.4.1 Steady-State UVVisible Absorption and Emission Spectroscopy 99

3.4.2 Time-Resolved Ultrafast Spectroscopic Techniques 101

3.4.3 Raman/Resonance Raman Spectroscopy 106

3.4.4 THz Spectroscopy and ICT Dynamics 109

References 111

4 Medium Effect on ICT Process: Theory and Experiments 115

4.1 Introduction 115

4.2 SomeTheories and Models of Solvation 115

4.3 Effect of Solvent Polarity, Viscosity, and Temperature in the ICT Process 121

4.4 Studies of Solvation in Some ICT Molecules 127

4.5 Effect of Hydrogen Bonding on ICT 136

4.6 Resonance-Assisted Hydrogen Bonding (RAHB) 139

4.7 Studies of ICT in Solvent Mixture and Confined Media 140

4.8 Studies of ICT in the Solid State 141

References 144

5 Nonlinear Optical Response of ICT Molecules 149

5.1 Introduction 149

5.2 The NLO Response to Electric Field 150

5.3 Theoretical Calculation of NLO Response of ICT Molecules 152

5.4 Studies of Two-Photon Absorption 166

5.5 Third-Order NLO Response of ICT Molecules 173

5.6 Experimental Studies on Nonlinear Optical Response 176

5.7 Studies of NLO Molecular Switches 186

References 191

6 Recent Technological Applications of ICT Molecules and Prospect of Designing NewMolecules 197

6.1 Introduction 197

6.2 Application of ICT-Based Molecules 197

6.2.1 ICT Molecules as Fluorescence Sensors 197

6.2.2 In Organic Light-Emitting Diodes 214

6.2.3 In Aggregation-Induced Emission 219

6.2.4 Solar Energy Conversion 224

6.2.5 ICT- Based Molecules for Sensing Temperature 224

References 229

7 Summary and Outlook 233

7.1 Introduction 233

7.2 Summary of Studies of ICT 233

Further Readings 237

Index 239