Preface

Modern Molecular Photochemistry of Organic Molecules is a comprehensive, standalone text that teaches students and researchers how to apply the paradigms of molecular organic photochemistry to an understanding of the mechanistic and synthetic applications of organic photoreactions. After an introduction to the fundamental principles of the photophysics and photochemistry of organic molecules, the spectroscopic techniques for determining organic photochemical mechanisms are described in some detail with numerous exemplars. The role of spin chemistry in controlling photochemical pathways is also described in detail. The functional group or chromophore approach is used to examine, classify, and understand the photochemical reactions of carbonyls, olefins, enones, and aromatic compounds in terms of the paradigms in the introduction of the book. For the first time, supramolecular organic photochemistry is described from fundamental principles of intermolecular interactions using a guest noncovalently bonded to a host as a paradigm. The text concludes with a chapter on the role of singlet oxygen in organic photoreactions and a chapter on how to extend the paradigms described in the earlier chapter to achieve an understanding of essentially any organic functional group. 

Level and Approach 

The goal of this textbook is to familiarize both students and researchers with the critical concepts and methodology involved in the investigation of organic photochemical reactions. A simple paradigm at the start of each chapter is elaborated with exemplars that provide the student with an understanding through examples of the underlying principles. The material can be understood easily by students with the fundamental knowledge of college general chemistry, organic chemistry, and physics. An important feature of the book is avoidance of complex mathematics and the translation of all concepts into familiar visualized representations. These representations provide a complete and unified theoretical background for an understanding of light absorption and emission, or radiationless processes and photochemical reactions. For example, the concept of electronic energy surfaces coupled with simple molecular orbital theory is used to visualize the triggers of photochemical processes and the analogies that intellectually reduce the thousands of organic photochemical reactions to a handful of fundamental primary photochemical reactions from electronically excited states. This book will be of use to students interested in a qualitative, pictorial interpretation of spectroscopic processes involving the absorption and emission of light by organic molecules and the photochemical processes that result from light absorption. 

History 

As a bit of history, it has been over three decades since the publication of Modern Molecular Photochemistry (MMP). During this period, the concepts and paradigms described in MMP have become part and parcel of modern synthetic and mechanistic photochemistry, and have been absorbed as routine intellectual tools in a wide range of fields, including physical organic chemistry, chemical biology, polymer chemistry, materials science, and nanoscience. Remarkably, most of the basic paradigms of MMP remain the bedrock of current mechanistic analyses, investigations, and application of photochemical reactions. However, the elaboration of these paradigms by the effect of spin and electron transfer was not covered in MMP. It was decided that a textbook, which included these factors and integrated them with the general successful pedagogical philosophy of MMP, would be of use and interest to not only practicing photochemists and their students, but also to those in a variety of other fields (e.g., biology scientists, polymer scientists, materials scientists, and nanoscientists) who integrate photochemistry and photophysics into their research and teaching. 

A primer, Principles of Molecular Photochemistry: An Introduction, published in 2008, consisted of seven chapters that introduced photochemical and photophysical concepts from a small set of principles that are familiar and understood by students of chemistry and other sciences. An initial paradigm is introduced that relates the photon and a reactant molecular structure to photochemistry through the structure of electronically excited states, reactive intermediates, and products. The same paradigm is readily adapted to incorporate the photon and a reactant molecular structure to photophysics. The role of electronically excited states, and electronic–vibrational and electronic–spin interactions are clearly described in pictorial terms that can be readily understood and applied to systems of interest. For the first time in any photochemical text, a fundamental description of electronic spin and its impact on photochemical and photophysical processes is described with an intuitive, pictorial, and powerful vector model. The mysterious processes of spin–orbit coupling, intersystem crossing, and magnetic effects on photochemical and photophysical processes are readily handled with this model. Also, for the first time in any photochemical text, the concepts of electronic energy transfer and electron transfer are treated from a common foundation and set of concepts. The tremendous progress in theoretical and experimental aspects of electron transfer is covered in depth and will be of great assistance as an introduction to these two critical aspects of molecular photochemistry. This book, Modern Molecular Photochemistry of Organic Molecules, builds on the platform of the seven chapters of the primer to use the functional group or chromophore approach to describe photochemistry of organic molecules based on the paradigms described in the primer. 

Acknowledgments 

This text is an outgrowth of courses and lectures on Organic Photochemistry. The authors are indebted to the many students of our three groups who have assisted in the development of the text through their probing and stimulating questions as they sought an understanding of molecular organic photochemistry. We are also thankful to many colleagues who allowed their “brains to be picked” and thereby enabled the authors to produce a translation of abstruse mathematical concepts into concrete representations that provide students with an understanding of the subject. We are also thankful to the photochemical community that kept the pressure on us to complete the book project that has taken a much longer time than we originally anticipated. Special thanks to Professor D. I. Schuster of New York University and Professor R. S. H. Liu of University of Hawaii for a careful and critical reading of drafts of the book. Thanks also to the following photochemists who have read and provided critical comments and suggestions: J. R. Scheffer, F. D. Lewis, L. Johnston, C. Bohne and A. Griesbeck. J. Michl is thanked for educating us on many aspects of photophysics through his publications and discussions. 

The authors have been blessed and supported throughout the adventure of writing this text by the unflagging enthusiastic encouragement and patience of Bruce Armbruster and Jane Ellis of University Science Books. They wish to thank J. Stiefel for outstanding copy editing of the complex manuscript; J. Choi, T. Webster, and L. Muller for the art production; and J. Snowden and P. Anagnostopoulos for transforming the manuscript into the final product. It was a wonderful and special journey for all of us. 

Each of the authors thank, profoundly, our wives and families for their incredible patience in putting up with us during the nearly two decades in which the primer and full text developed. 

Nicholas J. Turro 
V. Ramamurthy 
J. C. Scaiano