Modern Molecular Photochemistry
 of Organic Molecules

Nicholas J. Turro
Columbia University

V. Ramamurthy
University of Miami

J.C. Scaiano
University of Ottawa


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 howto 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 ofMMP

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