Photoactivation of Distal Groups in Polyfunctional Molecules

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This grant in the Organic and Macromolecular Chemistry Program supports research on the mechanisms of light-induced chemical reactions. Dr. Morrison's focus in photochemical reactions is the interaction of close, but formally non-conjugated functional groups which interact in the excited states generated by light absorption. Such systems are important as models for many of the light-induced chemical sequences of life processes. In photosynthesis, for example, one "antenna" group in chlorophyll harvests light energy and then transfers it to a nearby "receptor" for initiating chemical changes. Photochemical reactions of bifunctional molecules can be broadly subclassified into those (a) involving bond formation between the two functionalities, and (b) those primarily involving only one of the two groups, the non-reacting moiety then serving as an "antenna" to harvest photons. In the latter case, a variety of mechanisms are now recognized which can lead to activation of the distal, reacting group. The reacting group may either be relatively transparent in the ultraviolet spectrum (examples are chlorine, carbethoxy, and alkene substituents), or be itself capable of asborption (a ketone, for example), but still potentially selectively activated by the atenna. This research is primarily addressed to "Class b" systems. The basic questions for which answers are sought include: (1) How general, and with what stereoelectronic limitations, are the various mechanisms for activiting distal functionalities; (2) How may these phenomena be utilized synthetically; and (3) How are they reflected in the photostability of complex molecules? As an out growth of research previously supported by Foundation Grant CHE-8318825, Dr. Morrison has also initiated studies involving metal ion catalysis in photochemistry and photochemistry in the gas phase. Both projects have uncovered new and intriguing chemistry, the extensions of which are included in the present program.