27 Supramolecular Control of Photochemical Process of Olefins Using Cucurbiturils

Wednesday, November 4, 2009
Ballroom A+B (Camino Real Hotel)
Sarrah N. Babb , Department of Natural Sciences, Western New Mexico University, Silver City, NM
Alec C. Lutzke , Department of Natural Sciences, Western New Mexico University, Silver City, NM
Mahesh Pattabiraman, Dr. , Department of Natural Sciences, Western New Mexico University, Silver City, NM

Controlling excited state molecular dynamics to achieve product selectivity in photochemical reactions is challenging due to rapid nature of electronic transitions and fleeting existence of intermediate species. Supramolecular photochemistry is an interdisciplinary area of research where weak molecular forces and properties of molecular assemblies are employed to control photochemical outcomes. Previously a few groups, including ours, have shown that by complexing substituted olefins to cucurbit[8]uril (CB[8]), photochemistry of the olefins can be modified to significantly suppress isomerization while enhancing stereoselective dimerization(s). Our efforts in this area have shown that selectivities up to as high as 90% of a single photodimer (at 80% conversions or higher) can be achieved in aqueous solution by complexing bipyridyl ethylenes and stilbazoles to CB[8]. These guests do not yield any photodimers even in trace quantities otherwise in solution. Moreover neutral olefins such as cinnamic acids have been complexed and irradiated to selectively yield syn H-H dimers - this work is of particular importance as not many examples of neutral compound complexation to CB[8] is known in cucurbituril literature. Though the preference for photodimerization over isomerization for cinnamic acids was not as dramatic as in the case of ionic guests, remarkable selectivity among the dimers was observed. Our current research efforts are aimed at further extending the capabilities of CB[8] and strategizing means to realize selectivities in dimerization reactions involving less-symmetric olefins than was previously reported, and dimerization between two different olefins (hetero-dimerization). In order to achieve selectivity in photodimerization reactions with such systems, our strategy involves pre-organizing the guests within CB[8]'s cavity by tuning weak forces in the assembly such as electronic interaction between the guests, steric and electronic characteristics of the substituents, and dimensions of the guest(s). Our studies also include studying complexation characteristics, and determining physical constants of host-guest complex using spectroscopic techniques.

Photochemistry of A-=-B.jpg

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