Supramolecular Effects on Mechanisms of Photoisomerization: Hula Twist, Bicycle Pedal, and One‐Bond‐Flip

Abstract

Photoisomerization in the form of interconversion of the cis and trans isomers around a double bond is the key triggering process for many photosensitive biopigments. 1 They include the visual pigment rhodopsin, the proton pumping bacteriorhodopsin (bR), the phototaxis of photoactive yellow protein (PYP), the seed -germinating trigger protein phytochrome, and many other related pigments. Much spectroscopic and chemical effort has gone into elucidation of the primary processes and products associated with these important pigments. These efforts along with photochemical and theoretical work with simple organic systems 2 have led to improved understanding of mechanisms of photoisomerization, often controlled by host molecules in dictating the exact mechanism participating in a given system. In this chapter, an attempt is made to review medium -controlled photoisomerization processes and to provide an overview of different types of mechanisms that take place in nature and under laboratory conditions. Ever since the fi rst picosecond time -resolved spectroscopic study on events revealing the rapid isomerization following photoexcitation of the visual 547 547 Supramolecular Photochemistry: Controlling Photochemical Processes, First Edition. Edited by V. Ramamurthy and Yoshihisa Inoue.