Stereochemical Constraints and Lattice Relaxation in Crystal Photochemistry

Abstract

Abstract The relationship of crystal structure, molecular orientation and conformations of reactants and products is central to an understanding of solid state organic photochemistry. The calculation of the properties of lattices containing foreign molecules is described, with allowance for relaxation in position and orientation coordinates. The experimentally studied cleavage of dianthracene molecules in its crystal, and the cleavage of the photoisomer of 1,2-di-(9-anthryl)-ethane, are systems in which the effect of lattice constraints can be examined. It is shown that a useful degree of rationalization of experimental results is possible, in terms of the stable conformations available to the cleaved systems, within the “cage” or cavity enveloping the reactive site.