An ab initio MO study of the photochromic reaction of dithienylethenes

An ab initio MO study on a model system for photochromic compounds containing a dithienylethene unit is presented. On the basis of the obtained potential energy profile, a rationalization is provided for the proposed mechanism of the experimentally observed stepwise multiphoton process in the ring-opening cycloreversion reaction. An explanation, which correlates the experimental quantum yields with the calculated properties as a function of substituent effects, is provided. A method has been developed which can be utilized as a guiding principle for future molecular design.