Light driven molecular switches:: exploring and tuning their photophysical and photochemical properties

In recent years, computational photochemistry has become a valid tool for the investigation of photophysical properties and photochemical reaction mechanisms in organic chromophores. Theoretical chemists can now adapt their tools to the subject under investigation and to the type and accuracy of the desired information. Different computational strategies can now be adopted to characterize different aspects of the photoinduced molecular reactivity of a given chromophore and to provide, in principle, a quite detailed description of the reactive process from energy absorption to photoproducts formation. The basic aim is to establish a correlation between the structure of the molecule and its photochemical outcome, and, in particular, to assess the effect of modifications of the chromophore and of the molecular environment. In this perspective, recent advances and applications of photoinduced cis reversible arrow trans isomerizations involving some organic chromophores active in biologically or technologically relevant problems is reviewed here and discussed in the light of new results. In particular, the photochemistry of azobenzene, retinals and of the green fluorescent protein chromophore is considered, taking into account structural changes and environment effects. The results presented in this work are intended to be the first step toward the design of chromophores that can act as molecular photoswitches.