Proton transfer in the ground and excited electronic states of [2,2′-bipyridyl]-3,3′-diol. A semiempirical study

Abstract
Tautomerization of [2,2′-bipyridyl]-3,3′-diol in several electronic states has been studied theoretically by the semiempirical PM3 method. Particular attention has been devoted to the analysis of proton transfer, which can occur through one- or two-step mechanisms. On the grounds of energetic and structural determinations, it is suggested that this latter mechanism is more effective.The strong Stokes shift observed in fluorescence spectra can be ascribed to the significant skeletal modifications connected to electronic excitation. A good correspondence has been found between structural characteristics and composition of frontier orbitals.

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