Photophysics of arylsubstituted tropylium ions

Phenyl tropylium ion (TRPH) bearing different donor substituents were investigated both experimentally (absorption and fluorescence) and theoretically (semiempirical and ab initio calculations for ground and excited state structures and transitions). Generally, an increased donor strength of the substituent leads to a favoring of the planar geometry in the ground state. In the S-1-state, however, energetic minimum develops for orthogonal structures, which are characterized by strong charge shift (CSh) (electron transfer from the substituted aryl to the tropylium. fragment), forbidden transition moments and near-zero singlet-triplet energy gaps. These results can serve as a basis to interpret the completely non-emissive behavior of the tropylium. derivatives with strong donor substituents. (C) 2001 Elsevier Science B.V. All rights reserved.