Photophysics of arylsubstituted tropylium ions

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