Photoinduced intramolecular electron transfer in 4-dimethylaminopyridinesDedicated to Professor Dr Z. R. Grabowski and Professor Dr J. Wirz on the occasions of their 75th and 60th birthdays.

Contrary to 4-(dimethylamino)pyridine (DMAP), which revealed solvent-dependent dual fluorescence, its sterically hindered ortho-methylated derivatives: 3-methyl-4-(dimethylamino)pyridine and 3,5-dimethyl-4-(dimethylamino)pyridine show single charge transfer fluorescence band. The electronic structures of the lowest excited states and molecular geometries were investigated by stationary and kinetic absorption and fluorescence spectroscopy as well as time-dependent density functional response theory (TD-DFT) and semiempirical (INDO/S) calculations. The results can be interpreted in terms of the TICT state model.