The photophysical properties ofp-cyano-N,N-dimethylaniline (CDMA) and its derivatives in various surroundings are reviewed. New results on the luminescence in the solid phase near liquid helium temperature and in a supersonic beam are presented.

The dual fluorescence (a andb) of 4-(dialkylamino)pyrimidines (4-DAAP) in solutions is explained in terms of the TICT state model. 4-DAAP form complexes with protic solvents: efficient radiationless depopulation is “switched on” by hydrogen bonding (HB). The photoinduced electron transfer is modified by HB or by coordination to the metal ion. In nitriles, two emitting states of 4-(N,N-dimethylamino)pyrimidine (I) and 4-(N,N-diethylamino)pyrimidine (II) reach equilibrium. In protic solvents, the fluorescencesa andb are not kinetically coupled: the different ground state complexes are responsible for each band. Jet-cooled 4-DAAP show only primary excited fluorescenceb. Microsolvation of pretwistedo-methylated compoundsIII andIV by small polar molecules, contrary to more planarI andII, gives rise to the long-wave (probably TICT) fluorescence.