THE TICT EXCITED-STATE OF SECONDARY AROMATIC-AMINES

The fluorescence spectra, quantum yields and lifetimes of 4-(methylamino)benzonitrile (MABN), its 3-methylated derivative (3-MMABN) and of 4-(amino)benzonitrile (ABN) were measured and discussed. Only 3-MMABN shows dual fluorescence. The long wave anomalous band is of forbidden nature and therefore assigned to the TICT state. It occurs most strongly for water as solvent due to: i) its high polarity, ii) a specific protic-solvent induced quenching of the short wave band. The results are discussed on the basis of two sterically hindered ground state conformers for 3-MMABN, and of the energetic separation of 1L(a) and 1L(b) states. The explanation is supported by the results of force field calculations.