ELECTROOPTICAL AND LASER SPECTROFLUOROMETRY STUDY OF COUMARIN-7 AND COUMARIN-30 - EVIDENCE FOR THE EXISTENCE OF THE CLOSE-LYING ELECTRONIC STATES AND CONFORMERS

Our experiments and calculations reveal a set of anomalous and interes ting properties of coumarin 7 (CU7) and coumarin 30 (CU30) in solution , The spectral dependence of electro-optical coefficients and, consequ ently, dipole moments indicates that the absorption band is a superpos ition of several (at least two) electronic transitions. Probably, ther e are two close-lying pi,pi singlet electronic excited states which c ontribute to the first absorption band. The calculations using the MM2 program show that both dyes in the ground state have two stable plane anti conformers. From time-resolved spectrofluorimetric measurements we obtained evidence for the existence of conformers in paraffin oil s olutions of CU30. (C) 1997 Published by Elsevier Science S.A.