EXCITED-STATE DYNAMICS OF 4(1H-PYRROLE 1-YL) BENZOIC-ACID AND DIFFERENT ENVIRONMENTAL-EFFECTS

The absorption and fluorescence characteristics of 4(1H-pyrrole 1-yl) benzoic acid (PEA) in solvents of different polarities, acidities, gla ss matrices and also in P-cyclodextrin cavity were studied with regard to the influence of flexibility of the molecule in both the ground an d excited sates. The study of dynamics of excited state reveals the pr esence of two competitive fluorescence emission from a common excited state of PEA. Of these two fluorescence bands one originates from delo calized excited (DE) state [ i.e., Franck-Condon (F-C) excited state] and the other from twisted intramolecular charge transfer (TICT) state . The excitation of ground state of PEA leads to the immediate formati on of F-C excited state and the TICT state is formed within 220 ps fro m the parent F-C excited state. The 220 ps time has also been interpre ted as the time required for the molecule to relax by rotational motio n along the C-N bond of PEA to achieve the TICT state. The steady stat e photophysical measurements show that the molecule is very weakly flu orescent and nonradiative rate parameters get prominence compared to r adiative rate parameters. The fluorescence and phosphorescence studies at 77 K have also been reported. Quantum chemical calculations of the energies and dipole moments were performed for planar and different t wisted conformations to confirm experimental findings qualitatively. ( C) 1998 Elsevier Science S.A.