Excited state dynamics of 4(1 H-pyrrole 1-yl) benzoic acid and different environmental effects

Abstract

The absorption and fluorescence characteristics of 4(1 H-pyrrole 1-yl) benzoic acid (PBA) in solvents of different polarities, acidities, glass matrices and also in β-cyclodextrin cavity were studied with regard to the influence of flexibility of the molecule in both the ground and excited sates. The study of dynamics of excited state reveals the presence of two competitive fluorescence emission from a common excited state of PBA. Of these two fluorescence bands one originates from delocalized 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 PBA leads to the immediate formation of F-C excited state and the TICT state is formed within 220 ps from the parent F-C excited state. The 220 ps time has also been interpreted as the time required for the molecule to relax by rotational motion along the C-N bond of PBA to achieve the TICT state. The steady state photophysical measurements show that the molecule is very weakly fluorescent and nonradiative rate parameters get prominence compared to radiative 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 twisted conformations to confirm experimental findings qualitatively.