Pr. Bangal et al., EXCITED-STATE DYNAMICS OF 4(1H-PYRROLE 1-YL) BENZOIC-ACID AND DIFFERENT ENVIRONMENTAL-EFFECTS, Journal of photochemistry and photobiology. A, Chemistry, 113(1), 1998, pp. 35-43
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.