M. Maafi et al., SYNTHESIS, PHOTOPHYSICAL PROPERTIES, AND VALENCE PHOTOISOMERIZATION OF NEW FLUORESCENT AROMATIC NORBORNADIENES, New journal of chemistry, 20(5), 1996, pp. 559-570
Four norbornadiene (NBD) aromatic derivatives including electron-donor
and electron-acceptor substituents, potentially useful for light ener
gy photochemical storage, were synthesized by a Diels-Alder reaction,
using a phase-transfer catalysis method. Electronic absorption and the
fluorescence excitation and emission spectra were determined at room
temperature in solvents of different polarities. The photoisomerizatio
n kinetics of NBD aromatic derivatives into quadricyclane (QC) derivat
ives were measured in different solvents. It was found that photochemi
cal reactivities were rather high, between 0.1 and 0.3 s(-1), and that
quantum yields (Phi(p)) were relatively large, ranging from 0.18 to 0
.36. These kinetic parameters were markedly influenced by the aromatic
substituents and the solvent. The photochemical results support the h
ypothesis of a radical-cation mechanism for the photoisomerization rea
ction. The fluorescence quenching efficiency of NBD aromatic derivativ
es was investigated. Evidence was found for fluorescence quenching of
the fluorophore aromatic cycle (in QC derivatives) by the NBD moiety.