The role of the ring nitrogen and the amino group in the solvent dependence of the excited-state dynamics of 3-aminoquinoline

Abstract

The nonradiative rate in 3-aminoquinoline is found to exhibit anomalous solvent dependence, being rather fast in nonpolar solvents and remarkably slower in more polar and especially, more protic ones. The cause of such behavior is investigated by studying the dependence of fluorescence spectral and temporal parameters on the solvent properties such as polarity and hydrogen bonding ability. Complementary quantum mechanical calculations have been performed and the picture that emerges from these studies is that of an excited state with a short radiative lifetime due to the flipping of the amino group. This state is selectively populated in nonpolar, nonhydrogen bonding solvents, but is destabilized with respect to the more polar intramolecular charge transfer ͑ICT͒ state in polar solvents and even more so in protic solvents and dimethylsulfoxide. The slower nonradiative rates in the ICT state is attributed to the more restricted motion of the amino group in this state. The role of hydrogen bonding of the amino group and the ring nitrogen in stabilization/destabilization of the ICT state and therefore on the nonradiative rate is also explored.

Polarity‐Dependant Intramolecular Charge Transfer Characteristics of 9‐Cyano‐10‐(1H‐pyrrol‐1‐yl)anthracene: Photophysical Investigations

“…In most solvatochromic studies, Δf, which is a measure of the orientational polarizability of the solvent, is considered to be a good parameter for correlating the effects of solvent polarity with the observed photophysics ,,. This is based on the understanding that since electronic polarization is an instantaneous process, it is not reflected in the photophysical properties which are mainly governed by reactions and interactions taking place during the excited state lifetime of the chromophores .…”

The role of hydrogen bonding in excited state intramolecular charge transfer

“…Datta et al showed that the ICT emission of 3-aminoquinoline (20) was favored in aprotic solvents such as dimethyl sulfoxide by a similar type of hydrogen bonding (21). 56 On the other hand hydrogen bonding inhibits the ICT emission of 20 in protic solvents, where the charge donor acts as a hydrogen bond acceptor 22, but the protonation of the acceptor enhances the ICT process (23).…”

Evidence for covalent binding of epicocconone with proteins from synchronous fluorescence spectra and fluorescence lifetimes

“…The data are fitted to multiexponential functions after deconvolution of the instrument response function by an iterative reconvolution technique, using the IBH DAS 6⋅0 data analysis software, where reduced χ 2 and weighted residuals serve as parameters for goodness of fit. 9 Time-dependent anisotropy, r(t), is constructed from the decays in the parallel and perpendicular directions to that of the excitation polarization (I || (t) and I ⊥ (t) respectively) as:…”