Photophysics of the dications of cinchonine and cinchonidine

Abstract

Steady state and time-dependent fluorescence studies have been carried out for the dications of cinchonine (C2+) and cinchonidine (Cd2+). A red shift in the emission maximum is observed on excitation at the red edge of the absorption band. The fluorescence decay shows double-exponential behaviour. The shorter-lifetime (τ1) component remains almost constant across the emission band whereas the longer-lifetime (τ2) component increases with increase in emission wavelength. The presence of double-exponential decay in C2+ and Cd2+ has been shown to be due to the presence of two different isomers in the ground state. The photophysical behaviours of C2+ and Cd2+ have also been compared with the dications of other cinchona alkaloids such as quinidine (Qd2+) and quinine sulphate (QS2+).