Ground and excited state dipole moments of quinine sulfate dication: Solvatochromic shift of absorption and fluorescence spectra

Electronic absorption and fluorescence spectra of quinine sulfate dication (QSD) have been recorded at room temperature in a wide range of solvents of different polarities. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas a red shift in fluorescence emission maximum was observed. The ground-state dipole moment of QSD was obtained from quantum mechanical calculations and the first excited singlet state dipole moment of QSD was obtained from Bakhshiev's and Bilot-Kawski's equations by means of solvatochromic shift method. Very high value of dipole moment is observed for excited state as compared to the corresponding ground state value and this is attributed to the more polar excited state of QSD. Compared to the dipole moment of quinine sulfate, both the ground and excited state dipole moments of QSD are lower. (C) 2012 Elsevier B.V. All rights reserved.