Estimation of Dipole Moments and Quantum Yield of 5-chloro-2-methoxyphenyl Boronic Acid in Different Solvents Environment.

The Photophysical properties like ground state and excited state dipole moments, change in the dipole moment and fluorescence quantum yield of a boronic acid derivative 5-chloro-2-methoxy phenyl boronic acid (5CMPBA) are characterized. The study is carried out in various solvents at room temperature using absorption and steady-state fluorescence technique. The emission wavelength of 5CMPBA is quite sensitive to the polarity of solvents. With the increase in solvent polarity red shift or bathochromic shift of about 9 nm has been observed. The excited state and ground state dipole moments are estimated using solvatochromic shift method and effect of solvents on spectral properties of the molecule are investigated using Kamlet-Taft multiple linear regression approach. The changes in dipole moment (Δμ) are calculated both from solvatochromic shift method and microscopic solvent polarity parameter (E T (N) ), and the values are compared. The ground state dipole moment is also evaluated using quantum chemical calculations. The bathochromic shift of the emission spectra and the increase in the excited state dipole moment indicates π → π* transitions as well as the possibility of intramolecular charge transfer (ICT) character in the emitting singlet state of 5CMPBA. The relative quantum yield (Φ), radiative and non-radiative decay constants are calculated using single point method. It is found that the quantum yield of the molecule varies from 11 to 64% with the change in the solvent polarity indicating the dependency of fluorescence nature on the solvent environment.