Specific interactions of alcohols and non-alcohols with a biologically active boronic acid derivative: a spectroscopic study H. S. Geethanjali, a R. M. Melavanki, b * D. Nagaraja, a * N. R. Patil, c J. Thipperudrappa d and R. A. Kusanur e ABSTRACT: The photophysical properties of 4-fluoro-2-methoxyphenyl boronic acid (4FMPBA) are characterized using absorp- tion and fluorescence techniques in series of non-alcohols and alcohols. The results are analyzed using different solvent polarity functions and Kamlet and Catalan’s multiple regression approaches. The excited state dipole moment and change in dipole moment are calculated using both the solvatochromic shift method and Reichardt’s microscopic solvent polarity parameter E N T   . The ground state dipole moment is evaluated using quantum chemical calculations. It is found that general solute– solvent and hydrogen bond interactions are operative in this system. A red shift of ~ 9 nm in the emission spectra is observed with an increase in the solvent polarity, which depicts π→π * transitions, as well as the possibility of an intramolecular charge transfer (ICT) character in the emitting singlet state of 4FMPBA. The relative quantum yield, radiative and non-radiative decay constants are calculated in alkanes and alcohols using the single point method. It is found that the quantum yield of the molecule varies from 16.81% to 50.79% with the change in solvent polarity, indicating the dependence of fluorescence on the solvent environment. Copyright © 2015 John Wiley & Sons, Ltd. Keywords: boronic acid derivative; solvatochromic shift method; dipole moment; relative quantum yield Introduction Boronic acids have emerged as one of the most useful class of organo-boron molecules, with applications in synthesis, catalysis, analytical chemistry, biology and medicine (1). Highly water- soluble mono-boronic acid probes display the more desirable OFF–ON fluorescence response (2). They show remarkable sensi- tivity for glucose rather than fructose and galactose. A wide range of boronic acid probes for the detection and determination of monosaccharides in contact lens polymers have been developed (3). In biochemistry, boronic acids are used in the detection and sensing of peroxides, the recognition and sensing of the tetra ser- ine motif in proteins and the development of new magnetic reso- nance imaging contrast agents (4). Also, boronic acid derivatives act as strong fluorescent sugar sensors. For example, Czarnik re- ported the properties of anthrylboronic acid 3, which senses sugars in a neutral aqueous solution via a fluorescence quenching process (5). Some of these properties of boronic acid derivatives prompted us to study the fluorescent properties of the above- mentioned sample. Spectral changes may arise from intermolecular solute–solvent interactions such as dipolar interactions, electron transfers (ET), complex formation and isomerization. The polarity of a solvent is an important property for explaining the effects of solvents on many physical and chemical processes. Parameters such as the dielectric constant and refractive index represent various solvent properties. To discuss the effect of solvent polarity on the photophysical properties of a molecule, a number of models are often used (5). Some of these are the Lippert–Mataga model (6,7), Baksheiv model (8), Kawski–Chamma–Viallet model (9,10), Reichardt model (11) and Kamlet and Catalan approach (12–15). Several theoretical treatments have been developed to quantita- tively link solvent effects to the bulk properties of a solvent. Although the photophysics and photochemistry of different heterocyclic molecules such as thiophenes, coumarin derivatives and quinine derivatives (16–19) have been reported previously, the effect of solvent polarity on the photophysical properties of 4FMPBA has not been explored. In this work, the effect of solvent polarity on the wavenumbers of absorption and emission transi- tion, relative quantum efficiency, radiative and non-radiative decay constants are reported. Theoretical calculations were carried out using the Gaussian 03 program (20,21). The excited state dipole moment was calculated for both non-alcohols and alcohols using * Correspondence to: R. M. Melavanki, Department of Physics, M S Ramaiah Institute of Technology, Bangalore 560054, Karnataka, India. E-mail: melavanki73@gmail.com * D. Nagaraja, Department of Physics, Bangalore Institute of Technology, Bangalore 560004, Karnataka, India. E-mail: nagarajdd86@gmail.com a Department of Physics, Bangalore Institute of Technology, Bangalore 560004, Karnataka, India b Department of Physics, M S Ramaiah Institute of Technology, Bangalore 560054, Karnataka, India c Department of Physics, BVB College of Engineering and Technology, Hubli 580031, Karnataka, India d Department of Physics, B.N.M. Institute of Technology, Bangalore 560070, Karnataka, India e Department of Chemistry, R V College of Engineering, Bangalore 560059, Karnataka, India Luminescence 2015 Copyright © 2015 John Wiley & Sons, Ltd. Research article Received: 21 May 2015, Revised: 18 September 2015, Accepted: 29 October 2015 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/bio.3067