Solvent and substituent effect on the photophysical properties of pyrazoline derivatives: A spectroscopic study

Pyrazoline derivatives are among solvatochromic dyes and they are the most widely used in many fields such as sensors, labeling agent and optoelectronic devices. Therefore, synthesis of new pyrazoline derivatives and determination of their optical behavior in different solvents are a very important research area. In this study, the solvatochromic behaviors of seven new synthetic pyrazoline derivatives, (4-[3-(4-Hydroxypheny1)-5-aryl-4,5-dihydro-pyrazol-1-yl]benzenesulfonamides, compound 1-7), were determined in different solvents. As a result of the measurements, a large red shifts in the fluorescence spectra of the compounds studied were observed for each compound, when the polarity of the solvent increased. Kamlet-Taft and Catalan parameters were used to describe the solvent-soluble interactions. The obtained results showed that the solvatochromic behavior of the compounds is dependent on their solvent polarity as well as the effect of the hydrogen-bonding properties of the solvents. It was also found that the increases in the polarity of the solvent was facilitated the non-radiative transition. Furthermore, the changes in the dipole moments of compounds 1-7 in different solvents at room temperature were calculated by using the Lippert-Mataga equation. It was very impressive that calculated fluorescence quantum yield values of the compounds studied here by using different solvents were remarkably high than the ones reported in the literatures for pyrazolines. In addition, the effect of substituent on the photo-physical properties of the compounds was also investigated. It was observed that the fluorescence intensity of the substituted compounds 2-6 increased comparing to the compound 1, which is a non substituted derivative. These changes were not dependent on electronic nature of the substituent on phenyl ring (i.e. electron donating and electron withdrawing substituent). According to data obtained it can be stated that these novel solvatochromic dyes studied here can be find application in pharmaceutical industry, as labeling agent, sensor applications as biosensors or analytical sensors and/or optoelectronic devices. (C) 2017 Elsevier B.V. All rights reserved.