Fluorescence Spectroscopic Studies Of Some Organic Molecules

Abstract

Biologically active fluorescent organic molecules like coumarin newlinederivatives, boronic acid derivatives etc. play vital roles in the design and newlinesynthesis of sensors, utilized to detect biomolecules like proteins, lipids newlineand carbohydrates. A detailed knowledge of their photophysical newlineproperties is essential for this purpose. This research work focuses on newlinethe investigation of the spectroscopic properties and photophysical newlineproperties of three boronic acid derivatives namely, 5-chloro-2- newlinemethoxyphenylboronic acid (5CMPBA), 4-fluoro-2-methoxyphenylboronic newlineacid(4FMPBA) and 2-methoxypyridin-3-yl-3-boronic acid (2MPBA). newlineThe work is carried out using various polar and non-polar newlinesolvents. A red shift is observed in the fluorescence spectra as a result of newlinesolvent polarity. Various correlations are used to analyze the newlinesolvatochromic data and ground and excited state dipole moments are newlinethus estimated. Quantum chemical calculations are performed using DFT newlineB3LYP/6-31 G (d,p) level. The relative fluorescence quantum yield of newlinethese molecules is determined using a single point method by taking newlineTryptophan in water as the standard reference. Relative fluorescence newlinequantum yield being viscosity sensitive is also found to be polarity newlinesensitive and increases with increase in solvent polarity (especially in newlinealcohols). newlineBimolecular fluorescence quenching mechanism of boronic acid newlinederivatives in non-alcohols and alcohols, with aniline as a quencher, is newlineanalyzed using the Stern-Volmer equation. The simultaneous presence newlineof both static and dynamic quenching in non-alcohol environments is newlineconfirmed from positive Stern-Volmer(S-V) plots. The role of material newlinediffusion in dynamic quenching is understood using time dependent newlinestudies (transient studies). The conformational changes arising due to newlinethe formation of intramolecular and inter molecular hydrogen bonds newlinebetween solutes and alcohols, in an alcoholic environment is confirmed, newlinefrom the negative deviation in S-V plots. newlineWe have also extended our work, to understand the