R.A. Kusanur

Estimation of ground and excited state dipole moments of aryl boronic acid derivative by solvatochromic shift method

In the present work, the absorption and fluorescence spectra of newly synthesized aryl boronic acid derivative namely 2-Methylphenyl boronic acid (2MPBA) have been recorded in various solvents of different polarities. The ground state dipole moment of 2MPBA was obtained from quantum chemical calculations. Solvatochromic correlations were used to estimate the ground state (μg) and excited state (μe) dipole moments. The excited state dipole moments are observed to be greater than the ground state dipole moment and ground and excited state dipole moments are not parallel but subtend by an angle of 880. Further, the changes in dipole moment (Δμ) were calculated both from solvatochromic shift method and microscopic solvent polarity parameter (ETN), and the value are compared. The spectral variations were analyzed by Kamlet-Taft parameters.

Fluorescence characteristics of aryl boronic acid derivate (PBA)

The absorption and fluorescence spectra of newly synthesized aryl boronic acid derivative namely Phenyl boronic acid (PBA) have been recorded in various solvents of different polarities. The ground state dipole moment of PBA was obtained from quantum chemical calculations. Solvatochromic correlations were used to estimate the ground state (μg) and excited state (μe) dipole moments. The excited state dipole moments are observed to be greater than the ground state dipole moments. Further, the ground and excited state dipole moments are not parallel but subtend by an angle of 70°. The changes in dipole moment (Δμ) were calculated both from solvatochromic shift method and microscopic solvent polarity parameter (ET(N)), and the values are compared. Solvent effects on the absorption and fluorescence spectra were quantified using Reichardts and bulk solvent polarity parameters were complemented by the results of the Kamlet-Taft treatment.

Specific interactions of alcohols and non‐alcohols with a biologically active boronic acid derivative: a spectroscopic study

The photophysical properties of 4-fluoro-2-methoxyphenyl boronic acid (4FMPBA) are characterized using absorption and fluorescence techniques in series of non-alcohols and alcohols. The results are analyzed using different solvent polarity functions and Kamlet and Catalans multiple regression approaches. The excited state dipole moment and change in dipole moment are calculated using both the solvatochromic shift method and Reichardts microscopic solvent polarity parameter ETN. 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

Effect of viscosity and dielectric constant variation on fractional fluorescence quenching analysis of coumarin dye in binary solvent mixtures

Photo physical properties of fluorescent organic compounds give an immense improved knowledge on characteristics of excited state that is beneficial to devise innovate molecules and understand their performance in particular applications. Coumarin derivatives have been extensively investigated in this regard. This article narrates steady state fluorescence quenching measurements of a coumarin derivative namely 3-hydroxy-3-[2-oxo-2-(3-oxo-3H-benzo[f]chromen-2-yl)-ethyl]-1,3-dihydro-indol-2-one (3HBCD) in a binary mixture of acetonitrile and 1,4-dioxane. Aniline is used as quencher. Fluorescence intensity is large in acetonitrile and decreases as the percentage of 1,4-dioxane in the solvent mixture increases. With modest quencher concentration a deviation towards the x axis is noticed in the Stern-Volmer (S-V) plots. This downward curvature is interpreted as due to the presence of 3HBCD in different conformers in the lowest energy level. Ground state intramolecular hydrogen bonding formation is observed due to the conformational changes in the solute. Figured estimations of various quenching parameters recommend that, while dynamic quenching prompts linearity in S-V plot at lower quencher concentration, increasing quenching efficiency with increasing medium viscosity suggests that reaction is not entirely controlled by material diffusion. Stern-Volmer constant increases with decreasing medium dielectric constant.

Bimolecular fluorescence quenching reactions of the biologically active coumarin composite 2-acetyl-3H-benzo[f]chromen-3-one in different solvents

A study on fluorescence quenching was carried out for the coumarin derivative 2-acetyl-3H-benzo[f]chromen-3-one (2AHBC) with aniline at room temperature. Efficient fluorescence quenching was observed and Stern-Volmer (S-V) plots showed upward curves from linearity in all solvents of different polarities. For the solute 2AHBC, ground state complex formation does not hold in our study. The kinetic distance (r) value was found to be greater than the encounter distance (R) and indicated that the quenching reaction was held within the sphere of action. Diffusion-limited reactions were found to be more prominent in high polarity solvents, namely dimethyl sulfoxide (DMSO), DMF, ACN, methanol, ethanol, propanol and DCM. The relationships between quenching constant (KSV ) and dielectric constants (ε) of the different solvents were studied.

EFFECT OF HYDROGEN BONDING ON FLUORESCENCE QUENCHING OF QUINOLIN-8-OL - ANALYSIS USING NEGATIVE STERN-VOLMER PLOTS

Photophysics of fluorescent organic compounds give a better knowledge of the excited state properties which in turn will help in the design of newer molecules and understanding their performance in specific applications. Here we present the fluorescence quenching study of a Quinolin-8-ol (QO) in toluene and butanol solvents by steady state fluorescence measurements. Anilineis the quencher. Negative deviation in the Stern – Volmer (S-V) plots has been observed with moderate quencher concentration. The downward curvature in the S-V plot is interpreted in terms of existence of different conformers of the solute in the ground state. The formation of intermolecular and intra molecular hydrogen bonding is found to be responsible for the conformational changes in the ground state of the solute. Quenching data is analyzed by modified Stern-Volmer equation or Lehrer equation.