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Author(s):Mishra, Hirdyesh
Subject(s):Comparing theory and experiment
Abstract:Study of the photophysics and electronic structure properties of quinoline and its derivatives have been the subject of considerable interest because of their commercial and pharmaceutical applications. Some of the quinoline derivatives have been found as a potential probes for measuring the polarity of microenvironment in chemical and biological systems. Diffuse interstellar bands in the emission spectrum of the interstellar medium, indicate the presence of quinoline and other small polycyclic aromatic nitrogen heterocycles, which readily dissociate under exposure to interstellar radiation. Since the quinoline ring is the basic fluorophor unit in all its derivatives, it is important to understand the change in dynamics and electronic structure of quinoline in presence some external perturbation. Being isoelectronic with naphthalene, these molecules provide useful comparisons for checking the electronic and vibrational state assignments, ionization potentials, and other properties of the parent hydrocarbon. In addition, these molecules possess nonbonding electrons which give rise to n– $\pi^{*}$ states. The location and characterization of these states are of both theoretical and practical significance. Further, solvents have an important influence on the fluorescence property of N-heterocyclic compounds. Experimentally, Quinoline shows vibronic absorption spectrum and corresponding large Stoke shifted broad fluorescence emission spectrum having very low quantum yield and dual decay time, however protonated quinoline shows red shifted fluorescence spectrum with increase in quantum yield and fluorescence decay become mono-exponential. To understand the vibronic structure of electronic absorption spectra and photophysics of protonation of quinoline, both vibronic and electronic structure studies of quinoline (Q) and protonated quinoline (QH$^{+}$) were carried out along with vibrational calculations for absorption and fluorescence bands at B3LYP 6-311$++$G(d,p) level in ground and excited state by density functional methods (DFT) and (time-dependent density functional) TD-DFT methods respectively with the help of Gaussian 09 software. Normal mode mixing is taken into account by the Duschinsky transformation. The vibronic structure of strongly dipole-allowed transitions is calculated within the Franck–Condon approximation. A good correlation between computational spectroscopic calculations and experiment results are found to understand the photo-physics of protonation of quinoline.
Issue Date:24-Jun-20
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Date Available in IDEALS:2020-06-26

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