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Solvation and hydrogen bonding aided efficient non-radiative deactivation of polar excited state of 5-Aminoquinoline

Abstract

Fluorescence of 5-aminoquinoline (5AQ) is quenched strongly in alcoholic solvents, in stark contrast to the enhancement in fluorescence observed earlier for its positional isomer, 3-aminoquinoline (3AQ). This phenomenon has been explained by the involvement of a highly dipolar excited state, which is manifested in the solvatochromism of 5AQ. Marked wavelength dependence of fluorescence decays of 5AQ in alcoholic solvents is ascribed to ultrafast solvation of the highly dipolar excited state in these solvents. Resultant stabilization of this state leads to a decrease in the gap between its energy and lower lying triplet as well as ground singlet states, resulting in efficient non-radiative relaxation and consequently, fluorescence quenching. Solvation dynamics reported by 5AQ is somewhat slower than earlier reports with coumarin probes, due to the involvement of solute-solvent hydrogen bonds, especially in the excited state of the solute. At lower temperature, solvation is slowed down. An extreme case of this phenomenon is the absence of solvent relaxation at liquid nitrogen temperature. Fluorescence lifetime increases from tens of picoseconds at room temperature to tens of nanoseconds at cryogenic temperature, lending credence to the proposed model.

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Publication details

The article was received on 07 Jun 2018, accepted on 01 Aug 2018 and first published on 01 Aug 2018


Article type: Paper
DOI: 10.1039/C8CP03590C
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Solvation and hydrogen bonding aided efficient non-radiative deactivation of polar excited state of 5-Aminoquinoline

    A. Singh, S. Das, A. Karmakar, A. Kumar and A. Datta, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP03590C

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