Adhikari M, Pant S, Mishra H. Spectral and time domain fluorescence spectroscopy of gentisic acid molecule in protic and aprotic polymer matrix.
Spectrochim Acta A Mol Biomol Spectrosc 2022;
270:120825. [PMID:
34999357 DOI:
10.1016/j.saa.2021.120825]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2021] [Revised: 12/20/2021] [Accepted: 12/25/2021] [Indexed: 06/14/2023]
Abstract
In the present work, the effect of polymer microenvironment on the photophysics of gentisic acid molecule [2,5-dihydroxybenzoic acid] (GA), steady-state and time-domain fluorescence measurements at different pH conditions were carried out in protic [polyvinyl alcohol PVA] and aprotic [polymethyl methacrylate (PMMA)] polymer matrices. Change in the proticity of the microenvironment of the polymer traps different ionic species along with the neutral form of rotamer P and R conformers of GA molecule, are found to be responsible for the change in the spectral, multi-exponential decay behaviour. In protic polymer, the appearance of a single emission band indicates, dissociation of the GA molecule is very high, and it present as a monoanion along with hydrogen-bonded P and R rotamers. However, in the basic polymer film, most of the conformers of R converted to the anion. In contrast, protonation slows down the dissociation of both P and R forms in the acidic film. Unlike PVA matrix, in PMMA, dual emission band appears due to slow dissociation of GA molecule and hydrogen-bonded rotamer P, and R form exists with monoanion species. The magnitude of large stokes shifted red emission due to excited-state intramolecular proton transfers (ESIPT) found grater in rotamer P compared to its anionic species (green emission) and a blue emission corresponds to rotamer R.
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