Photochemistry and Spectroscopy Department

Institute of Physical Chemistry, Polish Academy of Sciences


Friday, March 29, 10:30, IChF Conference Room


Prof. Francis A. S. Chipem, Department of Chemistry, Manipur University, India


Importance of Solute-Solvent Intermolecular Hydrogen Bond in Solvation Study of ESIPT Exhibiting Molecules





Fluorescence is an important field that finds applications in various devices and as a tool of investigation in areas ranging from material science through analytical science to diagnosis. It involves the study of emission of light by a chromophore at a certain wavelength after being excited by light of higher energy. Emphasis is now shifted to molecules/chromophores with dual fluorescence or emission at two different wavelengths, as they have better advantages than those with single emission, particularly in analytical science. Dual fluorescence provides ratiometric measurements of emission or excitation intensities as ratiometric measurements eliminate the errors arising from concentration, photobleaching, or instrument. This dual emission is usually due to molecular transformation in the electronic excited state. One such transformation is a simple charge or proton transfer.

The presentation concentrates on the theoretical study, employing density functional theory, on the photophysics of 2-(2′-hydroxyphenyl)oxazolo[4,5-b]pyridine (HPOP). HPOP exhibits excited-state intramolecular proton transfer (ESIPT), which is a phototautomerization of enol to tautomer in the excited state through a cyclic intramolecular hydrogen-bonded ring. As a result, the molecules show dual fluorescence arising from local emission of the enol form (normal emission) and unusually large Stokes' shifted emission from the tautomer form (ESIPT product). The ratio of the emissions depends on the relative populations of the enol and tautomer forms. Manipulation of the relative population can be achieved by changing the solvents. The calculations employing the polarizable continuum model show that not only the solute cavity in the solvent and dielectric of the medium are required, introduction of explicit hydrogen bonding between solute and solvent molecules is essential in solvation study, particularly for protic solvents. As many as nine hydrogen-bonded clusters are identified in methanol and water. The ESIPT occurs in the S1 state from the Franck-Condon geometry of the corresponding ground state in a single OH stretching vibration to form the tautomer.

















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