Probing the effect of solvation on photoexcited 2-(2 `-hydroxyphenyl)benzothiazole via ultrafast Raman loss spectroscopic studies

Kayal, Surajit and Roy, Khokan and Lakshmanna, Y Adithya and Umapathy, Siva (2018) Probing the effect of solvation on photoexcited 2-(2 `-hydroxyphenyl)benzothiazole via ultrafast Raman loss spectroscopic studies. In: JOURNAL OF CHEMICAL PHYSICS, 149 (4).

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Abstract

2-(2 `-Hydroxyphenyl)benzothiazole (HBT) molecule is known to exhibit efficient excited state intramolecular proton transfer. As a consequence, it shows fluorescence with a large Stokes shift (similar to 10 000 cm(-1)) in non-polar solvents. However, fluorescence in polar solvents has a dual-band which corresponds to the emission from both the enol* and the keto* forms. Also, the excited state lifetime significantly varies with the solvent polarity. Recently, Mohammed et al. J. Phys. Chem. A 115, 7550 (2011)] have shown that the excited state of HBT in acetonitrile (ACN) relaxes back to its ground electronic state through two competitive decay pathways, i.e., intramolecular proton transfer and intramolecular twisting between hydroxyphenyl and benzothiazole units in contrast to its behavior when it is in tetrachloroethene, a non-polar solvent. Here, by following the time-evolution of vibrational features of excited state HBT in ACN through ultrafast Raman loss spectroscopy, we demonstrate a direct evidence for the involvement of torsional motion leading to an ultrashort lifetime of HBT. The time evolution of the C-7-N vibrational frequency exhibited a red-shift in its peak position, clearly indicating the evolution of the initially planar cis-keto* form to the more twisted keto* form. Density functional theory calculations also well corroborate the experimental findings. Furthermore, wavepacket analysis of this mode reveals a strong correlation with the torsional motion in ACN. Published by AIP Publishing.

Item Type:	Journal Article
Publication:	JOURNAL OF CHEMICAL PHYSICS
Publisher:	AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Additional Information:	Copy right for this article belong to AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry Division of Physical & Mathematical Sciences > Instrumentation Appiled Physics
Date Deposited:	23 Aug 2018 16:00
Last Modified:	23 Aug 2018 16:00
URI:	http://eprints.iisc.ac.in/id/eprint/60482

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