Excited state structural dynamics of 4-cyano-4 `-hydroxystilbene: deciphering the signatures of proton-coupled electron transfer using ultrafast Raman loss spectroscopy

Mathew, Reshma and Kayal, Surajit and Yapamanu, Adithya Lakshmanna (2019) Excited state structural dynamics of 4-cyano-4 `-hydroxystilbene: deciphering the signatures of proton-coupled electron transfer using ultrafast Raman loss spectroscopy. In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21 (40). pp. 22409-22419.

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Abstract

The photo-initiated proton-coupled electron transfer (PCET) process plays a crucial role in the context of light harvesting in various biological and chemical systems. Molecular model systems are typically employed to understand the mechanisms underlying the functioning of complex biological systems. Some molecular dyads based on the PCET property have been particularly designed to achieve efficient sunlight-to-fuel production. Organic photoacids are potential sources for such applications since they exhibit an enhancement in their acidity upon photoexcitation, facilitating the mimicking of some of the biological processes. p-Hydroxybenzylideneimidazolinone (p-HBI), an organic photoacid, is a key chromophore in green fluorescent protein, which exhibits green emission due to excited state proton transfer. Herein, we investigate the structural changes and dynamics of 4-cyano-4 `-hydroxystilbene (CHSB), an analogue of p-HBI, in the presence of an external base, t-butylamine (TBA), using the techniques of ultrafast transient absorption, emission and ultrafast Raman loss spectroscopy. Femtosecond fluorescence up-conversion measurements of the CHSB-TBA adduct reveal a precursor-successor relationship between the similar to 420 and similar to 530 nm emission bands, which implies that the adduct evolves predominantly through an electron-proton transferred state. Further, Raman measurements show a clear distinction in the dynamics of the C & xe001;C stretch of CHSB in the presence and absence of TBA in terms of the amplitude growth (0.45 ps vs. instantaneous) and the central frequency (1584 vs. 1523 cm(-1)).

Item Type:	Journal Article
Publication:	PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Publisher:	ROYAL SOC CHEMISTRY
Additional Information:	Copyright of this article belongs to ROYAL SOC CHEMISTRY
Keywords:	NONADIABATIC DYNAMICS; INTERNAL-CONVERSION; CONCERTED ELECTRON; SUPER-PHOTOACIDS; LINE-SHAPES; PHOTOISOMERIZATION; STILBENE; META; FLUORESCENCE; CHROMOPHORE
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	27 Nov 2019 09:25
Last Modified:	27 Nov 2019 09:25
URI:	http://eprints.iisc.ac.in/id/eprint/63813

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