Photomolecular rotor dynamics of the oxindole-based photoprotective bacterial pigment violacein

Bressan, Giovanni, Siddiqui, Khalid, Ashworth, Eleanor K., Chakraborty, Pratip, Banerjee, Dipanjan, Braun, Erico M., Meech, Stephen R. and Bull, James N. (2025) Photomolecular rotor dynamics of the oxindole-based photoprotective bacterial pigment violacein. Physical Chemistry Chemical Physics. ISSN 1463-9076

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Abstract

Conjugated molecules incorporating the oxindole motif offer a versatile scaffold for designing highperformance, light-responsive materials that exploit photomolecular rotor motion. Violacein, a purple coloured oxindole-based pigment produced by bacterial strains in superglacial Antarctic ice melts, serves as a natural photoprotectant. Using ultrafast spectroscopy combined with explicitlysolvated potential energy surfaces, we characterise the excited-state relaxation mechanism in violacein to involve initial relaxation to planar locally excited (LE) state(s), followed by passage through a twisted charge-transfer (CT) state along the molecular rotor coordinate to a nearby isomerising-like conical intersection seam. Propagation over the excited-state barrier connecting the LE and CT states along the photomolecular rotor axis leads to a strong viscosity dependence of the excited state lifetimes (ca. 4 ps in acetonitrile and 100 ps in ethylene glycol). These dynamics, leading to efficient electronic-to-vibrational energy conversion, coupled with a fast rate for thermal conversion of the possible Z photoisomer back to the starting E isomer, confer violacein with desirable photoprotectant properties.

Item Type:	Article
Additional Information:	Data availability: The data that support the findings of this study are available from the corresponding author upon reasonable request. Funding information: This work was funded by an EPSRC New Investigator Award (EP/W018691 to JNB) and an EPSRC Grant (EP/X011410/1 to SRM). GB is grateful to the Leverhulme Trust for funding him through an Early Career Fellowship (Grant no. ECF2023-195). EMB thanks the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for his studentship (SWE 200581/2025-2).
Faculty \ School:	Faculty of Science > School of Chemistry, Pharmacy and Pharmacology
Depositing User:	LivePure Connector
Date Deposited:	16 Dec 2025 15:30
Last Modified:	16 Dec 2025 15:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/101428
DOI:	10.1039/D5CP04151A

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