Photophysics of isolated Rose Bengal anions

Stockett, Mark H., Kjaer, Christina, Daly, Steven, Bieske, Evan J., Verlet, Jan R. R., Nielsen, Steen Brøndsted and Bull, James ORCID: https://orcid.org/0000-0003-0953-1716 (2020) Photophysics of isolated Rose Bengal anions. The Journal of Physical Chemistry A, 124 (41). 8429–8438. ISSN 1089-5639

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Abstract

Dye molecules based on the xanthene moiety are widely used as fluorescent probes in bioimaging and technological applications due to their large absorption cross-section for visible light and high fluorescence quantum yield. These applications require a clear understanding of the dye’s inherent photophysics and the effect of a condensed-phase environment. Here, the gas-phase photophysics of the rose bengal doubly deprotonated dianion [RB – 2H]2–, deprotonated monoanion [RB – H]−, and doubly deprotonated radical anion [RB – 2H]•– is investigated using photodetachment, photoelectron, and dispersed fluorescence action spectroscopies, and tandem ion mobility spectrometry (IMS) coupled with laser excitation. For [RB – 2H]2–, photodetachment action spectroscopy reveals a clear band in the visible (450–580 nm) with vibronic structure. Electron affinity and repulsive Coulomb barrier (RCB) properties of the dianion are characterized using frequency-resolved photoelectron spectroscopy, revealing a decreased RCB compared with that of fluorescein dianions due to electron delocalization over halogen atoms. Monoanions [RB – H]− and [RB – 2H]•– differ in nominal mass by 1 Da but are difficult to study individually using action spectroscopies that isolate target ions using low-resolution mass spectrometry. This work shows that the two monoanions are readily distinguished and probed using the IMS-photo-IMS and photo-IMS-photo-IMS strategies, providing distinct but overlapping photodissociation action spectra in the visible spectral range. Gas-phase fluorescence was not detected from photoexcited [RB – 2H]2– due to rapid electron ejection. However, both [RB – H]− and [RB – 2H]•– show a weak fluorescence signal. The [RB – H]− action spectra show a large Stokes shift of ∼1700 cm–1, while the [RB – 2H]•– action spectra show no appreciable Stokes shift. This difference is explained by considering geometries of the ground and fluorescing states.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: LivePure Connector
Date Deposited: 16 Oct 2020 23:58
Last Modified: 22 Oct 2022 07:18
URI: https://ueaeprints.uea.ac.uk/id/eprint/77319
DOI: 10.1021/acs.jpca.0c07123

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