화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.124, No.41, 8429-8438, 2020
Photophysics of Isolated Rose Bengal Anions
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](center dot-) 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](center dot-) 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 IMSphoto-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](center dot-) show a weak fluorescence signal. The [RB - H](-) action spectra show a large Stokes shift of similar to 1700cm(-1), while the [RB - 2H](center dot-) action spectra show no appreciable Stokes shift. This difference is explained by considering geometries of the ground and fluorescing states.