Cryogenic Fluorescence Spectroscopy of Ionic Fluorones in Gaseous and Condensed Phases: New Light on Their Intrinsic Photophysics

Abstract

Fluorescence spectroscopy of gas-phase ions generated through electrospray ionization is an emerging technique able to probe intrinsic molecular photophysics directly without perturbations from solvent interactions. While there is ample scope for the ongoing development of gas-phase fluorescence techniques, the recent expansion into low-temperature operating conditions accesses a wealth of data on intrinsic fluorophore photophysics, offering enhanced spectral resolution compared with room-temperature measurements, without matrix effects hindering the excited-state dynamics. This perspective reviews current progress on understanding the photophysics of anionic fluorone dyes, which exhibit an unusually large Stokes shift in the gas phase, and discusses how comparison of gas- and condensed-phase fluorescence spectra can fingerprint structural dynamics. The capacity for temperature-dependent measurements of both fluorescence emission and excitation spectra helps establish the foundation for the use of fluorone dyes as fluorescent tags in macromolecular structure determination. We suggest ideas for technique development.

Cryogenic fluorescence spectroscopy of oxazine ions isolated in vacuo

“…The fluorescence spectrum (blue) exhibits maximum intensity at 565.5 AE 0.5 nm, and the spectrum is significantly broader but still shows appreciable vibrational structure. In our previous work 9,14,25,26 on a range of similar fused three-ring systems (pyronin Y, rhodamines, fluorones) and dimethyl-oxyluciferin, the fluorescence spectra were also broader and more congested than the fluorescence-excitation spectra. We showed that it was caused by an increased effective temperature of the ions due to excess energy deposited by the absorbed laser photon.…”

“…Cryogenic ion spectroscopy has gained significant attention in recent years as it provides intrinsic information on the photophysics of isolated molecular ions. [1][2][3][4][5][6][7][8][9] At low temperatures, spectra exhibit reduced spectral congestion, which facilitates the assignment of bands and vibrational features as well as geometric structures. Experimental data on cold ions are better benchmarks for theoretical calculations of electronically excited states, which are still nontrivial and computational costly.…”

Alkylated green fluorescent protein chromophores: dynamics in the gas phase and in aqueous solution

“…17,18 Attempts to observe gas-phase fluorescence from pHBDI À at T E 300 K and T E 100 K using the LUNA2 instrument at Aarhus University, including by some of the present authors, have been unsuccessful. 19,20 Synthetic modification of the pHBDI chromophore to explore structure-function relationships has resulted in numerous analogues offering altered spectral properties and excited state dynamics. These analogues include halogenation [21][22][23][24] and/or alkylation 12 on the phenyl ring, methylation of the hydroxyl group, 25 replacement of the hydroxyl group with an amine group, [26][27][28] and shifted hydroxyl group positions.…”