Fluorescence Spectroscopy of Gas-Phase Molecular Ions

Fluorescence spectroscopy of gas-phase molecular ions combines mass spectrometric selection with optical excitation to probe the intrinsic electronic and structural properties of isolated ions. In a typical experiment, ions of defined mass-to-charge ratio are confined within an ion trap or guided through a beamline, then excited by laser light to higher electronic states. The ensuing fluorescence emission is collected by sensitive detectors, yielding spectra that reflect transition energies, vibrational structure and environmental perturbations free from solvent effects. Advances in ion cooling—either through cryogenic buffer gases or sympathetic cooling—have sharpened spectral features and reduced thermal broadening, allowing the resolution of fine rotational and vibrational levels. The technique delivers insights into intramolecular energy redistribution, charge localisation and photophysics of biomolecules, dyes and clusters. Moreover, the absence of a solvent cage unlocks direct observation of charge-driven shifts in transition energies, while multicolour excitation schemes enable intramolecular distance measurements via Förster resonance energy transfer. Applications span from elucidating protein folding motifs and organic dye photostability to modelling ion-molecule reactions in interstellar and atmospheric environments. Ongoing developments in time-resolved detection and cavity-enhanced collection promise further gains in sensitivity, underpinning a growing role for gas-phase fluorescence in structural chemistry and molecular physics.

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Fluorescence Spectroscopy of Gas-Phase Molecular Ions publication trend

The graph below shows the total number of articles in fluorescence spectroscopy of gas-phase molecular ions across all publications each year (not limited to Nature Index journals).

Technical terms

Fluorescence spectroscopy: An optical technique in which molecules are excited by light and the emitted photons are measured to reveal energy levels and dynamics.

Gas-phase molecular ion: A charged molecule isolated in the vapour phase, free from solvent interactions and suitable for mass spectrometric analysis.

Ion trap: A device employing electromagnetic fields to confine ions in space for extended interrogation by lasers or other probes.

Förster resonance energy transfer (FRET): A non-radiative mechanism of energy transfer between a donor and acceptor chromophore, dependent on their separation and spectral overlap.

Cryogenic cooling: The use of very low temperatures, often via cold buffer gas or refrigeration, to reduce thermal motion and sharpen spectral features of trapped ions.

References

1. Gas‐phase Förster resonance energy transfer in mass‐selected and trapped ions. Mass Spectrometry Reviews (2022).
2. Cryogenic Ion Fluorescence Spectroscopy: FRET in Rhodamine Homodimers and Heterodimers. Chemistry - A European Journal (2023).
3. Fluorescence-based Techniques to Study the Structure and Dynamics of Mass-selected Biomolecular Ions. CHIMIA International Journal for Chemistry (2021).