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Anomalous Water Fluorescence Induced by Solutes.
Anna Maria Villa1, Jessica Di Paola1, Diletta Ami1
1Department of Biotechnologies and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy.
The Journal of Physical Chemistry Letters
|June 30, 2025
Summary
Anomalous fluorescence in aqueous solutions is linked to charge-transfer-to-solvent excitations (CTTS). Solutes can prolong CTTS excited state lifetimes, enhancing fluorescence emission.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- Anomalous fluorescence emissions from aqueous solutions of nonaromatic solutes have been reported.
- The underlying mechanism and the influence of solute nature remain unclear.
Purpose of the Study:
- To investigate the origin of anomalous fluorescence in aqueous solutions.
- To determine if solute nature influences fluorescence characteristics.
- To identify a common emission mechanism.
Main Methods:
- Measured fluorescence spectra of 21 different aqueous solutions.
- Employed time-dependent density functional theory (TD-DFT) on large water, NaCl/water, and glycerol/water clusters.
Main Results:
- Observed similar emission characteristics across diverse solutes, indicating minimal solute influence.
- Attributed anomalous emission to charge-transfer-to-solvent (CTTS) excitations.
- Identified a diradical zwitterionic excited state at hydrogen-bond network defects.
Conclusions:
- The S1 nonradiative decay pathway involves diradical recombination via librational motion.
- Solute molecules appear to slow this recombination, increasing CTTS excited state lifetime and facilitating emission.
- A common mechanism for anomalous fluorescence in aqueous solutions is proposed.
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