Solvent-Dependent Excited-State Evolution of Prodan Dyes.
Petr Pospíšil1, Lukasz Cwiklik1, Jan Sýkora1
1J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, CZ-18223 Prague, Czech Republic.
The Journal of Physical Chemistry. B
|December 16, 2021
Summary
Prodan-type dyes exhibit solvation-driven charge separation in their excited state, influencing fluorescence shifts. This study reveals how dye dynamics reflect solvent relaxation and environment polarity.
Area of Science:
- Photochemistry
- Spectroscopy
- Chemical Dynamics
Background:
- 6-(dimethylamino)-2-acylnaphthalene dyes (Prodan and Badan-SCH2CH2OH) are widely used as fluorescent probes.
- Understanding their excited-state dynamics is crucial for interpreting environmental sensing applications.
Purpose of the Study:
- To investigate the excited-state character and dynamics of Prodan and Badan-SCH2CH2OH dyes.
- To elucidate the role of solvent polarity and relaxation in dye behavior.
- To provide evidence for solvation-driven charge separation in these dyes.
Main Methods:
- Picosecond time-resolved infrared spectroscopy (TRIR) was employed.
- Experiments were conducted in solvents of varying polarity and relaxation times (hexane, CD3OD, glycerol-d8).
- Time-dependent density functional theory (TDDFT) calculations were used for spectral assignment.
Main Results:
- Near-UV excitation initially formed an S1(ππ*) excited state in all solvents.
- In polar/H-bonding solvents, a fast conversion to an S1(ICT) state occurred, characterized by a downshifted C=O band.
- TRIR conversion kinetics correlated with fluorescence decay and red-shift, indicating solvation-driven charge separation.
Conclusions:
- Prodan-type dyes undergo significant charge separation in their excited state, driven by solvent interactions.
- The observed dynamic fluorescence Stokes shift is a direct consequence of this solvation-driven process.
- The time evolution of excited states reflects solvent relaxation, validating these dyes as probes of environment dynamics.
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