Non-Traditional Excited-State Deactivation in N-Containing Chromophores: A Combined Spectroscopic and Computational
Bhavika Kalal1, Surajit Maity1
1Department of Chemistry, IIT Hyderabad, Kandi, Sangareddy, Telangana 502284, India.
The Journal of Physical Chemistry Letters
|December 26, 2025
Summary
We determined the excited-state energy barrier for a hydrogen-bonded complex. This reveals a novel solvent-catalyzed deactivation pathway for N-containing chromophores without a protic NH group.
Area of Science:
- Photochemistry
- Spectroscopy
- Chemical Physics
Background:
- Hydrogen-bonded complexes play crucial roles in energy transfer and reaction mechanisms.
- Understanding excited-state deactivation pathways is essential for designing functional molecules.
- The 2-(2'-pyridyl)-benzimidazole (PBI)-H2O complex serves as a model for asymmetric hydrogen-bonded systems.
Purpose of the Study:
- To determine the excited-state deactivation energy barrier of the PBI-H2O complex in the gas phase.
- To elucidate the mechanism of excited-state proton transfer in this hydrogen-bonded system.
- To explore alternative deactivation pathways in N-containing chromophores.
Main Methods:
- Combined electronic and ion-dip infrared (IR) spectroscopy to identify hydrogen bonding.
- Long-range R2PI and UV-UV hole-burning spectroscopy to measure the excited-state energy barrier.
- Computational investigations to model the proton migration pathway and identify the barrier origin.
Main Results:
- Identified a PBI N···H-OH hydrogen bonding interaction in the complex.
- Determined an excited-state energy barrier of 893-1067 cm⁻¹ in the S1 state.
- Computational studies revealed proton migration from water to PBI in the S1 state, driven by a ππ*-nπ* intersection.
Conclusions:
- N-containing chromophores can deactivate efficiently via a solvent-catalyzed pathway, even without a protic NH group.
- This study presents an alternative mechanism for excited-state energy dissipation in asymmetric hydrogen-bonded systems.
- Findings expand design strategies for functional chromophores by highlighting solvent-mediated deactivation.
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