Resolving Mode-Specific Vibronic Coupling in Hydrogen-Bonded Systems Using Three-Dimensional Vibrational-Electronic Spectroscopy
ORAL
Abstract
Hydrogen bonding plays a critical role in modulating electronic excited states and photochemical reactivity across chemistry and biology, yet the precise vibrational mechanisms mediating coupling between nuclear motion and electronic transitions remain poorly understood. Traditional multidimensional spectroscopies operate within single frequency domains, limiting their ability to correlate vibrational dynamics with electronic processes when these occur at vastly different energy scales. We demonstrate that mixed frequency two dimensional vibrational electronic (2DVE) spectroscopy, combined with comprehensive three-dimensional Fourier analysis, can directly resolve mode-specific vibronic coupling mechanisms in strongly hydrogen-bonded molecular systems.
Using 10-hydroxybenzo[h]quinoline (HBQ) as a prototypical intramolecular hydrogen-bonded system undergoing excited state intramolecular proton transfer, we selectively pre-excite the hydrogen-bonded OH stretch vibration (~2800 cm⁻¹) with mid-IR pulses and probe its influence on the electronic charge-transfer transition (~24,000 cm⁻¹) with a broadband near UV pulse. Fourier transformation along the waiting time (delay between the second IR and the nUV pulse) generates a third frequency axis in the low-frequency region (<500 cm⁻¹), creating 3D correlation maps that reveal which skeletal modes mediate vibronic coupling. Our analysis uncovers striking mode selectivity: two distinct low-frequency modes at 220 and 243 cm⁻¹ exhibit dramatically different coupling topologies in the three-dimensional frequency space. The 243 cm⁻¹ in-plane skeletal mode couples preferentially to specific vibrational states within the anharmonic OH manifold. In contrast, the 220 cm⁻¹ out-of-plane ring deformation shows stronger detection-frequency dependence, indicating preferential modulation of the electronic transition itself.
These results establish that vibronic coupling in hydrogen-bonded systems proceeds through highly selective channels. This work provides both fundamental insight into hydrogen bond-mediated photochemistry and a practical framework for designing coherent control strategies targeting specific vibrational pathways.
Using 10-hydroxybenzo[h]quinoline (HBQ) as a prototypical intramolecular hydrogen-bonded system undergoing excited state intramolecular proton transfer, we selectively pre-excite the hydrogen-bonded OH stretch vibration (~2800 cm⁻¹) with mid-IR pulses and probe its influence on the electronic charge-transfer transition (~24,000 cm⁻¹) with a broadband near UV pulse. Fourier transformation along the waiting time (delay between the second IR and the nUV pulse) generates a third frequency axis in the low-frequency region (<500 cm⁻¹), creating 3D correlation maps that reveal which skeletal modes mediate vibronic coupling. Our analysis uncovers striking mode selectivity: two distinct low-frequency modes at 220 and 243 cm⁻¹ exhibit dramatically different coupling topologies in the three-dimensional frequency space. The 243 cm⁻¹ in-plane skeletal mode couples preferentially to specific vibrational states within the anharmonic OH manifold. In contrast, the 220 cm⁻¹ out-of-plane ring deformation shows stronger detection-frequency dependence, indicating preferential modulation of the electronic transition itself.
These results establish that vibronic coupling in hydrogen-bonded systems proceeds through highly selective channels. This work provides both fundamental insight into hydrogen bond-mediated photochemistry and a practical framework for designing coherent control strategies targeting specific vibrational pathways.
*Brown Investigator Award
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Publication: [1] C.M. Loe, S Chatterjee, R.B. Weakly, M. Khalil,J. Chem. Phys. 161, 174203 (2024)
Presenters
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Srijan Chatterjee
- UNIVERSITY OF WASHINGTON