Ultrafast solvent-to-solute proton transfer mediated by intermolecular coherent vibrations

Journal Article · Fri Jan 30 00:00:00 EST 2026 · Communications Chemistry

DOI:https://doi.org/10.1038/s42004-026-01917-8· OSTI ID:3025337

Jarupula, Ramesh ^[1]; Mao, Yuezhi ^[2]; Yong, Haiwang ^[1]

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1. University of California, San Diego, La Jolla, CA (United States)
2. San Diego State University, CA (United States)

Ultrafast photoinduced excited-state proton transfer (ESPT) plays a crucial role in protecting biomolecules and functional materials from photodamage. However, the influence of solute-solvent interactions on ESPT dynamics remains under active investigation. Here, we present an ultrafast spectroscopic study of ESPT in the photobase 2-(2´-pyridyl)benzimidazole (PBI) in methanol. Ultrafast absorption spectroscopy, supported by quantum chemical calculations, reveals three distinct kinetic steps: (1) a 2.2 ps solvent-to-solute proton transfer, (2) subsequent nonradiative relaxation to the ground state within 31 ps, producing a vibrationally hot ensemble with substantial excess kinetic energy, and (3) equilibration as this energy dissipates into the surrounding solvent bath over 186 ps. Femtosecond-resolved dynamics exhibit oscillatory signals indicative of coherent wavepacket motion on the S₁ potential energy surface. A phase flip in the excited-state absorption maximum confirms this assignment. Fourier analysis resolves two dominant periods (∼117 fs and ∼340 fs), corresponding to in-plane and out-of-plane vibrational modes coupled between PBI and the hydrogen-bonded methanol molecule. The rapid dephasing ( < 300 fs) suggests that the nuclear wavefunction evolves on an anharmonic potential energy surface while traversing the ESPT reaction coordinate.

• Research Organization: University of California, San Diego, La Jolla, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0026316
• OSTI ID: 3025337
• Journal Information: Communications Chemistry, Journal Name: Communications Chemistry Journal Issue: 1 Vol. 9; ISSN 2399-3669
• Publisher: Springer Nature
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
74 ATOMIC AND MOLECULAR PHYSICS
Chemical physics
Excited states
Optical spectroscopy
Reaction kinetics and dynamics