Active Role of Proton in Excited State Intramolecular Proton Transfer Reaction

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 117; no. 7; pp. 1400 - 1405
• Main Authors: Lee, Junghwa, Kim, Chul Hoon, Joo, Taiha
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 21.02.2013
• Subjects: Atomic and molecular physics; Benzothiazoles - chemistry; Biology; Coherence; Deuterium; Exact sciences and technology; Excitation; Fluorescence and phosphorescence spectra; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Isotopes; Molecular properties and interactions with photons; Molecular Structure; Phenols - chemistry; Physical chemistry; Physics; Protons; Quinolines - chemistry; Spectroscopy, Fourier Transform Infrared; Uncertainty; Wave packets; Deuterium; Fluorescence spectrum; Hydrogen; Nitrogen heterocycle; Proton transfer; Quinoline derivatives; Excited states; Intramolecular charge transfer; Wave packets; Emission spectra; Vibrational modes; Excitation; Absorption spectra; Organic compounds
• ISSN: 1089-5639; 1520-5215; 1520-5215
• DOI: 10.1021/jp311884b

Proton transfer is one of the most important elementary reactions in chemistry and biology. The role of proton in the course of proton transfer, whether it is active or passive, has been the subject of intense investigations. Here we demonstrate the active role of proton in the excited state intramolecular proton transfer (ESIPT) of 10-hydroxybenzo[h]quinoline (HBQ). The ESIPT of HBQ proceeds in 12 ± 6 fs, and the rate is slowed down to 25 ± 5 fs for DBQ where the reactive hydrogen is replaced by deuterium. The results are consistent with the ballistic proton wave packet transfer within the experimental uncertainty. This ultrafast proton transfer leads to the coherent excitation of the vibrational modes of the product state. In contrast, ESIPT of 2-(2′-hydroxyphenyl)benzothiazole (HBT) is much slower at 62 fs and shows no isotope dependence implying complete passive role of the proton.