Comprehensive Study of Ultrafast Excited-State Proton Transfer in Water and D2O Providing the Missing RO鈥?/sup>路路路H+ Ion-Pair Fingerprint

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• 作者：Ron Simkovitch ; Katherine Akulov ; Shay Shomer ; Michal E. Roth ; Doron Shabat ; Tal Schwartz ; Dan Huppert
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：June 26, 2014
• 年：2014
• 卷：118
• 期：25
• 页码：4425-4443
• 全文大小：946K
• ISSN：1520-5215

文摘

Steady-state and time-resolved optical techniques were employed to study the photoprotolytic mechanism of a general photoacid. Previously, a general scheme was suggested that includes an intermediate product that, up until now, had not been clearly observed experimentally. For our study, we used quinone cyanine 7 (QCy7) and QCy9, the strongest photoacids synthesized so far, to look for the missing intermediate product of an excited-state proton transfer to the solvent. Low-temperature steady-state emission spectra of both QCy7 and QCy9 clearly show an emission band at T < 165 K in H₂O ice that could be assigned to ion-pair RO^{鈥?/sup>*路路路H₃O+, the missing intermediate. Room-temperature femtosecond pump鈥損robe spectroscopy transient spectra at short times (t < 4 ps) also shows the existence of transient absorption and emission bands that we assigned to the RO鈥?/sup>*路路路H₃O+ ion pair. The intermediate dissociates on a time scale of 1 ps and about 1.5 ps in H₂O and D₂O samples, respectively.}