Excited-state double proton transfer in model base pairs: The stepwise reaction on the heterodimer of 7-azaindole analogues
Journal
ChemPhysChem
Journal Volume
9
Journal Issue
2
Pages
293-299
Date Issued
2008
Author(s)
Hsieh, Wan-Ting
Hsieh, Cheng-chih
Lai, Chin-Hung
Cheng, Yi-Ming
Ho, Mei-Lin
Wang, Kung K.
Lee, Gene-Hsiang
Abstract
A four fused-ring system 11-propyl-6H-indolo[2,3-b]quinoline (6 HIQ) is strategically designed and synthesized; it possesses a central moiety of 7-azaindole (7AI) and undergoes excited-state double proton transfer (ESDPT). Despite a barrierless type of ESDPT in the 6 HIQ dimer, femtosecond dynamics and a kinetic isotope effect provide indications for a stepwise ESDPT process in the 6 HIQ/7AI heterodimer, in which 6 HIQ (deuterated 6 HIQ) delivers the pyrrolyl proton (deuteron) to 7AI (deuterated 7AI) in less than 150 fs, forming an intermediate with a charge-transfer-like ion pair, followed by the transfer of a pyrrolyl proton (deuteron) from cation-like 7AI (deuterated 7AI) to the pyridinyl nitrogen of the anion-like 6 HIQ (deuterated 6 HIQ) in approximately 1.5+/-0.3 ps (3.5+/-0.3 ps). The barrier of second proton transfer is estimated to be 2.86 kcal mol(-1) for the 6 HIQ/7AI heterodimer.
Type
journal article
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