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Excited‐State Double Proton Transfer in Model Base Pairs: The Stepwise Reaction on the Heterodimer of 7‐Azaindole Analogues
Author(s) -
Hsieh WanTing,
Hsieh ChengChih,
Lai ChinHung,
Cheng YiMing,
Ho MeiLin,
Wang Kung K.,
Lee GeneHsiang,
Chou PiTai
Publication year - 2008
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200700578
Subject(s) - deuterium , chemistry , moiety , proton , excited state , dimer , kinetic isotope effect , stepwise reaction , quinoline , photochemistry , stereochemistry , organic chemistry , kinetics , physics , quantum mechanics , reaction rate constant , order of reaction , nuclear physics
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 ∼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.