CHIN-HUNG LAI2026-10-162026-10-162008-02-01Pure ID: 15481459Pure UUID: 354182fd-2e13-47e4-939b-dc24029a1e6510.1002/cphc.200700578https://www.scopus.com/pages/publications/38949218378https://scholars.csmu.edu.tw/handle/123456789/28242A 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) de livers 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.7enjournal article