Catalytic-Type Excited-State N−H Proton-Transfer Reaction in 7-Aminoquinoline and Its Derivatives
Journal
Chemistry - A European Journal
Journal Volume
25
Journal Issue
65
Pages
14972-14982
Date Issued
2019
Author(s)
Chang, K.-H.
Liu, Y.-H.
Liu, J.-C.
Peng, Y.-C.
Yang, Y.-H.
Li, Z.-B.
Jheng, R.-H.
Chao, C.-M.
Liu, K.-M.
Abstract
7-Aminoquinoline (7AQ) and various amino derivatives thereof (-NHR) have been strategically designed and synthesized to study their excited-state proton-transfer (ESPT) properties. Due to the large separation between the proton donor -NHR and the acceptor -N- site, ESPT in 7AQ derivatives, if available, should proceed under protic solvent catalysis. ESPT is found to be influenced by the acidity of -NHR and the basicity of the proton-acceptor -N- in the quinoline moiety. The latter is varied by the resonance effect at the quinoline -N- site induced by the -NHR substituent. For those 7AQ derivatives undergoing ESPT, increased quinoline basicity results in a faster rate of ESPT, implying that proton donation from methanol to the quinoline moiety may serve as a key step in the process. Our studies also indicate the existence of an equilibrium between cis and trans arrangements of -NHR in terms of its hydrogen-bond (H-bond) configuration with methanol, whereby only the cis-H-bonded form undergoes methanol-assisted ESPT. With one exception, the interconversion between cis and trans configurations is much faster than the rate of ESPT, yielding amino-type (normal form) and imine-type (proton-transfer tautomer) emissions with distinct relaxation dynamics.
SDGs
Type
journal article