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Catalytic‐Type Excited‐State N−H Proton‐Transfer Reaction in 7‐Aminoquinoline and Its Derivatives
Author(s) -
Chang KaiHsin,
Liu YingHsuan,
Liu JiunChi,
Peng YuChiang,
Yang YuHsuan,
Li ZhiBin,
Jheng RenHua,
Chao ChiMin,
Liu KuanMiao,
Chou PiTai
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201904027
Subject(s) - chemistry , moiety , quinoline , proton , catalysis , tautomer , methanol , photochemistry , substituent , hydrogen bond , medicinal chemistry , excited state , solvent , stereochemistry , molecule , organic chemistry , physics , quantum mechanics , nuclear physics
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.