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Synthesis and photophysical properties of fluorescent 2‐aryl‐1,3‐dialkylbenzimidazolium ions and a l‐alkyl‐2‐arylbenzimidazole with excited state intramolecular proton‐transfer
Author(s) -
Kauffman Joel M.,
Khalaj Ali,
Litak Peter T.,
Novinski John A.,
Bajwa Gurdip S.
Publication year - 1994
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570310444
Subject(s) - chemistry , excited state , photochemistry , fluorescence , quantum yield , alkyl , steric effects , intramolecular force , aryl , stokes shift , proton , singlet state , ion , yield (engineering) , stereochemistry , organic chemistry , atomic physics , materials science , metallurgy , physics , quantum mechanics
To improve the solubility, photostability and fluorescence quantum yield (Φ) of 2‐arylbenzimidazolium ions the N‐1 hydrogen was replaced by an alkyl group before N‐3 was quatemized; this substitution did not reduce Φ, proving the absence of steric inhibition to attainment of coplanarity in the excited state. A related symmetrical 2,2′‐arylenebis(1,3‐dimethyldibenzimidazolium ion) had Φ = 0.86. The related 2,5‐bis(1‐methyl‐2‐benzimidazolyl)phenol had Φ = 0.38 at 22° as well as a very large Stokes' shift due to proton‐transfer. These findings supported a new insight into the electron distribution of the first excited singlet state of oligophenylenes. The compounds are of interest as laser dyes and scintillation fluors.