title: Double proton transfer induced twisted intramolecular charge transfer emission in 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine.
abstract: The spectral characteristics of N,N-dimethyl-4-(4-methyl-4H-imidazo[4,5-b]pyridin-2-yl)benzenamine (PyN-Me), 1-methyl-2-(4'-(N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (ImNH-Me), and 2-phenylimidazo[4,5-b]pyridine (PIP) are investigated to understand the mechanism of protic solvent induced dual fluorescence of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b). No dual emission is observed from PyN-Me where pyridyl nitrogen blocked from hydrogen bonding with protic solvents confirms the importance of hydrogen bonding of protic solvents with the pyridyl nitrogen in dual emission of DMAPIP-b. Like DMAPIP-b, ImNH-Me also exhibits weak emission and has a shorter fluorescence lifetime in methanol. However, single emission is observed from ImNH-Me in all solvents including protic solvents. This suggests that the imidazole >NH hydrogen also plays a role in the dual emission process. The longer wavelength emission of DMAPIP-b in water increases with increase in pH of the solution owing to deprotonation of the imidazole >NH group. On the basis of these results, the mechanism for the dual emission of DMAPIP-b is proposed.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India.
authors.forename: Anasuya
authors.initials: A
authors.lastname: Mishra
authors.forename: Saugata
authors.initials: S
authors.lastname: Sahu
authors.forename: Nihar
authors.initials: N
authors.lastname: Dash
authors.forename: Santosh Kumar
authors.initials: SK
authors.lastname: Behera
authors.forename: G
authors.initials: G
authors.lastname: Krishnamoorthy
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry*; D005453:Fluorescence; D007093:Imidazoles / Q000737:chemistry*; D008958:Models, Molecular; D011522:Protons; D011725:Pyridines / Q000737:chemistry*
chemical_list: C587289:1-methyl-2-(4'-(N,N-dimethylaminophenyl))imidazo(4,5-b)pyridine; C549150:2-(4'-N,N-dimethylaminophenyl)imidazo(4,5-b)pyridine; C587290:2-phenylimidazo(4,5-b)pyridine; D000814:Aniline Compounds; D007093:Imidazoles; C587291:N,N-dimethyl-4-(4-methyl-4H-imidazo(4,5-b)pyridin-2-yl)benzenamine; D011522:Protons; D011725:Pyridines