Hydrogen bonding, protonation and twisting in the singlet excited state of some 2-(4-Aminophenyl)pyrido-oxa-, -thia-, and -imidazoles

• Published in: Journal of heterocyclic chemistry Vol. 30; no. 4; pp. 1041 - 1044
• Main Authors: Fasani, E., Albini, A., Savarino, P., Viscardi, G., Barni, E.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley-Blackwell 01-07-1993; Wiley‐Blackwell; HeteroCorporation
• Subjects: Atomic and molecular physics; Bond strengths, dissociation energies; Conformation (statistics and dynamics); Exact sciences and technology; Fluorescence and phosphorescence spectra; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Intensities and shapes of molecular spectral lines and bands; Line and band widths, shapes, and shifts; Macromolecules and polymer molecules; Molecular properties and interactions with photons; Physics; Studies of special atoms, molecules and their ions; clusters; Nitrogen heterocycle; Condensed aromatics; Fluorescence; Excited states; Experimental study; Spectral shift; Sulfur heterocycle; Imidazoles; Hydrogen bonds; Oxazoles; Emission spectra; Heterocyclic oxygen compounds; Thiazoles; Protonation; Charge transfer complexes; Absorption spectra; Organic compounds
• ISSN: 0022-152X; 1943-5193
• DOI: 10.1002/jhet.5570300433

The absorption and fluorescence characteristics of 2‐(4‐aminophenyl)pyrido[3,2‐d]oxazole (1), of its thiazole 2 and imidazole 3 analogues, as well as of the corresponding pyrido[3,4‐d]imidazole 4 have been examined. S1 is a planar ππ* ICT state, similarly to p‐electron‐withdrawing substituted anilines. In the protonated form, the chromophore is the heterocyclic moiety. With compounds 3 and 4 in alcohols, hydrogen bonding depending on proton donating and accepting properties of the medium determines the fluorescence. In this case, a red‐shifted emission attributed to a twisted TICT state is also observed.