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Optical behavior of substituted 4-(2′-hydroxyphenyl)imidazoles

: Jeżewski, A.; Hammann, T.; Cywinski, P.J.; Gryko, D.T.


Journal of physical chemistry. B 119 (2015), Nr.6, S.2507-2514
ISSN: 1089-5647
ISSN: 1520-6106
ISSN: 1520-5207
Fraunhofer IAP ()

A set of tetraarylimidazoles bearing a 2-hydroxyphenyl substituent at position 4, as well as their models lacking intramolecular hydrogen bonds, was efficiently synthesized. Structural investigations proved that the hydrogen bond strength for 4-(2′-hydroxyphenyl)imidazoles is weaker than that for analogous 2-(2′-hydroxyphenyl)imidazoles as estimated from dihedral angles and bond distances. Photophysical investigations revealed that these compounds have other properties than those observed for imidazoles bearing a 2-hydroxyphenyl substituent at position 2. They exhibit a negligible fluorescence quantum yield regardless of the solvent polarity. Additionally, dual fluorescence is observed in nonpolar solvents. Plausibly, although a hydrogen bond is present within their chemical structure in the solid state, it is not clear if excited-state intramolecular proton transfer occurs. The presence of OH groups triggers the radiationless deactivation channel if compared with model imidazole possessing a 2-methoxyphenyl group.