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Optical Behavior of Substituted 4‑(2′-Hydroxyphenyl)imidazoles

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posted on 12.02.2015 by Artur Jeżewski, Tommy Hammann, Piotr J. Cywiński, Daniel T. Gryko
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.