title: Remarkable solvatochromic color change via proton tautomerism of a phenol-linked imidazole derivative.
abstract: A unique solvatochromic 2-phenyl-4,5-diarylimidazole derivative linked with a phenol moiety and a p-quinonemethide moiety at the 4- and 5-positions of a imidazole ring, which shows remarkable color change via proton tautomerism, was synthesized and the mechanism of the solvatochromic color change was investigated. The yellow-colored OH tautomeric form (1_OH) exists as a dominant species in nonpolar solvents, whereas the blue-colored NH tautomeric form (1_NH) is stabilized in polar solvents. The molecular structures of these tautomers were determined by X-ray crystallographic analysis. The p-quinonemethide moiety and the imidazole ring of 1_OH are coplanar to one another and possess a planar quinoidal structure. On the other hand, 1_NH has a nonplanar twisted quinoidal structure causing large bathochromic shift in the visible absorption spectrum. Moreover, the X-ray crystallographic analysis and the DFT calculations support the closed-shell singlet character of 1_OH. In contrast 1_NH possesses partial single bond character that leads to the open-shell singlet biradical character and the decrease in the singlet-triplet energy gap. The twisting of the π-conjugated electron system induced by the proton tautomerization was found to be the origin of the open-shell biradical character of 1_NH and the enhanced solvatochromic color change.
authors: Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University , 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
authors: Hiroaki
authors: H
authors: Yamashita
authors: Jiro
authors: J
authors: Abe
mesh_terms: D003116:Color; D018360:Crystallography, X-Ray; D004583:Electrons; D007093:Imidazoles / Q000138:chemical synthesis / Q000737:chemistry*; D007536:Isomerism; D015394:Molecular Structure; D010636:Phenols / Q000138:chemical synthesis / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D007093:Imidazoles; D010636:Phenols; D011522:Protons