Studies on the anti-aromaticity and molecular recognition properties of luminescent heterocyclic compounds related to bioluminescence

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3,7-Dihydroimidazo[1,2-a]pyrazin-3-one (imidazopyrazinone) ring system is an important heterocyclic structure for bioluminescent substrates isolated from marine luminescent organisms and has various useful characteristics, such as chemiluminescent, fluorescent, and solvatochromic properties. To make the bases of bioluminescence chemistry and biological imaging science of imidazopyrazinone derivatives, this research project aims to establish the fundamental physical properties of imidazopyrazinone derivatives. (1) At first, the fundamental physical properties of simple imidazopyrazinone derivatives were investigated by X-ray crystallography, UV/vis absorption spectroscopy, and MO calculations. The crystal structural analyses showed that the imidazopyrazinone π-system had a planar ring structure and characteristic bond length alternations, indicating that the π-system has a character of a zwitter-ionic resonance structure to increase aromaticity. The results of absorption spectral measurements clarified that the origin of solvatochromism was hydrogen-bonding interactions with hydrogen-bond donor solvent molecules. These observations were consistently evaluated by MO calculations. (2) Secondly, the phenyl-substituent effect on the physical property of imidazopyrazinone derivatives was investigated. The result indicated that an introduction of phenyl group at C8 caused an efficient change of the property of the imidazopyrazinone π-system, and it was succeeded in to expand the color range of the solvatochromism. (3) Finally, the ability of imidazopyrazinone derivatives to make a complex with a metal ion has been established. The spectroscopic character of an imidazopyrazinone derivative was varied by complex formation, and the tendency of the spectral change was dependent upon a Lewis acidity of a metal ion. Therefore, imidazopyrazinone derivatives are applicable as an indicator of a Lewis acidity of a metal ion.