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

3,7-二氢咪唑[1,2-a]吡嗪-3-酮（咪唑吡嗪酮）环体系是从海洋发光生物中分离出来的重要的生物发光底物杂环结构，具有多种有用的特性，如化学发光、荧光和溶剂致变色性质。本课题旨在建立咪唑吡嗪酮衍生物的基本物理性质，为咪唑吡嗪酮衍生物的生物发光化学和生物成像科学奠定基础。(1)首先，通过x射线晶体学、紫外/可见吸收光谱和MO计算研究了简单咪唑吡嗪酮衍生物的基本物理性质。晶体结构分析表明，咪唑吡嗪酮π-体系具有平面环状结构和特征性键长变化，表明该π-体系具有提高芳构性的两性离子共振结构特征。吸收光谱测量结果表明，溶剂致变色是与氢键给体溶剂分子的氢键相互作用引起的。这些观测结果与MO计算一致。(2)其次，考察了苯基取代基对咪唑吡嗪酮衍生物物性的影响。结果表明，在C8位置引入苯基，有效地改变了咪唑吡嗪酮π体系的性质，成功地扩大了溶剂变色的颜色范围。(3)最后，确定了咪唑吡嗪酮衍生物与金属离子形成配合物的能力。配合物的形成改变了咪唑吡嗪酮衍生物的光谱特征，光谱变化的趋势取决于金属离子的刘易斯酸度。因此，咪唑吡嗪酮衍生物可作为金属离子路易斯酸度的指示剂。

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.