Morita Yasushi, Suzuki Shuichi, Fukui Kozo, Nakazawa Shigeaki, Kitagawa Hiroshi, Kishida Hideo, Okamoto Hiroshi, Naito Akira, Sekine Akiko, Ohashi Yuji, Shiro Motoo, Sasaki Katsunari, Shiomi Daisuke, Sato Kazunobu, Takui Takeji, Nakasuji Kazuhiro
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
Nat Mater. 2008 Jan;7(1):48-51. doi: 10.1038/nmat2067. Epub 2007 Dec 2.
Transition-metal complexes and organic radical molecules can be used to make electric conductors and ferromagnets, the optical properties of which can be controlled by changing temperature and are used as molecular switches and sensors. Whereas a number of organic radicals in solution show temperature-dependent optical properties, such behaviour in crystalline forms is more rare. Here, we show a fully reversible continuous thermochromism with a unique mechanism in purely organic crystals of diazaphenalenyl radical. This behaviour is based on changes in the diazaphenalenyl dimers coexisting in the crystal. From the X-ray crystal structure analyses and temperature-dependent visible spectra, we conclude the presence of a thermal equilibrium between sigma-bonded and pi-bonded dimers, which are separated by 2.62(6) kcal mol(-1). This conclusion is supported by room-temperature electron spin resonance spectra of the solid, which showed signals that are attributable to a thermally accessible triplet state of the pi-dimer structure. This proves the coexistence of two dimers of different bonding natures in the crystal, causing it to demonstrate thermometer-like behaviour.
过渡金属配合物和有机自由基分子可用于制造电导体和铁磁体，其光学性质可通过改变温度来控制，并用作分子开关和传感器。虽然溶液中的许多有机自由基表现出温度依赖性光学性质，但这种行为在晶体形式中更为罕见。在这里，我们展示了二氮杂菲烯基自由基的纯有机晶体中具有独特机制的完全可逆连续热致变色。这种行为基于晶体中共存的二氮杂菲烯基二聚体的变化。通过X射线晶体结构分析和温度依赖性可见光谱，我们得出结论，在σ键合和π键合二聚体之间存在热平衡，它们之间的能量差为2.62(6) kcal mol(-1)。固体的室温电子自旋共振光谱支持了这一结论，该光谱显示出可归因于π二聚体结构热可及三重态的信号。这证明了晶体中存在两种不同键合性质的二聚体，使其表现出类似温度计的行为。
