Fujitsuka Mamoru, Lu Chao, Iwamoto Takahiro, Kayahara Eiichi, Yamago Shigeru, Majima Tetsuro
The Institute of Scientific and Industrial Research (SANKEN), Osaka University , Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
J Phys Chem A. 2014 Jun 26;118(25):4527-32. doi: 10.1021/jp504689q. Epub 2014 Jun 17.
Cycloparaphenylenes (CPPs), a class of hoop-shaped conjugated macrocycles, have attracted the attention of researchers in various fields because of their interesting properties. Although their properties in the singlet-excited state have been reported, there is no systematic information on the triplet-excited state. In the present study, the properties of triplet-excited [n]CPP (n = 8-12, where n denotes the number of phenyl rings) were comprehensively investigated. The phosphorescence peak shifted to the shorter-wavelength side with increasing ring size of the CPPs, indicating smaller triplet energy for smaller CPPs. It was found that the triplet energy of a smaller CPP is even smaller than those of poly(p-phenylene)s, indicating that small hoop-shaped conjugated macrocycles are effective in realizing low-band gap materials. By applying laser flash photolysis, the Tn-T1 absorption spectra of CPPs were obtained, from which the size-dependence of energy levels of higher triplet states were also determined. Generation of singlet oxygen by the energy transfer from a triplet-excited CPP was confirmed. The generation yield became smaller with increasing size of the CPP in accordance with the triplet yield. From these observations, the size-dependence of the deactivation pathways is explained.
环对亚苯基（CPPs）是一类环状共轭大环化合物，因其有趣的性质而吸引了各个领域研究人员的关注。尽管已经报道了它们在单重激发态的性质，但关于三重激发态尚无系统的信息。在本研究中，对三重激发态的[n]CPP（n = 8 - 12，其中n表示苯环的数量）的性质进行了全面研究。随着CPPs环尺寸的增加，磷光峰向较短波长侧移动，这表明较小的CPPs具有较小的三重态能量。发现较小的CPP的三重态能量甚至比聚对亚苯基的三重态能量还要小，这表明小的环状共轭大环化合物在实现低带隙材料方面是有效的。通过应用激光闪光光解，获得了CPPs的Tn - T1吸收光谱，由此还确定了较高三重态能级的尺寸依赖性。证实了通过三重激发的CPP的能量转移产生单线态氧。根据三重态产率，随着CPP尺寸的增加，产生产率变小。从这些观察结果出发，解释了失活途径的尺寸依赖性。
