The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Ibaraki, Osaka, Japan.
Phys Chem Chem Phys. 2012 Nov 14;14(42):14585-8. doi: 10.1039/c2cp42712e. Epub 2012 Sep 27.
Hoop-shaped π-conjugated molecules such as cycloparaphenylene (CPP) have attracted the attention of many chemists because they exhibit interesting properties due to the distorted π-electron system. To gain a systematic understanding of the properties that result from distorted π-electron systems, it is important to know precisely how these properties depend on the hoop size. In the present study, we have investigated the size dependence of the fluorescence properties of CPPs. The fluorescence spectra of smaller CPPs showed red-shifted fluorescence peaks, smaller fluorescence quantum yields, and longer lifetimes, when compared to those of larger ones. One of the important factors that gave rise to these fluorescence properties of smaller CPPs was greater structural relaxation from the Franck-Condon state, which is a postulation supported by theoretical calculations. The structural relaxation in the picosecond domain was experimentally detected by the fluorescence upconversion method. The present results are an important example that confirms steric factors strongly governing the fluorescence properties of a molecule.
环形共轭分子，如并五苯（CPP），由于其扭曲的π电子体系而具有有趣的性质，因此引起了许多化学家的关注。为了系统地了解由扭曲的π电子体系产生的性质，精确了解这些性质如何依赖于环的大小是很重要的。在本研究中，我们研究了 CPP 的荧光性质的尺寸依赖性。与较大的 CPP 相比，较小的 CPP 的荧光光谱显示出荧光峰红移、荧光量子产率更小和寿命更长。导致较小 CPP 具有这些荧光性质的一个重要因素是，从 Franck-Condon 态发生了更大的结构弛豫，这一假设得到了理论计算的支持。皮秒域中的结构弛豫通过荧光上转换方法实验检测到。目前的结果是一个重要的例子，它证实了空间位阻因素强烈控制着分子的荧光性质。
