Lammi Robin K, Barbara Paul F
Department of Chemistry and Biochemistry, Center for Nano and Molecular Science and Technology, The University of Texas at Austin, Austin, TX 78712-1062, USA.
Photochem Photobiol Sci. 2005 Jan;4(1):95-9. doi: 10.1039/b417753n. Epub 2004 Dec 10.
Fluorescence spectroscopy was performed on single molecules of two 9,9-dialkylfluorene-benzothiadazole (FxBT) copolymers with a 10-fold difference in average molecular weight. Molecules of both polymers exhibit red-shifted emission indicative of energy migration to low-energy sites (LES) on the polymer chains; however, "red" spectra are much more common for the longer polymer. Since singlet-exciton migration is found to occur on the molecular length scale in both cases, the increased number of red-shifted spectra observed for the longer polymer is evidence that the likelihood of LES formation increases with chain length. This relationship is discussed in terms of three possible causes of low-energy sites: local polymer conformations, chromophores with extended conjugation lengths, and random chemical defects.
对两种平均分子量相差10倍的9,9 - 二烷基芴 - 苯并噻二唑（FxBT）共聚物的单分子进行了荧光光谱分析。两种聚合物的分子均表现出红移发射，这表明能量迁移到了聚合物链上的低能位点（LES）；然而，对于较长的聚合物，“红色”光谱更为常见。由于在这两种情况下均发现单线态激子迁移发生在分子长度尺度上，因此观察到较长聚合物的红移光谱数量增加证明了LES形成的可能性随链长增加。从低能位点的三种可能成因：局部聚合物构象、具有延长共轭长度的发色团以及随机化学缺陷的角度对这种关系进行了讨论。
