Efficient Light Harvesting by Sequential Energy Transfer across Aggregates in Polymers of Finite Conjugational Segments with Short Aliphatic Linkages
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- 作者：Kang-Yung Peng ; Show-An Chen ; and Wun-Shain Fann
- 刊名：Journal of the American Chemical Society
- 出版年：2001
- 出版时间：November 21, 2001
- 年：2001
- 卷：123
- 期：46
- 页码：11388 - 11397
- 全文大小：138K
- 年卷期：v.123,no.46(November 21, 2001)
- ISSN：1520-5126
文摘
Interactions between lumophores have a critical influence on the photophysical properties ofconjugated polymers. We synthesized a new series of light-harvesting polymers (poly-DSBs, I-IV) ofdialkyloxy- or dialkyl-substituted distyrylbenzene (the substituents being methoxy, 2-ethylhexyloxy, andcyclohexyl) with short aliphatic linkage (methylene or ethylene) and examined the effects of interactions betweenlumophores and of chemical structures on the absorption, emission, and excitation spectra. The proximitybetween distyrylbenzene lumophores was shown to be critical to the interactions between lumophores and tothe energy-transfer processes. In concentrated solutions and solid films, intermolecular aggregates exist resultingfrom different extents of interactions between lumophores and are found to involve at least three species:loose, compact, and the most aligned aggregates as observed by photoluminescence and excitation spectroscopies.We also found, for the first time, sequential energy transfer from individual lumophores to the most compact,aligned aggregates via the looser intermolecular aggregates, as observed directly by time-resolved fluorescencespectroscopy. Such a process mimics energy transfer in photosynthesis units and is so efficient such that thefluorescence color can be red-shifted drastically by the presence of comparatively few aggregates and that thelight evolved from concentrated solutions and films of poly-DSBs I-IV is entirely or almost the aggregationemission. Although the sequential energy-transfer process in fully conjugated electro-/photoluminescent polymersdue to inhomogenity other than distributed conjugation lengths has never been directly observed at roomtemperature, we suggest that events similar to those observed in poly-DSBs in conjugated polymers couldoccur but on a much shorter time scale, i.e., a few picoseconds.