The singlet-triplet exchange energy in conjugated polymers
The singlet-triplet exchange energy in conjugated polymers
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DOI：
10.1002/adfm.200305032
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发表时间：
2004-01-01
影响因子：
19
通讯作者：
Beljonne, D
中科院分区：
文献类型：
--
作者：
Köhler, A;Beljonne, D
有机半导体中的电子-电子相互作用通过交换能DeltaE(ST)分裂最低的单重态和三重态。测量了大量共轭聚合物的单重态和三重态发射光谱，得到了接近0.7 eV的几乎恒定的DeltaE(ST)值，这与分子中的情况相反，分子中的交换能取决于分子大小，并且在很大范围内变化。用量子化学方法计算了苯基共轭聚合物的恒定交换能的来源。在最低的单重态和三重态的激发态中，电子-空穴的分离与pi共轭主链无关，并且对于长于几个重复单元的链是饱和的，从而产生恒定的交换能量。在较短的共轭齐聚物中，激发态的限制通过交换相互作用破坏了单线态相对于三线态的稳定性，并导致了更大的和大小相关的单线态-三线态能量分离。
Electron-electron interactions in organic semiconductors split the lowest singlet and triplet states by the exchange energy, DeltaE(ST). Measurement of singlet and triplet emission spectra in a large number of conjugated polymers yield an almost constant DeltaE(ST) value close to 0.7 eV This is in contrast to the situation in molecules, where the exchange energy is found to depend on molecular size and to vary over a wide range. Quantum-chemical calculations are performed to address the origin of the constant exchange energy in phenylene-based conjugated polymers. The electron-hole separation in the lowest singlet and triplet excited states is found to be independent of the pi-conjugated backbone, and saturates for chains longer than a few repeating units, resulting in a constant exchange energy. In shorter conjugated, oligomers, confinement of the excitations destabilizes the singlet with respect to the triplet through exchange interactions and leads to a larger and size-dependent singlet-triplet energy separation.