摘要
聚(2 甲氧基 5 (2′ 乙基己氧基) 1,4 对苯乙炔)(MEH PPV)在溶液中的链构象依赖于溶剂的性质,共轭聚合物的发光特性受链构象影响明显。在稀溶液中,不良溶剂含量的增加使MEH PPV分子链更加紧缩卷曲,单个分子链内更多共轭链段发生聚集,光激发形成的链间激子增加。通过对MEH PPV稀溶液的光谱分析,发现链间激子的形成过程依赖于激发光的能量(hν)。在激发光能量大于聚合物的最低激发能(Ea)的情况下,大部分链内激子通过辐射复合发光,少部分链内激子沿分子链转移到聚集的共轭链段上形成链间激子。在hν<Ea的情况下,单个分子链内聚集共轭链段吸收光子能量形成链间激子并复合发光。
Since the discovery of light emitting diodes based on PPV in 1990, PPV and its derivatives have been investigated widely with experiments or theories due to their electroluminescence properties, but the excited state and the interchain species of them remain controversial. To study the nature of the interchain species, the optical properties of the isolated MEH-PPV chains in the dilute solutions are investigated. It has been found that the fluorescence of conjugated polymers is heavily influenced by the conformations of the polymer chains. The polymer chains become more tightly coiled in the poor solvent to make more conjugated segments aggregated and then to form more interchain excitons under photoexcitation. With increasing the proportions of the poor solvent in the dilute solutions, the intensities of the highest PL peaks (P1) (emission from intrachain excitons) are reduced due to the increase of conformational defects in the polymer chains, and the relative intensities of the peaks at about 590 nm (P2) (emission from interchain excitons) are increased. From the absorption and photoexcitation spectra of the dilute solutions, it can be found that the intensities of absorption peaks and photoexcitation at long wavelength are increased with increasing the proportions of the poor solvent in the dilute solutions. By analyzing the absorption and the luminescence spectra of MEH-PPV dilute solutions, it can be concluded reasonably that the formation processes of interchain exciton are dependent on the photoexci-tation energies. For hν>E_a, a majority of intrachain excitons are relaxed by radiative recombination, but a few of intrachain excitons can be transferred to the aggregated segments along the polymer chains, then π electrons are delocalized over the aggregated segments to form interchain excitons. In other words, interchain excitons have same photoexcitation process as intrachain excitons. For hν<E_a, the aggregated segments in the single chain can absorb photon energies to form interchain excitons.
出处
《发光学报》
EI
CAS
CSCD
北大核心
2004年第6期731-736,共6页
Chinese Journal of Luminescence
关键词
共轭聚合物
光致发光
链内激子
链间激子
conjugated polymers
photoluminescence
intrachain exciton
interchain exciton
