The red-phase of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV): a disordered HJ-aggregate.
The red-phase of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV): a disordered HJ-aggregate.
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DOI：
10.1063/1.4819906
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发表时间：
2013-09
期刊：
影响因子：
--
通讯作者：
H. Yamagata;N. Hestand;F. Spano;A. Köhler;Christina Scharsich;S. Hoffmann;H. Bässler
中科院分区：
文献类型：
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作者：
H. Yamagata;N. Hestand;F. Spano;A. Köhler;Christina Scharsich;S. Hoffmann;H. Bässler
红相聚[2-甲氧基-5-（2-乙基己氧基）-1，4-亚苯基亚乙烯基]（MEH-PPV）的光致发光（PL）光谱中0-0与0-1峰强度的比率相对于无序蓝相显著增强，并且在T = 5 K至180 K的范围内几乎与温度无关。PL寿命同样与温度无关。通过将红相MEH-PPV建模为无序的伸长链的π堆叠来解释测量的趋势。利用扩展到电子和空穴之间的无序的HJ-聚集体哈密顿量，计算了共面MEH-PPV二聚体的吸收光谱和PL光谱。PL 0-0/0-1线强度比直接响应于促进J聚集体样行为（增强的PL比）的链内相互作用和促进H聚集体样行为（减弱的PL比）的链间相互作用之间的竞争。在MEH-PPV聚集体中，J样行为受到相对较大的链内激子带宽（大约比链间带宽大一个数量级）和无序的青睐。后者对于允许在低温下的0-0发射是必不可少的，否则这是对称禁止的。对于高斯无序分布与测量的（不均匀的）线宽度的吸收光谱中的振动峰一致，计算表明，0-0峰保持其优势的0-1峰，与PL比和辐射寿命几乎独立于温度，在极好的协议与实验。有趣的是，链间相互作用仅导致PL比率下降约30%，这表明MEH-PPV π-堆叠-以及通常的强烈无序的HJ-聚集体-可以伪装成单个（伸长的）链。我们的研究结果可能对其他发光共轭聚合物，如聚芴的β相有重要的应用。
The ratio of the 0-0 to 0-1 peak intensities in the photoluminescence (PL) spectrum of red-phase poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], better known as MEH-PPV, is significantly enhanced relative to the disordered blue-phase and is practically temperature independent in the range from T = 5 K to 180 K. The PL lifetime is similarly temperature independent. The measured trends are accounted for by modeling red-phase MEH-PPV as disordered π-stacks of elongated chains. Using the HJ-aggregate Hamiltonian expanded to include site disorder amongst electrons and holes, the absorption and PL spectra of cofacial MEH-PPV dimers are calculated. The PL 0-0/0-1 line strength ratio directly responds to the competition between intrachain interactions which promote J-aggregate-like behavior (enhanced PL ratio) and interchain interactions which promote H-aggregate-like behavior (attenuated PL ratio). In MEH-PPV aggregates, J-like behavior is favored by a relatively large intrachain exciton bandwidth--roughly an order of magnitude greater than the interchain bandwidth--and the presence of disorder. The latter is essential for allowing 0-0 emission at low temperatures, which is otherwise symmetry forbidden. For Gaussian disorder distributions consistent with the measured (inhomogeneous) line widths of the vibronic peaks in the absorption spectrum, calculations show that the 0-0 peak maintains its dominance over the 0-1 peak, with the PL ratio and radiative lifetime practically independent of temperature, in excellent agreement with experiment. Interestingly, interchain interactions lead only to about a 30% drop in the PL ratio, suggesting that the MEH-PPV π-stacks--and strongly disordered HJ-aggregates in general--can masquerade as single (elongated) chains. Our results may have important applications to other emissive conjugated polymers such as the β-phase of polyfluorenes.