Emission Mechanism of Doubly ortho-Linked Quinoxaline/Diphenylfluorene or cis-Stilbene/Fluorene Hybrid Compounds Based on the Transient Absorption and Emission Measurements during Pulse Radiolysis
Emission Mechanism of Doubly ortho-Linked Quinoxaline/Diphenylfluorene or cis-Stilbene/Fluorene Hybrid Compounds Based on the Transient Absorption and Emission Measurements during Pulse Radiolysis
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DOI：
10.1021/ja8090005
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发表时间：
2009-05-20
影响因子：
15
通讯作者：
Majima, Tetsuro
中科院分区：
文献类型：
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作者：
Wei, Yi;Samori, Shingo;Majima, Tetsuro
对一系列双极有机电致发光材料进行了脉冲辐解实验，测定了它们对溶液中独立原位生成的自由基正离子和阴离子的瞬时吸收和寿命分布。此外，还用脉冲辐解方法测定了它们的自由基离子电荷复合的发射行为。研究发现，在喹恶啉模板的C5和C8位，双邻位连接的喹恶啉/二苯基荧杂化化合物La-e的吸收带随给电子性的增加而逐渐红移。La-e中的初始自由基阴离子主要分布在喹恶啉杂环上，而初始自由基阳离子主要分布在喹恶啉模板的C5和C8位上的给电子基上。对于其他双邻位连接的顺式二苯乙烯衍生物3d、3f和0，自由基阴离子主要分布在顺式二苯乙烯的中心部分，而自由基阳离子主要分布在顺式二苯乙烯模板的两个对位取代基上。研究还表明，它们的光电发射效率与辐射诱导发射强度之间存在一定的相关性。此外，还发现OLED器件中的电荷传输行为与自由基离子的瞬时吸收半衰期(tau(1/2))有关。OLED和脉冲辐解实验中的电荷复合机制被提出，以使这些观察结果合理化，使我们能够通过明智地选择光电模板中的局部电荷附件，为理想的双极光电材料的最终分子设计建立一些指导方针。
A series of bipolar OLED materials were subjected to pulsed radiolysis experiments to determine their transient absorption and lifetime profiles of the independently in situ generated radical cations and anions in solutions. Moreover, their emission behaviors from the charge recombination of their radical ions were also determined by the pulse radiolysis method. It was found the absorption bands in doubly ortho-linked quinoxaline/diphenylfluorene hybrids la-e are red-shifted progressively with increasing electron-donating nature at the C5 and C8 positions of the quinoxaline template. The incipient radical anions in la-e are mainly localized on the quinoxaline heterocyclic moiety, whereas the incipient radical cations are mainly distributed onto the attached electron-donating groups at the C5 and C8 positions of the quinoxaline template. For other doubly ortho-linked cis-stilbene derivatives 3d, 3f, and 0, the radical anions are mainly localized on the cis-stilbene central moiety and the radical cation is mainly distributed onto both para substituents of the cis-stilbene templates. It was also shown that there is a correlation between their optoelectronic emission efficiencies and the radiolysis induced emission intensities. In addition, the charge transporting behaviors within an OLED device were found to show the relationship with transient absorption half-lives (tau(1/2)) of the radical ions. Charge recombination mechanisms in both the OLED and pulsed radiolysis experiments were proposed to rationalize these observations, allowing us to establish some guidelines for an ultimate molecular design of ideal bipolar optoelectronic materials with a judicious choice of local charge appendages in the optoelectronic templates.