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Effect of ortho-biphenyl substitution on the excited state dynamics of a multi-carbazole TADF molecule
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2020-06-24 , DOI: 10.1039/d0tc02627a Seung-Je Woo 1, 2, 3, 4 , Yeon-Hee Ha 4, 5, 6, 7 , Yun-Hi Kim 4, 5, 6, 7 , Jang-Joo Kim 1, 2, 3, 4
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2020-06-24 , DOI: 10.1039/d0tc02627a Seung-Je Woo 1, 2, 3, 4 , Yeon-Hee Ha 4, 5, 6, 7 , Yun-Hi Kim 4, 5, 6, 7 , Jang-Joo Kim 1, 2, 3, 4
Affiliation
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We report a new thermally activated delayed fluorescence (TADF) molecule developed by the ortho-biphenyl substitution of a multi-carbazole TADF molecule. The new TADF molecule, 4mCzBN-BP, is composed of four dimethylcarbazole donors, a benzonitrile acceptor core and an ortho-biphenyl triplet scaffold. 4mCzBN-BP exhibits a bluish-green emission with a peak wavelength at 491 nm and a very high photoluminescence quantum yield (PLQY) of 95% in an mCBP host. To investigate the effect of the ortho-biphenyl substitution on the excited-state dynamics and photophysical properties of the TADF molecule, we performed time dependent density functional theory (TD-DFT) calculations of 4mCzBN-BP and two multi-carbazole TADF molecules with similar molecular structures. A local excited triplet state (3LE) with an energy (2.81 eV) close to the lowest singlet charge-transfer state (1CT) can be formed at the biphenyl of 4mCzBN-BP. However, due to the planarization of the biphenyl at the triplet state and a large steric hindrance caused by adjacent carbazole donors, 3LE at the biphenyl can only be formed by a subset of possible conformations of 4mCzBN-BP molecules in the solid mCBP host, leading to a multiexponential decay of the delayed fluorescence. Color coordinates of (0.196, 0.452), a high external quantum efficiency of 23.7% and a long operational lifetime (LT50) of 750 hours were achieved with the organic light emitting diodes based on 4mCzBN-BP.
中文翻译：
邻联苯取代对多咔唑TADF分子激发态动力学的影响
我们报告了由多咔唑TADF分子的邻-联苯取代开发的一种新的热激活延迟荧光（TADF）分子。新的TADF分子4mCzBN-BP由四个二甲基咔唑供体，一个苄腈受体核心和一个邻-联苯三重态支架组成。4mCzBN-BP在mCBP宿主中表现出蓝绿色发射，峰值波长为491 nm，非常高的光致发光量子产率（PLQY）为95％。为了研究邻联苯取代对TADF分子的激发态动力学和光物理性质的影响，我们对4mCzBN-BP进行了时间依赖性密度泛函理论（TD-DFT）计算和两个具有相似分子结构的多咔唑TADF分子。可以在4mCzBN-BP的联苯上形成能量（2.81 eV）接近最低单线态电荷转移态（1 CT）的局部激发三线态（3 LE）。然而，由于联苯在三重态下的平面化和相邻咔唑供体引起的大位阻，联苯上的3 LE只能由4mCzBN-BP可能构象的子集形成固体mCBP宿主中的分子，导致延迟荧光的多指数衰减。使用基于4mCzBN-BP的有机发光二极管实现了（0.196，0.452）的色坐标，23.7％的高外部量子效率和750小时的长使用寿命（LT50）。
更新日期：2020-06-24
中文翻译：
邻联苯取代对多咔唑TADF分子激发态动力学的影响
我们报告了由多咔唑TADF分子的邻-联苯取代开发的一种新的热激活延迟荧光（TADF）分子。新的TADF分子4mCzBN-BP由四个二甲基咔唑供体，一个苄腈受体核心和一个邻-联苯三重态支架组成。4mCzBN-BP在mCBP宿主中表现出蓝绿色发射，峰值波长为491 nm，非常高的光致发光量子产率（PLQY）为95％。为了研究邻联苯取代对TADF分子的激发态动力学和光物理性质的影响，我们对4mCzBN-BP进行了时间依赖性密度泛函理论（TD-DFT）计算和两个具有相似分子结构的多咔唑TADF分子。可以在4mCzBN-BP的联苯上形成能量（2.81 eV）接近最低单线态电荷转移态（1 CT）的局部激发三线态（3 LE）。然而，由于联苯在三重态下的平面化和相邻咔唑供体引起的大位阻，联苯上的3 LE只能由4mCzBN-BP可能构象的子集形成固体mCBP宿主中的分子，导致延迟荧光的多指数衰减。使用基于4mCzBN-BP的有机发光二极管实现了（0.196，0.452）的色坐标，23.7％的高外部量子效率和750小时的长使用寿命（LT50）。
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