Photophysics of an Asymmetric Donor-Acceptor-Donor' TADF Molecule and Reinterpretation of Aggregation-Induced TADF Emission in These Materials
Photophysics of an Asymmetric Donor-Acceptor-Donor' TADF Molecule and Reinterpretation of Aggregation-Induced TADF Emission in These Materials
复制标题
DOI：
10.1021/acs.jpcc.7b06299
复制
发表时间：
2017-08-24
影响因子：
3.7
通讯作者：
Monkman, Andrew P.
中科院分区：
文献类型：
--
作者：
Aydemir, Murat;Xu, Shidang;Monkman, Andrew P.
我们报道了一个不对称的供体-受体-供体‘ （D- a -D’）热激活延迟荧光（TADF）分子（4- （9h -咔唑-9-基）苯基）（4- （10 h -吩噻嗪-10-基）苯基）砜的深入光物理研究，并将其与母体对称的D- a -D和D‘- a -D’分子进行了比较。这些D-A-D型小分子均表现出较强的TADF。这项工作揭示了D-A （D'-A）基团的相对取向如何通过形成稳定的电荷转移（CT）状态来促进反向系统间交叉（rISC）。高效TADF发射器的关键要求是实现非常小的ct局部三重态能量分裂，这在不对称分子中被证明是复杂的。在整个研究过程中，我们发现在不对称的D-A-D‘体系中，即使E-CT (D-A) > E-CT (D’-A)，也没有观察到从D-A到A-D‘的能量转移的证据，也没有从激发的D到D’的能量转移的证据。这是由于D和D'单元的近正交性以及在CT状态下D和A上的电子的非常强的解耦。此外，还研究了聚集诱导的TADF （AI-TADF）的可能性，并证明这是这些特定分子溶剂致变色的一种表现。
We report an in-depth photophysical investigation of an asymmetric donor-acceptor-donor' (D-A-D') thermally activated delayed fluorescence (TADF) molecule (4- (9H-carbazol-9-yl)phenyl) (4- (10 H-phenothiazin-10-yl)-phenyl)sulfone and compare its photophysical properties to the parent symmetric D-A-D and D'-A-D' molecules. These D-A-D type small molecules all show strong TADF. The work reveals how the relative orientations of D-A (D'-A) moieties favor reverse intersystem crossing (rISC) by forming stable charge transfer (CT) states. The key requirement for the efficient TADF emitters is to achieve a very small CT-local triplet state energy splitting, which is shown to be complex in the asymmetric molecule. Throughout the investigations, we show that in the asymmetric D-A-D' system, even though E-CT (D-A) > E-CT (D'-A), no evidence of energy transfer from D-A to A-D' is observed, nor from excited D to D'. This is ascribed to the near orthogonality of the D and D' units and the very strong decoupling of the electrons on the D and A in the CT state. In addition, the possibility of aggregation-induced TADF (AI-TADF) is examined and shown to be a manifestation of solvatochromism in these particular molecules.