The role of excited-state character, structural relaxation, and symmetry breaking in enabling delayed fluorescence activity in push-pull chromophores.
The role of excited-state character, structural relaxation, and symmetry breaking in enabling delayed fluorescence activity in push-pull chromophores.
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激发态特征、结构弛豫和对称性破缺在推拉发色团延迟荧光活性中的作用。
DOI：
10.1039/d1cp03792g
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Kimber P
中科院分区：
文献类型：
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作者：
Kimber P
热激活延迟荧光（TADF）是目前产生高效发光器件的一种有前景的途径。然而，新发色团的设计过程受到复杂的光物理学的阻碍。在这项工作中，研究了四个密切相关的供体-π-受体-π-供体系统，其中两个是之前合成的，目的是阐明它们对 TADF 的不同有效性。我们概述了前沿轨道不足以区分分子。随后，在相关的从头开始水平上对激发态的详细分析强调了许多具有不同特征的紧密间隔的单线态和三线态的存在。将五种密度泛函的结果与该参考进行比较，揭示了随着哈特里-福克交换量的变化，激发态能量和波函数都发生了巨大的变化。激发态最小值在解决方案中进行了优化，显示了结构变化和对称性破缺对于产生强发射 S1 态的关键作用。由此获得的绝热单重态-三重态能隙在很大程度上取决于混合密度泛函计算中使用的范围分离参数。更一般地说，这项工作强调了单重态和三重态激发态波函数之间存在的复杂差异以及准确描述它们的挑战。
Thermally activated delayed fluorescence (TADF) is a current promising route for generating highly efficient light-emitting devices. However, the design process of new chromophores is hampered by the complicated underlying photophysics. In this work, four closely related donor–π–acceptor–π–donor systems are investigated, two of which were synthesised previously, with the aim of elucidating their varying effectiveness for TADF. We outline that the frontier orbitals are insufficient for discriminating between the molecules. Subsequently, a detailed analysis of the excited states at a correlated ab initio level highlights the presence of a number of closely spaced singlet and triplet states of varying character. Results from five density functionals are compared against this reference revealing dramatic changes in, both, excited state energies and wavefunctions following variations in the amount of Hartree–Fock exchange included. Excited-state minima are optimised in solution showing the crucial role of structural variations and symmetry breaking for producing a strongly emissive S1 state. The adiabatic singlet–triplet gaps thus obtained depend strongly on the range separation parameter used in the hybrid density functional calculations. More generally, this work highlights intricate differences present between singlet and triplet excited state wavefunctions and the challenges in describing them accurately.