分子内电荷转移化合物的跃迁能理论预测

In recent years, using time-dependent density functional method (TD-DFT) to reproduce the transition energies of conjugated molecules has been widely used in the studies of organic photonics and electronics. But so far, it is known that the calculations of the transition energies of intramolecular charge-transfer (ICT) molecules are exchange-correlation functional dependent. Although our pervious study showed that the transition energies of many ICT compounds can be accurately reproduced by using a relation exists between the amount of charge transferred in the transition process and the optimal Hartree−Fock percentage in XC functional, more universal and systemic method should be developed. On the basis of photochemistry theory combined with molecular simulation technique, a better method for the determination of transition energies from molecular spectra and a large and reliable experimental database will be established. Then, through error analysis and wave-function approach, a descriptor other than q allowing more accurately descripting the characteristic of ICT process may be found and used for functional selection or error correction. The novel computational method developed in this subject will first be used for the design of thermally activated delayed fluorescence (TADF) emitters, which are the next generation of organic electroluminescence materials, and then for other materials for organic photonics and electronics.

在有机光子学和电子学领域，含时密度泛函理论（TD-DFT）被广泛用于对共轭分子跃迁能的预测。但是TD-DFT计算结果的可靠性表现出严重的泛函依赖性，特别是对于分子内电荷转移（ICT）跃迁。虽然之前已经证明建立起杂化泛函中精确交换项应占比例和跃迁对应的电荷转移度（q）之间的关系可以精确预测出部分ICT分子在基态与激发态下的跃迁能，但该方法的普适性和系统性还有待提高。本项目立足于光化学理论和分子模拟技术的紧密结合，首先完善由分子光谱确定跃迁能的实验方法，建立起一套大容量、可靠的实验数据集来支持理论研究工作的顺利展开；其次通过分析计算误差来源并借助波函数分析技术在q之外寻找能更准确反映ICT体系特征的参数（即描述符），为泛函选择或结果修正建立最优指导模型。本项目的成果将首先在新一代有机电致发光材料——热活化延迟荧光分子的辅助设计上发挥作用，进而推广应用到其它光电子材料领域。

采用含时密度泛函理论精确预测包括热延迟荧光（TADF）分子在内的分子内电荷转移（CT）分子的激发能是计算材料学领域的一个难题，一是因为激发能实验值的不确定性，二是因为计算结果的可靠性表现出严重的泛函依赖性。本项目借助超快荧光光谱及中频介电谱深入研究了固态溶剂化对分子各个激发态能级的影响，证明了有机薄膜中存在足够的自由体积，能够让小分子在变化的电场中发生可逆的转动与重排。由于薄膜中的取向及去取向时间尺度分别与有机分子的单重态及三重态寿命接近，激发态分子在薄膜中的各激发态能级呈相对动态变化。因此对薄膜中有机小分子激发能的精准模拟需要建立在完善的固态溶剂化模型基础上。一种能同时预测分子在溶液及薄膜中发光特性的算法能加速TADF材料的开发。基于定域化轨道指示函数描述符，构建了一种高效的对范围分离泛函和介电屏蔽范围分离泛函中参数ω的调控方法，准确预测出各类TADF分子在溶液和薄膜中的垂直激发能和最低单/三重激发态能差（ΔEST）。此外基于此前开发的最优精确交换项比例（OHF）法，以理论激子结合能对OHF的关系构建了一种不依赖于泛函的CT描述符来确定泛函的OHF，避免了传统的基于跃迁密度的CT描述符自身存在泛函依赖性的问题。发现多数电荷转移型TADF分子在激发态下会发生几何扭转并降低辐射速率，而泛函包含的精确交换比例不足时会低估三重激发态的弛豫能。对激发能计算方法的改进以及对激发态几何与电子结构的准确模拟有力支持了高性能蓝光TADF材料和高效铜(I)基发光材料的开发。