（1）意义：通常分子的荧光磷光等特性无法通过简单的激发态计算。并不是所有的S0到S1的跃迁都是HOMO LUMO占主导的。对于晶体内分子聚集状态（J聚集 H聚集），系间窜越等的研究更是应该在激发态研究的方法下进行分析，不可以简单用HOMO LUMO分析。
（2）说明：a,b, Schematic diagrams showing the TD-DFT-calculated energy levels, isosurface and main orbital configurations of a DPhCzT monomer and its coplanar dimer at singlet (Sn) and triplet (Tn) states. Note that H and L refer to highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively. The molecular packing in b is derived from single-crystal diffraction data. The red and blue dashed arrows in a and b represent the intersystem crossing processes probably occurring from the S1 state to its higher- or lower-lying triplet states (Tn). The green lines refer to the triplet states available for effective intersystem crossing transitions.
d, Single-crystal structures of DPhCzT showing the formation of H-aggregates as evident by the measured angle (θ) of 80.9° between the transition dipoles and interconnected axis. e, Schematic energy diagram of J-aggregation (θ < 54.7°) and H-aggregation (θ > 54.7°). The blue and red solid curves represent the exciton energy levels of allowed transition for J- and H-aggregation, respectively. The dotted curve refers to the corresponding exciton energy level of forbidden transition.
f, Proposed energy transfer processes for fluorescence (Fluo.), phosphorescence (Phos.) and ultralong phosphorescence (Ultralong phos.) in DPhCzT aggregates. The n–π∗ transition derived from nitrogen atoms in the conjugated heterocycle enhances spin–orbit coupling. This in turn populates triplet states through singlet–triplet intersystem crossing (ISC). The triplet excitons are quickly stabilized because of the H-aggregation of DPhCzT molecules, resulting in the formation of stabilized triplet excited states (Tn∗) with extended lifetime needed for ultralong phosphorescence. The internal relaxation processes of the excitons are marked by grey wavy arrows.
文献来源：https://www.nature.com/articles/
说明：
(a) Different observation view of DFT calculated optimization SA3-Fe2+.
(b) NTO orbital of 225 and 226 (isovalue: 0.095). Both NTO orbital 225 and 226 exhibit typical d-orbital characteristics.
Moreover, both
orbital 225 and 226 exhibited typical d-orbital spatial distribution characteristics (Fig. b). Obviously, the lowest excited state transition of SA3-Fe2+ is mainly the d-d orbital transition of the Fe. According to the Laporte selection rule, the d-d orbital transition is a parity-forbidden transition, thus the fluorescence is quenched.
文献来源：https://linkinghub.elsevier.com/retrieve/pii/S0925400519314765
量子化学（quantum chemistry）是理论化学的一个分支学科，是应用量子力学的基本原理和方法研究化学问题的一门基础科学。研究范围包括稳定和不稳定分子的结构、性能及其结构与性能之间的关系；分子与分子之间的相互作用；分子与分子之间的相互碰撞和相互反应等问题。
适合的研究方向包括但不限于：有机合成、方法学研究、高分子等
可以计算的体系包括但不限于：小分子、团簇、低聚物、自由基、离子等
常用软件：Gaussian，ORCA，dmol3等
可以计算的内容包括但不限于：
分子性质，如键长键角二面角、HOMO/LUMO、电荷分布、键级、偶极矩、极化率、芳香性、静电势、Fukui函数、激发态研究等
光谱预测，如红外、紫外、拉曼、荧光、磷光、核磁、圆二色谱、旋光度等
能量计算，如结合能、解离能、电离能、弱相互作用分析等
反应相关，如过渡态搜索、势能面扫描、反应位点预测、反应路径、反应机理研究等
