发光材料在大面积照明、平板显示和生物成像等领域有着广阔的应用前景。它的迅速发展为推进高科技创新、加速人类文明进程做出了巨大贡献。研发发光效率高、能耗低、工艺简单、色彩丰富、成本低廉的发光材料一直是基础研究的前沿热点之一。随着研究的深入，实验发现在设计新型的光功能材料时，利用奇特的发光现象，比如热活化延迟荧光（TADF）、长余辉磷光、聚集诱导发光（AIE）等，通常可以获得高效的发光性能；但其背后的微观本质仍不清楚，其物理机制有待进一步研究和探索。在这方面，理论计算模拟起着重要作用。本论文主要围绕有机金属配合物的热活化延迟荧光和四苯乙烯衍生物的激发态失活等方面展开了系统的理论研究。下面分三部分进行简单介绍： 第一部分：有机发光二极管（OLED）技术凭借其低能耗、高对比度的优势在显示领域发挥着巨大作用。TADF材料能够同时捕获单重态和三重态激子，从而提高激子利用率和发光量子产率，是最具潜力的发光材料。Cu(I)配合物作为一类典型的TADF材料，结构多样，发光独特，价格低廉，引起了实验学家的广泛关注。近来，我们采用密度泛函理论（DFT）和含时DFT（TD-DFT）方法研究了具有TADF特性的Cu(I)配合物在气相、溶液和晶体中的激发态性质和光物理机理。基于光谱性质、轨道分析、计算得到的辐射及非辐射速率，我们发现这类体系的最低激发单重态和三重态均有明显的金属到配体的电荷转移特征；单三态之间小的能级差和适当的旋-轨耦合强度有助于反向系间窜跃（rISC）过程，且升高温度可以明显加速rISC过程，这些性质为TADF提供了有利条件。在单核Cu(I)配合物中，相比于气相和溶液，晶体提供了一个相对更为刚性的环境，晶体中的低频振动模式明显受到抑制，Huang-Rhys因子、正向和反向ISC速率都有一定程度的减小，说明环境效应对于单核Cu(I)配合物光物理性质的调节十分重要。我们的理论工作为发展基于Cu(I)配合物的、具有优异发光性能的TADF材料提供了重要的理论基础。 第二部分：不同于Cu原子，Au原子的重原子效应更加明显，旋-轨耦合作用也更强，普遍认为不存在较快的rISC过程，因此这类配合物的TADF现象少有报道。但是，近来的实验研究打破了这一传统观念。Che等合成了两个有TADF现象的芳基配位的Au(III)配合物，发光量子产率高达84%，但其内在的光物理过程和发光机制却模糊不清。为了探究该类Au配合物的TADF机理，我们采用DFT和TD-DFT方法结合极化连续介质模型（PCM）和量子力学/分子力学（QM/MM）模型研究了这两个Au(III)配合物在甲苯溶液和晶体中的发光机理。计算结果表明，芳基和C^N^C配体之间明显的扭转有助于分离HOMO和LUMO的空间和减小单重态和三重态之间的能级差；其次，取代基对几何结构的影响不大，但是对电子结构、相关的辐射和非辐射速率有明显影响，可以通过改变取代基调节Au(III)配合物的TADF行为。目前的计算工作不仅有助于更好地理解Au(III)配合物的TADF发光机理，而且为设计和丰富金属有机TADF材料提供了帮助。 此外，金属有机磷光材料在晶体、药物和材料科学等领域都有广泛应用，但蓝色磷光材料的稳定性较差是其市场化进程的绊脚石之一。近来实验上制备了一种可以发射蓝色磷光的Au(III)配合物，克服了发光体在溶液中稳定性差的问题，但是该配合物在溶液中的发光量子产率很低（0.001）。为了从根源上弄清楚其发光效率低的原因、进而设计合成磷光量子产率高的新型Au(III)配合物，我们通过理论方法研究了Au(III)配合物在溶液中的激发态性质和光物理机制，优化得到了不同激发态势能面上的极小能量结构、过渡态及极小能量交叉结构，找到了可能的激发态失活途径。我们发现Au(III)配合物在紫外光照射下被激发至较高激发单重态，之后迅速内转换到达第一激发单重态。由于Au(III)的旋-轨耦合较大，S1态会先通过ISC过程转换至三重态3MLCT/3LCTRZ1和3MLCT/3LCTRZ2，之后克服较低的能垒到达3MC态，最后通过最小能量交叉点（MECP）以非辐射失活的方式回到基态。其中，3MC态在激发态的非辐射失活过程中起了关键作用。我们的理论工作解释了该配合物发光量子产率极低的微观机理，为设计高效的蓝色磷光Au(III)配合物提供了理论参考。 第三部分，四苯乙烯（TPE）衍生物被广泛用作AIE材料的骨架分子，弄清楚单分子的光物理和光化学机理对于设计优异性能的发光材料至关重要。早期的理论工作均认为TPE中间双键的光异构化路径是其主要的激发态失活通道，但是近期大量的实验研究并未观测到异构化的产物。其次，实验发现TPE上修饰的取代基位置不同时，光物理性质存在明显差异：当四个甲基位于间位（TPE-4mM）或者邻位（TPE-4oM）时，相应的发光量子产率分别为0.1%和64.3%。为了研究TPE衍生物不同的发光现象背后的光物理机理，我们采用了静态电子结构计算和非绝热动力学模拟相结合的方法，发现体系存在两种不同的激发态失活途径，一种是TPE中心的乙烯双键的光异构化；另一种是相邻苯环之间的光环化。TPE-4mM在S1激发态上的光环化过程是无能垒、超快的，导致其发光量子产率低；相反，TPE-4oM的两种激发态失活途径均受到不同程度的抑制，导致相对较高的荧光量子产率。我们的理论工作解决了实验和先前理论研究之间的分歧，发现了TPE-4mM分子存在通过光环化反应的激发态失活路径。我们理论上所预测的光环化路径及其中间体也被后续的超快时间分辨光谱实验所证实。

Photoluminescence materials are one important part of advanced materials and its application prospects are encouraging. The rapid development of photoluminescence materials have made outstanding contributions to high-tech innovation and human civilization. Therefore, how to prepare photoluminescence materials with high efficiency, low energy consumption, facile process, broad color gamut and low cost is still the focus and hotspot in academia. In recent years, people find some novel luminescence phenomena, such as aggregation-induced emission, phosphorescence and thermally activated delayed fluorescence, can be applied to the design of high efficient photoluminescence material. However, the mechanisms hidden behind the fascinating phenomena are still elusive. Motivated by this question, we focus on the following aspects. In the first section: thermally activated delayed fluorescence materials that make full use of both singlet and triplet state excitons, resulting in the fluorescence internal quantum efficiency reach to 100% theoretically, has jumped into ranks of the most promising optical functional materials. Combined DFT and TD-DFT methods, the TADF mechanism of mononuclear and dinuclear Cu(I) complexes has been explored systematically. Based on geometric and electronic structures, simulated spectra and calculated radiative and nonradiative rates, we have found that the excited characters of excited S1 and T1 states are metal to ligand charge transfer. The small energy gap between S1 and T1 states and appropriate spin-orbit coupling strength provide favorable conditions for TADF. The reverse intersystem crossing processes are more sensitivity to temperature, and accelerate with the rise of temperature. In mononuclear Cu(I) complexes, since crystal offers a more rigid surrounding than gas and liquid phase, the Huang-Rhys factors are reduced in crystal, resulting the ISC and rISC processes are slightly slower than those in gas and liquid phases. We believe our works establish important theoretical basis for developing high-performance TADF materials based on Cu(I) complexes. In the second section: Many organometallic complexes have been confirmed to display TADF, however, the reports involving Au(III) complexes with TADF are scarce. Recently, stable TADF have been obtained in two synthetic Au(IIII) complexes experimentally and the QY reach up to 84%. In order to illuminate the essential TADF mechanism, we have employed polarizable continuum model and ONIOM model to systematically study the excited state processes of two Au(III) complexes in toluene solution and crystal, respectively. The distinct twists between aryl and C^N^C ligands help to separate HOMO and LUMO, serving the purpose of minimizing the energy gap between S1 and T1 states. Substituents have small influence on geometric sturctures, but have obvious effects on radiative and nonradiative rates. Therefore, the TADF performance can be tuned by tailoring substituents groups. These investigations help us understand the TADF photophysical insights of Au(III) complexes and offer help to design and enrich organometallic complexes with TADF. The Au(III) complex with deep blue phosphorescenceis stable in solvents, but the corresponding photoluminescence quantum yields (QYs) is ultralow (0.001). The hidden mechanisms are still elusive. In older to clarify the relevant mechanisms, we have investigated excited state properties and photophysical mechanism of Au(III) complex by DFT and TD-DFT methods. We have optimized minima, transient state and minimum energy crossing points (MECP) of Au(III) complex in solution. We found that the 3MC state plays a critical role in excitons nonradiative decay process and then described integrally the potential energy surface. The breakthroughs in the comprehending of the nonradiative process explain why luminous efficiency is unsatisfying in solution. We hope that our work can provide valuable information for designing Au(III) complexes with high-efficiency luminescence. In the third section: different position of substituents on tetraphenylethene (TPE) leads to distinctly different photophysical properties. When four methyl substituents in the meta-position of TPE (TPE-4mM), the fluorescence quantum yield (QY) is only 0.1%, while place them to the ortho-positon (TPE-4oM), the QY is enhanced to 64.3%. Static electronic structure calculations in combination with nonadiabatic dynamics simulations have been employed to investigate the detail mechanisms. We have found two kinds of excited-state decay channels: photoisomerization involving the central C=C bond and photocyclization regarding to adjacent phenyl rings. The accessible S1 cyclization should be responsible for the ultralow QY in TPE-4mM, while two kinds paths are blocked and the fluorescence is easy-realizable in TPE-4oM. Nonadiabatic dynamics simulations further confirmed these conclusions.