金属复合物因其独特的光响应特性，广泛应用于高性能发光材料的制备和惰性共价键的光催化活化。其激发和弛豫过程不仅包括定域在金属或配体的电子跃迁，同时还涉及极其复杂的金属–配体相互作用，加之d、f电子激发组态的多样性和强相对论效应，导致重金属复合物在很窄的范围内聚集多个能量近简并的激发态，且表现出很强的电子相关和自旋轨道相互作用。这使得实验上精准指认和分辨其吸收和发射光谱及实时跟踪由这些复合物触发的光物理和光化学过程极其困难。同时，强相关和强相对论效应的金属复合物高精度激发态计算亦是极具挑战性的科学难题。 针对这些难题，我们发展和应用多组态微扰理论，拓展了以组态优选为核心的激发态数值模拟方案，实现了铀（VI），铕（III）和金（I）复合物的高精度激发态计算，提出了铀酰（UO22+）光催化活化C–H键的激发态电子转移机理，发现了铕（Eu）–天线配合物的共振能量传递机制，揭示了控制金（Au）团簇发光机理的关键因素。本论文主要科学贡献如下： （1）铀酰复合物的可见光氧化还原催化C(sp3)–H键氟化机理。运用多组态微扰的CASPT2//CASSCF方法并结合标量相对论赝势，系统研究了铀酰光催化环辛烷氟化反应 中激发态单电子转移（SET）的触发、弛豫和失活过程。首先，在可见光照射下，铀酰催化剂发生σu成键轨道到f空轨道的电子跃迁，因此缺电子的σu轨道易于接受环辛烷C(sp3)–H成键轨道（σC–H）提供的一个电子，触发激发态单电子转移。随后诱发了底物和催化剂之间质子耦合的电子转移，即从环辛烷到携带更多负电荷的铀酰轴向氧原子的氢转移（HAT），生成碳自由基中间体。最后，底物氟化试剂发生N–F键断裂，沿着几乎无垒的势能面，与碳自由基中间体通过构造C–F键高效地生成催化产物。同时催化剂发生协同非同步的O–H键断裂，将释放的氢原子转移至氟化试剂，实现催化剂的复原。计算发现：i）通过光诱导的单电子转移，在底物和催化剂之间发生有利于反应进行的电荷重新分布，从而有效降低反应能垒，使惰性共价键的活化成为可能；ii）正是由于金属U强相对论效应能显著提高光催化剂的自旋–轨道相互作用，从而加速光催化剂Sσ→Tσ和Tσ→S0*的系间窜越速率，提高催化效率；iii）光激发的催化剂能与非选择的酮类、芳香类底物形成激基复合物，并通过能量可及的单三态交叉点弛豫到基态，关闭催化通道。从而解释了在烷基苯和环酮存在的条件下，铀酰催化剂依然能高选择性地催化活化环辛烷惰性C(sp3)–H键。 （2）Eu–天线配合物的共振能量转移模型和分子设计。运用高精度的CASPT2//IRC// CASSCF方法，计算了一系列Eu–天线配合物的辐射弛豫途径，提出了九重态–五重态势能面交叉调控的能量共振理论模型，并指出配体的3ππ* → S0系间窜越是配合物发光过程的决速步骤。在此基础上，设计了一类以配位聚合物为天线基团的新型分子探针，并在合作者实验室成功合成。借助时间分辨的光谱技术，我们首次发现从天线基团到Eu3+中心的能量共振转移信号，同时发现在天线基团引入重原子Br，提高了自旋–轨道相互作用，能量转移时间由250 ns缩短为75 ns。这一发现，印证了我们提出的共振能量转移模型的普适性，并指导我们设计合成性能优异的红光材料。通过计算配合物九重态–五重态共振区的能量和旋轨耦合作用，发现未发生Br取代的配合物Eu–L1九重态能级与能量转移的优势通道5D1更接近，能量转移效率和发光量子效率较高（0.61）。对位Br取代的配合物Eu–L2虽然决速步3ππ* → S0的旋轨耦合作用得到近一倍提升，但Br的引入降低了配合物的九重态能级，使能量转移主要通过5D0通道进行，因而量子产率不是很高（0.46）。间位Br取代的配合物Eu–L3决速步的旋轨耦合作用和九重态能级均为最优，但由于晶体结构中配位水的存在导致激发态的Eu3+离子可以通过振动作用无辐射失活。配合物Eu–L3即使在结晶水强的淬灭效应下依然保持高量子效率（0.55）。 （3）金团簇的发光和催化机理。运用多组态微扰理论，研究了一系列中小尺寸金团簇辐射弛豫途径和催化反应过程。光激发后，金团簇首先布居到1σσ*明态，由于金超强的重原子效应，体系经历一次或多次系间窜越或内转换过程，弛豫至能量最低的三重态发出磷光。计算表明：i) 构成金团簇的亚单元倾向于形成垂直或变形多面体的构型增强彼此的亲金作用；ii) 揭示了控制金团簇吸收和发射的电子组态是由金6s，6p轨道线性组合而成的σ成键及其σ*反键轨道之间的跃迁；iii）归属了金团簇发射的磷光属性。相应的机理讨论对类似金属团簇的形成机制和发光机理有很强的借鉴作用。对金团簇催化鲁米诺化学发光机理的研究，发现在金团簇作用下，自由基调控的自旋转移过程更容易发生，从理论角度揭示了金团簇催化作用的本质。对鲁米诺化学发光体的指认，揭示了T2(3ππ*) → S0辐射跃迁发出磷光是鲁米诺化学发光的本质。

The metal complexes are of great interest to both experimental and theoretical chemists due to their wide application in luminescent materials and photocatalytic activation of inert covalent bonds. These light–responsive metal complexes cumulate most of the complexities inherent to theoretical studies: high density of electronic states, nearly degenerate states, d-d transitions, metal to ligand and ligand to metal charge transfer states, relativistic effects, especially the spin–orbit (SO) coupling. The inherent microscopic nature of the photoluminescence and photocatalysis processes cannot be fully disclosed by only using the experimental techniques due to the high complexity of the involved photophysical and photochemical processes. In addition, the strong electron correlation effects introducing by the heavy metals also make the high accuracy calculations of the photoinduced excited state electron transfer and energy transfer be much more difficult. Focus on these problems, we conducted the multi–configurational perturbation computations upon the representative metals, including actinide uranium (U), lanthanide europium (Eu) and transition metal gold (Au), to present a detailed mapping of the involved photophysical and photochemical excited state evolutions. The main contributions of this dissertation can be summarized as follows: (1) We reported a viable mechanism for the visible light photocatalysis for C(sp3)?H fluorination by uranyl (UO22+). By employing a multi?configurational correlated relativistic quantum chemical approach, the whole energy landscape relevant for the photophysical and photochemical processes of the photocatalytic cycle was studied in detail. We found that the hydrogen atom abstraction (HAT) induced by the ‘tentacle’?like oxygen of uranyl was the rate?limiting process for the photocatalytic reaction. The carbon radical produced by the HAT reaction readily triggers the nearly barrierless concerted asynchronous breakages of the N?F and O?H bonds leading to the targeted fluorinated product and the recovered photocatalyst. The single electron transfer plays a fundamental role in the breaking and formation of chemical bonds during the whole photocatalysis reaction. The strong SO couplings originating from the uranium center are of vital importance for the effective intersystem crossing to the reactive triplet state and the recovery to the ground state of the photo?induced processes. The existence of triplet?ground state crossing in the collision complex for ketone substrates and the stable π complex for aromatic substrates does not only explain the quenching mechanisms of uranyl by ketone and aromatic substrates but also explains the catalytic selectivity towards the inert C?H bonds in the presence of alkylbenzenes and cyclic ketones. Moreover, the disclosed electron shifts mechanism can help to understand analogous metal?oxo catalytic processes and may inspire the design of the novel catalysts. (2) We presented the resonant energy transfer mechanism and the mechanism?based design for the photoluminescence of Eu?antenna complexes. Based on the multi?configurational CASPT2//IRC//RASSCF calculations associated with relativistic energy-consistent ab initio pseudopotentials, we present an innovative energy transfer model that is governed by the nonet–quintet intersystem crossing (NQC) and the spin?orbit coupling (SOC) among the involved states. We proposed that the ligand?centered 3ππ*?S0 intersystem crossing (ISC) is the rate?determining step for the Eu?complex luminescence. We therefore design and synthesize a novel ligand (L1) with Br?substituted at different positions (L2 and L3) as well as their corresponding complexes Eu?Ln (n=1?3). From the time?resolved spectroscopy, we directly observe the improved energy transfer rate (Eu?L1: 250 ns, Eu?L2: 75 ns) from the ligand to the Eu3+ ion by incorporating Br into the Eu?complex. The energy and SOC analysis in the NQC region shows that the nonet of Eu?L1 is resonant with the preferable high?lying 5(S0/5D1) sublevel of the quintet state and therefore has the higher ET rate and the higher luminescence quantum yield (LQY, 0.61). Although the Eu?L2 complex has the obvious improvement for the rate?determining SOC due to the existence of para?Br, the lower nonet energy level makes the complex low efficient in the ET process and finally the lower LQY is obtained (0.46). For the Eu?L3 complex, the optimal SOC and nonet level is achieved. The overall LQY is as high as 0.55 even though the coordinated water molecules can quench the excited Eu3+ via the vibronic interactions. Based on both theoretical and experimental considerations, our proposed resonant ET mechanism has been verified to be reliable and the introducing of the heavy Br atom into the Eu?complex also provides innovative ideas for the luminescent materials designation. (3) The photoluminescence and catalysis mechanism of gold clusters. We reported for the first time Franck–Condon excitation and the subsequent photophysical mechanisms for a series of small gold clusters based on CASPT2//CASSCF calculations. The computational results reveal that the topological features and the number of diamagnetic electrons codetermine the low?lying emissive 3σ*σ or 3σ*π state and the phosphorescent emission character. These mechanistic insights are beneficial to further understand the gold clusters and may also facilitate the mechanism?based design of nanometal modules. The following study of radical?mediated spin?transfer accelerated by gold nanoclusters has disclosed the catalytic role of Au clusters in the chemiluminescence of luminol. The multi–configurational computation of the generated triplet state emitter reveals that the phosphorescent emission from T2(3ππ*) state to S0 state is predominant over the fluorescent emission.