【JACS】北邮夏安东、匡卓然联手中科大周蒙|中心对称四极矩发光体的激发态对称性破缺动力学，解锁“>3 V”的级联弛豫路径#

Scheme 1. Molecular Structural Formulas and Molecular Fragment Partition of the DAD and Its Single-Branch Analogue DA, with the Donor Highlighted in Blue and the Acceptor Highlighted in Red#

Figure 1. Solvent-dependent steady-state absorption (solid lines) and fluorescence (dashed lined) spectra of DA (upper panel) and DAD (lower panel). (CHX, cyclohexane; TOL, toluene; DBE, di-n-butyl ether; CHCl3, chloroform; EtOAc, ethyl acetate; THF, tetrahydrofuran; DCM, dichloromethane; BZN, benzonitrile; DMF, N,N-dimethylformamide; ACN, acetonitrile).#

Figure 2. Basis of the Lippert–Mataga plots of Stokes shift (𝜈˜abs – 𝜈˜fl) vs the solvent polarity function, Δ_f_. The solvents are (from left to right) CHX, TOL, DBE, CHCl3, EtOAc, THF, DCM, BZN, DMF, and ACN. The asterisks represent TOL and BZN solvents.#

Figure 3. Evolution-associated difference spectra (EADS) and corresponding time constants obtained from global analysis of fs-TA spectra of (A) DA and (B) DAD in TOL (upper panel) and BZN (lower panel). Global spectral analysis is based on a sequential evolution model of three (A → B → C) or four (A → B → C → D) transient species for the measurements in TOL and BZN, respectively. The green and red vertical lines represent the allowed and forbidden S1 → S_n_>1 transition judged by the Laporte rule, supported by the calculations of DAD and DA in toluene (PCM) (Tables S2 and S3). The scaled stationary absorption and fluorescence spectra are shown in blue and red shading, respectively.#

Figure 4. Contour plots of NIR fs-TA spectra of DAD in (A) TOL and (B) BZN. (C) ESA-band kinetic traces at 1540 nm (S1 → S2, Laporte-allowed) and 1360 nm (S1 → S4, Laporte-allowed) for DAD in TOL. (D) ESA-band kinetic traces at 1490 nm (S1 → S3, Laporte-forbidden), 1260 nm (S1 → S4, Laporte-allowed, used to replace the peak dynamics at 1360 nm for avoiding the overlapping by the S1 → S3 ESA), and 1160 nm (S1 → S5, Laporte-forbidden) for DAD in BZN. The corresponding SE shift dynamics are also plotted (gray dots) with the right y-axis for kinetic comparison in panels C and D.#

为了阐明这一动力学行为的背后的物理本质，研究人员引入了融合振动偶合与溶剂化效应的三能级本质态模型，成功构建了绝热势能面并映射出对应的弛豫轨迹。理论模拟精确再现了受溶剂调控的势垒变化，解释了弱极性溶剂中因势垒极低、快速互变而导致的“假对称性破缺”现象。更为关键的是，该研究首次推导出了预测此类分子发生对称性破缺的定量通用判据，即分子的Stokes位移能量必须大于电子支间耦合能的3倍（>3 V），为理性设计和精准调控四极矩发光材料的激态行为建立起一个可预测的全新理论框架。

Figure 5. Isosurface plots of frontier molecular orbitals (FMOs) involved in the lowest S0 → S_n_>1 electronic transitions of DA and DAD at their optimized S1 geometries in TOL. (72) The dark blue and light blue arrows represent the major and the minor orbital transitions, respectively. The u and g in parentheses denote the _A_g (gerade) and _A_u (ungerade) parities, respectively.#

Figure 6. Energy scheme of electronic levels of DAD. The gray and blue horizontal lines represent electronic states with _A_g and _A_u parities, respectively. Transitions between electronic states of the same parity, which are Laporte-forbidden (denoted by red arrows), become allowed (denoted by green arrows) after the ES-SB. The parity of the states is also indicated.#

Figure 7. PESs of DAD in TOL and BZN. The blue surfaces and orange surfaces represent the S0- and S1-state PESs, respectively. In the left panel, the red dots indicate the minima of each PES, while the blue and red arrows represent the absorption transition and relaxation emission transition in the BZN solvent, respectively. The orange arrow represents the relaxation emission transition in the TOL solvent. In the right panel, the colored curves indicate the depth of the minima, and the black arrows show the direction of the relaxation path. The thick arrows lie on the gray plane (where x = 0), and the thin arrows indicate the direction along the x-axis.#