Fig.1 Azobenzene switches with light-harvesting antennae. (a) Chemical structures of AzoB, AzoZnN, and their parent motifs. (b) Photosensitivity (εΦ) of AzoB, AzoZn10, and azobenzene derivatives reported in the previous literature (Figure S1 and Table S1). (32, 34, 41, 56−70) (c) Schematic illustration of the strategy in this work for achieving a molecular system with high photosensitivity.#

实验采用甲苯、二氯甲烷与丙酮等不同极性溶剂，通过365纳米、455纳米及505纳米发光二极管进行多波长辐照，结合单晶X射线衍射、核磁共振氢谱积分与紫外-可见吸收光谱对异构化动力学进行精确拟合。实验数据显示，在505纳米绿光辐照下，AzoB在甲苯中的摩尔吸光系数达到$9.0 \times 10^4\text{ M}^{-1}\text{cm}^{-1}$，光异构化量子产率为$8.3\%$，所得光敏度$\epsilon\Phi$高达$7.5 \times 10^3\text{ M}^{-1}\text{cm}^{-1}$，相比未取代偶氮苯（$34\text{ M}^{-1}\text{cm}^{-1}$）提升了200倍以上，同时其顺式结构在25°C下的热弛豫半衰期长达9.2天，荧光量子产率被抑制至0.01。对于系列配位纳米链$\text{AzoZn}_N$，随着核数$N$从1增至10，其在505纳米处的摩尔吸光系数线性攀升至$4.8 \times 10^5\text{ M}^{-1}\text{cm}^{-1}$，且定量激子迁移避免了量子产率的恶化，使得十核纳米链$\text{AzoZn}_{10}$的光敏度达到$8.1 \times 10^3\text{ M}^{-1}\text{cm}^{-1}$（八核产物可达$1.0 \times 10^4\text{ M}^{-1}\text{cm}^{-1}$）。

Fig.2 AzoB and its photochemical response. (a) Synthetic scheme of AzoB. (b) Crystal structure of AzoB with thermal ellipsoids set at the 50% probability level. Black: carbon; white: hydrogen; blue: nitrogen; pink: boron, lime yellow: fluorine. (c) UV–vis absorption spectra of AzoB in toluene in the trans (black) and cis (red) conformations as well as at the PSS of 455 nm (blue), 505 nm (green), and 365 nm (purple). Natural transition orbitals (NTOs) for the S0 → S4 and S0 → S2 transitions of trans-AzoB in toluene were also described, corresponding to the band broadened over 300–350 nm and the sharp band at 505 nm, respectively. (d) Repetitive photoisomerization of AzoB in toluene with 365 and 505 nm irradiations. (e) Stack of 1H NMR spectra of AzoB in toluene-d8 in the trans conformation (blue), at the photostationary state (PSS) under 365 nm irradiation (red), and after being heated (yellow). Signal sets highlighted in orange and yellow correspond to the trans and cis isomers, respectively.#

Fig.3 Time course analysis. (a) Time-dependent cis-isomer ratio of AzoB in toluene under 365 nm (purple), 455 nm (blue), and 505 nm (green) irradiation. The sample concentrations were 12 μM, 12 μM, and 11 μM, respectively. (b) Time-dependent cis-isomer ratio of azobenzene in toluene under 365 nm (purple), 455 nm (blue), and 505 nm (green) irradiation. The sample concentrations were 15 μM, 15 μM, and 18 μM, respectively. Note that the photon flux of the 455 and 505 nm LED used for azobenzene was >4 times stronger than those used for AzoB (Table S22). (c) The cis-isomer ratio of AzoB in toluene (red dots), azobenzene in acetone (purple dots), AzoZn1 in toluene (blue dots), 4-dimethylaminoazobenzene in n-hexane (yellow dots), and 4,4′-dimethoxyazobenzene in toluene (green dots), as a function of the number of irradiated photons (Np). The sample solutions of AzoB and AzoZn1 were irradiated under 505 nm LED, whereas 365 nm LED was adopted for the other solutions. The concentrations were uniformly adjusted at 8 μM. The lines show the initial slopes of their curves determined by fitting the concentration profiles of the isomers with the differential equation for the photoisomerization dynamics (see Section 16 in Supporting Information for the calculation method).#

Fig.4 Calculated energy landscape of AzoB and AzoZn1′. (a) Theoretical mechanism of rotational photoisomerization and photoluminescence of AzoB (green) compared to azobenzene (orange). The schematic illustrates the potential energy surfaces (PESs) of AzoB along the φ1 and φ2 dihedral angles in DCM. Energies are shown relative to the respective stable ground states (S0) of AzoB and azobenzene. (b) Theoretical mechanism of rotational photoisomerization of AzoZn1′ (cyan) compared to azobenzene (orange). The schematic illustrates the potential energy surfaces (PESs) of AzoZn1′ along the φ1 and φ2 dihedral angles in DCM. Energies are shown relative to the respective stable ground states (S0) of AzoZn1′ and azobenzene.#

从执行机理来看，量子化学计算阐明了完整的能量耗散路径：AzoB在吸收可见光激发至低能量激发态后，通过较低势垒的锥形交叉点（$\text{CI S}_2/\text{S}_1$和$\text{CI S}_1/\text{S}_0$）沿旋转坐标快速实现非辐射去活化并完成异构化。其跃迁至锥形交叉所需的能量损失（0.39电子伏与0.68电子伏）显著低于传统偶氮苯（0.73电子伏与1.35电子伏），不仅合理解释了天线荧光被完全淬灭的原因，也揭示了低能光子高效驱动分子旋转异构的深层物理机制。此外，在不同极性溶剂和反复交替光照测试中，该体系均展现出优异的抗疲劳特性与稳定的光稳态比例。

Fig.5 Synthesis and analysis of AzoZnN. (a) Synthetic scheme of AzoZnN. (b) Crystal structure of AzoZn2 with thermal ellipsoids set at the 50% probability level. Black: carbon; white: hydrogen; blue: nitrogen; dark blue: zinc. (c) Molar absorption coefficients of AzoZnN (N = 1–10) in toluene. The spectra of AzoZnN (N = 6–10) are determined by calculation (see Section 14 in Supporting Information). (d) Plot of εΦ value against the nuclear number of AzoZnN.#