【Nat.Chem.】单分子内驱动“双轮”不同频运转！利用高达10.2倍的光化学转子偏好实现分子“转向”#

a, Advances in rotational complexity of light-driven overcrowded alkene-based molecular motors from systems with a single rotor to mixed dual-rotor systems. Mixed motors (substituents: R1 ≠ R2) generate two different rotational frequencies, instead of the typical single rotational frequency. b, The disrotary movement of the rotor units is represented as the movement of a wheel on an axis for symmetric and mixed systems. Mixed motors are no longer CS symmetric. c, CD spectra of (R)-(ZSZS)-3 and (S)-(ZSZS)-3 in Et2O at 20 °C.#

The rotation mechanism of mixed motors (R1 ≠ R2) connects three dimensions of intermediates (stable, single metastable and double metastable states) through PEZ isomerization and THI processes. The label of each intermediate denotes the E/Z configuration of the central C=C bonds, first of the bond connected to the orange rotor, followed by the one linked to the blue rotor. The subscript label indicates a stable (S) or metastable (M) geometry of the associated rotor. PEZ isomerization transforms a single rotor from a stable to a metastable configuration. In a THI, a rotor moves to the opposite face of the core, which converts its metastable configuration to a stable configuration. Each four-step cycle represents the 360° unidirectional rotation of one of the rotors. Coupled rotor motion provides thermal access to double metastable intermediates _E_M_Z_M and _Z_M_E_M (centre), which interconnect all single metastable states via additional PEZ isomerisation and THI steps (off-cycle steps).#

a, Compositional changes of (_Z_S_Z_S)-1 upon irradiation to the PSS with 455 nm at −85 °C and subsequent thermal relaxation. The kinetic profile was followed via the core (right) and rotor (left) 19F signals. b, The proposed mechanism with the operating processes highlighted under these conditions (t = 0–295 min). c, The corresponding partial 19F NMR spectra (470 MHz) of (_Z_S_Z_S)-1 (5 mM in CD2Cl2) showing the signals of the core fluorine substituent upon irradiation and after partial and full relaxation. All motor intermediates are labelled with symbols: dark green square, _Z_S_Z_S; light blue circle, _Z_S_E_S; blue circle, _E_S_Z_S; grey triangle, _Z_S_E_M; light green triangle down, _E_M_Z_S; orange triangle up, _E_S_E_S; green diamond, _E_M_Z_M; light blue diamond, _Z_M_E_M; light orange triangle right, _Z_M_E_S; and dark orange triangle right, _E_S_Z_M.#

在进一步的定量调控实验中，研究团队发现这种光化学偏好表现出对环境和激发光源的高度敏感性。对于马达1，在特定溶剂与可见光照射下，其中一个甲氧基取代的转子被激活的概率是另一个氟取代转子的近5倍（4.8倍）；而在针对马达2的测试中，仅通过改变溶剂或调节光照波长，其光化学转子选择性偏好比就能从0.9大幅调节至7.7甚至10.2。这一实验结果无可辩驳地证明，通过对转子的精细电子结构调整和外部条件的变换，能够对双转子系统的相对运动频率进行精准且主动的操纵。

Overview of the experimentally determined activation barriers (Δ‡G) for the thermal processes of mixed motor 1 (5 mM, CD2Cl2) sorted by the involved rotor: MeO-substituted (orange) and F-substituted (blue) and compared with the symmetric parent motor 5 (grey). For clarity, a simplified mechanistic overview is shown. The label of each intermediate denotes the E/Z configuration of the central C=C bonds, first of the bond connected to the orange rotor, followed by the one linked to the blue rotor.#