【Angew.Chem.】效率提升！光能驱动的人造分子泵实现0.9%能量转化率#

文章标题： An Artificial Molecular Pump Powered by Light

通讯作者： Jessica Groppi, Alberto Credi

文章链接： https://doi.org/10.1002/anie.8103353

文章概要#

引言#

生物系统在维持生命活动时，能够精妙地将外部能量转化为定向分子运动，从而实现离子输运或信号传递等功能。在纳米科学领域，如何模仿这种生物分子泵，利用外部能源（如化学能、电能或光能）驱动底物逆着能量梯度进行“做功输运”一直是核心挑战。尽管已有化学或电驱动的分子泵问世，但开发一种能够自主运行且可光控、能将光能直接存储为化学势的合成系统依然极具难度。本研究基于光驱动的能量棘轮机制，成功设计并运行了一种极简且稳健的人造分子泵，能够通过连续光照将溶液中的大环分子泵入并锁死在轴向分子的高能室中，为开发自适应材料和太阳能转换系统奠定了坚实的基础。

Chemical structure and functional elements of the investigated system. (a) Molecular formula and cartoon representation of the pump components, axle E-1 and macrocycle 2. (b) The reversible isomerization of the azobenzene unit of the investigated compounds between E- and Z-configurations. (c) Molecular formula of model compounds E-3 and 4.#

Reaction scheme and operating principle of the molecular pump. (a) The network of reactions that describes the operation of the molecular pump; The complexation equilibria and isomerization reactions are the horizontal and vertical processes, respectively; light is involved only in the vertical processes. _k_n are the rate constants of the corresponding reactions, while the subscripts hν and Δ denote the photochemical and thermal isomerization processes, respectively. The pink arrows and yellow background highlight respectively the ring steps and reactions that are functional to pumping. (b) Simplified energetic profiles (potential energy versus ring-axle relative position) that describe the light-driven energy ratchet at the basis of pumping. The number of pink disks represents the ring population in the various states: uncomplexed, complexed at station I, and complexed at station II. Overall, repeated E ⇆ Z isomerization by continuous light irradiation results in the accumulation of the [3]pseudorotaxane and in the depletion of the free macrocycle.#

主要实验及结论#

该分子泵的设计巧妙地整合了光活性模块和收集储槽。研究人员合成了由偶氮苯光开关连接的两个铵盐识别位点组成的轴分子。在黑暗条件下，体系处于热力学平衡态，大环冠醚分子倾向于停留在结合力较强的位点。当施加波长为365nm的光照时，偶氮苯发生顺反异构化，这一过程引发了两个关键效应：一是降低了原泵位点的结合常数，二是显著提升了分子链末端的动力学势垒。这种机制迫使冠醚分子定向移动至收集腔室内。通过核磁共振波谱（NMR） 的实时监测发现，光照能够诱导溶液中自由冠醚分子的浓度显著下降，证明了宏观上的耗散非平衡态。通过精确的动力学模拟，研究团队证实了体系每泵送一个大环分子平均需要消耗900个光子。在连续光照下，该系统实现了约0.9%的光能到化学能转换效率。尽管这一数值看似不高，但它成功证明了人造系统可以在不需要宏观不对称条件的情况下，仅依靠分子层面的工程设计实现能量的有效存储。

Partial NMR spectra (CD2Cl2/CD3CN 3:7, 298 K) showing the changes in the peaks associated with the ─CH2─NH2+─CH2— moiety of axle 1 (a, c, e; 1H NMR) and the ─CF3 group of ring 2 (b, d, f; 19F NMR). (a) 1H NMR spectrum of E-1 (10 mM, 500 MHz). (b) 19F NMR spectrum of 2 (10 mM, 470 MHz). (c) 1H NMR (10 mM, 500 MHz) and (d) 19F NMR (10 mM, 470 MHz) spectra of an equilibrated 1:1 mixture of E-1 and 2. (e) 1H NMR (10 mM, 500 MHz) and (f) 19F NMR (10 mM, 470 MHz) of an equilibrated 1:1 mixture of E-1 and 2 after exhaustive irradiation at λ = 365 nm. The signals of the stations in a, c, and e are color-coded and those corresponding to stations encircled by a macrocycle are marked with a magenta dot. In (d) and (f), each coloured dot on a particular signal identifies the station encircled by the ring. The colours are coherent with those of the cartoons in Figure 2a, namely: blue, station E-I; orange, station Z-I; cyan, station II; magenta, ring 2. Given the impossibility to deconvolute the signals of the individual compounds, each label in the graph (except 2) refers to all the species that have the same azobenzene configuration and/or station occupancy. Hence, the signals labelled E-I are the convolution of the resonances of the species that possess an E-azobenzene unit and an uncomplexed station I, namely E-1 and E-1⊂2II; similarly, II = E-1 + E-1⊂2I + Z-1 + Z-1⊂2I; E-I⊂2 (or 2⊃E-I) = E-1⊂2I + E-1⊂(2)2; Z-I⊂2 (or 2⊃Z-I) = Z-1⊂2I + Z-1⊂(2)2. II⊂2 (or 2⊃II) = E-1⊂2II + E-1⊂(2)2 + Z-1⊂2II + Z-1⊂(2)2. See the text for details.#

(a) Concentration-time traces extracted from an array of 19F NMR spectra (470 MHz, 298 K) recorded on a mixture of E-1 (10.1 mM) and 2 (10.2 mM) in CD3CN/CD2Cl2 7:3 upon irradiation (yellow background) and in the dark (grey background). The spectra were recorded at intervals of 20 s, and irradiation was performed with light of λ = 369 ± 15 nm at an estimated photon flow of 4.65 × 10−8 Einstein s−1. About 300 s of irradiation were required to reach an E/Z photostationary state. (b) Simulated concentration profiles corresponding to the experimental conditions adopted in a. (c) Magnified view of the concentration profile of the free macrocycle 2 (experimental: magenta dots; simulated: pink line). (d) Concentration changes of free 2 extracted from an array of 19F NMR spectra (470 MHz, 298 K) recorded on a mixture of E-1 (9.8 mM) and 2 (11 mM) in CD3CN/CD2Cl2 7:3. The spectra were recorded at intervals of 10 s in a fatigue resistance test performed by alternating irradiation (300 s) and dark (300 s) periods. Irradiation was performed with light of λ = 369 ± 15 nm at an estimated photon flow of 8.46 × 10−8 Einstein s−1. The meaning of colors and labels is described in the caption of Figure 3.#

总结及展望#

本项工作标志着分子机器领域取得了重要进展，首次展示了一种能够自主收集并存储光能的人造分子泵系统。该系统不仅揭示了光驱动能量棘轮机制在分子尺度做功的巨大潜力，还通过完整的动力学和热力学参数表征，构建了详尽的机理模型。未来，这种基于自下而上策略构建的光活性纳米结构有望进一步优化。研究人员计划通过调整分子结构进一步提升泵送效率和储能密度，并尝试将其整合到更复杂的集成功能体系中。这一成果不仅为人工光合作用提供了新的视角，也为设计具有响应能力的智能材料提供了核心组件。