Albu Nicolae M, Bergin Edward, Yaron David J
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
J Phys Chem A. 2009 Jun 25;113(25):7090-6. doi: 10.1021/jp811521s.
Light-driven molecular motors may be useful for nanotechnology applications. The possibility of building such a motor based on the tolane framework is explored here. In the ground electronic state of tolane, the barrier to internal rotation is comparable to room temperature thermal energies, k(B)T. The barrier increases substantially in the excited state, causing the molecule to planarize after absorption of a photon. This tendency to planarize may be converted into unidirectional rotational motion by placing chiral substituents on the phenyl rings. A potential advantage of this class of motors is that they may undergo rapid, nanosecond scale rotation. Computational design of appropriate substituents was done using semiempirical quantum chemical methods, SAM1 for the ground electronic state coupled to INDO for the excitation energy. The torsional surfaces of the best candidate were then generated using ab initio DFT methods, which confirm that the molecule should undergo unidirectional rotation upon photoexcitation. The results provide a proof of principle for this class of motors; however, two aspects of the final candidate are nonideal. First, although the design goal was to use steric interactions between substituents to induce the rotation, decomposition of the interaction energy suggests attractive interactions play a role. Solvent interactions may interfere with these attractive interactions. Second, TDDFT calculations suggest that interactions between excited states lower the rotational driving force in the excited state.
光驱动分子马达可能对纳米技术应用有用。本文探讨了基于二苯乙炔骨架构建此类马达的可能性。在二苯乙炔的基态电子态中，内旋转势垒与室温热能(k_BT)相当。在激发态下，势垒大幅增加，导致分子在吸收光子后平面化。通过在苯环上放置手性取代基，这种平面化趋势可转化为单向旋转运动。这类马达的一个潜在优势是它们可能进行快速的纳秒级旋转。使用半经验量子化学方法进行了合适取代基的计算设计，基态电子态用SAM1，激发能用INDO。然后使用从头算DFT方法生成了最佳候选分子的扭转面，证实该分子在光激发时应进行单向旋转。这些结果为此类马达提供了原理证明；然而，最终候选分子的两个方面并不理想。首先，尽管设计目标是利用取代基之间的空间相互作用来诱导旋转，但相互作用能的分解表明吸引相互作用也起作用。溶剂相互作用可能会干扰这些吸引相互作用。其次，含时密度泛函理论计算表明，激发态之间的相互作用会降低激发态下的旋转驱动力。
