Photo-driven Molecular Wankel Engine

Arxiv – Photo-driven Molecular Wankel Engine (4 pages)

Technology Review – Clusters of boron atoms should behave like rotary Wankel engines when bathed in circularly polarised light. Nanotechnologists have identified many molecular motors and even a few rotary versions (ATP springs to mind). What makes this one special is that the polarised light doesn’t excite the molecule’s electronic ground state, leaving it free to be chemically active. By contrast, other forms of molecular power such as chemical or electric current can generate heat that has a critical effect on the system. For the moment, the photon-powered molecular Wankel engine is merely an idea, the result of some detailed chemical modelling.

We report a molecular Wankel motor, the dual-ring structure B13+, driven by circularly-polarized infrared elec-tromagnetic radiation, under which a guided uni-directional rotation of the outer ring is achieved with rotational frequency of the order of 300 MHz.

(a) Schematic of the outer ring rotation. Three identical counterclockwise elementary rotations are involved in the sequence 1-2-3-4. The orientation of the molecule is defined by the blue arrow, which is aligned with the C2v axis of the molecule. (b) Rela-tive ground state energies (left axis, solid black line) and vibrational frequencies (right axis, red dashed line) of the elementary rotation of the B13+ as a function of the angle when a constant electric field ( V/m) is applied. (less than 180º) is defined as the angle between the field direction and the molecule. The blue (red) region indicates that a counterclockwise rotation depicted in (a) is favored (unfavored) at a given angle (see text).

We propose a model molecular Wankel motor B13+ driven by circularly polarized IR radiation near 3 THz, as a potential building block for nano machines. The rotating fre-quency of the outer ring of is approximately 250 MHz. A simi-lar principle could be used for creating other uni-directrional molecular motors, based on pure boron, and other types of clusters.

The calculations were performed at density functional theory level with the Perdew-Burke-Ernzerhof (PBE) functional,10 plane-wave basis set and ultrasoft pseudopo-tentials implemented in Quantum Espresso.

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