Calculations of Molecular Rotors and Motor

Abstract

We use Newton equations of motion and Universal Force Field to simulate large systems containing altitudinal and azimuthal molecular rotors. Gas flow, water flow, electric fields and light absorption are used to drive the rotors. These devices might be useful in electronics, molecular electronics and to decrease the friction of surfaces and interfaces. While most of the investigated structures work fine in gas flow, only little response was found in water flow. We want to implement massive new simulations to find out what rotors are needed to work also in the water flow. Recently we have also designed a synthetically accessible active rotor molecule that contains a paddlewheel on an axis, and performed molecular dynamics simulations that suggest that the absorption of a pulse of light will cause the rotor to make half a turn in the course of a few picoseconds, soon thereafter completed to a full turn. A train of light pulses would thus be expected to induce a fast and steady unidirectional rotation of the rotor, which could be used to propel a thin layer of a fluid along a surface (molecular pump) if the rotors were mounted in an organized array on a surface. The principle behind the drive is charge separation upon excitation followed by electrostatic attraction of the now positively charged donor (one of the paddles on the wheel) to the now negatively charged acceptor (located asymmetrically next to the paddlewheel), and thermal relaxation to the starting position. The structure has been designed in a way that favors unidirectional motion. A customized molecular dynamics simulation program was used in the calculations.