Comparative Theoretical Study on the Electronic Structures of the Isolated Molecular Gyroscopes with Polar and Nonpolar Phenylene Rotator

Abstract

Over the past decade, an assembly of the molecular components that produces quasi-mechanical movements in response to specific stimuli has become an intriguing research area. Interestingly, a rationally designed and strategically synthesized macroscopic gyroscope like molecular model with a closed topology has already demonstrated such remarkable behavior of the molecular machine. As its representative examples, the chemically synthesized siloxaalkane molecular gyroscopes (SMGs) with polar (e.g. ROT-2F and ROT-2Cl) and nonpolar (e.g. ROT-2H) rotating units (rotators) are considered here, and investigated their ground state electronic structures theoretically under non-crystalline condition by using density functional theory (DFT) model. We found this theoretical model has semiquantitatively reproduced one or more X-ray observed equilibrium structures of all the three SMGs. While comparing their DFT derived structures, the siloxaalkane spokes of the ROT-2F and ROT-2Cl are found to be deformed significantly as in experimental results, and this structural deformation is reconfirmed here by the DFT computed values of the “free volume” units present around each central rotator. The present DFT findings can be used to check whether its calculations are qualitatively agreed to the DFTB (Density Functional based Tight Binding) so that one can access the latter method directly while predicting reliable crystal structures and rotational dynamics of these SMGs under crystalline condition. This insight not only emphasizes the importance of molecular topology but also stresses the necessity of creating "free volume" unit around the central rotator to exhibit gyroscopic functions smoothly.