Theoretical research of second generation molecular motor with unidirectional rotary motion

Abstract

AbstractThe rotational process and conformation inversion of the second generation molecular motor (9‐(5‐methoxy‐2‐methyl‐2, 3‐dihydro‐1H‐cyclopentyl[a]naphthalene‐1‐subunit)‐9H‐fluorene) are calculated and analyzed by potential energy surface scanning at the level of density functional theory, the M06‐2X functional combined with the def‐TZVP basis set. The effects of four different donor–acceptor substituents on the molecular stability are mainly explored. The fully optimized geometries of molecular motors 1–5 are discussed at the M06‐2X/def‐TZVP theoretical level. The energy barrier analysis of molecular motors shows that the nature of the substituents will not have a significant impact on the thermal isomerization barrier of the motor. Theoretical analysis of frontier molecular orbital (FMO) shows that after replacing the methyl group with phenyl, methoxy, fluorine, and cyano, the stability of the molecule is reduced. It can be seen from the absorption spectrum that the substituent makes the molecular motor absorption peak significantly red shifted from the absorption spectrum. The study of nuclear magnetic resonance (NMR) shows that it may be affected by deshielding effects, and the substitution of the methyl substituent causes most of the chemical shift (δ) of the molecular motor to a downfield. Finally, it is verified that the conformation of the motors changed from a stable state to unstable state during the photoisomerization process. The calculated results have explained the rotation of molecular motor well and can be used in the design of molecular motor.