Molecular dynamics simulation study on the isomerization and molecular orientation of liquid crystals formed by azobenzene and (1-cyclohexenyl)phenyldiazene

Abstract

Atomistic molecular dynamics simulations have are used to investigate the liquid crystal systems based on [4-pentyl-(1-cyclohexenyl)]-(4-cyanophenyl)diazene (5CPDCN) and 4-cyano-4′-pentylazobenzene (5AZCN). The results show the growth process of a nematic phase from a disordered phase. Then the phase transition caused by isomerization reaction is studied based on a temporary modification of the dihedral potential. The properties of 5AZCN and 5CPDCN are compared, showing that the orientation of trans-5CPDCN is more highly ordered than trans-5AZCN. This can be attributed to the more extended dihedral angles φ₂ (i.e. the dihedral angle between the ring system and the terminal chain) in trans-5CPDCN enhance the rod-like conformation of the molecules. The orientational correlation functions g_l(r) (l = 1, 2) are also calculated, by which we find that both 5CPDCN and 5AZCN systems in nematic phase present parallel and anti-parallel dipole correlations. The anti-parallel dipole correlation is localized for the 5CPDCN system; on the contrary, the parallel dipole correlation is weakly localized for the 5AZCN system.