Quantum chemical DFT calculations of electronic and geometric structure of 4-(2-hexyloxy-ethoxy)-4`-cyano biphenyl (6O2OCB)

Density functional theory (DFT) calculations for 6020CB cyano biphenyl derivative were performed (using StoBe code). Total energy was calculated for different possible conformations of the rod-like molecule and the optimal conformation was found for the terminal chain lying in the plane of attached phenyl ring, whereas the rings of biphenyl were twisted ca. 35°. The calculation of molecular geometry with removal of restrictions for all atoms changed rod-like shape of molecule towards banana-like with the angle between axes of phenyl rings and chain ca. 150°. Electron densities for the lowest energy conformations were studied showing the decay of electron cloud at 2 Å. Finally the interactions of two molecules both rod-like and banana-like were also analyzed for different positions of rigid cores vs. terminal chains. Minimum energy criterion was used for each geometry of the system. It was found that rod-like conformations has reached the lowest energy for slightly shifted position of molecules whereas banana-like were packed close together. Many conformations with similar energies may give some hints towards interpretation of rich polymorphism of 6020CB which has been observed experimentally.