Phase-dependent intermolecular interactions of nematic liquid-crystal molecules probed by carbon K-edge x-ray absorption spectroscopy

This study employed carbon K-edge soft x-ray absorption spectroscopy (XAS) to investigate phase-dependent intermolecular interactions in the nematic liquid-crystal molecule 4-cyano-4'-pentylbiphenyl. Temperature-dependent XAS measurements revealed discontinuous shifts in core excitation peak energies across the solid, liquid-crystal, and liquid phases. Density functional theory calculations were used to assign spectral peaks to specific functional groups, namely, biphenyl and cyano, elucidating their distinct roles in intermolecular interactions. The results indicate that π-π interactions between biphenyl rings dominate in the solid phase, whereas in the liquid-crystal phase, antiparallel dimerization is primarily driven by interactions involving cyano groups. Overall, these findings demonstrate that soft XAS, combined with theoretical modeling, can provide critical insights into the weak intermolecular interactions that govern phase behavior in soft matter systems.