Quinquephenyl: The Simplest Rigid-Rod-Like Nematic Liquid Crystal, or is it? An Atomistic Simulation

We have performed an atomistic molecular-dynamics study on the molecular organization and liquid-crystalline properties of quinquephenyl (P5), a prototypical mesogen that is of interest for organic electronics. The thermotropic behavior reveals different mesophases. When cooling down from the isotropic phase, a transition to nematic (approximate to 715 K) is found, then a smectic S-A (approximate to 657 K) and another smectic, S-A(X) (approximate to 642 K), before a crystalline phase is recovered (approximate to 617 K). This phase sequence is compared with experimental findings. The different phases are described in terms of their molecular organization, orientational and positional order parameters, and pair distribution functions, as well as of their dynamics properties. In particular, the smectic phases that have not yet been characterized experimentally are discussed. By analyzing the effective shape of P5, it is concluded that its internal torsions and bending make it less rigid than could be expected