4′-Octyloxy-4-biphenylcarbonitrile (8OCB), CAS number 52364-73-5, is consisted of a biphenyl structure with octyloxy and cyano groups at 4,4'-postions. 8OCB belongs to the well known family of liquid crystal 4-oxy-4'-cyano­biphenyls (OCBs). In its solid form, 8OCB packs in lamellar-type bilayers structure, through hydrogen bonding induced by the CN group.

Three different metastable crystal polymorphs of 8OCB are observed from grown from its solution, square-plate, needle phase and long parallelepiped (PP) phase. Two different crystalline states of 8OCB are observed on cooling from its melt, a metastable long parallelepiped (PP) crystal phase and a stable crystal phase known as the commercial powder (CP) phase. Three transition temperatures temperature are measured for 8OCB from its crystal from to isotropic solution, crystalline–smectic A transition temperature, TCrA = 52.86 °C, smectic A–nematic transition temperature, TAN = 66.65 °C, and nematic–isotropic transition temperature, TNI = 79.10 °C.

Binary system of 4-octyl-4′-cyanobiphenyl (8CB) and 4-octyloxy-4′-cyanobiphenyl (8OCB) mixture also shows the existence of three phase transitions, crystalline-smectic A, smectic A-nematic, and nematic-isotropic transitions. The maximum absorption wavelength of the 8CB/8OCB mixtures decreases with increasing percent weight of 8CB in 8OCB.

When presented in P3HT:PC60BM mixture, 4′-octyloxy-4-biphenylcarbonitrile molecules in the liquid crystalline state offer good template for the crystallization of P3HT, as well as the phase separation between P3HT and PCBM. A maximum PCE value of 3.5% was achieved by incorporating of 6 wt% nematic liquid crystals (NLCs) of 8OCB in P3HT:PC60BM active layer mixture, after annealing at the temperature of 70 °C in liquid crystalline transitions.

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