Molecular Crystals and Liquid Crystals, Vol.407, 553-561, 2003
Preparation and optical properties of uniaxially oriented dihydrodipyrazinopyrazine thin film
Two dicyanopyrazine derivatives (2,3,7,8-tetracyano-5,10-dimethyl-5,10-dihydrodipyrazino[2,3-b:2',3'-e]pyrazine (DM-dicyanopyrazine) and 2,3,7,8-tetracyano-5,10-di(n-dodecyl)-5,10-dihydrodipyrazino[2,3-b:2',3'-e]pyrazine (DD- dicyanopyrazine)) were synthesized by intermolecular cyclization of 2-alkylamino-3-chloro-5,6-dicyanopyrazines in the presence of triethyl amine. The crystal structures of DM- and DD-dicyanopyrazine were monoclinic, space group P2(1)/c with dimensions of a = 1.10 nm, b = 0.97 nm, c = 1.32 nm and beta = 100.17degrees, and space group P-2/1a with dimensions of a = 1.36 nm, b = 0.84 nm, 1.60 nm and beta = 88.9degrees, respectively. DM- and DD-dicyanopyrazine grew epitaxially on a friction-transferred PTFE layer from vapor phase. Dicyanopyrazine molecules adsorbed their side chain almost perpendicular to the substrate surface. The anisotropic features of the DM-dicyanopyrazine/PTFE and DD-dicyanopyrazine/PTFE double layers in optical properties were discussed based on the molecular orientation.