Novel organic crystals with red–violet metallic luster: 1-aryl-2-(2-thienyl)-5-[5-(tricyanoethenyl)-2-thienyl]pyrrole derivatives bearing a heteroatom combined methyl substituent

A new class of π-conjugated organic compounds that form crystals with red-violet metallic luster were obtained upon introduction of a heteroatom combined methyl substituent (OMe, SMe, or NMe2) into the para-position of the central N-phenyl group of 1-phenyl-2-(2-thienyl)-5-[5-(tricyanoethenyl)-2-thienyl]pyrrole. The molecule in crystals adopts a heaving ribbon-like molecular arrangement. This is obviously different from the planar arrangement of the gold-like analogues that bear halogen, cyano, or short alkyl group at para-position of the central N-phenyl group. Within the crystal lattice, an intermolecular C–H⋯N hydrogen bond occurs to make the adjacent π-systems (CN⋯CC) close enough, which is suggested to be responsible for the red-violet metallic color.