Substitution degree engineering the crystal packing and optoelectronic properties of benzofuranvinylsubstituted benzene-cored derivatives

In order to explore new furan-based functional materials, investigate the effect of the degree of branching on their optoelectronic properties and search for three-dimensional organic semiconductors from planar p-conjugated molecules, the compounds 1,4-bis[2-(benzofuran-2-yl) vinyl] benzene (2BFVB) with a linear shape, 1,3,5-tris[2-(benzofuran-2-yl) vinyl] benzene (3BFVB) with a star shape and 1,2,4,5-tetra[2( benzofuran-2-yl) vinyl] benzene (4BFVB) with a cruciform shape were synthesized and compared. 2BFVB adopts a two-dimensional herringbone packing motif and there are two kinds of molecular conformation. The crystal packing of 3BFVB is more sensitive to the crystallization conditions. Two single-crystal phases and one thin-film phase were found. 3BFVB (b-phase) molecules pack into a threedimensional cofacial herringbone structure. 4BFVB forms an inter-inserted two-dimensional hexagonal packing structure. The molecular shape and aggregate packing exert remarkable effects on the optoelectronic properties. The quantum yield of 2BFVB is very high both in the solution (74%) and in the crystalline solid (76%) states. The high solid emission efficiency of 2BFVB is possibly related to the two molecular conformations in the herringbone-arranged H-aggregates. Both 2BFVB and 3BFVB display hole-transport abilities. The performance of 3BFVB amorphous film is nearly equal to that of its crystalline film, which would be helpful in simplifying device fabrication. This study shows that the substitution degree exerts drastic effects on solubility, polymorphism, crystal packing and optoelectronic properties.