Effect of molecular shape on the optoelectronic properties of benzothienylvinyl-substituted benzene-cored derivatives

In order to investigate the effect of molecular shape on the optoelectronic properties, compounds 1,4-bis[2-(benzothien-2-yl)vinyl]benzene (2BTVB) with linear shape, 1,3,5-tris[2-(benzothien-2-yl)vinyl]benzene (3BTVB) with star shape and 1,2,4,5-tetra[2-(benzothien-2-yl)vinyl]benzene (4BTVB) with cruciform shape were synthesized and compared. The molecular shape exerts marked effects on the thermal stability, film morphology and optoelectronic properties. Compounds 2BTVB and 3BTVB are thermally stable before the melting point. In contrast, 4BTVB solid is decomposed upon heating. Single-crystal structure analyses show that 3BTVB molecules pack into a three-dimensional cofacial herringbone structure. In comparison with 2BTVB and 4BTVB, both the absorption and emission spectra of 3BTVB display a blue-shift feature. This is possibly related to the discontinued π-conjugation through meta-substitution. The evaporated film of 2BTVB is high crystalline. In contrast, 3BTVB molecules pack disorderly in the evaporated film. The molecular shape and film morphology exert remarkable effects on the carrier-transport ability.