Four Distyryl Derivatives Designed by Mathematical Combination of Five Benzene Rings and Two Double Bonds: Effect of Minor Backbone Modification on the Optoelectronic Properties

The different combinations of five benzene rings and two CC double bonds yield four isomers: 4,4″-bistyryl-p-terphenyl (BSTP), 4-styryl-4′-[2-(p-biphenyl)vinyl]biphenyl (SBVB), 1-styryl-4-[2-(p-terphenyl)vinyl]benzene (STVB), and 1,4-bis[2-(p-biphenyl)vinyl]benzene (BBVB). The position variations of two CC double bonds affect aggregate microstructures, as well as thermal and optoelectronic properties. Except BBVB, the other three isomers all have a phase transition upon heating. X-ray diffraction and optical absorption analyses reveal that the molecules of four isomers all take an H-aggregation in the crystalline solid. However, the microstructures are different for orientation disorder exists in STVB crystals. Both the absorption and emission spectra of these four isomers display a bathochromic shift when the position interval between two double bonds ranges from three, two, to one benzene rings. The CH2Cl2 solutions of these four isomers are highly emissive with quantum yields ranging from 83% to 96%. Intriguingly, though the molecules crystallize into an H aggregation, the quantum yields of polycrystalline samples are also extraordinarily high, from 73% to 94%. All the isomers display moderate hole-transport ability. Different-oriented grains coexist in the vacuum-deposited films, which play different roles in the carrier transport.