Theoretical investigation of electroluminescent alkoxy substituted 4,4′-bis(2-phenylethenyl)biphenyls as guest in blue OLEDs

A quantum-chemical investigation on the structural and opto-electronic properties of several alkoxy substituted 4,4′-bis(2-phenylethenyl)biphenyls (PEBP) as building blocks for π-conjugate polymer is performed in order to display the effect of changing the position of alkoxy substituents on the peripheral phenyl rings on their opto-electronic and physico-chemical properties. Added to the good agreement between theoretical and experimental observations, it has been observed that the substitution effect depends on the position of the methoxy group: in ortho- or para-positions it acts as a mesomeric electrons donor, while as an inductive electrons acceptor in meta-positions. Substitution in ortho-positions causes significant structural deformations of PEBP backbone due to the steric interaction between the substituents and the hydrogens of the vinylene functions. Bridging of ortho, para-PEBP (24PEBP) by CC(CN)2 decreases significantly its band gap. This model can have very interesting opto-electronic ownerships.