Influence of donor and acceptor substituents on the electronic characteristics of poly(fluorene-phenylene)

We investigate theoretically the influence of electron acceptors such as cyano groups and donors such as methoxy and amino groups on the geometric and electronic properties of the poly(9,9-dihexylfluorene-1,4-phenylene) unit cell. The trends derived from quantum chemistry calculations fully represent the properties observed at the scale of long polymer chains. It is shown that sizable effects can be obtained. In particular, the use of diamino or dicyano substituents on the phenylene ring allows the bandgaps to decrease significantly. This information is of prime importance in the design of new chemical structures aimed at a fine-tuning of the emitted color and at a significant improvement in quantum efficiency.