Enhanced Charge-Transfer Emission in Polyimides by Cyano-Groups Doping

Conjugated polyimides (PI) are successfully synthesized by chemical imidization through in situ silylation of diamines by the alteration of different donor–acceptor monomers. A detailed photophysical characterization is performed in the monomers and different polymers in tetrahydrofuran solutions. The emission spectra of the related donor–acceptor polymers with electron withdrawing cyano groups showed broader and more intense fluorescence bands in comparison to the polymer without −CN groups. The new emission band results from the contribution of two different charge-transfer (CT) pathways: (i) An intramolecular CT (ICT) state in the donor monomers due to the presence of strong electron withdrawing CN groups, and (ii) a intramolecular CT complex (CTC) in the PI polymer between the donor–acceptor monomers, which is red-shifted and shows longer lifetime respect to the ICT of the diamine monomers. The very wide emission band is a very interesting feature for obtaining white light from UV light.