Polymers containing bis(indolyl)maleimides and aminophenylsuccinimides as electroluminescent materials: Solvatochromic properties and the effect of blending toward white light emission

Polymers containing bis(indolyl)maleimides (P2b) and aminophenylsuccinimides (P1 and P3) were prepared from norbornene derivatives through ring-opening metathesis polymerization process. The chromophores P1-P3 exhibit intensive blue or red fluorescence in solutions, which showed significant solvatochromic effect due to intramolecular charge transfers. Mixing the blue emitting polymer with the red one formed a heterogeneous blend, which displayed dual emissions with compatible intensity. The light-emitting diodes (LEDs) fabricated by a single layer of such polymer blend displayed a broad range of visual colors depending on the relative ratio of the two components. White light can be obtained by a mixture of P1 (or P3) and P2b in a wt ratio of 10/3-10/5. The dual emission character was ascribed to the low miscibility between the two types of polymers, whereas energy transfer from the blue domain to the red one was retarded. The morphology of the solid film was verified by polarized-light optical microscopy. The emitting nature was also compared with those of random copolymers and monomer mixtures.