Control of the Aggregation of a Phenylenevinylenediimide Chromophore by Use of Supramolecular Chemistry: Enhanced Electroluminescence in Supramolecular Organic Devices
Résumé
A new approach toward the tuning of the supramolecular organization of π-conjugated substructures containing imide functional groups has been investigated using the concept of supramolecular chemistry. This approach, which allows enhanced emission properties of the active material, was evaluated in the fabrication of optoelectronic devices. A linear ditopic chromophore H-ImPV was synthesized. This N−H imide constitutes a recognizing unit with an acceptor−donor−acceptor (ADA) hydrogen bond motif. End-capping of this new chromophore with a monotopic structuring unit allowed control of the supramolecular aggregation of the π-conjugated chromophore. The studies of the absorption and emission properties of the H-ImPV, in solution or in the solid state (thin films, powders), clearly revealed different aggregation behaviors, depending on the presence of the monotopic structuring unit: hindered unit (Cy-DAT) led to the formation of J-aggregates. In all cases, evidence for the heteromolecular association H-ImPV···Cy-DAT was obtained from an infrared absorption band located at 2715 cm−1, which was typical of the hydrogen bonding present in the ADA···DAD triplet. This has been illustrated by the fabrication of light-emitting devices based on films of H-ImPV and [H-ImPV.(Cy-DAT)2]. H-ImPV presents a poor ability to emit light, because of its aggregation, which induces quenching of luminescence. The high efficiencies exhibited by the devices based on a single layer of [H-ImPV.(Cy-DAT)2] are the result of the J-aggregation of chromophores, because of the bulky cyclohexyl fragments of the Cy-DAT. Tuning of the supramolecular organization of the H-ImPV by the addition of two equivalents of Cy-DAT in the active layer allowed recovery of the performances exhibited by the organic light-emitting devices (OLEDs) of the isolated chromophore. Therefore, the use of Cy-DAT is an interesting alternative to avoid aggregation and to significantly increase luminance. As a consequence, the luminous efficiencies of the devices are much better for the coassembled active layer.