| Summary: | The design, synthesis and photophysics is presented for a new series of fluorescent carbazole-2,5-diphenyl-1,3,4-oxadiazole dyad molecules and in which the topology and electronic properties are systematically varied by chemical modification. Cyclic voltammetric data, HOMO-LUMO calculations, and X-ray crystallographic analyses are also presented. Our study sheds new light on designing ambipolar molecules and we demonstrate a strategy for precisely tuning the singlet and triplet levels in charge transfer molecules. A family of new 2,5-diphenyl-1,3,4-oxadiazole (OXDs) derivatives bearing ortho-alkyl substituents on one of the phenyl rings is reported. The reactions of these OXDs with IrCl3 under standard cyclometalating conditions did not give the usual μ-dichloro bridged diiridium OXDs complexes. Instead, novel diiridium complexes and monoiridium complexes were isolated and characterised by X-ray crystallography. It is proposed that the unusual structures arise due to the ortho-alkyl substituents leading to a substantial twisting of part of the OXDs system which, for steric reasons, changes the normal course of the metal-ligand coordination reactions. A new high triplet host polymer was synthesised and characterised. Photophysical studies and device data are presented. The triplet energy of this polymer is 2.73 eV. Also, the unoptimised device efficiency (device architecture: ITO/PEDOT:PSS/8% 145 and 40 wt% OXD-7 doped in polymer 133/Ba:Al) is 4.5 cd/A. Our study sheds new light on designing high triplet polymers and we demonstrate a strategy for possessing a high triplet level in a polymer by interrupting the conjugation on the polymer backbone.
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