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We report the development of light-emitting dendrimers with heteroleptic or homoleptic iridium(III) complexes at the core, with one, two, or three first- or second-generation biphenyl-based dendrons attached to the 2-phenylpyridyl ligand that is involved in the emission of light. The 5-phenyl-1-methyl3-n-propyl-1H-1,2,4-triazole co-ligand was not dendronised and was not involved in the emission process. The dendrimers with two emissive ligands were found to have the highest solution photoluminescence quantum yields (PLQYs) which were greater than 90% independent of the dendrimer generation. The second-generation dendrimers were all found to have higher neat film PLQYs than their first-generation counterparts due to the increased shielding of the emissive core by the dendrons and surface groups. The maximum external quantum efficiencies of devices made from the neat film and a guest:host blend of the second-generation dendrimer with two emissive ligands were found to be the highest (7.5% and 15.8%, respectively), which was attributed to a balance between the interactions required for charge transport and minimising those that lead to non-radiative processes. Thus, we have demonstrated that combining dendrimer generation and number of emissive dendronised ligands is a viable strategy for optimising light-emitting dendrimer OLED performance. [ABSTRACT FROM AUTHOR]

A series of solution-processable green emitting dendronised bis-tridentate iridium(III) complexes composed of [2,6-diimidazolylidene]benzene and the dianionic ligand, 2-[3-(trifluoromethyl)-1H-pyrazol-5-yl]-6-[4-(trifluoromethyl)phenyl]pyridine, have been synthesised to investigate the role of surface groups (t-butyl versus 2-ethylhexyloxy) and dendron generation (first versus second) on the photoluminescent (PL) and electroluminescent (EL) properties of the dendrimers. The dendrimers exhibited similar solution photoluminescent quantum yields (PLQYs) in toluene (60–70%) independent of the surface groups and dendrimer generation. In contrast, the PLQY values of the second-generation dendrimers were significantly higher than those with the first-generation dendrons in the neat film due to the higher generation dendrons providing more effective encapsulation of the emissive cores. When the dendrimers were blended at a concentration of 2 mol% in tris[4-carbazoyl-9-ylphenyl]amine (TCTA) the PLQYs increased but were still below the values measured in solution suggesting that the dendrimers were not evenly distributed throughout the host. Emission from the guest and host in the 2 mol% blends provided evidence for uneven distribution of the guest and inefficient energy transfer from the host to the dendrimers. The difference in encapsulation of the cores by the dendrons also affected charge transport in the neat films. In the case of the second-generation dendrimer with 2-ethylhexyloxy groups, the hole mobility was <10−8 cm2 V−1 s−1, which was an order of magnitude lower than for the less sterically encumbered dendrimers. Simple two-layer organic light-emitting diodes (OLEDs) with a solution-processed light-emitting layer were prepared. The best of the host-free devices exhibited a maximum external quantum efficiency (EQE) of 13.4%. The devices with the dendrimers blended with TCTA had more uniform EQEs of 12.2% to 13.5%, which are amongst the highest reported for solution-processed OLEDs containing a bis-tridentate iridium(III) complex emitter. Finally, it was found that devices containing the dendrimer with the t-butyl surface groups had greater stability. [ABSTRACT FROM AUTHOR]

Cyclohexa-2,4-dien-1-one derivatives, upon reaction with N-heterocycles in the presence of scandium(III) triflate, underwent a tandem Michael addition reaction followed by aromatization of the Michael adduct generated in situ to give N-aryl heterocycles in good yields. Because of the ready accessibility of variously substituted cyclohexa- 2,4-dien-1-ones, a range of N-aryl heterocycles have become available. [ABSTRACT FROM AUTHOR]

A facile pyridine-mediated α-halogenation approach to functionalize cyclohexa-2,4-dienones is developed. A range of reactions, including organometallic coupling protocols, have been applied on these newly obtained halogenated cyclohexa-2,4-dienones, and the results are presented herein. [ABSTRACT FROM AUTHOR]