Twisted Carbazole Dendrons for Solution-Processable Green Emissive Phosphorescent Dendrimers

Abstract

A family of first-generation dendrimers containing 3,5-bis(carbazolyl)phenyl dendrons attached to a green emissive fac-tris(2-phenylpyridyl)iridium(III) core were prepared. The solubility of the dendrimers was imparted by the attachment of tertbutyl surface groups to the carbazole moieties. The dendrimers differed in the number of dendrons attached to each ligand (one or two dendrons) as well as the degree of rotational restriction within the dendrons. The densities of the films containing the doubly dendronized materials were higher than those of their mono-dendronized counterparts, with the dendrimer containing two rotationally constrained dendrons per ligand having the highest density at 1.12 ± 0.04 g cm −3 . The dendrimers were found to have high photoluminescence quantum yields (PLQYs) in solution of between 80 and 90%, with the doubly dendronized materials having the lower values and a red-shifted emission. The neat film PLQY values of the dendrimers were less than those measured in solution although the relative decrease was smaller for the doubly dendronized materials. The dendrimers were incorporated into solution-processed bilayer organic light-emitting diodes (OLEDs) composed of neat or blend emissive layers and an electron transport layer. The best-performing devices had the dendrimers blended with a host material and external quantum efficiencies as high as 14.0%, which is higher than previously reported results for carbazoleincorporating emissive dendrimers. A feature of the devices containing blends of the doubly dendronized materials was that the maximum efficiency was relatively insensitive to the concentration in the host between 1 and 7 mol %.

Exploring the Versatile Uses of Triplet States: Working Principles, Limitations, and Recent Progress in Phosphorescence, TADF, and TTA

“…Apart from these typical TADF molecules, researchers have also extended these structures to design of TADF polymers and macromolecules (e.g., dendrimers), ,− aiming to improve the capability of solution-processing materials, potentially reduce processing cost, and enhance suitability for large-scale applications. − Among the examples, Hudson et al . designed a TADF dendimer based on the BPPZ acceptor substituted with dendritic donors, while Yang et al .…”

Effect of dendrimer generation and surface groups on the optoelectronic properties of green emitting bis-tridentate iridium(iii) complexes designed for OLEDs

“…In the latter case, dendronisation of the iridium(III) complex has led to solution-processable materials and OLEDs with good efficiencies in simple architectures. [5][6][7][8][9] Phosphorescent light-emitting dendrimers have generally been designed to have the emissive iridium(III) complex at the core, with the dendrons reducing core-core interactions that can lead to a decrease in the PLQY in the solid state. It has been previously shown that dendron generation, surface groups, and/or the number of dendrons attached to the complex can be used to control solubility and intermolecular interactions.…”

Theoretical investigation of the influence of heterocycles on the radiative and non-radiative decay processes of iridium(iii) complexes

“…Because of their good color purities, high quantum efficiencies, relatively short phosphorescence lifetimes and high thermal stabilities, iridium(III) complexes are being applied as phosphorescent materials for OLEDs. [1][2][3][4][5][6][7][8][9][10][11] For Ir(III)cyclometalate complexes, the metal-to-ligand charge transfer ( 3 MLCT) involved in the emissive triplet excited state and the rigid octahedral structure can effectively facilitate the radiative decay process and suppress the non-radiative decay route. In addition, the color purities of iridium(III) complexes can be tuned via the addition of various substituents.…”