Poly(dendrimers) with Phosphorescent Iridium(III) Complex-Based Side Chains Prepared via Ring-Opening Metathesis Polymerization

Abstract

Phosphorescent poly(dendrimers) with a norbornene-derived backbone have been synthesized using ringopening metathesis polymerization with the Grubbs III catalyst. The dendrimers are comprised of a heteroleptic iridium(III) complex core with two 2-phenylpyridyl ligands and a phenyltriazolyl ligand, biphenyl-based dendrons, and 2ethylhexyloxy surface groups. The phenyltriazolyl ligand provides the attachment point to the polymer backbone, and the two poly(dendrimers) differ in the number of dendrons attached to the 2-phenylpyridyl ligands. The poly(dendrimer) with one and two dendrons per ligand are termed mono-and doubly dendronized. The mono-and doubly dendronized poly(dendrimers) were found to have relatively narrow polydispersities, around 1.4, viscosities approaching those required for inkjet printing, and could be solution processed to form thin films. The dendrons played an important role in controlling the photophysical properties of the materials. The parent homopolymer with the same iridium(III) complex but no dendrons attached to the ligands had a solution photoluminescence quantum yield (PLQY) of 48%. The solution PLQY was found to increase with increasing number of dendrons with the mono-and doubly dendronized materials having solution PLQYs of 65% and 71%, respectively. The increase in PLQY is due to decreased intrachain interchromophore interactions. A similar trend was observed in the solid state with the parent, mono-, and doubly dendronized polymers having film PLQYs of 2%, 44%, and 58%, respectively, demonstrating that both intra-and interchain interactions are controlled by the dendrons.

An external quantum efficiency of >20% from solution-processed poly(dendrimer) organic light-emitting diodes

“…The norbornenyl-derived 1,3-divinylcyclopentane-polymer backbone was chosen as it could be formed by ring opening metathesis polymerisation to give materials with bulky dendritic side groups of high-molecular weight and relatively low polydispersity. 19,20 Gel permeation chromatography against poly(styrene) standards showed P1 had an Mw and dispersity of 1.6 × 10 5 Da and 1.3, respectively, and it is interesting to note that based on the number average molecular weight of the polymer and monomer, the degree of polymerisation can be calculated as ≈55 units, which would correspond to a polymer length (assuming an extended polymer chain) of ≈50 nm. Furthermore, it should be noted that P1 is a homopolymer, that is, every 'monomer' unit along the polymer backbone has a dendrimer attached.…”

Recent Advances in Polymer Organic Light-Emitting Diodes (PLED) Using Non-conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts

“…8) whose backbone was derived from norbornene using ring-opening metathesis polymerization (ROMP). 32 The key merit of these polymers was their narrower polydispersity index (PDI) of ca. 1.4 than those with polystyrene backbone (Ir-P1, DIr-P1 and DDIr-P1) 31 prepared by free-radical copolymerization (e.g., DDIr-P1 had a PDI as high as 4).…”

“…A high molecular weight is important to attain sufficient viscosity of the polymer solution for generating high-quality thin film. 32 Conjugated polymers with higher molecular weight are shown to have better charge mobility because long polymer chains serve as interconnections between ordered phases of the polymer film. 124 In addition, high-molecular-weight alternating copolymer of fluorene and MeH-PPV showed a much higher U PL of 61.2% than the low molecular weight analogue (U PL : 26.8%) whose short polymer chains were more rod-like, which resulted in more pronounced p-p stacking and hence greater energy transfer to the quenching site.…”

Luminescent poly(dendrimer)s for the detection of explosives

“…1), which were synthesised using a ring opening metathesis polymerisation. 24 The chromophores of the poly(dendrimer)s were all triphenylamine centred, as this moiety has been previously used in materials designed to detect nitro-based explosives, [25][26][27] and in some cases selective detection has been demonstrated. 25 The poly(dendrimer)s differ with respect to the conjugated unit attached to the triphenylamine centre.…”