Bridging Small Molecules to Conjugated Polymers: Efficient Thermally Activated Delayed Fluorescence with a Methyl‐Substituted Phenylene Linker

Abstract

Based on a “TADF + Linker” strategy (TADF=thermally activated delayed fluorescence), demonstrated here is the successful construction of conjugated polymers that allow highly efficient delayed fluorescence. Small molecular TADF blocks are linked together using a methyl‐substituted phenylene linker to form polymers. With the growing number of methyl groups on the phenylene, the energy level of the local excited triplet state (3LEb) from the delocalized polymer backbone gradually increases, and finally surpasses the charge‐transfer triplet state (3CT). As a result, the diminished delayed fluorescence can be recovered for the tetramethyl phenylene containing polymer, revealing a record‐high external quantum efficiency (EQE) of 23.5 % (68.8 cd A−1, 60.0 lm W−1) and Commission Internationale de l′Eclairage (CIE) coordinates of (0.25, 0.52). Combined with an orange‐red TADF emitter, a bright white electroluminescence is also obtained with a peak EQE of 20.9 % (61.1 cd A−1, 56.4 lm W−1) and CIE coordinates of (0.36, 0.51).

Tris(triazolo)triazine-based emitters for solution-processed blue thermally activated delayed fluorescence organic light-emitting diodes

“…TADF polymers have shown promise as emitters in solution-processed devices. 23,[26][27][28] However, the synthesis of polymers will lead to a mixture of compounds with different molecular weight, each of which will have a slightly different set of photophysical properties that will result in a broadened emission spectrum. 29 Moreover, the photophysical properties of TADF polymers usually suffer due to quenching via intra-and inter-molecular charge transfer between the TADF units on the polymer.…”

An Electroactive Pure Organic Room‐Temperature Phosphorescence Polymer Based on a Donor‐Oxygen‐Acceptor Geometry

“…Finally, a nucleophilic aromatic substitution polymerization [32] between M1 and M2 was performed to afford P(DMPAc‐O‐TPTrz) with a D‐O‐A geometry. For comparison, the reference polymer P(DMPAc‐TPTrz) with a D‐A geometry was simultaneously synthesized via a Suzuki polymerization [33] . Their molecular structures were thoroughly characterized by 1 H and 13 C NMR, elementary analysis and gel permeation chromatography (GPC).…”

“…Nevertheless, their electrophosphorescence device applications under electric excitation have been seldomly reported so far [30] . The main reason is that these RTP polymers are not suitable for polymer light‐emitting diodes (PLEDs), [31–33] because most of used polymer matrixes including poly(methyl methacrylate) (PMMA), [23, 24] poly(vinyl alcohol) (PVA), [19, 25] poly(lactic acid) (PLA), [26, 27] and poly(acrylamide) (PAM) [28, 29] are electrically insulating.…”

Recent Advances in Thermally Activated Delayed Fluorescent Polymer—Molecular Designing Strategies

“…Through device optimization, the efficiency of the PLED based on P(BOPACTRZ-BPA) reaches 29.7 cd/A (21.2 lm/W, 13.2%) with a small roll-off, and the CIE coordinate is (0.18, 0.32). Recently, the team (Rao et al, 2020 ) made breakthroughs in conjugated TADF polymers. They designed a variety of methyl substituted phenylene linking units as backbone spacer groups, and through polymerization of these groups with D-A-D TADF fragments (AcBPCz), successively synthesized a series of TADF conjugated polymers, Poly(AcBPCz-P), Poly(AcBPCz-DMP), and Poly(AcBPCz-TMP), as shown in Figure 9 .…”