Heorhi K. Belavusau1, Aliaksei A. Vaitusionak1,2, Irina V. Vasilenko1, Juozas V. Grazulevicius2, Sergei V. Kostjuk3
1Research Institute for Physical Chemical Problems of the Belarusian State University, 14 Leningradskaya St., 220006, Minsk, Belarus – Email: george.vusau@gmail.com
2Department of Polymer Chemistry and Technology, Kaunas University of Technology, K. Barsausko g. 59, 51423, Kaunas, Lithuania
3Sorbonne Universite, CNRS, Institut Parisien de Chimie Moleculaire, Equipe Chimie des Polymeres, 4 place Jussieu, 75252 Paris Cedex 05, France
Recent advancements in the field of emissive materials for OLEDs have been characterized by two predominant trends. Firstly, there has been a notable inclination toward the thermally activated delayed fluorescence (TADF) mechanism of electroluminescence, a phenomenon that facilitates the attainment of high quantum yields without the necessity of using heavy metals. Secondly, there has been a transition from low-molecular-weight emitters to polymers, a shift that significantly streamlines the OLED manufacturing process by enabling the utilization of "wet" methods (spin-coating, inkjet printing, etc.) instead of expensive vacuum deposition. In addition, polymeric emitters are characterized by much higher morphological and thermal stability than organic TADF materials that allows devices based on them to be exploited longer.
In our work, a new strategy for the synthesis of polymeric through-space charge-transfer TADF emitters with tunable colour of the emission from blue to orange is reported (Figure 1). The strategy is based on RAFT-mediated alternating copolymerization of styrene-based donor monomers with acceptor maleimide-type monomers. Most of these alternating copolymers exhibit exciplex emission via through-space charge-transfer mechanism and display aggregation-induced emission. The alternating copolymers in solid state demonstrated delayed fluorescence with the lifetimes in the range between 0.35 and 6.2 µs making them promising materials for emitting layers of OLEDs. Indeed, multicolor hosts-free solution-processable TADF OLEDs were fabricated using the synthesized copolymers as blue, green and orange emitters. The devices showed good stability of electroluminescence spectra at the different voltages, with the highest external quantum efficiency of 7.84 % was reached for green device.