S-Vinyl Sulfide-Derived Pendant-Type Sulfone/Phenoxazine-Based Polymers Exhibiting Thermally Activated Delayed Fluorescence: Synthesis and Photophysical Property Characterization

Pendant sulfone/phenoxazine-based homo- and copolymers were synthesized via the radical (co)polymerization of 4-bromophenyl vinyl sulfide (BPVS) and styrene (St) followed by oxidation of the thus-produced sulfides, P(BPVS) and P(BPVS-r-St)s, to the corresponding sulfones and Pd-catalyzed coupling with phenoxazine-substituted phenyl boronate ester (PXZPhBpin) to afford P(PVSO2-PhPXZ) and P(PVSO2-PhPXZ-r-St)s, respectively. The prepared homo- and copolymers, featuring a π-conjugated phenylene unit between the electron-accepting sulfone (SO2) unit and the electron-donating phenyl phenoxazine (PhPXZ) unit in their side chains, exhibited thermally activated delayed fluorescence (TADF) and were used to fabricate organic light-emitting diodes (OLEDs). The device with spin-coated P(PVSO2-PhPXZ) as an emitting layer showed a maximum external quantum efficiency (EQEmax) of 1.0%, whereas that with an emitting layer of spin-coated 75 mol %-St P(PVSO2-PhPXZ-r-St) exhibited efficient bluish-green emission with EQEmax = 4.1%. The presented design strategy allows one to manipulate the polarity and electrochemical properties of pendant units as well as design molecular structures with suitable spacers between donor and acceptor units in the TADF side chain, thus helping to achieve the desired (opto)electronic properties. Thus, this work significantly extends the range of nonconjugated TADF polymers and paves the way for the fabrication of next-generation OLEDs.