Thermally Activated Delayed Fluorescence Emitters Based on a Special Tetrahedral Silane Core

Narrowband Emissive Solution-Processed Polymer Organic Light-Emitting Diodes with External Quantum Efficiency Above 30

Achieving both high-efficiency and narrowband emission in thermally activated delayed fluorescence (TADF) polymers remains a formidable challenge. In this work, a proof of concept for narrowband-emissive TADF polymers with a partially conjugated structure is proposed by embedding a silicon─carbon σ-bond saturated spacer between the multiresonance (MR) TADF unit and the polycarbazole backbone. A series of TADF polymers PSix (x = 1, 3, and 6) is then prepared and characterized. All the polymers show narrowband emission with full width at half maximum (FWHM) values of 28-30 nm in a toluene solution. Impressively, polymer PSi3 has the highest photoluminescence quantum yield, reaching 97%, in the doped films due to the efficient reverse intersystem crossing process. The solution-processed devices based on PSi3 exhibit the best performance with a maximum external quantum efficiency (EQEmax) of 28.8% and an FWHM of 42 nm. By employing the TADF molecule 5Cz-TRZ as the sensitizer, enhanced device performance with an EQEmax of 30.2% is achieved, which is in the first tier among the MR-TADF polymers reported to date. This work provides an effective strategy for achieving highly efficient and narrowband-emissive TADF polymers by controlling the σ-bond saturated spacer between the MR-TADF chromophore and the polymer backbone.

Strategic Insertion of Heavy Atom to Tailor TADF OLED Material for the Development of Type I Photosensitizing Catalytic Red Emissive Assemblies

The work presented in the manuscript describes a simple strategy for transforming thermally activated delayed fluorescent organic light-emitting diodes (TADF OLEDs) compound 10-(dibenzo[a,c]phenazin-11-yl)-10H-phenoxazine (DPZ-PXZ) into type I photosensitizer 10-(dibenzo[a,c]phenazin-11-yl)-10H-phenothiazine (DPZ-PHZ) by strategically introducing sulfur atom in the photosensitizing core. The synthesized compound DPZ-PHZ exhibits aggregation-induced enhancement (AIE) and through-space charge transfer (TSCT) characteristics and generates red emissive assemblies in mixed aqueous media. The original compound DPZ-PXZ exhibits well-separated HOMO and LUMO levels and is reported to have highly efficient reverse intersystem crossing (RISC). In comparison, the incorporation of sulfur atom in the phenothiazine donor regulates the electronic communication between donor and acceptor units and promotes the intersystem crossing (ISC) in DPZ-PHZ molecules. Interestingly, compound DPZ-PHZ exhibits rapid activation of aerial oxygen for instant generation of superoxide radical anion. Backed by excellent type I photosensitizing activity, DPZ-PHZ assemblies have high catalytic potential for the synthesis of benzimidazoles, benzothiazoles and quinazolines derivatives under mild reaction conditions. The work presented in the manuscript provides an insight into the combination of heavy atom approach and TSCT for achieving adequate electronic communication between donor and acceptor units, balanced RISC/ISC, and stabilized-charge separated state for the development of efficient type I photosensitizing assemblies.