Acceptor Derivatization of the 4CzIPN TADF System: Color Tuning and Introduction of Functional Groups

Abstract

Abstract We demonstrate modular modifications of the widely employed emitter 2,4,5,6‐tetra(9H‐carbazol‐9‐yl)isophthalonitrile (4CzIPN) by replacing one or both nitrile acceptors with oxadiazole groups via a tetrazole intermediate. This allows the introduction of various functional groups including halides, alkynes, alkenes, nitriles, esters, ethers and a protected amino acid while preserving the thermally activated delayed fluorescence (TADF) properties. The substituents control the emission maximum of the corresponding emitters, ranging between 472–527 nm, and show high solid‐state photoluminescence quantum yields up to 85 %. The TADF emission of two compounds, 4CzCNOXDtBu and 4CzdOXDtBu, a mono‐ and a bis‐oxadiazole substituted 4CzIPN is characterized in detail by time‐ and temperature‐dependent photoluminescence. Solution‐processed OLEDs comprising 4CzCNOXDtBu and 4CzdOXDtBu show a significant blue‐shift of the emission compared to the reference 4CzIPN, with external quantum efficiencies of 16 %, 5.9 % and 17 % at 100 cd m−2, respectively.

Keywords

• thermally activated delayed fluorescence
• organic light emitting diodes (OLED)
• oxadiazoles
• color-tuning
• functionalization