Organic light‐emitting diodes (OLEDs) have come a long way ever since their first introduction in 1987 at Eastman Kodak. Today, OLEDs are especially valued in the display and lighting industry for their promising features. As one of the research fields that equally inspires and drives development in academia and industry, OLED device technology has continuously evolved over more than 30 years. OLED devices have come forward based on three generations of emitter materials relying on fluorescence (first generation), phosphorescence (second generation), and thermally activated delayed fluorescence (third generation). Furthermore, research in academia and industry toward the fourth generation of OLEDs is in progress. Excerpts from the history of green, orange‐red, and blue OLED emitter development on the side of academia and milestones achieved by key players in the industry are included in this report.

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 temperaturedependent 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 À 2 , respectively.

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