Strategies for Enabling RGB Emission in Fused Carbazole Derivatives

The development of organic light-emitting diodes (OLEDs) has witnessed remarkable progress in material design and device architecture. Recent advancements, particularly in the fourth generation of OLEDs, have introduced groundbreaking innovations such as hyperfluorescence and multiresonance (MR) thermally activated delayed fluorescence (MRTADF) emitters. Carbazole has emerged as a versatile scaffold, playing a pivotal role in conventional fluorescence, TADF, roomtemperature phosphorescence (RTP), and MRTADF systems. In recent years, fused carbazole derivatives have gained significant attention as both emitting and host materials in OLEDs. The fusion of carbazole units enhances molecular rigidity and extends the πconjugation, enabling precise tuning of optoelectronic properties across a wide color gamut, including blue, green, orange, yellow, and red emissions. This review systematically explores the application of various fused carbazole systems such as indolocarbazole, thienocarbazole, furocarbazole, indenocarbazole, triazatruxene, acridinecarbazole, chromenocarbazole, pyrenocarbazole, helicene carbazole, and carbazolefused boron/carbonyl MRTADF emitters in OLEDs. The discussion is organized into three sections based on their application in blue, green, and red OLEDs, providing a comprehensive understanding of structure-property relationships. Additionally, other color-emitting OLEDs are discussed where relevant, offering a holistic perspective on the potential of fused carbazole derivatives in next-generation OLED technologies.