Recent Advances in the Design of Multi‐Substituted Carbazoles for Optoelectronics: Synthesis and Structure‐Property Outlook

Abstract Organic synthesis plays a pivotal role in the development of innovative organic functional materials for optoelectronic applications such as organic light emitting diodes (OLEDs), photovoltaics (OPVs), non‐linear optics (NLOs), field effect transistors (OFETs) and sensors. Chemical functionalization methods available for polyaromatic hydrocarbons (PAHs) are particularly attractive as they provide opportunities to fine‐tune the physicochemical, charge transporting and device parameters. Among the PAHs containing heteroatoms, carbazole is recognized as one of the most promising building blocks for assembling the functional materials for organic electronics, particularly for OLED and OPVs due to its unique features such as good hole transporting ability, excellent thermal and morphological stability, amorphous nature, low cost, high triplet energy and flexibility for functionalization. Until 2011, carbazole‐based functional materials were limited to use as a donor in donor–acceptor molecular configurations and as difunctionalized (C3,C6‐ or C2,C7‐ or N ‐) derivatives capable of hole transporting/emitting characteristics. Recently, polyfunctionalization on carbazole at various positions has drawn significant attention as a result of their promising structure–function relationships. Although some reviews have focused on structure–property relationships within difunctionalized carbazoles, recent synthetic advances in the field of polyfunctionalized carbazoles and their resultant structure–property relationships remain unreviewed. To bridge this gap, in this article we review newly emerged synthetic approaches for polyfunctionalization of carbazole and discuss the effects of substitution pattern, chromophore nature and its density on the photophysical and device properties.