9-Acridinecarboxylic acid hydrate is a heterocyclic aromatic compound featuring a carboxylic acid functional group attached to the acridine core. It is commonly supplied as a hydrate. The acridine moiety is a classic electron-rich, planar aromatic system, making this derivative a valuable building block in materials science. Its primary and most significant application is in the field of organic electronics and photonics. It serves as a key precursor for the synthesis of various functional materials, particularly for organic light-emitting diodes (OLEDs). The carboxylic acid group allows for easy derivatization and incorporation into larger conjugated systems or metal-organic complexes used as emitters, host materials, or electron-transporting materials (ETMs) in OLED devices. Its planar structure facilitates π-π stacking, which is beneficial for charge transport. Due to its well-defined heterocyclic structure and reactive handle, it is also utilized as a specialized organic synthesis building block in academic and industrial research for constructing more complex nitrogen-containing aromatic systems.