Phenanthrene-9-carboxylic acid is primarily used in organic synthesis and research applications due to its unique structural properties. It serves as a building block in the development of complex organic compounds, particularly in the synthesis of pharmaceuticals and dyes. Its rigid polycyclic aromatic structure makes it valuable in studying molecular interactions and designing materials with specific electronic properties. Additionally, it is utilized in the field of fluorescence studies, where its aromatic system aids in understanding photophysical behaviors. Researchers also explore its potential in creating advanced materials for optoelectronic devices, leveraging its ability to enhance light absorption and emission characteristics.