9-Methylphenanthrene is primarily used in research and development within the field of organic chemistry, particularly in studies related to polycyclic aromatic hydrocarbons (PAHs). It serves as a model compound to investigate the environmental behavior, degradation pathways, and toxicological effects of PAHs, which are significant pollutants. Additionally, it is utilized in the synthesis of complex organic molecules and as a reference standard in analytical chemistry for the identification and quantification of PAHs in environmental samples. Its properties also make it valuable in photochemical studies and in the development of advanced materials.