9,9'-Spirobifluorene is a rigid, three-dimensional organic compound featuring two fluorene units connected through a spiro carbon atom. This unique structure imparts excellent thermal stability, morphological stability, and high triplet energy levels, making it a highly valuable building block in advanced materials science. Its primary and most significant application is in the field of organic electronics, particularly as a core structural unit for organic light-emitting diodes (OLEDs). It is widely used to construct host materials, hole-transporting materials (HTMs), and electron-transporting materials (ETMs) for both fluorescent and phosphorescent OLED devices. The spirobifluorene core effectively suppresses molecular aggregation and crystallization, leading to improved device efficiency and operational lifetime. Furthermore, it serves as a key monomer for synthesizing high-performance polymers used in organic photovoltaics (OPVs) and other optoelectronic applications. Due to its robust and versatile scaffold, 9,9'-spirobifluorene derivatives are also explored in the development of organic semiconductors, lasers, and sensors. Its synthesis and functionalization are active areas of research to tailor its photophysical and electronic properties for next-generation display and lighting technologies.