Fluorene is an aromatic hydrocarbon with a fused benzene ring system that has high thermal stability and excellent hole transport properties. Fluorenones are fluorene derivatives with a keto group that also have good electronic properties. Fluorenes and fluorenones can be easily functionalized with various substituents to tailor their electronic and optical properties for specific applications. Due to their stable and rigid aromatic frameworks, they are often used as core structures in the synthesis of small molecule semiconductors. In OLEDs (organic light emitting diodes), fluorenes and fluorenones are used as hole transport materials, while in OPVs (organic photovoltaic cells), they can be used as electron donating elements. Their versatile chemistry and properties make them attractive for the development of high-performance organic electronic devices.