What of flourene in organic compound

Fluorene is a polycyclic aromatic hydrocarbon (PAH) that consists of three fused rings. Unlike anthracene and phenanthrene, which are made of three fused six-membered benzene rings, fluorene has two benzene rings fused to a central five-membered cyclopentadiene ring. This central five-membered ring contains a methylene ($\text{CH}_2$) bridge.