The physical and chemical properties of organic semiconductors play key roles in the performance of optoelectronic devices. The manipulation of these properties offers research opportunities and challenges in physical chemistry. The spectral stability and the origin of the low-energy emission band (LEEB) in polyfluorenes-based blue light-emitting diodes have received much attention over the past few decades. In this review, we cate rized various LEEB phenomena according to characterization and related mechanisms, including inter-chain aggregates and/or excimers, on-chain ketone defect emissions, interchain ketone-based excimers, and hydroxy-terminated oxidation on the interface of devices. Recent advances in highly stable blue light-emitting polyfluorenes are cate rically summarized. This review highlighted the contributions of the steric hindrance effects of various nonplanar bulky groups, molecular conformations and topologies of chains and antioxidant hindered amine light stabilizers (HALS), together with physical blending as well as interface engineering.