Photoluminescence in Polymer Non-conjugated Systems: Emerging Trends and Applications

Abstract: Non-conjugated luminescent materials (NCLMs) have attracted much attention in the fields of bioimaging, optoelectronic devices and sensing technologies due to their unique photophysical properties, excellent biocompatibility and environmental sustainability. However, NCLMs molecules usually lack conventional luminescent groups and exhibit aggregation-induced luminescence only at high concentrations or in the solid state, which is attributed to changes in molecular conformation and intermolecular stacking, resulting in luminescent phenomena such as aggregationinduced luminescence (AIE), concentration-enhanced luminescence, excitation-dependent luminescence, and generalized phosphorescence. It has been shown that electron-rich groups, aggregation of electron leaving domains and through spatial conjugation (TSC)-induced molecular conformational rigidity in NCLMs play a crucial role in luminescence. The aim of this review is to systematically investigate the photoluminescence mechanisms of NCLMs and to study the relationship of these mechanisms with molecular structures, aggregation states and environmental factors, with special focus on AIE, cluster-triggered emission (CTE), and crosslink-enhanced emission (CEE). This review establishes a theoretical foundation for the rational design and development of NCLMs, offers novel insights into their luminescence mechanisms, and broadens the scope of their potential practical applications.