Multicolour luminescence phenomena of vibration-induced emission

This review provides an overview of vibration-induced emission (VIE), a new approach that allows molecules to emit multiple colors by undergoing conformational changes. The focus is on sterically hindered dihydrophenazine (DHP) derivatives, especially the N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC) core, illustrating how large-amplitude "butterfly" vibrational motions in the excited state govern their light emission behavior. Key molecular design strategies for VIE-active compounds are highlighted, revealing how the interplay of steric hindrance and electronic properties modulates excited-state energies and facilitates color tuning from blue to red, including the realization of intrinsic triple fluorescence. Advanced spectroscopy and theoretical studies are employed to explore the link between molecular conformation and emission properties. Additionally, innovative applications of VIE systems are discussed, especially in molecular cursor calipers for differential sensing, and microenvironment-responsive probes corresponding to different matrices. This review aims to stimulate broad interest across diverse fields, expanding both the scope of VIE research and the development of advanced functional materials.