Photoinduced electron transfer (PET) is a critical process in many functional materials, underpinning various technological applications (i.e., fluorescent probes and photocatalysts). Despite its significance, the detailed structural dynamics of PET, particularly during the excited state, remain poorly understood. This study investigates the mechanisms of conformational folding and their implications for activating PET in molecular systems characterized by a fluorophore-spacer-receptor configuration. We demonstrate that traditional computational models, primarily based on frontier molecular orbitals, often fall short in capturing these conformational dynamics, leading to inadequate explanations of PET phenomena. With the incorporation of conformational folding, our computational model has achieved excellent agreement with experimental data, thereby resolving several long-standing debates on PET mechanisms. This mechanistic advancement not only deepens our understanding of PET but also opens new avenues for designing advanced functional materials. We have thus successfully demonstrated the imaging of lysosomes in live cells using a PET probe.

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