Recently, polymerization-induced self-assembly (PISA), as a novel approach to synthesize functional polymer nanomaterials, has attracted enormous attention. The understanding of the PISA process and gelation behavior is fundamentally important; however, the current study approach is still limited. Based on the clustering-triggered emission mechanism, the photoluminescence of polymers with nonaromatic chromophores is highly dependent on the molecular arrangement, which might be utilized for in situ monitoring of the PISA process. Herein, we proposed a new PISA formulation based on light-triggered thiol–ene based click polymerization and gelation via a one-step process. The photoluminescence increased steadily with increasing polymerization time, and a significant change was observed when the gel formed, which might be attributed to the aggregation of chromophores in poly(thioether) chains. Quantitative information about the polymerization and self-assembly process could be easily obtained without destroying the reaction system. This work proposed a novel powerful platform for the monitoring and understanding of the PISA process.