Host Dearomatization for Prolonging Room‐Temperature Phosphorescence

Host–guest doping has emerged as a powerful platform for constructing organic room‐temperature phosphorescence (RTP) materials, owing to its structural tunability and facile fabrication. However, molecular design has largely focused on guest molecules, while host screening lacks systematic theoretical guidance. Here, we propose a host dearomatization strategy that prolongs the afterglow of doped systems. By converting the benzene ring into a cyclohexane structure in the host, the RTP lifetimes of the doped systems are significantly prolonged, with the maximum enhancement reaching a 58.65‐fold increase. Mechanistic studies indicate that the extended lifetime arises from enhanced triplet‐triplet energy transfer and electronic coupling, enabled by the reduced intermolecular distance upon dearomatization. This strategy exhibits universality across diverse host and guest systems. These doped systems are further applied in time‐resolved information encryption systems and switchable adhesive materials. Starting from the host molecular framework, this study provides a universal and efficient strategy for the rational design of organic RTP materials.