Unveiling the Power of Dark State Photocages: An Efficient Pathway to Triplet State Under Near‐Infrared Light Irradiation

Abstract The photocage platform provides a synergistic approach to photodynamic therapy (PDT) and chemotherapy. Before light activation, both pro‐photosensitizers and pro‐drugs remain inert, ensuring safety. Upon near‐infrared (NIR) light irradiation, they undergo photoactivation and controlled release in deep tissues. However, the low photolysis efficiency of conventional singlet‐state photocages limits their in vivo applications, necessitating an exploration of how excited‐state dynamics influence photolysis. In this study, we introduce the concept of a “dark state photocage” and establish a photocage platform responsive to NIR light by incorporating phenoxazine or phenothiazine groups. Mechanistic investigations reveal that the dark state enhances triplet‐state formation and facilitates intersystem crossing, thereby promoting photolysis. These photocages achieve functional molecule release under low‐power NIR light (15 mW cm⁻ 2 ), with an efficiency of up to 90%. This advancement enables a sharp transition from an “OFF” to an “ON” tumor imaging signal and significantly enhances the therapeutic efficacy against triple‐negative breast cancer under NIR light irradiation, effectively integrating PDT and chemotherapy.