Transient Activation Windows Program Adaptive Photochemical Responses

Biological systems regulate photochemical functions through transient activation states that determine when a stimulus can produce a response. Inspired by this principle, we develop a temporally gated molecular platform in which dynamic pH evolution controls visible‐light photochemistry. The system integrates a proton‐responsive charge‐transfer complex (CTC) sensitizer and a diarylethene photoswitch. Reversible protonation of the CTC enables chemical gating of triplet‐sensitized photochromism, which further generates a transient activation window via coupling with a dissipative, pH‐regulation network. As a result, identical optical stimuli lead to distinct outcomes depending on when they are applied during chemical evolution, effectively promoting chemical gating to temporal gating of molecular photoswitch. The progressive modulation of the sensitizer induces a time‐dependent attenuation of photochemical responses, enabling adaptive behaviors reminiscent of visual fatigue in biological photo‐reception.