Valency‐Controlled Multiphotochromism: Gated Switching and Photoswitchable Lewis Superacidity at Silicon

Multiphotochromic systems promise multistate molecular information storage, yet strategies to control their switching‐state distributions and interchromophore communication remain scarce. Here, we demonstrate that silicon valency can serve as a molecular control element to gate multiphotochromism. Two silicon‐based diarylethene Lewis acids undergo stepwise twofold cyclization, with interconversion between tetra‐ and pentacoordinate states modulating electronic coupling between ligands. Donor coordination enables selective monocyclization, wavelength‐gated activation, or complete suppression of photoreactivity, depending on the bound base. In the donor‐free state, stepwise cyclization progressively enhances Lewis acidity and culminates in the first example of photoswitchable Lewis superacidity. In addition, dynamic Si─N/Si─O bond metathesis provides thermodynamic access to switching‐state distributions beyond statistical photochemical limits. These findings establish valency control as a design principle for multiphotochromic architectures.