Quantification of Synergistic Two‐Color Covalent Bond Formation

The emergence of highly wavelength resolved reactivity information for complex photochemical reaction processes allows the establishment of multi‐color reaction modes. One particularly powerful mode is the synergistic two‐color reaction, where two colors of light have to be present in the same volume element to either enable or enhance photochemical reactivity that leads to a specific photoproduct. Herein, we introduce a two‐color synergistic photochemical reaction system based on a diaryl indenone epoxide (DIO) photoswitch and the cis ‐to‐ trans isomerization of a bridged ring‐strained azobenzene (SA), which respond to ultraviolet (365 nm) and visible light (430 nm), respectively, with different rates, forming a well‐defined heterocyclic photoadduct, DIOSA, that we structurally confirm via single crystal x‐ray diffraction (SXRD). To quantitatively capture the effectiveness of the dual‐color irradiation as a function of the reaction conditions such as light intensity and starting material ratio as a function of product yield, we introduce a parameter, the photochemical synergistic ratio . A reduced termed —that extrapolates to conditions of infinitesimal conversions—allows to compare the efficiency of the synergistic photochemistry at varying reaction conditions.