Photochemical Action Plots Reveal the Fundamental Mismatch Between Absorptivity and Photochemical Reactivity

Over the last years, the authors' laboratory has employed monochromatic tuneable laser systems to reveal a fundamental mismatch between the absorptivity of a chromophore and its photochemical reactivity for the vast majority of covalent bond forming reactions as well as specific bond cleavage reactions. In the general chemistry community, however, the long‐held assumption pervades that effective photochemical reactions are obtained in situations where there is strong overlap between the absorption spectrum and the excitation wavelength. The current Perspective illustrates that the absorption spectrum of a molecule only provides information about electronic excitations and remains entirely silent on other energy redistribution mechanisms that follow, which critically influence photochemical reactivity. Future avenues of enquiry on how action plots can be understood are proposed and the importance of action plots for tailoring photochemical applications with never‐before‐seen precision is explored. Absorptivity and photochemical reactivity of molecules do not align in the majority of cases, evidenced by photochemical action plots for bond forming and cleaving reactions. Wavelength resolved action plots capture the sum of all photochemical effects and are the key tool for designing precision orthogonal, synergistic, cooperative and antagonistic photochemical systems in applications ranging from biology to additive manufacturing.