Light as a reaction parameter - systematic wavelength screening in photochemical synthesis

We unfold light as a reaction parameter in a continuous-flow photoreactor using 16 LED arrays with different emission bands (350-700 nm) but identical irradiances. For the perfluoroalkylation of 2-methylindole, three reaction mechanisms are revealed wavelength-selectively and subsequently transferred into independent synthetic routes: i) photoredox catalyzed by eosin Y, ii) via amine-based electron donor-acceptor (EDA) complexes (catalyst-free), and iii) via indole-based EDA complexes (catalyst- and additive-free). The presented methodology enables routine and systematic screening of irradiation wavelengths and intensities in photochemical synthesis.