Near‐Infrared Boron Difluoride Formazanate Dyes

Near-infrared (NIR) dyes are sought after for their utility in light harvesting, bioimaging, and light-mediated therapies. Since long-wavelength photoluminescence typically involves extensive π-conjugated systems of double bonds aromatic rings, it is often assumed that NIR have to be large molecules require complex syntheses. We challenge this assumption by demonstrating facile incorporation tertiary amine groups into readily available 3-cyanoformazans affords efficient production relatively simple NIR-active BF2 formazanate (λabs=691–760 nm, λPL=834–904 nm toluene). Cyclic voltammetry experiments on these compounds reveal multiple reversible redox waves linked the interplay between moieties. Density-functional calculations indicate electronic transitions formazanates π→π*-type, but do not always involve strong charge transfer.