Lewis Acid Modulation of meso‐Pyridyl BODIPY Chromophores

Abstract Two pyridyl‐substituted boron dipyrromethene (BODIPY) compounds are shown to interact with the strong Lewis acid B(C 6 F 5 ) 3 . The borane adducts are characterized by multinuclear NMR and in one case by X‐ray crystallography. The titration of pyridyl‐substituted BODIPYs with B(C 6 F 5 ) 3 results in a bathochromic shift of the UV/Vis absorption and emission spectra, with the magnitude of the shift depending on the distance of the bound borane from the BODIPY core. In meso ‐4‐pyridyl‐BODIPY, binding of B(C 6 F 5 ) 3 induces a small circa 230 cm −1 red shift in the UV/Vis absorption maximum, with a much larger 1950 cm −1 shift in the photoluminescence maximum. In meso ‐4‐pyridylphenyl‐BODIPY, where the pyridine Lewis base is separated from the BODIPY core by a phenyl spacer, smaller shifts of circa 120 cm −1 in UV/Vis absorption and 330 cm −1 in photoluminescence are observed. This work shows that these organic chromophores can interact with Lewis acids as a means of systematically perturbing the electronic structure and excited‐state properties.