Journal of Organic Chemistry
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The effect of extended π-conjugation on the spectroscopic and electrochemical properties of boron difluoride (BF2) formazanate complexes was studied by the systematic comparison of phenyl- and naphthyl-substituted derivatives. Each of the BF2 complexes described was characterized by 1H, 13C, 11B and 19F NMR spectroscopy, cyclic voltammetry, infrared spectroscopy, UV-vis absorption and emission spectroscopy and mass spectrometry. X-ray crystallography and electronic structure calculations were used to rationalize the trends observed, including direct comparison of 3-cyano-, 3-nitro- and 3-phenyl-substituted BF2 formazanate complexes. In all cases, the wavelength of maximum absorption and emission were red-shifted as π-conjugation was systematically extended (by replacing phenyl with naphthyl), fluorescence quantum yields increased (up to tenfold) and electrochemical conversion of the formazanate complexes to their radical anion and dianion forms occurred at less negative potentials (easier to reduce).