Decorating BODIPY with Electron-Withdrawing NO Group: Spectroelectrochemical Consequences and Computational Investigation

4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY) and derivatives are an outstanding class of fluorescent dyes. Herein, we report on the introduction of a nitrosyl moiety into the BODIPY structure and its dramatic effect on the observed electrochemical reaction mechanism. 6-Nitrosyl-8-phenyl-BODIPY and its 5-nitrosyl positional isomer, compounds 2 and 3, respectively, were obtained from the meso precursor, 8-phenyl-BODIPY (1), by nitrosation. Electrochemical studies for 1-3 are reported. Cyclic voltammetry and differential pulse voltammetry in degassed DMF or in MeCN (reduction+oxidation), both with n-Bu4NPF6 (0.1 mol L-1), were obtained. Compound 1 displays the usual behaviour for 8-phenyl substituted BODIPYs. The addition of the acceptor nitroso group in compounds 2 (in position beta) and 3 (in position alpha), leads to a different profile. For all the compounds, the nitroso group greatly facilitates the reductions. For compound 3 (EpIc=-0.238 V), the first to be reduced is the nitroso group, due to the stability of the electrogenerated radical anion, along with non-bonding interactions with the electronegative boron difluoride. This is different from compound 2 (EpIc=-0.351 V) with a beta-nitroso group, where the nitroso-based facilitated reduction occurs in the substituted BODIPY core. Spectroelectrochemistry coupled with analysis through conceptual density functional theory (CDFT) corroborate the voltammetric results and explain the unexpected reactivity differences.