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

Abstract

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 β) and 3 (in position α), 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 β‐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.