Introducing\nof an Unexplored Aza-BODIPY Diradicaloids\nwith 4‑(2,6-Di<i>tert</i>-butyl)phenoxyl Radicals\nLocated in 1,7-Positions of the Aza-BODIPY Core

We have prepared and characterized two diradicaloid systems <b>5a</b> and <b>5b</b> that originated from the oxidation\nof a 1,7-(4-(2,6-di-<i>tert</i>-butyl)phenol)-substituted\naza-BODIPY core. The aza-BODIPY diradicaloids were characterized by\na large array of experimental and computational methods. The diamagnetic\nclosed-shell state was postulated as the ground state in solution\nand a solid-state with the substantial thermal population originating\nfrom both open-shell diradical and open-shell triplet states observed\nat room temperature. Transient absorption spectroscopy indicates fast\n(<10 ps) excited state deactivation pathways associated with the\ntarget compounds’ diradical character in solution at room temperature.\nVariable-temperature <sup>1</sup>H NMR spectra indicate the solvent\ndependency of the diradical character in <b>5a</b> and <b>5b</b>. The diradicaloids could be stepwise reduced to the mixed-valence\nradical-anion and dianion states upon consequent single-electron reductions.\nSimilarly, deprotonated 1,7-(4-(2,6-di-<i>tert</i>-butyl)phenol)-substituted\naza-BODIPYs can be oxidized to the diradicaloid form. Both mixed-valence\nand dianionic forms exhibit an intense absorption in the NIR region.\nDensity functional theory (DFT) and time-dependent DFT calculations\nwere used to explain the transformations in the UV–Vis-NIR\nspectra of all target compounds.