Design of Stable Diradicals Based on Group 13 Dyes of NO-Bis(phenolate) Aza-Dipyrromethene and Aza-BODIPY.

We have prepared a series of strongly fluorescent NO-bis (phenolate) aza-dipyrromethene dyes incorporating boron (aza-BODIPY), aluminum (aza-ALDIPY), gallium (aza-GADIPY), and indium (aza-INDIPY). These compounds were oxidized both chemically and electrochemically to give diradical molecules - with an open-shell singlet ground state and a thermally accessible triplet excited state. The ground state behavior of these diradical molecules was confirmed by a wide array of magnetic spectroscopies, including variable-temperature H NMR, EPR, and SQUID. X-ray crystallography confirmed the NO coordination sphere in these systems. DFT and TDDFT quantum chemical calculations were used to determine their electronic structures, nature of the excited states, diradical character (), and spin density distributions for both open-shell singlet and triplet states. Spectroelectrochemical studies on the deprotonated dianions to showed the formation of mixed-valent radical anion species with intense absorption and broad intervalence charge transfer bands in the near-infrared region. Upon further oxidation of the mixed-valent radical anion species, diradical molecules were generated.