Tuning phenoxyl-substituted diketopyrrolopyrroles from quinoidal to biradical ground states through (hetero-)aromatic linkers.

Strongly fluorescent halochromic 2,6-di--butyl-phenol-functionalised phenyl-, thienyl- and furyl-substituted diketopyrrolopyrrole (DPP) dyes were deprotonated and oxidised to give either phenylene-linked biradical ( = 0.75) with a singlet open shell ground state and a thermally populated triplet state (Δ = 19 meV; 1.8 kJ mol; 0.

Nitronyl Nitroxide Bifunctionalized Electron-Poor Chromophores: Synthesis of Stable Dye Biradicals by Lewis Acid Promoted Desilylation.

Open shell organic molecules bearing π-cores are of great interest for optical, electronic, and magnetic applications but frequently suffer fast decomposition or lack synthetic accessibility. In this regard, nitronyl nitroxides are promising candidates for stable (bi-)radicals due to their high degree of spin delocalization along the O-N-C-N-O pentad unit. Unfortunately, they are limited to electron-rich systems so far.

Stable Organic (Bi)Radicals by Delocalization of Spin Density into the Electron-Poor Chromophore Core of Isoindigo.

The first isoindigo (bi)radicals were obtained by proton coupled oxidation of their 4-hydroxyaryl substituted precursors. Optical and magnetic spectroscopic studies revealed a singlet open-shell biradicaloid electronic ground state for the bisphenoxyl-isoindigo (=1.20) with a small singlet-triplet energy gap of 0.