3-Carbaldehyde-substituted 2,3′-biimidazo[1,2-a]pyridin-2′-one radicals: Interesting π-stacking structures and magnetic properties

A new 3-formyl-2,3′-biimidazo[1,2-a]pyridin-2′-one radical was synthesized via Vilsmeier reaction under mild conditions, which exists as 1D double-stranded chain formed by lateral close contacts between π-dimers. Its perchlorate salt exists as 1D slipped π-stacking chain. The different stacking structures obviously affect their magnetic and photoluminescence properties in solid state. Neutral radical shows a dominant antiferromagnetic interaction between radicals and the magnetic phase transition at ∼72 K, while radical salt exhibits a strong irreversibility between FC and ZFC states, attributed to the anisotropic contraction and nonuniform slippage of π-stacking chain.