Stabilization of naphthalene-1,8:4,5-dicarboximide radicals in zirconium phosphonate solid materials and thin films

Solid zirconium phosphonate (ZP) materials were prepared by direct precipitation of N,N'-bis(2-phosphonoethyl) naphthalene-1,8:4,5-dicarboximide (NDI-BP) from aqueous solution by addition of a ZrOCl2 solution. Slow precipitation in the presence of HF gave crystalline NDI-BP/ZP materials with a layered structure, whereas rapid precipitation in the absence of HF gave mainly amorphous materials. When ZrOCl2 solutions were added to photolyzed NDI-BP solutions, radical-doped solid materials with intense EPR response were obtained. Multilayer thin films of NDI-BP/ZP were grown on gold substrates in a layer-by-layer fashion, by exposing the phosphonate-rich modified surface to solutions of ZrOCl2 and NDI-BP, alternately. Electrochemical reduction of 20-layer films resulted in the formation of stable NDI-BP radical anions and dianions.