Phenazine and meso-1,2-diphenyl-1,2-ethanediol - Partners in photochromic cocrystals

A hydrogen-bonded network in a 1:1 cocrystal of phenazine and meso-1,2-diph enyl-1,2-ethandiol places phenazine and diol in such a way that a thermally reversible photochromism is produced. The structure of the cocrystal is de termined by X-ray crystallography. Thermally reversible changes in the UV/V is and TR spectrum on irradiation, in combination with the generation of pa ramagnetism (ESR) lead to the interpretation that a light induced electron transfer between two phenazine molecules is followed by a double proton tra nsfer to the nitrogen atoms of the radical anion of phenazine.