Redox-responsive fluorescence emission output of a synthetic phenazine derivative

Molecules presenting reversible photoreaction are highly interesting because, in principle, can be used as photocatalysts in electron transfer reactions for the designing of molecular switches. Herein we present the results obtained for dipyridoquinoxalinophenazine (dpqpz), a non-photoluminescent product of a condensation reaction between 1,10-phenanthroline-5,6-dione and 2,3-diaminophenazine. After 2-electron/2-proton electrochemical or chemical reduction, the product dihydro-dpqpz exhibits red emission with maximum at 610 nm under excitation at 530 nm. Spectroelectrochemical studies showed this is a reversible process wherein the dpqpz molecule is recovered upon air contact. Theoretical calculations showed a new allowed electronic transition emerges after 2-electron reduction making the photoreduction possible. The emission efficiency of dihydro-dpqpz showed to be dependent on the solvent nature with the polarity being the dominant effect. The strong emission suppression in protic solvents (quantum yields of 0.02 and 0.15 in ethanol and acetonitrile, respectively) was ascribed to the influence of hydrogen bonds. The reversible redox-responsive fluorescence emission property of dihydro-dpqpz in the absence of a sacrificial donor and under visible light irradiation is an essential feature that qualifies its application as a feasible switch material.