Charge separation of photosensitized phenothiazines for applications in catalysis and nanotechnology

Phenothiazines are a class of molecules that have been applied in antipsychotic therapy, photodynamic therapy, dyes, sunscreen, and more recently light-harvesting for energy applications. In the present study, the photochemical properties of phenothiazine aggregates were used for oxidative catalysis and synthesis of gold nanoparticles with potential applications in Boolean logic operations. Phenothiazines have the peculiar photochemical property, which is the stabilization of the photochemically-generated radical cation in their supramolecular aggregates. The phenothiazine radical cations exhibit pink color related to a broad visible spectral band with a peak at 520 nm. In the present study, the pair radical cation/reduced form of two phenothiazines, 10H-phenothiazine (PHT) and 3,7-bis (phenylamino) phenothiazine-5-iodide, named here phenoaniline (PHA) were photochemically generated and characterized by absorbance with a peak at the range of 520–550 nm, direct and spin-trapping EPR measurements. The radical cation was separated from the reduced form using the resin styrene-divinylbenzene copolymer containing iminodiacetate ions (Chelex 100®). The radical cation entrapped in the resin remained stable and could be used for catalytic oxidation processes. The reduced form remained in aqueous solution and had its reducing properties used to produce gold nanoparticles. Reduced PHT produced gold nanoparticles with dimensions around 7 nm that were arranged in monodispersed supramolecular aggregates of ~60 nm, stabilized by oligomerized phenothiazine, whereas PHA formed anisotropic gold nanoparticles. The supramolecular aggregates of AuNP PHT showed the potential to be applied in Boolean logic systems using CTAB dispersion and citrate reaggregation. •The photochemistry of phenothiazine nucleus (PHT) and phenoaniline derivative (PHA) was studied.•Under irradiation, PHT and PHA aggregates undergo charge separation with formation of stable cation radical.•The PHT and PHA cation radicals were trapped by anionic resin to be used as oxidant catalyst.•The reduced form of the phenothiazines was useful for the fabrication of gold nanoparticles.