Photochemical and photophysical properties of phenothiazinic dyes at the interface of metallic nanoparticles

Abstract

Methylene blue and other thiazine dyes have relevance in a variety of applications covering the biological, materials, bioelectronics, and energy fields. Previous and ongoing studies in our laboratory have shown that the aggregate states of thiazine compounds acquire the property of stabilizing photochemically generated radical species. In the case of methylene blue, the stabilization of the leuco form when the dye is aggregated in the resin and collagen matrix allows its use as a reducing agent for the synthesis of gold nanoparticles. In the case of phenothiazines, the aggregate states stabilize the photochemically generated radical/reduced form cation such that each species can be catalytically used as oxidizing and reducing agents, respectively. Another exciting aspect of thiazine compounds is the formation of different types of aggregates, those of type J and H, which have specific luminescent properties. More recently, the energy applications of phenothiazines have been evidenced by the ability to transfer holes (h) of phenothiazines to conjugated aromatic compounds. In the present project, we aim to characterize the properties of the thiazine molecule aggregate states in different types of gold nanostructures, i.e., spherical nanoparticles larger than and equal to 10 nm in diameter, anisotropic urchin nanoparticles, nanoplates and nanorods of gold. Phenothiazine molecules to be studied in combination with the gold nanostructures will be methylene blue, phenothiazine nucleus (PHT), phenaniline, and the antipsychotics thioridazine, fluphenazine and trifluoperazine. Aggregate states will be investigated by UV-visible and FTIR-ATR spectroscopy, circular dichroism, and XPS. For the characterization of the photophysical properties, the techniques of Electron Paramagnetic Resonance (EPR) and SQUID will be used. The photochemical properties will be investigated by spectroelectrochemistry. (AU)