Interaction between meso-tetra-(4-hydroxyphenyl)porphyrin and SDS in aqueous solutions: Premicellar porphyrin-surfactant J-aggregate formation

[Display omitted] •Aggregation of tetra(hydroxyphenyl)porphyrin (THPP) is studied at 0.5–50 mM SDS.•Premicellar porphyrin-surfactant J-aggregate formation is observed in 2–5 mM SDS.•The surfactant cmc decreases down to 6 mM in the presence of THPP.•Spin probe EPR spectroscopy reveals on surface binding of THPP to SDS micelles.•Residual DMF (0.5 vol%) decreases packing density of SDS molecules in the micelles. Interactions between meso-tetra(4-hydroxyphenyl)porphyrin (THPP) and anionic sodium n-dodecyl sulfate (SDS) in a wide surfactant concentration range (0.5–50 mM) have been studied by UV–vis absorption and fluorescence spectroscopy, resonance light scattering (RLS), spin probe EPR spectroscopy and dynamic light scattering (DLS). J-type aggregate formation has been observed for THPP within 2–5 mM surfactant concentration range, accompanied by a significant bathochromic shift of the absorption bands, fluorescence quenching and emergence of an intense RLS signal. Porphyrin binding to the surfactant micelles above the cmc and aggregate formation below the cmc have been observed in SDS solutions containing THPP by DLS and EPR spectroscopy. SEM and optical microscopy revealed a rod-like morphology of the microparticles crystallized from an air dried suspension of THPP J-aggregates. The results obtained contribute to understanding of the mechanism of porphyrin-surfactant interactions both below and above the surfactant cmc.