Aggregation-controlled photophysics of m-THPP: restoring singlet oxygen generation via albumin and pluronic carriers

The photophysical properties of meso-tetra(hydroxyphenyl)porphyrin (m-THPP) were investigated to elucidate how aggregation in aqueous media affects its ground- and excited-state behavior and to identify carrier systems capable of preserving its photodynamic activity under near-physiological conditions. Spectroscopic studies in methanol-phosphate-buffered saline mixtures showed that m-THPP undergoes pronounced aggregation at high water content, leading to strong broadening and red shifting of the absorption bands, quenching of singlet and triplet excited states, and complete suppression of singlet oxygen generation in aqueous buffer. To prevent aggregation, m-THPP was formulated using polymeric micelles based on Pluronic P123 and Pluronic F127, as well as by complexation with bovine serum albumin. All carrier systems stabilized predominantly monomeric m-THPP in buffer, but with markedly different efficiencies. The albumin complex and P123 micelles provided superior stabilization, yielding higher fluorescence efficiencies, longer triplet lifetimes, and enhanced singlet oxygen generation in contrast, incorporation into the more hydrophilic F127 micelles promoted partial aggregation of m-THPP, leading to reduced photodynamic performance. These results demonstrate that aggregation is the key factor limiting the activity of m-THPP in aqueous media and that rational selection of carrier systems enables effective control of its photophysical properties and photodynamic efficiency.