H-aggregation of cationic palladium-porphyrin as a function of anionic surfactant studied using phosphorescence, absorption and RLS spectra

Room temperature phosphorescence (RTP) was used as a useful analytical tool to investigate the interaction behavior between tetracationic meso-tetrakis (4-trimethylaminophenyl) porphyrin palladium (Pd-TAPP) and anionic sodium dodecyl sulfate (SDS). UV–vis absorption and resonance light scattering (RLS) were further applied to characterize the system. It was presumably suggested that nonspecific self-aggregates among porphyrins formed considering the relatively high concentration of Pd-TAPP. Furthermore, Pd-TAPP changed from free monomer/nonspecific aggregate to H-aggregate and then to out-micellized monomer/nonspecific aggregate as a function of SDS concentration. The fact that RTP signal enhanced obviously and excitation spectrum was blue-shifted by 1580 cm−1 in energy with respect to energy of free Pd-TAPP monomer demonstrated that 1:4 electrostatic interaction between Pd-TAPP and SDS led to the formation of the premicellar porphyrin-surfactant H-aggregates. The RLS spectrum reviewed that the formed H-aggregates were multiple porphyrin units, and UV–vis spectra revealed that cationic groups of monomers/nonspecific aggregates of Pd-TAPP were electrostatically attracted in favor of the surface of anionic micelles but were not encapsulated within apolar regions of SDS micelles when the concentration of SDS was above its critical micelle concentration (CMC).