Self-Aggregation of Lipophilic Porphyrins in Reverse Micelles of Aerosol OT

The aggregation process of meso -tetra(4-aminosulfonylphenyl)porphyrin (PC 0 ), of butyl and dodecyl derivatives (PC 4 and PC 12, respectively) in the presence of aerosol-OT (AOT) reversed micelles with different values of ω 0 = [water]/[AOT] was investigated using steady-state extinction, fluorescence, and resonance light scattering (RLS) techniques. The scattering has been accounted for and the absorption spectra corrected from the extinction spectra. In homogeneous solutions, the porphyrins exist as a monomer showing the Soret band around 420 nm and emission bands at 650 and 716 nm. In reverse micelles, the spectra vary according to the chain length and the amount of solubilized water. Only PC 12 is dissolved as a monomer at ω 0 = 0, and PC 4 shows some degree of aggregation. PC 0 is present largely as an aggregate. At ω 0 ≠ 0, a complete aggregation is observed for PC 4 and PC 12, whereas in PC 0, some degree of disaggregation was detected. The extinction spectra of PC 0 and PC 4 in aggregate forms show a broad and red shifted Soret band indicating J aggregates. By contrast, the Soret band intensity of PC 12 decreases and a new band around 376 nm appears with a broadening of the monomer Soret band which reflects H aggregates. RLS shows a strong signal for PC 12 at red spectral region at high ω 0 indicating J aggregate types. The fluorescence spectra showed the new band around 670 nm for PC 0 and PC 12, whereas in PC 4, only blue shifted bands were observed with ω 0 increase. The global fluorescence quantum yield of the PC 12 aggregates is lower than the respective monomer. The aggregate sizes were followed by RLS measurements which showed an increase of intensity at around 440 nm. The aggregation dynamics is dependent on both the porphyrin concentration and ω 0 .