Absorption, fluorescence and transient triplet–triplet absorption spectra of zinc tetramethylpyridylporphyrin in reverse micelles and microemulsions of aerosol OT–(AOT)

Abstract

The photophysical properties of water soluble Zn(II) meso-tetrakis(N-methylpyridinium-4-yl)-porphyrin were studied in reverse micelles of the iso-octane–AOT–water system. Broadening of absorption and emission bands as well as shifts and increase of maxima intensities were observed with different values of W₀ = [H₂O]/[AOT], with a fixed AOT (0.1 M) concentration. These effects are generally good evidence for distinct probe locations inside the aggregates, but no clear evidence of equilibria (isosbestic and isoemissive points) was detected. The decomposition of the Soret absorption band into Gaussian functions showed the presence of two species, one near the well known blue Soret band in water (435 nm) and another more displaced to the red (442 nm). Transient triplet–triplet absorption spectra confirm the different locations of the porphyrin in the micelle interface. One of the species, which is located in a more hydrophobic region of the interface has a triplet decay constant around ten times slower than the other one located at the hydrophilic region of the interface with lower singlet energy and a fast triplet decay rate constant.