Tautomerism process of single fluorescent molecules was studied by means of confocal microscopy in combination with azimuthally or radially polarized laser beams. During a tautomerism process the transition dipole moment (TDM) of a molecule changes its orientation which can be visualized by the fluorescence excitation image of the molecule. We present experimental and theoretical studies of two porphyrazine-type molecules and one type of porphyrin molecule: a symmetrically substituted metal-free phthalocyanine and porphyrin, and nonsymmetrically substituted porphyrazine. In the case of phthalocyanine the fluorescence excitation patterns show that the angle between the transition dipole moments of the two tautomeric forms is near 90°, in agreement with quantum chemical calculations. For porphyrazine we find that the orientation change of the TDM is less than 60° or larger than 120°, as theoretically predicted. Most of the porphyrin molecules show no photoinduced tautomerization, while for 7% of the total number of investigated molecules we observed excitation patterns of two different trans forms of the same single molecule. We demonstrate for the first time that a molecule, undergoing a tautomerism process stays in one tautomeric trans conformation during a time comparable with the acquisition time of one excitation pattern. This allowed us to visualize the existence of each of the two trans forms of one single porphyrin molecule, as well as the sudden switching between these tautomers.

Several tetra- and octaglycosylated PcZn 's 1a, 2a–2d, 3a-b and 4 were investigated for their aggregation behavior using different concentrations of the PcZn -species in pure DMSO, water and in various DMSO/water mixtures by comparing their UV-vis spectra. The PcZn 's 1–4 are independent of the concentration in pure DMSO and in up to 25 vol.% water/DMSO mixtures are non aggregated. Increasing amounts of water leads to higher aggregation ratios. The aggregation behavior is influenced by the nature and the position of the sugar substituents on the Pc-ring. PcZn 4 was found the least aggregated compound even in pure water.

Photophysical and photochemical properties of a series of tetra- and octaglycosylated zinc phthalocyanines (ZnPcs) substituted with glucose and galactose moieties have been reported. Spectral properties of these phthalocyanines are compared in DMSO. Absorption spectra of the non-peripherally tetra-substituted ZnPcs 2 showed a significant red shift in their Q-band maxima as compared to the peripherally substituted analog 1. All the complexes gave high triplet quantum yields ranging from 0.68 to 0.88, whereas triplet lifetimes were in the range of 100-430 μs in argon-saturated solutions. The octagalactosylated ZnPc 3b showed the highest triplet quantum yield and singlet oxygen quantum yield of 0.88 and 0.69, respectively. The fluorescence quantum yields and lifetimes of all the compounds under investigation were within the range of zinc phthalocyanine complexes.

We report the syntheses of the dimeric homonuclear Pcs 9a and 9b and of the dimeric heteronuclear Pc 9c, starting from the unsymmetrical phthalocyanines 7a and 7b, each containing a phenolic OH group in one of its substituents. Compounds 9a and 9b were obtained by single-step alkylations of 7a and 7b with 1,6-dibromohexane or, in better yields, by