A novel 4-((3,5-dimethyl-1H-pyrazol-1-yl)phenylthio)phthalonitrile 3 and corresponding zinc phthalocyanine 5 has been synthesized and characterized. There has been investigated the effect of nature of the linker heteroatom (S or O) on spectroscopic, photophysical and photochemical properties of zinc phthalocyanine 5 and zinc phthalocyanine 6, containing 4-(3,5-dimethyl-1H-pyrazol-1-yl)phenoxy moiety. The zinc phthalocyanines 5 and 6 are highly soluble in common organic solvents. The solvatochromic effects were evaluated by changes in UV–Vis spectra. A correlation between the Q band frequency and the refractive index of 20 organic solvents was examined. The aggregation behavior and photochemical properties (quantum yields singlet oxygen generation and photodegradation) of zinc phthalocyanines were investigated at different concentrations in DMSO, DMF, THF and water-organic solvents mixtures. The water content in the mixture has a crucial effect on the aggregation behavior and the generation of singlet oxygen. In DMSO aggregation of 5 takes place with the addition of any amount of water, whereas for 6 the formation of dimers is observed at a water concentration of more than 10%. However, in THF the formation of aggregates is observed at a water concentration above 30% for 5 and 50% for 6. The synthesized novel phthalocyanines have high quantum yield of singlet oxygen (Φ_Δ) values (the range of 0.50–0.70) and can be considered as potential photosensitizers for photodynamic therapy. The highest Φ_Δ values were obtained for zinc phthalocyanine 6 containing oxygen linker heteroatom in all solvents.