Synthesis and photophysical properties of metal free, titanium, magnesium and zinc phthalocyanines substituted with a single carboxyl and hexylthio groups

2,3,9,10,16,17,23,24-Octakis(hexylthio)phthalocyanines (4a-6a) and 2-carboxy-9,10,16,17,23,24-hexakis(hexylthio)phthalocyanines (4b-6b) were synthesized using a one-pot method by cyclotetramerization of the phthalonitriles: 4,5-bis(hexylthio)phthalonitrile and carboxylic acid phthalonitrile. 2-Carboxycatecholato-2,3,9,10,16,17,23,24-octakis(hexylthio)phthalocyaninatotitanium(IV) (8) was prepared from 2,3,9,10,16,17,23,24-octakis(hexylthio)phthalocyaninatooxotitanium(IV) (7). The structures of these compounds were characterized by using elemental analyses, UV-Vis, FT-IR, ¹H NMR and mass spectroscopies. Their photophysical properties were also studied. The Φ_F values are 0.12, 0.02, 0.10, 0.06, 0.10, 0.06, 0.65, 0.80 and the Φ_T values are 0.58, 0.56, 0.57, 0.64, 0.22, 0.48, 0.17, 0.12 for 4-8, respectively. The Φ_F value for complex 8 is higher than ever reported for phthalocyanine complexes. The triplet lifetimes (τ_T) values for all the complexes were generally good, ranging from 50 to 310 μs, and generally increased in the presence of the single carboxyl group. These complexes showed reasonable triplet quantum yields and lifetimes, and hence have potential for use as photosensitizers in photodynamic therapy (PDT) of cancer.