Synthesis, characterization and photochemistry of 5,10,15,20-tetrakis(4-N-pentylpyridyl)porphyrins, [(TPePyP)H2]4+ and [(TPePyP)ZnII]4+

Abstract

Tetracationic 5,10,15,20-tetrakis(4- N -pentylpyridyl)porphyrins, [( TPePyP ) H 2]4+ and its zinc-porphyrin analogue [( TPePyP ) Zn II]4+ have been synthesized and characterized by 1 H NMR and UV-visible spectroscopic techniques. Photobleaching studies carried out in solutions of varying pH show that, in the presence of oxygen, [( TPePyP ) H 2]4+ undergoes fast photodegradation in aqueous medium when the solution is irradiated with 560 nm light. The steady-state singlet oxygen quantum yields (ΦΔ) for [( TPePyP ) H 2]4+ is 0.80 and that for its Zn analogue is 0.85. These quantities were measured using 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen scavenger, in N,N-dimethyl-formamide solution. These ΦΔ values are compared with those for other well known sensitizers such as protoporphyrindimethylester PPDME and hematoporphyrindihydrochloride HPDHC.