New asymmetric AB3-type free-base and metalloporphyrin-cyclotriphosphazene conjugates: Synthesis and photophysical-photochemical properties

Abstract

In this work, new asymmetric H2-(3), Zn(II)-(4) and Pd(II)-(5) porphyrin derivatives conjugated with a cyclotriphosphazene ring bearing 2‑naphtoxy groups in paraposition were synthesized and fully characterized. For investigation of photophysical and photochemical properties of these compounds; their ground state absorption, fluorescence emission, fluorescence lifetime, fluorescence quantum yield and singlet oxygen quantum yield measurements were studied in THF. The singlet oxygen quantum yields were determined as 0.62 for 3, 0.49 for 4 and 0.64 for 5 in THF, respectively. As a result, conjugation of the porphyrin macrocycle with the cyclotriphosphazene ring have improved the singlet oxygen generation except compound 4 when compared to tetraphenylporphyrin (TPP) (0.58) and ZnTPP (0.61) in THF. Especially, compound 5 has the highest singlet oxygen quantum yield (0.64) due to the heavy metal effect of Pd(II).