Singlet Oxygen Generation in Peripherally Modified Platinum and Palladium Porphyrins: Effect of Triplet Excited State Lifetimes andmeso‐Substituents on¹O₂Quantum Yields

Abstract

A series of meso-substituted with aromatic (= tolyl, pyrenyl, fluorenyl, naphthyl, and triphenylamine) substituents, platinum (Pt), and palladium (Pd) porphyrins have been synthesized and characterized by spectroscopic and single-crystal X-ray diffraction studies to probe structure-reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum yields and lifetimes. In the X-ray structures, the aromatic mesosubstituents were rotated to some extent from the planarity of the porphyrin ring to minimize steric hindrance. Both Pt and Pd porphyrins revealed higher electrochemical redox gaps as compared to their free-base porphyrin analogs as a result of the harder oxidation and reduction processes. The ability of both Pt and Pd porphyrins to generate singlet oxygen was probed by monitoring the photoluminescence of 1 O 2 at 1270 nm. Higher quantum yields for both triplet sensitizers compared to their free-base analogs were witnessed. Singlet oxygen quantum yields close to unity were possible to achieve in the case of Pt and Pd porphyrins bearing triphenylamine substituents at the meso-position. The present study brings out the importance of different meso-substituents on the triplet porphyrin sensitizers in governing singlet oxygen quantum yields; a key property of photosensitizers needed for photodynamic therapy, chemical synthesis, and other pertinent applications.

Sn(iv)-porphyrinoids for photodynamic anticancer and antimicrobial chemotherapy

“…Functionalized porphyrins with central coordinated metal ions such as Zn 2+ , Pd 2+ , Pt 2+ , In 3+ , and Ga 3+ have been reported to have significant PDT activity against different cancer cell lines. 10,[14][15][16][17][18][19] These metal porphyrins typically lack significant absorbance at wavelengths >620 nm, which is problematic since absorption bands in the PDT window (620-850 nm) are usually preferred. Another drawback of metal porphyrins, including the FDA-approved Photofrin ® PDT drug and other hematoporphyrin derivatives, is that they tend to aggregate (J/H type) in an aqueous medium or cellular media because of their exposed π-conjugation systems.…”

β-Pyrrole Functionalized Push or Pull Porphyrins: Excited Charge Transfer Promoted Singlet Oxygen Generation

“…Further, femtosecond transient absorption (fs-TA) spectroscopy has been utilized on selected compounds to examine the excited state charge transfer involving peripheral substituents. Finally, the photoluminescence in the near-IR region (1270 nm) of singlet oxygen ( 1 O 2 ) − produced by these porphyrins in dioxygen-saturated solutions has been monitored and quantified. Our findings show that both free-base and zinc porphyrins carrying push groups improve singlet oxygen generation, while those porphyrins carrying pull groups diminish singlet oxygen production.…”

Synthesis, Characterization, and Singlet Oxygen Sensitization by Antimony (III/V) Corrole Complexes

“…[5] In addition, their redox properties are versatile and have a longer excitedstate lifetime. [6] Metallo-porphyrinoid complexes bearing main group metals like antimony having strong absorption at the red region of the spectrum have great potential as chromophores. [7][8][9][10][11][12][13] Thus, the porphyrin complexes bearing the central atom, antimony, will be an ideal choice as a photosensitizer.…”