Optimization of Triplet Excited State and Singlet Oxygen Quantum Yields of Picolylamine–Porphyrin Conjugates through Zinc Insertion

Abstract

We synthesized a new class of picolylamine-porphyrin conjugates 1-3 and have investigated the effect of heavy atom insertion on their intersystem crossing efficiency through spin-orbit perturbations. By incorporating zinc ions in the core as well as periphery positions of the porphyrin ring, we have successfully optimized their triplet excited state quantum yields and their efficiency to generate singlet oxygen. Uniquely, the picolylamine-porphyrin conjugate 3 having five zinc ions exhibited a triplet excited state quantum yield of ca. 0.97 and a sensitized singlet oxygen generation yield of ca. 0.92. In contrast, the free base porphyrin derivative 1 exhibited ca. 0.64 and 0.5 of the triplet excited state and singlet oxygen quantum yields, respectively. Our results demonstrate that the insertion of zinc metal ions in the picolylamine-porphyrin conjugates not only quantitatively enhances the triplet excited state and singlet oxygen yields but also imparts hydrophilicity, thereby their potential use as sensitizers in photodynamic therapy and green photooxygenation reactions.

Developments in PDT Sensitizers for Increased Selectivity and Singlet Oxygen Production

“…Placing one or five Zn atoms into a picolylamine-based porphyrin raised the 1 O 2 quantum yield from the 0.5 to 0.82 and 0.92, respectively [106]. …”

Spectroscopic and electrochemical behavior of a supramolecular tetrapyridylporphyrin encompassing four terpyridine(oxalate)chloridoruthenium(II) complexes and its use in nitrite sensors

“…Another important characteristic of porphyrins is their luminescent properties. The so called base free porphyrins (without metal coordinated to central ring) and those coordinated with closed shell metal ions [31], such as Mg 2+ and Zn 2+ , exhibit high fluorescence, with quantum yields between 10 À1 and 10 À3 [32].…”

Kinetic model for the molecular system of Zinc(II)-2,9,16,23-phthalocyanine tetracarboxylate

“…Then, energy is transferred from |T 1 state to triplet molecular oxygen ( 3 O 2 ) to generate highly reactive singlet oxygen ( 1 O 2 ) which is the most important cytotoxic species. 21,27,41 Because 1 ∆ + g state of 1 O 2 lies at 0.98 eV above the triplet ground state of molecular oxygen (Fig. 5), the energy difference between |S 0 and |T 1 states of a fluorophore must be equal or around this value to allow the production of singlet oxygen.…”