Modulation of Molecular Singlet Oxygen (1Δg) Generation with a Magnetic Field

Abstract

Molecular singlet oxygen (1Δg) (MSO) is the oxygen molecule in its first excited state. It is known as one of the reactive oxygen species (ROS), which is responsible to the cell aging, photo-damage of dye molecules, malignant skin tumors and so forth. It also plays important roles in organic syntheses and photodynamic therapy. MSO can be generated by energy transfer to the molecular oxygen at ground state (3Σg-) from excited photosensitizers. The energy transfer to the triplet ground state oxygen molecule from the triplet excited photosensitizer is more efficient than from the singlet excited photosensitizer. We used a Pyrene-based photosensitizer (Pyrene-(CH2)12-O-(CH2)2- N,N-dimethylaniline) that produces radical ion-pair (RIP) intermediate whose total spin state can be modulated between singlet (1RIP) and triplet (3RIP) states with an external magnetic field. This phenomenon is called magnetic field effect (MFE). By using this photosensitizer, generation of MSO can be modulated. In this work, I demonstrate that the modulated 1RIP/3RIP ratio of the excited photosensitizer results in change in MSO generated with the magnetic field. The amount of MSO is detected by its phosphorescence (P) at 1275 nm.