Photophysical Properties of the Electron-Deficient Phosphorus Corroles Bearing meso-Fluorophenyl Substituents

Abstract

The photophysical properties of a series of phosphorus corroles in a noncoordinating solvent, toluene, were investigated using steady-state and transient absorption spectroscopy (TAS). The compounds studied─P–F0, P–F5, P–F10, and P–F15─share the same axial ligands (two hydroxyl groups) but differ in the number of electron-withdrawing meso-pentafluorophenyl substituents. Fluorination resulted in a slight decrease in the fluorescence quantum yield (Φ_F) from 0.19 to 0.15, while the quantum yields of singlet oxygen (¹O₂) (Φ_Δ) significantly increased from 0.68 to 0.97, making P–F15 a promising candidate for photodynamic therapy (PDT). TAS results revealed that the four compounds exhibited similar kinetic behaviors: internal conversion (IC) around 0.6–0.7 ps, vibrational relaxation (VR) in the 14–18 ps range, and intersystem crossing (ISC) ∼ 3 ns. The only distinct difference was observed in the triplet-state decay process (τ_T⁰), which was prolonged with fluorination from ∼150 to 200 μs. The longer-lived T₁ plays an important role in promoting the production of ¹O₂. Additionally, time-dependent density functional theory (TDDFT) calculations were conducted for all four molecules. The HOMO/LUMO energy levels and oscillator strengths of several electronic transitions were examined.