Facile Synthesis, Triplet-State Properties, and Electrochemistry of Hexaiodo-Subphthalocyanine

In view of the ever-growing demand for efficient triplet photosensitizers and photoactive components of various optoelectronic devices, we herein report the synthesis and properties of hexaiodo-subphthalocyanines (I₆ SubPcs). The improved five-step route to 4,5-diiodophthalonitrile, which serves as precursor for the synthesis of the I₆ SubPcs, is reported. The improved synthesis merely required one chromatographic separation to afford the high-purity target product. Highly desirable photophysical and photochemical properties were induced in the I₆ SubPcs due to the presence of six heavy iodine atoms. In particular, high values of the singlet-oxygen quantum yields (Φ_Δ ) ranging from 0.83 to 0.9 were measured. The I₆ SubPcs investigated proved to be phosphorescent at 77 K in 2-MeTHF with emission band maxima (λ_P ) located at λ=957 and 970 nm. The excited-triplet-state energies (E_T ) were estimated to be approximately 1.30 eV, whereas the triplet lifetimes (τ_T ) were found to be 27.7 and 30.1 μs. The CV/DPV measurements indicated that both I₆ SubPcs exhibited one irreversible oxidation and one quasi-reversible reduction. The spectroelectrochemical measurements pointed to a relative stability and reversibility of the electrochemically formed anion radical, that is, I₆ SubPc^.- , and an instability of the species formed upon one-electron oxidation, that is, I₆ SubPc^.+ . Estimation of E_HOMO gave a value of approximately -5.8 eV whereas E_LUMO was found to be located at around -3.8 eV.