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 (ΦΔ ) 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 (λP ) located at λ=957 and 970 nm. The excited-triplet-state energies (ET ) were estimated to be approximately 1.30 eV, whereas the triplet lifetimes (τT ) 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 EHOMO gave a value of approximately -5.8 eV whereas ELUMO was found to be located at around -3.8 eV.
Keywords: excited triplet states; phosphorescence; photosensitizers; singlet oxygen; subphthalocyanines.
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