Synthesis, optical properties, and electronic structures of fully core-modified porphyrin dications and isophlorins

The synthesis, structures, optical properties, and electronic structures of the tetraphenyltetrathiaporphyrin dication (S ₄TPP ²⁺, 6) and tetrakis(pentafluorophenyl)tetrathiaisophlorin (S ₄F ₂₀TPP, 7) are reported. S ₄TPP ²⁺ (6) and S ₄F ₂₀TPP (7) were synthesized by acid-catalyzed condensation of the corresponding hydroxylmethylthiophene, followed by oxidation. The electronic structures of S ₄TPP ²⁺ (6) and S ₄F ₂₀TPP (7) were analyzed by using UV/Vis-absorption spectroscopy and by magnetic /ular dichroism (MCD) spectroscopy and the bands were assigned by using time-dependent density functional theory (TD-DFT) and ZINDO/s calculations. A red-shift of the Q bands of S ₄TPP ²⁺ (6) is observed relative to the spectra of tetraphenylporphyrins because a destabilization of the HOMO leads to a narrower HOMO-LUMO band-gap. Michl's perimeter model was used to assign the absorption bands and MCD spectra of S ₄F ₂₀TPP (7). Current-density maps and nucleus-independent chemical-shift (NICS) calculations of S ₄TPP ²⁺ (6) and of a model compound predict marked modification to the diamagnetic ring current, whilst nonaromatic character is predicted for S ₄F ₂₀TPP (7).