Synthesis of dithiaporphyrin-based singlet–singlet energy transfer systems

The synthesis of the first alkynyl core-modified porphyrin building block, 5,10,15,20-tetrakis(4-ethynylphenyl)-21,23-dithiaporphyrin (N2S2 core), is reported. The building block was used to construct donor-appended dithiaporphyrin systems under mild palladium-coupling conditions. The porphyrin building block appended to four boron–dipyrrin units, (BDPY)4S2TPP, did not show any energy transfer from the BDPY unit to the central dithiaporphyrin core. However, the pentaporphyrin containing a central dithiaporphyrin sub-unit and four peripheral normal porphyrin sub-units (N4 core) showed efficient energy transfer from the peripheral N4 porphyrins to the central N2S2 porphyrin.