Intramolecular\nCharge Transfer and Spin–Orbit\nCoupled Intersystem Crossing in Hypervalent Phosphorus(V) and Antimony(V)\nPorphyrin Black Dyes

Porphyrin dyes with\nstrong push–pull type intramolecular\ncharge transfer (ICT) character and broad absorption across the visible\nspectrum are reported. This combination of properties has been achieved\nby functionalizing the periphery of hypervalent and highly electron-deficient\n phosphorus(V) and antimony(V) centered porphyrins with electron-rich\ntriphenylamine (TPA) groups. As a result of the large difference in\nelectronegativity between the porphyrin ring and the peripheral groups,\ntheir absorption profiles show several strong charge transfer transitions,\nwhich in addition to the porphyrin-centered π → π*\ntransitions, make them panchromatic black dyes with high absorption\ncoefficients between 200 and 800 nm. Time-resolved optical and electron\nparamagnetic resonance (EPR) studies show that the lowest triplet\nstate also has ICT character and is populated by spin–orbit\ncoupled intersystem crossing.