Switchable Triplet Charge Transfer in a Highly Stable Panchromatic Hypervalent Phosphorus(V) Porphyrin

A panchromatic hypervalent phosphorus(V) porphyrin exhibiting reversible intramolecular charge transfer (CT) is reported. The complex was constructed by coupling the electron-deficient phosphorus(V) porphyrin core with electron-rich N,N-dimethylaniline (DMA) substituents, creating an electronic disparity between the central macrocycle and peripheral donor groups. As a result, the compound displays intense charge-transfer absorption bands spanning 200–800 nm. Steady-state and transient optical spectroscopy, transient EPR spectroscopy, and DFT studies reveal the CT character of the excited states and that the emission at ambient temperature arises from both singlet and triplet CT states, with the latter being populated via spin–orbit-coupling mediated intersystem crossing. Notably, the CT process can be reversibly switched ON and OFF via protonation of the DMA nitrogen atoms. The combination of singlet and triplet CT states with appreciable lifetimes, their switching via simple protonation of peripheral DMA groups, photostability, and broad optical coverage makes these dyes highly promising chromophores for artificial photosynthesis, optoelectronics, and photocatalysis, and strengthens our fundamental understanding of these phenomena.