Photophysical characterization of a bisacridinium-diphenylporphyrin conjugate

A molecular conjugate made of a free-base diphenyl porphyrin chromophore (DPP) trans-linked to two N-acridinium units has been synthesized and photophysically characterized in acetonitrile. Interestingly, the emission of both fluorophores is quenched in the array at room temperature. Steady-state and time-resolved optical analysis proved that an ultrafast electron transfer from the porphyrin to the acridinium units occurs upon excitation of either the porphyrin or the acridinium moiety. On the other hand, at low temperature (77 K) the emission of the porphyrin is completely recovered, thanks to the inhibition of the electron transfer, and a photoinduced energy transfer from the acridinium to the porphyrin component is observed. The photophysical properties of a bis-acridinium-diphenylporphyrin conjugate have been investigated, revealing ultrafast photoinduced electron transfer (eT) from the porphyrin to the acridinium moiety at room temperature and efficient energy transfer (EnT) from the acridinium to the porphyrin at low temperature.