Excited and ground-state complexes of tetraphenylporphyrin (TPP) with some organic electron acceptors

Abstract

Bimolecular reactions between singlet excited TPP (¹TPP*) and various nitroaromatic acceptors were investigated in solvents with various polarity. The reactions between ¹TPP* as electron donor and both picric acid (PIC) and 3,5-dinitrosalicylic acid (DNS) as electron acceptors were accompanied by the appearance of a new emission band in non-polar and slightly polar solvents. A new absorption charge-transfer (CT) band was also observed between TPP and both PIC and DNS. This effect was not observed for other nitroaromatic acceptors. The new emission of the CT complexes was interpreted as a CT excited complex (exciplex). The rate constant (k_q) of the deactivation process, excited-state dipole moment, fluorescence lifetime and activation energies of the CT exciplex are presented. In addition, the association constant, molar absorption coefficients and thermodyn-amic standard reaction quantities of the ground-state complexes were also investigated in solvents of various polarities.