Sequential charge separation in two axially linked phenothiazine- aluminum(III) porphyrin-fullerene triads

New supramolecular triads (PTZpy→AlPor - C₆₀, TPTZpy→AlPor - C₆₀), containing aluminum(III) porphyrin (AlPor), fullerene (C₆₀), and phenothiazine (phenothiazine = PTZ, 2-methylthiophenothaizine = TPTZ) have been constructed. In these triads the fullerene and phenothiazine units are bound axially to opposite faces of the porphyrin plane via covalent and coordination bonds, respectively. The ground-and excited-state properties of the triads and reference dyads are studied using steady-state and time-resolved spectroscopic techniques. The time-resolved data show that photoexcitation results in charge separation from the excited singlet state of the porphyrin to the C₆₀ unit, generating (Donor)py→AlPor^•+ - C₆₀ ^•-, Donor = PTZ and TPTZ. A subsequent hole shift from the porphyrin to phenothiazine generates the charge-separated state (Donor) ^•+ py→AlPor - C₆₀^•-. The lifetime of the charge separation exhibits a modest increase from 39 ns in the absence of the donor to 100 ns in PTZpy→AlPor - C₆₀ and 83 ns in TPTZpy→AlPor - C₆₀. These lifetimes are discussed in terms of the electronic coupling between phenothiazine, the porphyrin, and C ₆₀.