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...