Journal of Physical Chemistry A, Vol.115, No.5, 709-717, 2011
Sequential Charge Separation in Two Axially Linked Phenothiazine-Aluminum(III) Porphyrin-Fullerene Triads
New supramolecular triads (PTZpy -> AlPor-C-60, TPTZpy -> AlP0r-C-60), containing aluminum(III) porphyrin (AlPor), fullerene (C-60), 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 C-60 unit, generating (Donor)py -> AlPor(center dot+)-C-60(center dot-), Donor = PTZ and TPTZ. A subsequent hole shift from the porphyrin to phenothiazine generates the charge-separated state (Donor)(center dot+)py -> AlPor-C-60(center dot-). 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-C-60 and 83 ns in TPTZpy -> AlPor-C-60. These lifetimes are discussed in terms of the electronic coupling between phenothiazine, the porphyrin, and C-60.