Photosensitizers with high energy, long lasting charge-transfer states are important components in systems designed for solar energy conversion by multistep electron transfer. Here, we show that in a push-pull type, μ-oxo-bridged porphyrin heterodimer composed of octaethylporphyrinatoaluminum(iii) and octaethylporphyrinatophosphorus(v), the strong excitonic coupling between the porphyrins and the different electron withdrawing abilities of Al(iii) and P(v) promote the formation of a high energy CT state. Using, an array of optical and magnetic resonance spectroscopic methods along with theoretical calculations, we demonstrate photodynamics of the heterodimer that involves the initial formation of a singlet CT which relaxes to a triplet CT state with a lifetime of ∼130 ps. The high-energy triplet CT state (3CT = 1.68 eV) lasts for nearly 105 μs prior to relaxing to the ground state.
Bibliographical noteFunding Information:
This work was supported by Grant-in-Aid (GIA No. 380228 to PPK) from the University of Minnesota Duluth, by the National Science Foundation (Grant No. 2000988 to FD), and by an NSERC Discovery Grant (2015-04021 to AvdE). The computational work was completed utilizing the Holland Computing Center of the University of Nebraska, which receives support from the Nebraska Research Initiative. A. B. thanks Dip. Scienze Chimiche and Un. degli Studi di Padova for financial support (p-Disc 2020).
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