Efficient Photoinduced Energy and Electron Transfer in ZnII–Porphyrin/Fullerene Dyads with Interchromophoric Distances up to 2.6 nm and No Wire-like Connectivity

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Efficient Photoinduced Energy and Electron Transfer in ZnII–Porphyrin/Fullerene Dyads with Interchromophoric Distances up to 2.6 nm and No Wire-like Connectivity

Maida Vartanian, Nicola Armaroli, Uwe Hahn, Julien Iehl, Fernando Langa, María Vizuete, Jean-François Nierengarten, John Mohanraj, Béatrice Delavaux-Nicot, Andrea Barbieri

The dyads 1–3 made of an alkynylated ZnII–porphyrin and a bis-methanofullerene derivative connected through a copper-catalyzed azide–alkyne cycloaddition have been synthesized. The porphyrin and fullerene chromophores are separated through a bridge made of a bismethanofullerene tether linked to different spacers conjugated to the porphyrin moiety [i.e., m-phenylene (1), p-phenylene (2), di-p-phenylene-ethynylene (3)]. Compounds 1–3 exhibit relatively rigid structures with an interchromophoric separation of 1.7, 2.0, and 2.6 nm, respectively, and no face-to-face or direct through-bond conjugation. The photophysical properties of compounds 1–3 have been investigated in toluene and benzonitrile with steady-state and time-resolved techniques as well as model calculations on the Förster energy transfer. Excited-state interchromophoric electronic interactions are observed with a distinct solvent and distance dependence. The latter effect is evidenced in benzonitrile, where compounds 1 and 2 exhibit a photoinduced electron transfer in the Marcus-inverted region, with charge-separated (CS) states living for 0.44 and 0.59 μs, respectively, whereas compound 3 only undergoes energy transfer, as in apolar toluene. The quantum yield of the charge separation (φCS) of compounds 1 and 2 in benzonitrile is ≥0.75. It is therefore demonstrated that photoinduced energy and electron transfers in porphyrin–fullerene systems with long interchromophoric distances may efficiently occur also when the bridge does not provide a wire-like conjugation and proceed through the triplet states of the chromophoric moieties. Mixed bridge: A series of rigid fullerene–porphyrin conjugates has been prepared. An efficient photoinduced electron transfer occurs up to an interchromophoric distance of 2.0 nm, despite the “hybrid” nature of the bridge that does not guarantee a direct conjugation (see figure). Above 2.5 nm, only an energy transfer is observed, even in the polar solvent benzonitrile.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701668