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π-Conjugated Multidonor/Acceptor Arrays of Fullerene−Cobaltadithiolene−Tetrathiafulvalene: From Synthesis and Structure to Electronic Interactions

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journal contribution
posted on 2009-09-09, 00:00 authored by Yutaka Matsuo, Masashi Maruyama, S. Shankara Gayathri, Tomoya Uchida, Dirk M. Guldi, Hideo Kishida, Arao Nakamura, Eiichi Nakamura
The synthesis, structure, photoelectrochemical behavior, and nonlinear optical (NLO) properties of a symmetric acceptor−acceptor−donor−acceptor−acceptor array, C60-Co−TTF−Co-C60, have been described. The precursors, namely, cobalt dicarbonyl complexes Co(C60Ar5)(CO)2 were synthesized from the penta(organo)[60]fullerenes, C60Ar5H, as starting materials. In the next step, two cobalt−fullerene complexes were connected to a tetrathiafulvalene (TTF) tetrathiolate bridge to obtain the C60-Co−TTF−Co-C60 array. In addition, the monomeric compounds, Co(C60Ar5)(S2C2R2) (R = CO2Me and CN) and Co(C60Ar5)(S2C2S2 C = CS2C2R2) were synthesized as references. The C60-Co−TTF−Co-C60 array exhibits very strong transitions in the near-infrared region (λmax = 1,100 nm, ε = 30 000 M−1·cm−1) due to a ligand-to-metal-charge-transfer (LMCT) transition and six reversible electron transfer processes. In the crystal, a fullerene/TTF-layered packing structure is evident. Femtosecond flash photolysis revealed that photoexcitation of the array results in a charge separated state involving the strongly interacting cobaltadithiolene and TTF constituents which electronically relax via a resonance effect that extends all throughout the acceptor parts of the C60-Co−TTF−Co-C60 array. The third-order NLO measurement of the array gave the magnitude of the third-order nonlinear susceptibility, |χ(3)|, values to be 9.28 × 10−12 esu, suggesting the π-conjugation of donors and acceptors in the array.

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