The first pyrrolidine and cyclopropane derivatives of the trimetallic nitride templated (TNT) endohedral metallofullerenes I(h)-Sc(3)N@C(80) and I(h)-Y(3)N@C(80) connected to an electron-donor unit (i.e., tetrathiafulvalene, phthalocyanine or ferrocene) were successfully prepared by 1,3-dipolar cycloaddition reactions of azomethine ylides and Bingel-Hirsch-type reactions. Electrochemical studies confirmed the formation of the [6,6] regioisomers for the Y(3)N@C(80)-based dyads and the [5,6] regioisomers in the case of Sc(3)N@C(80)-based dyads. Similar to other TNT endohedral metallofullerene systems previously synthesized, irreversible reductive behavior was observed for the [6,6]-Y(3)N@C(80)-based dyads, whereas the [5,6]-Sc(3)N@C(80)-based dyads exhibited reversible reductive electrochemistry. Density functional calculations were also carried out on these dyads confirming the importance of these structures as electron transfer model systems. Furthermore, photophysical investigations on a ferrocenyl-Sc(3)N@C(80)-fulleropyrrolidine dyad demonstrated the existence of a photoinduced electron-transfer process that yields a radical ion pair with a lifetime three times longer than that obtained for the analogous C(60) dyad.

Intriguing materials for photovoltaics: The first trimetallic nitride endohedral metallofullerene covalently connected to a donor group is efficiently synthesized in a 1,3‐dipolar cycloaddition reaction. Exclusive formation of the [5,6]‐regioisomer in the isolated N‐methyl‐2‐ferrocenyl‐Ih‐Sc3N@C80‐fulleropyrrolidine is confirmed by NMR spectroscopy and electrochemistry (see picture).

On the ball: Charge transfer occurs readily in tightly interacting complexes formed from π‐extended tetrathiafulvalenes, which act as pincerlike receptors, and C60 in a variety of solvents upon photoexcitation (see picture; PET=photoelectron transfer). It should be feasible to construct simple photovoltaic devices from systems based on similar recognition motifs.

Mit Potenzial für die Photovoltaik: Das erste Konstrukt, in dem ein endohedrales Trimetallnitridfulleren kovalent mit einer Donorgruppe verknüpft ist, wurde durch eine effiziente 1,3‐dipolare Cycloaddition erhalten. Dass das N‐Methyl‐2‐ferrocenyl‐Ih‐Sc3N@C80‐fulleropyrrolidin ausschließlich in Form des [5,6]‐Regioisomers isoliert wird, ließ sich NMR‐spektroskopisch und elektrochemisch nachweisen (siehe Bild).

The synthesis, structure, photoelectrochemical behavior, and nonlinear optical (NLO) properties of a symmetric acceptor-acceptor-donor-acceptor-acceptor array, C(60)-Co-TTF-Co-C(60), have been described. The precursors, namely, cobalt dicarbonyl complexes Co(C(60)Ar(5))(CO)(2) were synthesized from the penta(organo)[60]fullerenes, C(60)Ar(5)H, as starting materials. In the next step, two cobalt-fullerene complexes were connected to a tetrathiafulvalene (TTF) tetrathiolate bridge to obtain the C(60)-Co-TTF-Co-C(60) array. In addition, the monomeric compounds, Co(C(60)Ar(5))(S(2)C(2)R(2)) (R = CO(2)Me and CN) and Co(C(60)Ar(5))(S(2)C(2)S(2) C = CS(2)C(2)R(2)) were synthesized as references. The C(60)-Co-TTF-Co-C(60) array exhibits very strong transitions in the near-infrared region (lambda(max) = 1,100 nm, epsilon = 30 000 M(-1) x 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 C(60)-Co-TTF-Co-C(60) array. The third-order NLO measurement of the array gave the magnitude of the third-order nonlinear susceptibility, |chi((3))|, values to be 9.28 x 10(-12) esu, suggesting the pi-conjugation of donors and acceptors in the array.