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.

Two isomeric [5,6]-pyrrolidine-I h -Sc 3 N@C 80 electron donor acceptor conjugates containing triphenylamine (TPA) as the donor system were synthesized. Electrochemical and photophysical studies of the novel conjugates were made and compared with those of their C 60 analogues, in order to determine i) the effect of the linkage position (N-substituted versus 2-substituted pyrrolidine) of the donor system in the formation of photoinduced charge separated states, ii) the thermal stability towards the retro-cycloaddition reaction and iii) the effect of changing C 60 for I h -Sc 3 N@C 80 as the electron acceptor. It was found that when the donor is connected to the pyrrolidine nitrogen atom, the resulting dyad produces a significantly longer lived radical pair than the corresponding 2-substituted isomer for both the C 60 and I h -Sc 3 N@C 80 dyads. In addition to that, the N-substituted TPA-I h -Sc 3 N@C 80 dyad has much better thermal stability than the 2-subtituted one. Finally, the I hSc 3 N@C 80 dyads have considerably longer lived charge separated states than their C 60 analogues, thus approving the advantage of using I h -Sc 3 N@C 80 instead of C 60 as the acceptor for the construction of fullerene based donor acceptor conjugates. These findings are important for the design and future application of I h -Sc 3 N@C 80 dyads as materials for the construction of plastic organic solar cells.

By introducing SO(2) as the sulfur source, the synthesis of an extensive family of cluster endohedral fullerenes Sc(2)S@C(2n) (n = 40-50) was demonstrated and a new isomer of Sc(2)S@C(82) (C(s) : 6) was isolated and characterized by spectroscopic and electrochemical methods for the first time.

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).

The clusterfullerene Sc(4)O(2)@C(80) with a mixed redox state of scandium was found to be an exciting molecule for endohedral electrochemistry as demonstrated by means of an in situ electron spin resonance (ESR) spectroelectrochemical study of the spin density distribution in its electrochemically generated cation and anion radicals. The compound exhibits two reversible reduction and oxidation steps with a relatively small electrochemical gap of 1.10 V. The ESR spectra of the ion radicals have a rich hyperfine structure caused by two pairs of equivalent Sc atoms. The Sc-based hyperfine structure with large hyperfine coupling constants shows that both oxidation and reduction of Sc(4)O(2)@C(80) are in cavea redox processes, which is the subject of endohedral electrochemistry. The assignment of the experimentally determined a((45)Sc) values to the two types of Sc atoms in the Sc(4)O(2) cluster was accomplished by extended density functional theory and molecular dynamics simulations. Sc atoms adopting a divalent state in the neutral Sc(4)O(2)@C(80) exhibited an especially large coupling constant of 150.4 G in the cation radical, which is the record high a((45)Sc) value for Sc-based endohedral metallofullerenes. Such a high value is explained by the nature of the highest occupied molecular orbital (HOMO) localized on the six-atom Sc(4)O(2) cluster. This HOMO is a Sc-Sc bonding MO and hence has large contributions from the 4s atomic orbitals of Sc(II). We claim that ESR spectroelectrochemistry is an invaluable experimental tool in the studies of metal-metal bonding in endohedral metallofullerenes and in endohedral electrochemistry.