Photochemistry and Photophysics of Coordination Compounds

Photochemistry and Photophysics of Coordination Compounds: Copper 93
ically porphyrins and fullerenes. Intercomponent light-induced energy- and
electron-transfer processes have been investigated in [2]- [93, 94] and [3]catenanes
[29, 95, 96], dinuclear knots [97], fullerene- [98] and porphyrinstoppered
rotaxanes [99–108], dendrimers with [Cu(NN)2] + cores [38], and
helicates with Cu(I)-complexed cores and peripheral methano- [109] or
bismethano-fullerenes [41, 109, 110]. The latter, which constitute the most recently
investigated systems, are depicted in Fig. 23.
Fig. 23 Fullerohelicates based on a dinuclear [Cu(NN)2] + complex (Z=C8H17,R=C12H25).
The peripheral moieties are different in the two cases, namely bismethano (left) vs.
methanofullerenes (right)
Upon excitation of the Cu(I)-complexed moiety and population of the related
MLCT level, electron transfer to the fullerene subunit is observed for
both compounds shown in Fig. 23. By contrast, although the same process
is thermodynamically allowed also by populating the fullerene lowest singlet
state, it is observed only in the case of the methanofullerene system. This
is related to the inherently different electronic structure of the two fullerene
derivatives. By means of an analysis of their fluorescence spectra, which
are substantially different, it was possible to conclude that the singlet excited
state of methanofullerenes is more prone to undergo electron transfer than
that of bismethanofullerenes, thanks to the associated smaller internal reorganization
energy [109]. In addition, methanofullerenes are slightly easier to
reduce than bismethanofullerenes, giving also a thermodynamic advantage
for electron transfer in multicomponent arrays containing the monofunc-