crystal. To reach this goal, anthraquinone molecules, good elec-
tron acceptors, were inserted by gas-phase inclusion. The photo-
induced electron transfer process results in an exoergonic
reaction (DG¼0.51 eV) for the cationic component, thus lead-
ing to the oxidized2aand the reduced anthraquinone. As a con-
sequence of the strong quenching of the emission of the red
component, the emission spectrum of the crystal displayed an
ipsochromic shift, with a shortening of the excited-state lifetime
of the red-emitting component (seeFig. 10).
These findings demonstrated for the first time that lumines-
cent complexes made of complementary colors and charges can
be used for the creation of a new class of noncovalently linked
porous materials and that their properties depend strongly on
the intermolecular interactions and on the guests entrapped
in their network. Further, due to the different oxidation states of
the metals employed, multiredox reactions could be envisaged just
upon light excitation. Color modulation has been demonstrated
and the active framework could be designed to lead to on/off signal
upon recognition of different guests, therefore acting as sensor
materials.
FIG. 10. Confocal microscope emission spectra of a single crystal of
complex 1 before (black spectrum) and after (red spectrum) insertion
of anthraquinone molecules inside the pores. As can be seen by eyes
the emission of the crystal change from orange to green. Reproduced
with the permission of Wiley-VCH ( 170 ).
70 CRISTIAN A. STRASSERTet al.