such as micelles, vesicles, and gels, and finish with crystalline
materials. Along our journey, we will elaborate on design
features, photophysical properties, structure–activity correlation,
and potential applications. The selected examples are based
on noncovalently linked luminescent systems in which the
self-assembly process generates new functions.
II. Basic Photophysics of Selected Transition Metal ComplexesMany excellent reviews and books have been written
concerning the photophysics of organometallic species( 16 – 22 ),a
detailed discussion exceeds the scope of this work. We wish to
give to the reader only the photophysical basis of selected d^6
and d^8 complexes to follow better the discussion in the next
sections. In brief, in a metal complex, its molecular constitution
can be described as a metallic center surrounded by an organic
coordination sphere. The electronic interplay between these
units defines the character of the electronic excited states, which
are the ones to undergo subsequent photophysical or photochem-
ical processes.
Ground and excited-state electronic wave functions facilitate
the presentation of electron density relocations that can be
visualized and interpreted as transitions involving localized
molecular orbitals (MOs). However, the limitation of this model
should be kept in mind. This is particularly true for the nature
of the transitions, which actually occur between electronic states
that cannot even be regarded as purely zero-order in nature. Due
to electron correlation, interconfigurational mixing is indeed
introduced for a more accurate description, namely as configura-
tion interaction of zero-order wave functions. Electronic states
are then approximated as combinations of zero-order wave
functions, yielding representations of mixed nature(23,24).
For complexes, the combination of metal-centered (MC) d and
ligand-centered (LC) orbitals leads to MOs which are den-
ominated according to the predominant atomic orbital con-
tributions. Therefore, transitions between zero-order electronic
configurations can be classified as LC, MC, or CT electron den-
sity displacements. If contrasted with the ground state, the first
two mainly involve changes within the organic portions (LC) or
the inorganic part (MC) of the molecule. The latter one (CT)
involves a vectorial redistribution within or between the organic
ligands (intra- or interligand charge transfer, respectively,
ILCT), or more frequently, between the organic part and the
metal center. According to the directionality of the electron
50 CRISTIAN A. STRASSERTet al.