inorganic chemistry

dz^2 orbitals of the central Pt(II) atoms. In this case, this phenom-
enon only becomes evident in frozen matrix and in thin film
where aggregate formation is favored. Therefore, the turn on of
the bright luminescence upon aggregation can be employed to
monitor the assembling process with high sensitivity.
The formation of fibers in solution was clearly revealed by fluo-
rescence microscopy and scanning electron microscopy (see
Fig. 21). The fibers self-assemble in larger entangled structures
but their emission properties remain unchanged. Diffusion of
hexane into the colorless, nonemissive solution of the complex
in CHCl 3 , affords a self-assembled yellow gel that appears highly
luminescent under UV irradiation (see Fig. 21, bottom right).
A close inspection by SEM revealed a 3D network of fibers
responsible for the structure of the emissive soft material, and
TEM analysis (see Fig. 21, bottom right) showed the interlocking
nature of the nanofibers. The spectroscopic features prove that
the gel is an extremely efficient emitter, with up to 90% emission

ca. 8 Å

Self-assembly Gelation

ca. 17

Å

10 mm

200 nm^1 mm 200 nm

20 zm

N

Pt

NNN

N N N

NNN

FIG. 21. Top: schematic representation of the subsequent aggrega-
tion and gelation processes with the Pt(II) complex. Middle: fluores-
cence microscopy images of the aggregates, and (right) of the gel.
Bottom (left and center): SEM: micrographs of the self-assembled fibers
and TEM micrograph (bottom, right) of the self-assembled gel.
Reproduced with the permission of Wiley-VCH ( 217 ).

84 CRISTIAN A. STRASSERTet al.