quantum yield. The soft assembly also displays not only the
highest photoluminescence quantum yield and radiative rate
constant but also the lowest radiationless deactivation rate, if
compared with doped polymethylmetacrylate and neat films.
This points to the high degree of order within the filaments,
which favors radiative processes and minimizes nonradiative
pathways.
Self-assembly of Pt(II) complexes yielding luminescent liquid
crystals (210,211,274) and AIE ( 275 – 279 ) have been already
described, but metal complexes forming soft structures with such
intense phosphorescence are very rare.
Further, the use of aggregates to build up electroluminescent
devices is a new interesting strategy not only to develop novel
colors but also to take advantage of the AIE in real applications.
Therefore, we have explored the application of the Pt aggregates
in solution-processed OLED devices, showing high brightness
and good color purity( 217 ).
Dötz et al.( 218 ) developed robust functional organometallic
compounds as low-molecular mass gelators, with the aim to
introduce the unique properties of organopalladium catalysts
into organometallic gelators. They described a palladium pincer
bis(carbene) complex constituting an efficient organometallic
gelator for a variety of protic and aprotic organic solvents even
in concentrations as low as 0.2 wt% (Fig. 22). NMR spectroscopy
and X-ray diffraction studies indicated that pstacking of the
heteroarene moieties, van der Waals interactions between the
alkyl chains, and metal–metal interactions may be responsible
for the aggregation. It represents an air-stable organometallic
low-molecular mass gelator that is readily accessible from com-
mercial precursors and, moreover, reveals promising catalytic
activity in CC bond formation even in the gel state.
The approach was further extended by the introduction of novel
pincer-type, pyridine-bridged bis(benzimidazolylidene)–palladium
complexes, which were synthesized reacting readily accessible com-
mercial precursors under microwave assistance( 219 ). Despite the
simplicity of their structures, the carbene complexes constituted
low-molecular mass metallogelators (Fig. 23). They efficiently gel-
ate not only a broad variety of protic and aprotic organic solvents
but also different types of ionic liquids (such as imidazolium,
pyridinium, pyrazolidinium, piperidinium, and ammonium salts)
at concentrations as low as 0.5 mg mL–^1. The morphologies of the
resulting 3D gel networks composed of long and thin fibers were
studied by TEM and light microscopy for a selection of organic and
ionic liquids, showing that the achiralgelators assemble into helical
fibers. The thermal stability of the gel is enhanced at increasing
PHOTOPHYSICS OF MOLECULAR ASSEMBLIES 85