inorganic chemistry

are based on noncovalent interactions, such asp-stacking, van
der Waals forces, and hydrogen and metal–metal bonding. Pure
ionic liquids and those entrapped within the gels showed compa-
rably high conductivities, which renders pyridine-bridged bis
(benzimidazolylidene)–palladium pincer complexes as air-stable
metallogelators that efficiently immobilize ionic liquids in low
gelator concentrations indicating, apart from catalysis, their poten-
tial application in electrochemical devices.
Shinkaiet al.( 265 ), however, employed bidentate ligands to
produce planar, stacking complexes of Cu(II), Pd(II), and Pt(II).
8-quinolinol/copper(II)-, palladium(II)-, and platinum(II)-chelate-
based organogelators and their nongelling reference compounds
were synthesized. The complexes gelated various organic
solvents at very low concentrations. Electron microscopy gave
visual images of well-developed fibrous structures characteristic
of low-molecular weight organogels. UV/vis and FTIR spectros-
copy revealed that the outstanding gelation ability arises from
thep–pinteractions of the chelate moieties and the hydrogen-
bond interactions between the amide groups. The nanofibers
are evidently different depending on the electronic states of the
different central metals. The Pt gel shows unique thermo- and
solvatochromism of absorption and emission color in response
to a sol–gel transition (Fig. 24). Further, the Pt gel possesses
an attractive ability to avoid dioxygen quenching of excited
triplet states, which has a positive effect on the phosphorescence

R–NH

O

M = Cu, Pd, Pt

R =

R =

O

O

O

O

H

N

550

Phosphorescence intensity ( a.u.)

600

Wavelength(nm)

650 700

5 mm

Gel

Sol

Sol Gel

O

O-n-C 12 H 25

O-n-C 12 H 25

n-C 12 H 25

HN-R

N

N

M

FIG. 24. Quinolinate metal complexes described by Shinkaiet al.
Phosphorescence spectra and photographs of sol and gel phases of a
gelating Pt(II) complex are shown, as well as a confocal scanning laser
microscopy micrograph of the gel. Reproduced with the permission of
Wiley-VCH ( 265 ).

PHOTOPHYSICS OF MOLECULAR ASSEMBLIES 87