process can tolerate chemical modification on the cyclometalated
ligand, which further expands the capabilities of such
assemblies.
This work could therefore trigger some interesting develop-
ments in the use of labile ligands which could induce conforma-
tional changes in nano/microstructures resulting in modulation
of mechanical properties.
Employing a rather different structural motif, Aida and
coworkers ( 212 ) successfully developed different types of nan-
otubes with walls of pyridine–platinum(II) coordination layers
by using pyridyl-appended hexabenzocoronene. The self-assem-
bling process was triggered by vapor diffusion or heat–cool
cycles. When the nanotubes were suspended in CH 2 Cl 2 solutions,
all of them disassembled into the corresponding monomers. In
contrast, the nanotube obtained by the coassembly with cross-
linkingtrans-[Pt(PhCN) 2 Cl 2 ] under heat–cool conditions was tol-
erant against dissociation. However, in the coassembly with
trans-[Pt(PhCN) 2 Cl 2 ], the metal coordination could take place
both at an inter and intramolecular level (Fig. 15). Interestingly,
structure of the nanotubes affects the electrochemical properties
that depend on the degree of shielding of the metallic centers.
B. 2D ARRAYS
Che and coworkers( 258 ) accomplished a further dimensional-
ity in free-standing and crystalline nanosheets self-assembled
from neutral pincer-type cyclometalated platinum(II) aryl
acetylides. The complexes in solid state display various colors,
depending on the substituent on the aryl acetylide ligand
(Fig. 16). When electron-withdrawing groups, electron-donating
groups, or neutral groups are introduced, the solid is bright yel-
low, deep red, or dark green in color, respectively. They showed
that these organoplatinum(II) complexes can self-assemble into
nearly bidimensional nanostructures displaying near infrared
phosphorescence and light-modulated conductivity. The molecu-
lar organization in the nanosheets is due to orthogonal PtPt
and CHp(CC) interactions, highlighting that phosphores-
cent platinum complexes provide an entry to 2D supramolecular
nanomaterials with particular optoelectronic properties derived
from metal–metal interactions.
Yam et al.( 259 ), however, employed platinum(II) 2,6-bis(1-
alkylpyrazol-3-yl)pyridyl complexes with various chain lengths
of the alkyl groups on the nitrogen atom of the pyrazolyl units
to form stable and reproducible Langmuir–Blodgett films at the
PHOTOPHYSICS OF MOLECULAR ASSEMBLIES 77