see cross-section of Figure 5b) are clearly visible.
Interestingly,a diluted dodecane gel of compound 2b
deposited by spin-coating on freshly cleaved HOPG leads to
self-assembly of molecular fibers that follow mainly the
preferential crystallographic directions of the underlying
HOPG substrate (Figure 5c).The threefold symmetry of
the segment pattern is particularly visible at intercepts where
the fibers form angles of 608 and 1208 to each other.The crosssections
show the presence of two types of fibers corresponding
to two different molecular heights,namely (2.0x050.1) nm
and (4.0x050.3) nm (Figure 5d).The 2-nm high fibers can be
considered to be made of single molecular layers that lie flat
on the surface (Figure S1 in the Supporting Information).The
4-nm high fibers are made of two such piled up layers,with
their alkyl chains still lying parallel to the surface.As can be
seen from the width determined by atomic force microscopy
(AFM) measurements,the fibers show a lateral extension of
several tens of nanometers.As the full lateral extension of a
single molecular wire is only about 3 nm,this result leads us to
the conclusion that the fibers are made of monolayer and
bilayer stripes that involve several molecular wires in the
lateral xy direction.
The key feature of the present molecular design is the
introduction of a flat Pt(terpy) luminophore to a 3,5-
diacylamido framework that bears gallate-substituted derivatives.
Such highly colored complexes exhibit three out-standing features:1) relative ease of synthesis and high
stability; 2) strong solvatochromism and phosphorescence
depending on the state of matter (solution or gel); and 3) the
formation of nanofibril structures or extended columnar
mesophases by switching from linear chains in 2b to branched
chains in 2c.TEM and AFM studies confirm the presence of
linear fibrils with lengths of several hundred nanometers in
dodecane gels,with their 2-nm wide core consistent with
complexes that strongly interacting through metal···metal (at
ca.3.6 G) and metal···acetylide (at ca.3.8 G) contacts.The
deep-green color and the near-infrared emission are testimony
for highly aggregated complexes and effective Pt···Pt
interactions.Additionally,amide functions are engaged in
hydrogen bonding,which accounts for additional stabilization
of the entire edifice.Fiber alignment on oriented polymer
substrates would be auspicious for charge-separation devices.
Studies along these lines are currently in progress