Self-Organization of Isocyanide-Containing Dendrimers
A R T I C L E S
Chart 1. Schematic Structures of Metallodendrimersa
mentalization (alternated or segmented constitutive lobes) of
the dendrimeric structure and toplology. As a matter of fact,
concomitant with judicious molecular designs, metallodendrim-
ers have been found to be particularly efficient materials in
catalysis,10 as molecular devices,11 or as environmental tools
for site isolation and/or recyclability.12
In this study, we report on the design of novel metal-
containing dendrimers endowed with mesomorphic properties.
The overall core architecture of the dendrimers consists of a
highly flexible polyaryl ether-based core, with the trivalent
phloroglucinol as central node, and the branching benzene rings
at each generation are connected by undecylene aliphatic
spacers. The dendrimers are end-functionalized by isocyanide
groups, versatile moieties owing to their outstanding coordina-
tion ability to give very stable complexes with many transition
metals. Mesomorphism is induced in these systems upon
complexion of gold-containing fragments, and the type of
mesophases depends strongly on the molecular shape of the gold
complex connected at the dendritic extremities. Thus, smectic
phases are obtained after bonding of rodlike gold chloride and
gold acetylide fragments, whereas columnar hexagonal phases
are formed upon complexion with tapered shape gold-acetylide
fragments.
a With emphasis on the different locations of metal fragments within
the dendritic frame: at the center (I), at the branching points (II), and at
the periphery (III).
scaffoldings for the elaboration of new liquid-crystalline (LC)
multifunctional materials. Furthermore, as multicomponent
systems, they possess a high density of active groups per
unit volume, and it is anticipated that some of the incorpo-
rated functions can additionally be amplified within the
induced low-dimensional LC mesophases ordering by coop-
erative and synergistic effects.8
While the majority of dendrimers reported so far are purely
organic in nature, there is a rising interest in dendrimers
containing transition metal ions.1,9 These so-called metalloden-
drimers are particularly attractive as the metallic moieties can
be easily integrated into different parts of the dendritic scaffold,
including the nodal core, branching points, and periphery (Chart
1),9 and their specific properties (e.g., redox, electronic, optic,
magnetic, etc.) can be modulated accordingly by collective
effects through the hierarchization (generations) and compart-
Results and Discussion
Design and Synthesis. LC dendrimers have now reached a
high degree of sophistication, and the type and nature of the
mesophases can be predicted and controlled through dedicated
structural engineering at the molecular level by manipulating
the intrinsic dendritic connectivity or by modulating the core
flexibility and the nature and type of peripheral substitution.6,7
Surprisingly, however, very few dendritic metallomesogens13
(i.e., mesomorphic metallodendrimers) have been yet reported.
A simple and well-known synthetic route to prepare metallo-
dendrimers is to use metallic species as nodal linking groups
and coordinate protomesomorphic dendritic fragments that can
act as ligands (Chart 1, structure I). This is the most commonly
applied strategy for obtaining metallodendrimer-containing
LCs.14 In this case, the metallic fragment is shielded by the
dense organic dendritic shell, and mesomorphism is solely
governed by the structure and conformation of the dendritic
branches. Alternatively, functionalization of the dendritic pe-
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