unit exhibit fascinating spectroscopic and redox properties
as well as electronic communication between the metal-based
units.4 Their distinct photophysical, electrochemical, and
magnetic properties create the potential for designing new
functional materials.2,4 The blue-emitting ligands might be
very important as the hosts for photoinduced energy and
electron-transfer processes in supramolecular chemistry.4
However, up to now, there were only a few reports of the
synthesis and studies of rigid linear or star-shaped π-con-
jugated 2,2′:6′,2′′-terpyridines.5 Therefore, their applications
have not been investigated as thoroughly as those of 2,2′-
bipyridines.6
Scheme 1. Synthesis of Three 2,2′:6′,2′′-Terpyridine
Precursors
In this contribution, we present the design, synthesis, and
photophysical properties of nine novel rigid linear and star-
shaped 2,2′:6′,2′′-terpyridine derivatives, in which various
linkages are employed to fix 2,2′:6′,2′′-terpyridine units and
conjugated moieties. The introduction of such fluorene and
truxene units efficiently improves the solubility and the
properties of desired molecules. These building blocks can
not only construct linear conjugated metallic wires but also
afford the large-sized dendritic complexes, which might be
useful to understand the structure-property relationships in
supramolecular chemistry and to develop new functionalized
materials for optoelectronic devices.
synthetic strategies from 4′-aryl-2,2′:6′,2′′-terpyridine. Scheme
1 illustrates synthetic approaches to three 2,2′:6′,2′′-terpy-
ridine precursors for the Suzuki, the Sonogashira, and the
Wittig reactions, respectively. The Miyaura coupling between
1 and bis(pinacolato)diboron with catalyst Pd(pddf)2Cl2
afforded 2 without a homocoupling byproduct.8 The Sono-
gashira coupling reaction of 1 with 2-methyl-3-butyn-2-ol
catalyzed by Pd(PPh3)2Cl2 revealed an alcohol followed by
the deprotection using NaOH to produce ethylene-terminating
3 in 67% yield.9 We also obtained 4 for the Wittig reaction.10
Scheme 2 exhibits the Suzuki coupling to 2,2′:6′,2′′-
terpyridine derivatives 5a-c, in which a C-C single bond
was employed to link conjugated moieties with 2,2′:6′,2′′-
terpyridine units. The Suzuki coupling of 1 and 9,9-
dihexylfluoren-2-ylboronic acid with Pd(PPh3)4 afforded
monotopic 2,2′:6′,2′′-terpyridine derivative 5a in 87% yield.11
Following the same procedures, we also obtained ditopic
ligand 5b in 79% yield. Compound 2 reacted with 812
afforded tritopic ligand 5c. The Sonogashira route to 6a-c
is outlined in Scheme 3. Compound 3 reacted with 9,9-
dihexyl-2-bromofluorene, 9,9-dihexyl-2,7-diiodofluorene, and
8 catalyzed by Pd(PPh3)Cl2 produced three ligands 6a, 6b,
and 6c in good yields, respectively.12
The preparation of 4′-(4-bromophenyl)-2,2′:6′,2′′-terpyri-
dine 1 followed the typical procedures.7 We constructed
various topic functionalized systems employing versatile
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in Scheme 4.13 We also employed the same procedures to
produce 7b and 7c, respectively. From their NMR spectra,
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