The remarkably high binding affinity toward most transi-
tion metal ions by dπfpπ* bonding, together with their
chelation properties, make terpyridines attractive building
blocks for the construction of supramolecular assemblies.
2,2′:6′,2′′-Terpyridines bearing π-conjugated substituents at
the 4′-position are known to present interesting photophysical
and electrochemical properties.1b,2e,4 The electronic com-
munication between the metal-complexed units of bis- and
tristerpyridines is another fascinating feature pointing out
their potentials in the design of new functional materials.2-4
Light-emitting ligands are considered to be important
structures as hosts for photoinduced energy and electron
transfers in supramolecular chemistry.4 However, unlike for
their 2,2′-bipyridyl counterparts,5 the applications of π-con-
jugated terpyridines in these fields have not been elaborated
so far and only a few publications deal with the synthesis
and properties of rigid-linear or star-shaped derivatives.6
rigid π-conjugated mono-, bis-, and tris(2,2′:6′,2′′-terpyrid-
ines). The structures shown in this contribution bearing
various conjugated linkagessincluding alkene, alkyne, and
phenyl moietiessand solubilizing alkoxy chains are promis-
ing with respect to the design of new supramolecular
assemblies, molecular wires, or dendritic structures.
A set of 4′-substituted 2,2′:6′,2′′-terpyridines were chosen
as the starting point for the construction of the rigid mono-,
bis-, and tristerpyridines via Pd(0)-catalyzed coupling reac-
tions and the Horner-Wadsworth-Emmons reaction (HWE).
For this purpose, the Kro¨hnke-type derivatives 1 and 2 were
prepared according to methods published previously.9 Scheme
1 summarizes the straightforward syntheses of the key
substrates 4 and 5 for the HWE reactions.10
Scheme 1. Synthesis of 4′-Substituted 2,2′:6′,2′′-Terpyridines
In continuation of prior work in the field of terpyridines
and their applications in supramolecular chemistry,1b,c,7 as
well on the design of PPV/PPE hybrid polymers,8 we now
present the synthesis and photophysical investigations of new
(2) (a) Erkkila, K. E.; Odom, D. T.; Barton, J. K. Chem. ReV. 1999, 99,
2777-2795. (b) Barigeletti, F.; Flamigni, L. Chem. Soc. ReV. 2000, 29,
1-12. (c) Ott, S.; Kritikos, M.; A° kermark, B.; Sun, L. Angew. Chem., Int.
Ed. 2003, 42, 3285-3288. (d) Andres, P. R.; Schubert, U. S. AdV. Mater.
2004, 16, 1043-1068. (e) Hofmeier, H.; Schubert, U. S. Chem. Soc. ReV.
2004, 33, 373-399. (f) Bianke´, G.; Ha¨ner, R. ChemBioChem 2004, 5,
1063-1068. (g) Schmittel, M.; Kalsani, V.; Mal, P.; Bats, J. W. Inorg.
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L.; Newkome, G. R. Chem. Mater. 2006, 18, 4019-4022.
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Chem. ReV. 1998, 178-180, 1251-1598. (b) Balzani, V.; Ceroni, P.; Juris,
A.; Venturi, A.; Venturi, M.; Campagna, S.; Puntoriero, F.; Serroni, S.
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J. F.; Steuerman, D. W.; Heath, J. R. Science 2004, 306, 2055-2056. (d)
Ciofini, I.; Laine´, P. P.; Bedioui, F.; Adamo, C. J. Am. Chem. Soc. 2004,
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Jørgensen, M.; Krebs, F. C. J. Org. Chem. 2006, 71, 5546-5559. (g)
Benniston, A.; Harriman, A.; Li, P.; Patel, P. V.; Sams, C. A. J. Org. Chem.
2006, 71, 3481-3493.
The Pd(0)-catalyzed Sonogahira cross-coupling reaction
of the ethynyl-functionalized terpyridine 2 (see Supporting
Information for details) with bis(alkoxy)-arylbromides in the
presence of Pd(PPh3)4/CuI as catalyst directly provided the
(4) (a) Barigeletti, F.; Flamigni, L.; Balzani, V.; Collin, J.-P.; Sauvage,
J.-P.; Sour, A.; Constable, E. C.; Cargill Thompson, A. M. W. J. Am. Chem.
Soc. 1994, 116, 7692-7699. (b) Barigeletti, F.; Flamigni, L.; Calogero,
G.; Hammarstro¨m, L.; Sauvage, J.-P.; Collin, J.-P. Chem. Commun. 1998,
2333-2334. (c) Hissler, M.; El-ghayoury, A.; Harriman, A.; Ziessel, R.
Angew. Chem., Int. Ed. 1998, 37, 1717-1720. (d) Berhard, S.; Goldsmith,
J. I.; Takada, K.; Abrun˜a, H. D. Inorg. Chem. 2003, 42, 4389-4393. (e)
Duncan, T. V.; Rubtson, I. V.; Uyela, H. T.; Therien, M. J. J. Am. Chem.
Soc. 2004, 126, 9474-9475. (f) Barbieri, A.; Ventura, B.; Barigeletti, F.;
de Nicolar, A.; Quesada, M.; Ziessel, R. Inorg. Chem. 2004, 43, 7359-
7368.
Scheme 2. Sonogashira Coupling of Ethynyl Terpyridine 2
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