Synthesis of rigid π-conjugated mono-, bis-, tris-, and tetrakis(terpyridine)s: Influence of the degree and pattern of substitution on the photophysical Properties

Article abstract of DOI:10.1002/ejoc.200800857

A series of rigid π-conjugated mono-, bis-, tris-, and tetrakis-(terpyridine)s 3-8 was synthesized in high yields by means of Horner-Wadsworth-Emmons (HWE) reactions between benzyl phosphonates 1 and an aldehyde-functionalized ter-pyridine derivative 2. The photophysical properties of the materials in solution and in the solid state depend strongly both on the numbers of terpyridine moieties attached to the central phenyl cores and on the geometries of the compounds. The photophysical behavior of the ortho-substituted compounds 5 and 8 indicated significant changes in the geometries, together with major extensions of the effective π-conjugated systems upon excitation. Bright green emission with high quantum yields was observed for the tetrakis(ter-pyridine) derivative 8.

Full text of DOI:10.1002/ejoc.200800857

FULL PAPER
DOI: 10.1002/ejoc.200800857
Synthesis of Rigid π-Conjugated Mono-, Bis-, Tris-, and Tetrakis(terpyridine)s:
Influence of the Degree and Pattern of Substitution on the Photophysical
Properties
Andreas Winter,[a] Christian Friebe,[b] Martin D. Hager,[a] and Ulrich S. Schubert*[a,b]
Keywords: Absorption / Fluorescence / Supramolecular chemistry / Terpyridines / Wittig reactions
A series of rigid π-conjugated mono-, bis-, tris-, and tetrakis-
(terpyridine)s 3–8 was synthesized in high yields by means
of Horner–Wadsworth–Emmons (HWE) reactions between
benzyl phosphonates 1 and an aldehyde-functionalized ter-
pyridine derivative 2. The photophysical properties of the
materials in solution and in the solid state depend strongly
both on the numbers of terpyridine moieties attached to the
pounds. The photophysical behavior of the ortho-substituted
compounds 5 and 8 indicated significant changes in the geo-
metries, together with major extensions of the effective π-
conjugated systems upon excitation. Bright green emission
with high quantum yields was observed for the tetrakis(ter-
pyridine) derivative 8.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
central phenyl cores and on the geometries of the com- Germany, 2009)
tion of the 2,2Ј:6Ј,2ЈЈ-terpyridine moiety.[5–6] Thanks to
Introduction
their electro-optical properties, the development of efficient
and straightforward routes to tailor-made 2,2Ј:6Ј,2ЈЈ-terpyr-
idines is a focus of current research.[7] It has been demon-
strated that appropriate combinations of such chelating ter-
pyridines and transition metal ions enable the synthesis of
complexes featuring interesting luminescent properties.
These structures are thus important candidates as hosts for
photoinduced energy- and electron-transfer processes in the
field of supramolecular chemistry.[6]
The self-assembly of functional structures into metallo-
supramolecular architectures through the interaction of
transition metal ions and appropriate ligands is a highly
active area in modern supramolecular chemistry. The char-
acteristics of these interactions are defined by combinations
of various parameters, including the coordination numbers,
geometries, and donor-types of the transition metal ions,
and the numbers, types, and arrangements of the donor
atoms of the ligands.[1]
Furthermore, oligo(terpyridine)s are also used for the
construction of supramolecular metallo-polymers. The elec-
tronic communication between the metal-complexed moie-
ties within these structures is another aspect that highlights
their potential in the design of new functional materi-
als,[1,5–6] and a large number of studies on the construction
of linear-rod polymers based on such conjugated oligo(ter-
pyridine) moieties through the use of heavy transition metal
ions – such as ruthenium(II), iridium(III) or osmium(II) –
have been published.[8] Zinc(II) ions have also recently at-
tracted much interest as novel templates for the fabrication
of structurally well defined photoluminescent and electrolu-
minescent supramolecular metallo-cycles and metallo-poly-
mers.[9]
In addition to the intensively elaborated N-heterocyclic
systems based on 2,2Ј-bipyridine[2] and 1,10-phenan-
throline,[3] 2,2Ј:6Ј,2ЈЈ-terpyridine derivatives have in recent
years attracted much interest as versatile templates in supra-
molecular and coordination chemistry, as well as in materi-
als science.[1,4–5] Their rich coordination chemistry and re-
markably high binding affinities towards most transition
metal ions, through dπǞpπ* bonding, make them highly
attractive building blocks for the construction of complex
metallo-supramolecular architectures with advanced photo-
physical, electrochemical, catalytic, and magnetic proper-
ties.[1] These properties can be influenced and tuned by vari-
ation of π-conjugated substituents attached at the 4Ј-posi-
The photophysical properties of oligo(terpyridine)s and
their transition metal complexes can be easily controlled
through the electronic properties of the π-conjugated link-
ages. So far, only a few publications have dealt with the
synthesis and properties of such rigid-linear or even star-
shaped derivatives.[10] We have previously reported on the
synthesis and characterization of a library of soluble rigid-
linear π-conjugated bis(terpyridine)s.[10a] Those compounds
[a] Eindhoven University of Technology, Laboratory of Macromo-
lecular Chemistry and Nanoscience,
P. O. Box 513, 5600 MB Eindhoven, The Netherlands
Fax: +31-40-247-4186
E-mail: u.s.schubert@tue.nl
[b] Friedrich-Schiller-University Jena, Laboratory of Organic and
Macromolecular Chemistry,
Humboldtstr. 10, 07743 Jena, Germany
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Eur. J. Org. Chem. 2009, 801–809
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
801

A. Winter, C. Friebe, M. D. Hager, U. S. Schubert
FULL PAPER
exhibited bright emissions in the blue range (λPL,max = 440–
The HWE reaction has been found to represent a power-
490 nm), with high quantum yields (ΦPL) of up to 0.85 in ful tool for the straightforward synthesis of rigid π-conju-
dilute solutions. Variation in the conjugated system – in- gated bis(terpyridine)s.[10a,10b] In continuation of previous
cluding alkene, alkyne, and (hetero)aromatic moieties – was work, we have now coupled a series of benzylic phosphona-
achieved through combinations of Pd0-catalyzed coupling tes (1) with the aldehyde derivative 2 in the appropriate stoi-
reactions and the Horner–Wadsworth–Emmons (HWE) re- chiometry in the presence of KOtBu as base (Scheme 3). All
action.
oligo(terpyridine)s 3–8 were isolated in yields higher than
Here we describe a general protocol for the effective syn- 75% after column chromatography and subsequent precipi-
thesis of mono(terpyridine)s, rigid-linear and -angular bis- tation into methanol. The efficiency of the HWE reaction
(terpyridine)s, and star-shaped tris- and tetrakis(terpyrid- is demonstrated by the fact that no major decreases in the
ine)s based on the same π-conjugated backbone. The influ- obtained yields were observed for the sterically hindered or-
ences of the substitution pattern and the number of terpyri- tho-substituted compounds 5 and 8. The results of the
dine units attached to a central phenyl core on the photo- HWE reactions are summarized in Table 2. All synthesized
physical properties in solution and in the solid state are also terpyridine derivatives have been fully characterized by
investigated in detail. The described oligo(terpyridine)s NMR spectroscopy, mass spectrometry, and elemental
1
should in future work serve as templates for self-assembly analysis. As shown by H NMR spectroscopy (Figure 1),
with suitable transition metal ions to form linear and the formation of the C=C bonds occurred with very high E
crosslinked metallo-polymers for potential optoelectronic selectivity (3JH,H = 15–17 Hz for the E configuration). The
applications.
Z isomers were not detected spectroscopically. In all cases
the NMR spectra showed well resolved signals; this indi-
cates that aggregation of the highly conjugated systems
through π–π stacking is generally prevented.
Since the film-forming abilities of rigid (unsubstituted)
terpyridines are often very poor, only a few publications
have dealt with the solid-state properties of these com-
Results and Discussion
Synthesis and Characterization
For our investigations we chose a system based on ben- pounds.[9a] As expected, though, thanks to the attached alk-
zene as the central core with the terpyridine units attached oxy chains used here, improved solubilities in organic sol-
to this through C=C links; the target compounds are sum- vents of medium polarity relative to analogous structures
marized in Scheme 1. The alkoxy chains (i.e., n-octyloxy known from the literature have been achieved. Further-
groups) were introduced to assure good solubility of the more, we have obtained homogeneous and transparent
rigid terpyridine structures in common organic solvents. Be- films by spin-coating the linear bis(terpyridine) 4 and the
cause their yields are significantly higher than those of Pd0- star-shaped systems 7 and 8 from CHCl3 solutions onto
catalyzed coupling reactions and their starting materials are glass slides. The film thicknesses have been determined to
easily accessible, Wittig-type condensation reactions have be in the range of 50 nm. As expected, the film-forming
been found to be the methods of choice for the attachment ability of the one-armed derivative 3 is very low. In the cases
of π-conjugated building blocks to the terpyridine moie- of 5 and 6 we were also unable to obtain homogeneous
ties.[9a] A general synthetic approach in which a previously films, and so these materials could not be investigated fur-
introduced aldehyde-functionalized mono(terpyridine)[10a] ther in the solid state.
is prepared and subsequently treated with an appropriate
benzylic phosphonate 1 was therefore selected (Scheme 1).
The Michaelis–Arbusov reaction was used for the prepa-
Photophysical Properties
ration of the benzylic phosphonates 1.[11] The phosphonates
1a–f were synthesized from the corresponding starting ben-
The photophysical properties of the π-conjugated oligo-
zyl bromides by the general protocol in very high (terpyridine)s 3–8 were investigated by absorption and
yields (Ն90%; Scheme 2, Table 1). The reactions were car- photoluminescence (PL) spectroscopy both in dilute solu-
ried out neat under inert conditions with excess triethyl- tion and in the solid state.
phosphite as both reactant and solvent (12 h, 120 °C). The
As illustrated in Figure 2 (top), the absorption spectra of
structures of the phosphonates were confirmed by NMR 3–8 in dilute CHCl3 solutions are in general each charac-
spectroscopy and mass spectrometry. The 31P NMR spectra terized by two intense bands. The band around 300 nm has
of compounds 1 recorded in CDCl3 in each case showed been assigned to the characteristic πǞπ* transitions of the
the characteristic singlet with the expected chemical shift in terpyridine moieties, whereas the broad band in the visible
the range of 26–27 ppm.[12]
region (375–425 nm; Table 3) corresponds to πǞπ* transi-
As shown previously, Sonogashira cross-coupling be- tions based on the overall π-conjugated system.[10a] For the
tween 4Ј-(4-ethynylphenyl)-2,2Ј:6Ј,2ЈЈ-terpyridine and 4- mono(terpyridine) 3 this absorption maximum was found
bromo-2,5-bis(octyloxy)benzaldehyde in the presence of at 380 nm. With increasing numbers of π-conjugated terpyr-
Pd(PPh3)4/CuI as catalytic system can directly result in the idine moieties on the central phenyl core, significant red
aldehyde-functionalized mono(terpyridine) 2 in good yield shifts of the absorption maximum are observed, together
(52%; Scheme 3).[10a]
with increases in the molar extinction coefficient. As would
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Photophysical Properties of Terpyridine Systems
Scheme 1. Schematic representation of the targeted oligo(terpyridine)s 3–8.

A. Winter, C. Friebe, M. D. Hager, U. S. Schubert
FULL PAPER
Table 2. Overview of the HWE reactions between the benzylic
phosphonates 1 and the aldehyde-functionalized terpyridine 2.
Entry
Substitution pattern
Yield [%][a]
3
4
5
6
7
8
mono
1,4-bis
1,2-bis
1,3-bis
1,3,5-tris
1,2,4,5-tetrakis
92
88
79
83
81
75
[a] Isolated yield after column chromatography and precipitation
into methanol.
Scheme 2. Schematic representation of the synthesis of the benzylic
phosphonates 1a–f.
Table 1. Synthesis of the benzylic phosphonates 1.
Entry
Substitution pattern
Yield
(%)
31P NMR[c]
δP (ppm)
1a
1b
1c
1d
1e
1f
mono
1,4-bis
1,2-bis
1,3-bis
1,3,5-tris
1,2,4,5-tetrakis
92[a]
97[b]
90[a]
93[b]
95[b]
96[b]
26.40
26.25
26.75
26.26
26.03
26.39
[a] Isolated yield after kugelrohr distillation. [b] Isolated yield after
precipitation from hexane. [c] Measured in CDCl3 (400 MHz, room
temperature).
1
Figure 1. Aromatic region of the H NMR spectra of 3 (top) and
4 (bottom). Both spectra: 400 MHz, CDCl3, room temperature.
Scheme 3. Synthesis of the series of π-conjugated terpyridines 3–8 by HWE reactions.
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Photophysical Properties of Terpyridine Systems
be expected, because of the 1,4-substitution and the linear hindrance and tilt of the two ortho-arranged substituents,
alignment of the overall molecule, the bis(terpyridine) 4 ex- and so a distinct disturbance of the electron delocalization
hibits the most pronounced red shift (λabs,max = 425 nm), can be observed, even leading to a blue shift of 2 nm in
indicating the highest effective conjugation length within relation to 3. Because π-conjugation through meta substitu-
the series investigated. It is known from detailed studies on tion is generally discontinued,[15] the bis(terpyridine) 6 and
various types of poly(phenylenevinylene)s that the geome- the tris(terpyridine) 7 show only relatively small red shifts
tries (i.e., the substitution patterns) have an important im- in their absorption maxima. From an electronic point of
pact on the overall photophysical properties of the materi- view, these compounds feature π-conjugated systems simi-
als.[13] Although the π-conjugated system is also extended larly as effective as that of the mono(terpyridine) 3.
for the ortho-angular bis(terpyridine) 5, this is to a minor
Table 3. Absorption properties of the oligo(terpyridine)s 3–8 in di-
degree in relation to 4, due to the kinked arrangement of
lute solution and in the solid state.
the two chromophores.[14] In the present case, the influence
of the π-extension is overcompensated by the strong steric
Entry
λabs [nm]
εϫ107
Eogpt [eV][c]
Solution[a]
Film[b]
[cm2mol–1][a]
Solution[a]
Film[b]
[d]
[d]
3
4
5
6
7
8
380
425
378
392
398
409
–
3.3
10.0
6.9
6.1
13.2
11.3
2.86
2.61
2.77
2.84
2.80
2.57
–
427
2.51
[d]
[d]
–
–
–
–
[d]
[d]
399
410
2.71
2.47
[a] 10–6  in CHCl3 at room temperature. [b] Thin solid films on
glass substrates at room temperature. [c] Estimated from the ab-
sorption spectra by extrapolation of the tails of the lower energy
levels. [d] The films were not investigated because of inhomo-
geneity.
In general, the rise in the extinction coefficients is par-
tially attributable to the increasing numbers of chromo-
phores per molecule. However, the growth in intensity
(S[16]) of the absorption bands appears to be more than
proportionate (Table 4). The largest step is found between
3 and 4, once more emphasizing the electronic communica-
tion through the entire molecule. The intensities per terpyr-
idine side-chain for 3 and for the meta derivative 6 are in the
same range; for the tris(terpyridine) 7 a slightly increased
intensity is observed. The values for the bandwidth (b) are
in the 4650Ϯ350 cm–1 range, except for 5 and 8 (5089 cm–1
and 6006 cm–1, respectively). This broadening of the ab-
sorption maximum can be unambiguously explained by
strong intramolecular steric interaction between the neigh-
boring terpyridine side-chains.
The tetrakis(terpyridine) 8 combines both ortho and para
substitution within one molecular structure, so the elec-
tronic and steric effects discussed above independently for
4 and 5 now have to be considered simultaneously. Gen-
erally, such cross-shaped chromophores cannot simply be
described as superpositions of two linear analogues.[17] Al-
though the global picture appears to be more complex and
is currently under investigation,[18] a few basic characteris-
Figure 2. Top: Normalized absorption spectra of oligo(terpyr-
idine)s 3–8 in dilute solution (all spectra 10–6  in CHCl3). Bottom:
Normalized absorption spectra of oligo(terpyridine)s 4, 7, and 8 in
the solid state (thin solid films on glass substrates). All spectra were
measured at room temperature.
Table 4. Characteristics of the longest-wavelength absorption maxima of the oligo(terpyridine)s 3–8 in dilute solution.[a]
Entry
λabs
[nm]
εϫ107
Half-width b
Intensity S[c]
S per terpyridine unit
[cm2 mol–1]
[cm–1][b]
[1011 cmmol–1]
[1011 cmmol–1]
3
4
5
6
7
8
380
425
378
392
398
409
3.3
10.0
6.9
6.1
13.2
11.3
4296
4390
5348
5089
4889
6006
1.41
4.37
3.67
3.08
6.45
6.79
1.41
2.18
1.83
1.54
2.15
1.70
[a] 10–6  in CHCl3 at room temperature. [b] Estimated by linear extrapolation of the low-wavelength value. [c] Calculated: S = bε.
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A. Winter, C. Friebe, M. D. Hager, U. S. Schubert
FULL PAPER
tics can be addressed. The para arrangement of the π-conju- Table 5. PL properties of the oligo(terpyridine)s 3–8 in dilute solu-
tion and in the solid state.
gated systems is expressed by a pronounced red shift of
S
S
λabs,max of about 30 nm relative to 3. Concurrently, the or-
tho substitution pattern, resulting in torsions of the substit-
uents relative to each other, mainly leads to a considerable
decrease in the intensity with respect to the number of ter-
pyridine side-chains. The optical bandgaps (Egopt) were esti-
mated from the absorption spectra by extrapolation of the
tails on the longer-wavelength side (i.e., at 10% absorption).
The Egopt values for bis(terpyridine) 4 and tetrakis(terpyr-
idine) 8 are significantly lower than those for the other de-
rivatives (2.61 eV and 2.57 eV, respectively). This addition-
ally shows that – thanks to the para linkages of the terpyrid-
ine groups – the effective π-conjugated system is extended.
The bandgaps determined for the meta-substituted com-
pounds 6 and 7 are comparable to the value for the simple
mono(terpyridine) 3 (2.86 eV).
Entry λsol,film
∆
ΦPL,sol λPL,film
∆
ΦPL,film
sol
film
[nm][a]
[cm–1]
[nm][b,c] [cm–1]
[a,c]
[b,c,d]
[e]
[e]
[e]
3
4
5
6
7
8
445
482
462
445
445
496
3840
2780
4810
3040
2650
4290
0.80
0.98
0.84
0.85
0.87
0.53
–
–
–
538
4830
0.48
[e]
[e]
[e]
–
–
–
[e]
[e]
[e]
–
–
–
507
555
5340
6370
0.15
0.18
[a] Ca. 10–6  in CHCl3 at room temperature. [b] Thin solid films
on glass substrates at room temperature. [c] Absolute quantum
yields; uncorrected with respect to reabsorption. [d] Absolute quan-
tum yields in the solid state (see ref. 19); uncorrected with respect
to reabsorption. [e] The films were not investigated because of their
inhomogeneity.
No significant changes in the absorption behavior of the
π-conjugated systems were detected for the thin solid films
of the three oligo(terpyridine)s investigated (Figure 2, bot-
tom). From this we conclude that the structural and elec-
tronic characteristics discussed for the corresponding dilute
solutions can also be observed in the solid state.
The photoluminescence (PL) spectra and the absolute
quantum yields (ΦPL[19]) of the series of terpyridines were
also studied, and the results are summarized in Table 5. All
PL spectra and the ΦPL values were obtained upon exci-
tation at the corresponding absorption maximum. The PL
spectra of the oligo(terpyridine)s are also strongly influ-
enced by the numbers of attached π-conjugated terpyridine
moieties and the substitution patterns of the central phenyl
rings. Because of the meta substitution in 6 and 7, the con-
jugated side groups have to be treated as isolated chromo-
phores rather than as uniform chromophores, with their
structures resembling that of the mono(terpyridine) 3. The
maxima of the emission bands (λPL,max) of these three de-
rivatives (3, 6, and 7) are therefore located at about 445 nm,
displaying a bright blue color (Figures 3 and 4). As in the
case of the extinction coefficient ε, the increase in ΦPL for
6 and 7 relative to 3 is attributable to the increasing num-
bers of chromophores within the molecules (Tables 4 and
5). A remarkably high quantum yield of 0.98 and a red shift
of the emission maximum of about 40 nm relative to 3 was
determined for the linear bis(terpyridine) 4. As a conse-
quence of its long effective conjugation length, 4 emits with
Figure 3. Top: normalized photoluminescence spectra of oligo(ter-
an intense cyan color (λPL,max = 482 nm, Stokes shift: pyridine)s 3–8 in dilute solution (10–6  in CHCl3 for all spectra).
2780 cm–1, see Figures 3 and 4).[10a,10b]
Bottom: normalized photoluminescence spectra of the oligo(ter-
pyridine)s 4, 7, and 8 in the solid state (thin solid films on glass
substrates).
For the ortho-substituted bis(terpyridine) 5, a large
Stokes shift of 4810 cm–1 can be observed (λPL,max
=
462 nm). As can be seen from the absorption behavior, a
distinct tilt of the conjugated side groups, due to strong Because of its large Stokes shift of almost 4290 cm–1 the
steric hindrance, would be expected for the ground state star-shaped terpyridine 8 features a bright green emission
(S0). We assume that the molecular geometry is changed in (λabs,max = 409 nm, λPL,max = 496 nm) with high quantum
the excited state (S1) and that the overall π-conjugated sys- yields (ΦPL = 0.53).
tem could consequently be enlarged significantly.[19] The
The results from NMR spectroscopy indicate that aggre-
same effect was observed for the tetrakis(terpyridine) 8. To gation of the molecules is strongly discouraged in dilute
the best of our knowledge, green emitting oligo(terpyr- solutions thanks to the solubilizing alkoxy groups. How-
idine)s have not previously been reported in the literature. ever, aggregation cannot be fully prevented in the solid
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Photophysical Properties of Terpyridine Systems
Experimental Section
General: Unless stated otherwise, all reagents were purchased from
commercial sources and were used without further purification.
The solvents were obtained from Biosolve and were dried and dis-
tilled by standard procedures. Chromatographic separations were
performed on aluminium oxide (neutral, Macherey–Nagel, 0.063–
0.200 mm). The set of benzylic phosphonates 1[10] and the alde-
hyde-functionalized terpyridine 2[9a] were prepared by known pro-
cedures (see Supporting Information for details).
1
Instrumentation: H, 13C, and 31P NMR spectra were recorded in
deuterated solvents (Cambridge Isotope Laboratories, Inc.) at
25 °C on a Varian Mercury 400 MHz instrument. Chemical shifts
are reported in ppm downfield from TMS (1H and 13C NMR) and
H3PO4 (31P NMR). Matrix-assisted laser desorption-ionization
time-of-flight mass spectrometry (MALDI-ToF MS) was per-
formed on a Voyager-DE PRO biospectrometry workstation (Ap-
plied Biosystems) time-of-flight mass spectrometer, with dithranol
as matrix. Elemental analysis was obtained with a EuroVector
EuroEA3000 elemental analyzer for CHNS-O. UV/Vis spectra were
measured with a Perkin–Elmer Lambda-19 spectrometer, photolu-
minescence spectra were recorded with a Perkin–Elmer LS50B lu-
minescence spectrometer. Absolute quantum yields were obtained
with a Hamamatsu Photonic Multi-Channel Analyzer C10027. For
these techniques concentrations of 10–6  in degassed CHCl3 (1 cm
cuvette) at 25 °C were used. Thin solid films were spin-coated on
glass substrates from CHCl3 solutions with concentrations of ca.
2.5 mgmL–1. A Laurell Technologies WS 400/500 Series spin-coater
was used; the spin-coating rate was 1000 rpm for 30 s. The glass
slides were cleaned by consecutive ultrasonication in water, acetone,
and isopropanol (each 15 min) prior to use. Film thicknesses were
determined with an optical profilometer (Fogale Zoomsurf).
Figure 4. Representation of the photoluminescence (excitation at
375 nm) of dilute solutions (top) and thin solid films (bottom). For
both representations: 7 (left), 8 (middle), and 4 (right).
state. Here, pronounced red shifts (50–60 nm) of the emis-
sion maxima relative to the dilute solutions were observed
for 4, 7, and 8 (Table 4, Figure 3). All thin spin-coated films
show emissions with their maxima in the 507 to 555 nm
range. While bis(terpyridine) 4 still features a strong cyan
emission (ΦPL = 0.48), for the star-shaped derivatives 7 and
8 the emission in the solid state is reduced significantly.
General Procedure for the HWE Reaction: The synthesis of terpyri-
dines 3–8 was performed as follows: KOtBu (1.05 equiv. per phos-
phonate group of 1) was added to a solution of a benzylic phos-
phonate 1 (0.5 mmol) and 2 (1 equiv. per phosphonate group of 1)
in dry and degassed toluene (50 mL). The reaction mixture was
heated at reflux for 12 h, allowed to cool to room temperature, and
extracted with brine (3ϫ15 mL). The organic phase was dried with
anhydrous MgSO4 and then concentrated. The residue was tritu-
Conclusions
A series of mono-, bis-, tris-, and tetrakis(terpyridine)s
based on a common rigid π-conjugated building block has rated with methanol to yield the crude products, which were further
purified by column chromatography (neutral alumina, CH2Cl2/
been synthesized by straightforward Horner–Wadsworth–
Emmons reactions. The numbers of conjugated terpyridine-
based side groups and the overall geometries of the mole-
cules have a distinct influence on their photophysical prop-
MeOH as eluent).[9a]
4Ј-(4-{[2,5-Bis(octyloxy)-4-styrylphenyl]ethynyl}phenyl)-2,2Ј:6Ј,2ЈЈ-
1
terpyridine (3): H NMR (400 MHz, CDCl3): δ = 8.77 (s, 2 H, 3Ј-/
3
3
erties in dilute solution and in the solid state. The highest 5Ј-H), 8.75 (d, J = 4.2 Hz, 2 H, 6-/6ЈЈ-H), 8.69 (d, J = 8.0 Hz, 2
3
H, 3-/3ЈЈ-H), 7.91 (mc, 4 H, 4-/4ЈЈ-H, Haryl), 7.68 (d, J = 8.1 Hz,
2 H, Haryl), 7.54 (d, 3J = 7.5 Hz, 2 H, Haryl), 7.47 (d, 3J = 15.8 Hz,
1 H, Holefin), 7.37 (mc, 4 H, 5-/5ЈЈ-H, Haryl), 7.26 (mc, 1 H, Haryl),
effective conjugation length within the series was observed
for the rigid-linear bis(terpyridine). For the ortho-substi-
tuted linear and star-shaped derivatives, significant changes
in the molecular structure upon excitation have been de-
duced from the photophysical investigations. All com-
pounds exhibited strong blue to green emission with very
high quantum yields in solution. In the solid state, three
different emission colors – cyan, green, and orange – were
observed. Overall, the π-conjugated oligo(terpyridine)s
3
7.17 (d, J = 15.8 Hz, 1 H, Holefin), 7.15 (s, 1 H, Haryl), 7.05 (s, 1
3
3
H, Haryl), 4.12 (t, J = 6.8 Hz, 2 H, Halkyl), 4.03 (t, J = 6.8 Hz, 2
H, Halkyl), 1.88 (mc, 4 H, Halkyl), 1.61 (mc, 4 H, Halkyl), 1.44–1.27
(m, 16 H, Halkyl), 0.88 (mc, 6 H, Halkyl) ppm. 13C NMR (100 MHz,
CDCl3): δ = 156.1, 155.5, 152.8, 151.9, 149.0, 145.6, 142.3, 137.8,
137.3, 133.1, 128.9, 128.6, 128.4, 127.8, 124.8, 124.0, 123.7, 123.5,
120.9, 118.1, 117.8, 115.3, 112.0, 111.2, 97.5, 83.9, 68.8, 32.1, 29.7,
shown here are promising candidates for the design of func- 29.6, 29.3, 25.7, 22.8, 14.3 ppm. MALDI-ToF MS (dithranol): m/z
= 768.59 [M + H]+. C53H57N3O2 (768.0): calcd. C 82.88, H 7.48,
N 5.47; found C 83.01, H 7.35, N 5.32.
tional materials and, in combination with transition metal
complexation, suitable building blocks for the construction
of functional supramolecular assemblies and metallo-poly-
mers with potential for, for example, optoelectronic applica-
tions.
1,4-Bis(4-{[4-(2,2Ј:6Ј,2ЈЈ-terpyridin-4Ј-yl)phenyl]ethynyl}-2,5-bis-
(octyloxy)styryl)benzene (4): 1H NMR (400 MHz, CDCl3): δ = 8.77
(s, 4 H, 3Ј-/5Ј-H), 8.75 (d, J = 5.4 Hz, 4 H, 6-/6ЈЈ-H), 8.69 (d, J
3
3
Eur. J. Org. Chem. 2009, 801–809
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
807

A. Winter, C. Friebe, M. D. Hager, U. S. Schubert
= 8.2 Hz, 4 H, 3-/3ЈЈ-H), 7.91 (mc, 8 H, 4-/4ЈЈ-H, Haryl), 7.68 (d, J = 8.78 (s, 8 H, 3Ј-/5Ј-H), 8.74 (mc, 8 H, 6-/6ЈЈ-H), 8.67 (d, 3J =
FULL PAPER
3
3
3
= 8.7 Hz, 4 H, Haryl), 7.54 (s, 4 H, Haryl), 7.50 (d, J = 16.6 Hz, 2 8.2 Hz, 8 H, 3-/3ЈЈ-H), 7.90 (mc, 16 H, 4-/4ЈЈ-H, Haryl), 7.67 (d, J
H, Holefin), 7.37 (mc, 4 H, 5-/5ЈЈ-H), 7.18 (d, 3J = 16.9 Hz, 2 H, = 7.9 Hz, 8 H, Haryl), 7.44 (d, 3J = 16.2 Hz, 4 H, Holefin), 7.34 (mc,
Holefin), 7.16 (s, 2 H, Haryl), 7.06 (s, 2 H, Haryl), 4.13 (t, 3J = 5.8 Hz,
4 H, Halkyl), 4.04 (t, 3J = 6.7 Hz, 4 H, Halkyl), 1.90 (mc, 8 H, Halkyl),
1.68–1.52 (m, 8 H, Halkyl), 1.46–1.25 (m, 32 H, Halkyl), 0.92–0.85
8 H, 5-/5ЈЈ-H), 7.25 (s, 2 H, Haryl), 7.15 (d, 3J = 15.8 Hz, 4 H,
olefin), 7.12 (s, 4 H, Haryl), 7.04 (s, 4 H, Haryl), 4.10 (mc, 8 H,
Halkyl), 4.05 (mc, 8 H, Halkyl), 1.95–1.83 1.88 (m, 16 H, Halkyl),
H
(m, 12 H, Halkyl) ppm. 13C NMR (100 MHz, CDCl3): δ = 155.9, 1.66–1.52 (mc, 16 H, Halkyl), 1.47–1.23 (m, 64 H, Halkyl), 0.95–0.85
155.2, 153.0, 152.1, 148.7, 145.5, 142.4, 137.2, 136.5, 133.3, 129.1,
128.5, 124.7, 124.2, 123.8, 123.4, 121.1, 117.9, 117.8, 115.2, 112.1,
111.1, 98.0, 84.2, 68.7, 32.0, 29.8, 29.7, 29.2, 25.7, 22.8, 14.3 ppm.
(m, 24 H, Halkyl) ppm. 13C NMR (100 MHz, CDCl3): δ = 156.5,
155.3, 153.1, 152.1, 149.3, 145.4, 142.1, 137.1, 134.1 133.3, 128.5,
124.5, 124.2, 123.8, 123.3, 122.7, 121.2, 117.9, 117.5, 115.1, 112.2,
MALDI-ToF MS (dithranol): m/z = 1457.97 [M + H]+ . 111.5, 97.9, 84.2, 69.1, 32.0, 29.8, 29.6, 29.1, 25.5, 22.9, 14.2 ppm.
C
100H108N6O4 (1458.0): calcd. C 82.38, H 7.47, N 5.76; found C
MALDI-ToF MS (dithranol): m/z = 2836.68 [M +
H]+.
82.52, H 7.64, N 5.52.
C194H210N12O8 (2837.8): calcd. C 82.11, H 7.46, N 5.92; found C
82.35, H 7.66, N 6.11.
1,2-Bis(4-{[4-(2,2Ј:6Ј,2ЈЈ-terpyridin-4Ј-yl)phenyl]ethynyl}-2,5-bis-
(octyloxy)styryl)benzene (5): 1H NMR (400 MHz, CDCl3): δ = 8.78
(s, 4 H, 3Ј-/5Ј-H), 8.75 (d, J = 5.9 Hz, 4 H, 6-/6ЈЈ-H), 8.68 (d, J
= 8.0 Hz, 4 H, 3-/3ЈЈ-H), 7.92 (mc, 8 H, 4-/4ЈЈ-H, Haryl), 7.69 (d, J
= 8.5 Hz, 4 H, Haryl), 7.68 (mc, 4 H, Haryl), 7.48 (d, J = 16.1 Hz,
Supporting Information (see footnote on the first page of this arti-
cle): Synthesis and full characterization of all described com-
pounds, 1H NMR spectra of all compounds and selected additional
spectra.
3
3
3
3
3
2 H, Holefin), 7.36 (mc, 4 H, 5-/5ЈЈ-H), 7.17 (d, J = 16.2 Hz, 2 H,
Holefin), 7.14 (s, 2 H, Haryl), 7.07 (s, 2 H, Haryl), 4.14 (t, 3J = 6.5 Hz,
4 H, Halkyl), 4.08 (t, 3J = 6.4 Hz, 4 H, Halkyl), 1.88 (mc, 8 H, Halkyl),
1.69–1.54 (m, 8 H, Halkyl), 1.44–1.21 (m, 32 H, Halkyl), 0.95–0.82
(m, 12 H, Halkyl) ppm. 13C NMR (100 MHz, CDCl3): δ = 156.3,
155.6, 153.1, 152.0, 149.2, 145.7, 142.5, 137.2, 134.8, 133.4, 128.4,
128.2, 127.9, 124.7, 124.1, 123.5, 123.3, 121.2, 118.5, 117.9, 115.4,
111.8, 111.5, 97.2, 84.5, 69.2, 32.3, 30.0, 29.7, 29.3, 25.7, 22.9,
14.1 ppm. MALDI-ToF MS (dithranol): m/z = 1457.95 [M + H]+.
C100H108N6O4 (1458.0): calcd. C 82.38, H 7.47, N 5.76; found C
82.19, H 7.22, N 5.87.
Acknowledgments
The authors acknowledge financial support from the Nederlandse
Organisatie voor Wetenschappelijk Onderzoek (VICI award to
U. S. S.) and the Fonds der Chemischen Industrie. We also thank
Rebecca Eckardt (elemental analysis) and Tina Erdmenger
(MALDI-ToF MS) for help with the respective measurements.
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1,3-Bis(4-{[4-(2,2Ј:6Ј,2ЈЈ-terpyridin-4Ј-yl)phenyl]ethynyl}-2,5-bis-
(octyloxy)styryl)benzene (6): 1H NMR (400 MHz, CDCl3): δ = 8.77
3
3
(s, 4 H, 3Ј-/5Ј-H), 8.74 (d, J = 5.7 Hz, 4 H, 6-/6ЈЈ-H), 8.67 (d, J
3
= 8.2 Hz, 4 H, 3-/3ЈЈ-H), 7.91 (mc, 8 H, 4-/4ЈЈ-H, Haryl), 7.68 (d, J
= 8.5 Hz, 4 H, Haryl), 7.68 (mc, 2 H, Haryl), 7.52 (s, 1 H, Haryl),
3
7.48 (d, J = 15.8 Hz, 2 H, Holefin), 7.36 (mc, 5 H, 5-/5ЈЈ-H, Haryl),
3
7.16 (d, J = 15.7 Hz, 2 H, Holefin), 7.13 (s, 2 H, Haryl), 7.08 (s, 2
3
3
H, Haryl), 4.13 (t, J = 6.8 Hz, 4 H, Halkyl), 4.05 (t, J = 6.7 Hz, 4
H, Halkyl), 1.87 (mc, 8 H, Halkyl), 1.67–1.55 (m, 8 H, Halkyl), 1.42–
1.23 (m, 32 H, Halkyl), 0.96–0.80 (m, 12 H, Halkyl) ppm. 13C NMR
(100 MHz, CDCl3): δ = 156.3, 155.4, 153.1, 151.5, 148.7, 145.7,
142.5, 138.2, 137.1, 132.8, 128.7, 128.5, 127.7, 124.4, 124.2, 123.8,
123.1, 122.8, 121.0, 117.8, 117.9, 115.4, 111.9, 110.9, 98.0, 84.0,
68.5, 31.8, 29.6, 29.5, 29.3, 25.7, 22.7, 14.2 ppm. MALDI-ToF MS
(dithranol): m/z = 1457.96 [M + H]+. C100H108N6O4 (1458.0):
calcd. C 82.38, H 7.47, N 5.76; found C 82.27, H 7.34, N 5.97.
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(octyloxy)styryl)benzene (7): 1H NMR (400 MHz, CDCl3): δ = 8.78
3
3
(s, 6 H, 3Ј-/5Ј-H), 8.75 (d, J = 5.2 Hz, 6 H, 6-/6ЈЈ-H), 8.68 (d, J
= 8.0 Hz, 6 H, 3-/3ЈЈ-H), 7.90 (mc, 12 H, 4-/4ЈЈ-H, Haryl), 7.67 (d,
3J = 8.5 Hz, 6 H, Haryl), 7.48 (d, J = 15.9 Hz, 3 H, Holefin), 7.35
(mc, 6 H, 5-/5ЈЈ-H), 7.17 (d, J = 15.9 Hz, 3 H, Holefin), 7.14 (s, 3
3
3
H, Haryl), 7.11 (s, 3 H, Haryl), 7.04 (s, 3 H, Haryl), 4.15 (t, 3J =
6.0 Hz, 6 H, Halkyl), 4.01 (t, 3J = 6.7 Hz, 6 H, Halkyl), 1.92–1.82 (m,
12 H, Halkyl), 1.70–1.51 (m, 12 H, Halkyl), 1.48–1.20 (m, 48 H,
Halkyl), 0.95–0.82 (m, 18 H, Halkyl) ppm. 13C NMR (100 MHz,
CDCl3): δ = 155.9, 155.2, 153.1, 151.5, 148.9, 145.7, 142.1, 137.0,
136.1, 133.3, 128.1, 124.9, 124.3, 123.9, 123.5, 122.5, 121.2, 118.5,
117.9, 115.1, 111.9, 111.1, 97.1, 84.2, 68.9, 32.0, 30.0, 29.9, 29.1,
25.6, 22.5, 14.1 ppm. MALDI-ToF MS (dithranol): m/z = 2147.29
[M + H]+. C147H159N9O6 (2147.9): calcd. C 82.20, H 7.46, N 5.87;
found C 82.05, H 7.61, N 6.02.
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808
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 801–809

Photophysical Properties of Terpyridine Systems
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spectrometer.
A
custom-designed integrating sphere
(model 05–105, AMKO) with an inner diameter of 105 mm
coated inside with BaSO4 was used. For those purposes, exci-
tation was carried out with a tungsten lamp of variable inten-
sity in order to provide suitable conditions to measure the fluo-
rescence of the sample and the scattered excitation light with
the same slit widths of the spectrometer. For further infor-
mation see: E. Tekin, D. A. M. Egbe, J. M. Kranenburg, C. Ul-
bricht, S. Rathgeber, E. Birckner, N. Rehmann, K. Meerholz,
U. S. Schubert, Chem. Mater. 2008, 20, 2727–2735.
Received: September 5, 2008
Published Online: December 12, 2008
Eur. J. Org. Chem. 2009, 801–809
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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