Tris[oligo(1,4-phenylenevinylene)]methylium dyes

Article abstract of DOI:10.1002/ejoc.200801165

The tris[oligo(1,4-phenylenevinylene)]carbinols 2a-f (n = 1-4) and the tris(4-styrylphenyl)methanes 7a,b have been prepared by Wittig-Horner (3 + 4a-f → 2a-f) and Siegrist reactions (S + 6a,b → 7a,b). The Wittig-Horner reactions in these examples are acco

Full text of DOI:10.1002/ejoc.200801165

FULL PAPER
DOI: 10.1002/ejoc.200801165
Tris[oligo(1,4-phenylenevinylene)]methylium Dyes
Soungkyoo Kim,[a] Helga Kalbitz,[a] Sabine Hillmann,[a] and Herbert Meier*[a]
Keywords: Conjugation / Carbocations / Dyes/pigments / Oligomers / Protonation / Push–pull effects
The tris[oligo(1,4-phenylenevinylene)]carbinols 2a–f (n
=
due to a decreasing donor–acceptor interaction with increas-
ing D–A distance. The N-protonated methylium salts 2ЈЈЈa–c
show long-wavelength absorptions in the region of the Vis/
NIR border. Their values apporach, for increasing numbers n
of repeat units, λϱ = 877 nm. The structures and possible
1–4) and the tris(4-styrylphenyl)methanes 7a,b have been
prepared by Wittig–Horner (3 + 4a–f Ǟ 2a–f) and Siegrist
reactions (5 + 6a,b Ǟ 7a,b). The Wittig–Horner reactions in
these examples are accompanied by an autoxidation,
whereas a reduction occurs in the Siegrist reactions. Com- push–pull effects of the salts 2Јa and 2ЈЈЈa–c were studied by
pound 2a, the lowest member (n = 1) of the series 2a–d with
terminal dialkylamino groups, generates first, on treatment
with acids, the methylium dye 2Јa, which absorbs far into the
NIR region (λmax = 1100 nm). The higher members 2b,c (n =
2,3) of the carbinol series yield by acidic treatment only N-
protonated methylium dyes 2ЈЈЈb,c. The different behavior is
NMR and UV/Vis/NIR spectroscopy and compared with the
selected model compounds 2e and 7a. The results shed new
light on previously published triphenylmethane dyes with
extended conjugation.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
C3h symmetry of such methylium ions, these disc-like sys-
tems do not have dipole moments, but they represent ex-
tended octupoles, which promise high first-order hyper-
polarizabilities β (second-harmonic generation SHG) and
large cross-sections for two-photon absorption (TPA).
Introduction
Triphenylmethane dyes 1Ј are a well-known class of com-
pounds with numerous industrial applications. In recent
years the strong demand for near-infrared (NIR) absorbing
dyes and functional dyes for laser techniques and optoelec-
tronics has provoked a variety of new efforts in this
area.[1–4] We report herein on star-shaped systems 2Ј in
which the three aryl groups of 1Ј are replaced by three
oligo(1,4-phenylenevinylene) [OPV] chains (Figure 1). Car-
binols serve as precursors in both cases.
Results and Discussion
Synthesis
The preparation of the target carbinols 2a–d (n = 1–4)
(Scheme 1) was based on three-fold Wittig–Horner reac-
tions between the triphosphonate 3 and the OPV aldehydes
4a–d. Carbinol 2a (n = 1) was obtained in a yield of 68%,
which corresponds to an average of 88% for each of the
three olefination steps. The yields decrease with increasing
numbers n of repeat units to 48% for 2b (n = 2), 45% for
2c (n = 3), and 8% for 2d (n = 4). In the presence of air,
no special oxidant was necessary for the formation of the
carbinols 2. Owing to the low yield of compound 2d (n =
4), we characterized its structure by 1H and 13C NMR spec-
troscopy and its molecular mass and then excluded it from
further studies.
For comparison with 2a–d, which contain terminal dialk-
ylamino groups, we synthesized the carbinols 2e,f
(Scheme 1) and the tris(stilbenyl)methanes 7a,b (Scheme 2),
all of which contain terminal alkoxy groups. Facile proton-
ations of 2a–d can occur on the central OH group and on
the terminal amino groups, 2e,f can be protonated on the
central OH group, whereas 7a,b have none of these options.
The basicity of the ether groups in 2e,f and 7a,b is low. The
Figure 1. Triphenylmethylium ions 1Ј and tris[oligo(1,4-phenyl-
enevinylene)]methylium ions 2Ј and their precursor carbinols 1 and
2.
The idea to extend the conjugation of 1Ј by the introduc-
tion of trans-stilbene units is old,[5,6] and several tris(stilb-
enyl)methylium salts have been reported.[5–12] To shift the
absorption far into the NIR region, the OPV chains should
bear dialkylamino groups as electron-donor groups in the
terminal positions. We have used bis(2-hexyloctyl)amino
groups, which guarantee a good solubility even when the
OPV arms are longer (n = 1–4). According to the de facto
[a] Institute of Organic Chemistry, University of Mainz,
Duesbergweg 10–14, 55099 Mainz, Germany
Fax: +49-6131-39225396
E-mail: hmeier@mail.uni-mainz.de
1976
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Eur. J. Org. Chem. 2009, 1976–1983

Tris[oligo(1,4-phenylenevinylene)]methylium Dyes
191.0 ppm in 2Јe. This difference ∆δ of about 109 ppm is
typical for a partially delocalized positive charge. Further
strong downfield shifts (∆δ = 12.0, 14.1, and 8.8 ppm) can
be observed for the alternating positions α, β, and γ (Fig-
ure 2), which also bear partial positive charges. The polar-
ization of the three arms is, for example, documented by
the ∆δЈ(13C) value of the two olefinic carbon atoms in each
arm, which rises from 2.7 ppm in 2e to 13.6 ppm in 2Јe. The
methylium ion 2Јe represents a typical star-shaped donor–
acceptor system AD3.[14]
Scheme 1. Preparation of the carbinols 2a–f by three-fold Wittig–
Horner reactions.
solubility of 2e and 7a, which bear hexyloxy groups, proved
to be sufficient, so we finally selected these two compounds
as model compounds for treatment with acids.
1
Figure 2. H and 13C NMR chemical shifts of 2e (CDCl3) and its
cation 2Јe (CDCl3/CF3COOD, 7:3).
The molar ratio 2e/CF3COOH used for the NMR mea-
surements was approximately 1:200. The 13C NMR chemi-
cal shifts change slightly with a smaller excess of acid
(1:100). The equilibrium 2e + CF3COOD i 2Јe + H2O is
not responsible for this result because we found an equiva-
lent effect for model compound 7a, which does not contain
an OH group. We assume that the acid concentration is
important for solvation complexes formed between the hex-
yloxy groups of 2e or 7a and CF3COOD.
Scheme 2. Preparation of the tris(stilbenyl)methanes 7a,b by three-
fold Siegrist reactions.
The Siegrist reaction of ether 5 and Schiff base 6a or 6b
yielded in a strongly alkaline medium the compounds 7a,b
(Scheme 2). Whereas the methine center is oxidized in the
process 3Ǟ2, the ether function of 5 is cleaved and reduced
in the process 5Ǟ7. These results reveal the high sensitivity
of the trityl systems towards redox reactions.
The treatment of the carbinols 2a–c with CF3COOD
proved to be much more complex. Scheme 3 summarizes
the processes. Carbinol 2a behaves like the model com-
pound 2e. Protonation leads directly to the methylium salt
2Јa, which then can be subjected to further stepwise proton-
ations (m = 1–3) to give 2ЈЈЈa. In contrast, carbinols 2b,c
are first protonated on the amino groups to give the N-
protonated carbinols 2ЈЈb,c before the N-protonated meth-
ylium ions 2ЈЈЈb,c are generated. Accordingly, the unproton-
ated methylium salts 2Јb and 2Јc are not accessible. As the
following discussion reveals, these results were obtained by
The kinetically controlled Siegrist reaction is an ex-
tremely stereoselective trans olefination.[13] The Wittig–
Horner olefination can lead to a small number of cis config-
urations in the stilbenoid series. Their proportion here was
1
below the detection limit in the H and 13C NMR spectra
(ca. 3%).
1
studying the protonation by H and 13C NMR as well as
Formation of Methylium Salts
by UV/Vis/NIR spectroscopy.
1
Treatment of 2a–c and the selected model compound 2e
Figure 3 shows that all the H NMR chemical shifts of
with CF3COOH/D led to the formation of dark-blue meth- 2a are strongly downfield shifted for 2ЈЈЈa, which exists in
1
ylium ions. Figure 2 shows the change in the H and 13C a high excess of acid (CDCl3/CF3COOD, 7:3). The greatest
NMR spectroscopic data for the process 2e + D+ Ǟ 2Јe + shift difference, ∆δ = 0.93 ppm, is observed for the aromatic
HDO. The largest downfield shift is observed for the central protons in the position ortho to the dialkylamino group.
carbon atom, which has a δ value of 81.8 ppm in 2e and The highest ∆δ(1H) values for 2e Ǟ 2Јe were observed for
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S. Kim, H. Kalbitz, S. Hillmann, H. Meier
FULL PAPER
Scheme 3. Protonation of the carbinols 2a–c,e,f.
Figure 3. Low-field region of the 1H NMR spectrum of 2a in CDCl3 (bottom) and of 2ЈЈЈa in CDCl3/CF3COOD (7:3) (top). (The
numbering does not correspond to the nomenclature.).
positions that are close to the central methylium carbon acid protonates/deuteriates the dialkyamino groups. The N-
atom (Figure 2).
CH2 groups show a signal shift from δ = 57.2 to 66.2 ppm
The 13C NMR spectrum of 2ЈЈЈa indicates the formation and the carbon atoms ortho to the dialkylamino group shift
of a delocalized methylium ion as the signal of the central from δ = 113.4 to 122.6 ppm. The sizes of the ∆δ values
carbon atom in 2a is shifted from δ = 83.5 ppm in CDCl3 to indicate that the major component in the strongly acidic
198.2 ppm in CDCl3/CF3COOD (7:3). Moreover, the excess medium is the tetracation 2ЈЈЈ (m = 3).[15] An equilibrium
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Tris[oligo(1,4-phenylenevinylene)]methylium Dyes
with the trication 2ЈЈЈa (m = 2) as a minor component can-
not be completely excluded. The de facto C3h symmetry is
preserved in both cases.[16]
N-Protonation weakens and finally cancels the push–pull
character of the methylium dyes AD3. Thus, the crucial
question was: can the ratio 2a–c/CF3COOD be so assessed
that the tris(OPV)methylium dyes 2Јa–c are present without
N-protonation? An NMR study of the equilibria 2Ј i 2ЈЈЈ
(m = 1) i 2ЈЈЈ (m = 2) i 2ЈЈЈ (m = 3) proved to be very
difficult. Owing to the exchange processes many signals be-
come very broad and can finally disappear in the electronic
noise.[17] However, because UV/Vis/NIR absorption oper-
ates on a much faster timescale than NMR spectroscopy,
absorption measurements were used to study the equilibria.
Compound 2a in CH2Cl2 or CHCl3 exhibits a long-wave-
length band (Figure 4, a) with a maximum at 375 nm (ε =
84590 Lmol–1 cm–1). Slowly increasing the protonation
(1.2ϫ10–5  2a and 1.2ϫ10–5 to 2.2ϫ10–4  CF3COOH)
leads to the disappearance of this band, the formation of a
few low-intensity bands in the region between 300 and
565 nm, and a strong NIR band at 1100 nm (Figure 4, a).
Further increases in the CF3COOH concentration in
CH2Cl2 cause a steady decrease and a continuous blueshift
of the maximum to 1050 nm. The solution used for the
NMR measurements, which has a molar ratio for 2a/
CF3COOD of 1:200, does not show any NIR absorption at
all. Concomitant to the decrease in the NIR band, a new
intense band with λmax = 622 nm increases (Figure 4).
We assume that the NIR band corresponds to the equi-
librium 2Јa i 2ЈЈЈa (m = 1) with 2Јa as the major compo-
nent (λmax = 1100 nm). The chromophore of 2Јa contains
three donor arms, which are cross-conjugated through the
central acceptor to an AD3 system. Figure 5 shows the im-
monium resonance structure of such an OPV arm. Only the
cross-conjugated third arm has lost its donor character in
2ЈЈЈa (m = 1) and therefore its electron transition should be
only slightly higher in energy (λmax ≈ 1050 nm) than that of
2Јa. A high excess of CF3COOH/D certainly leads to 2ЈЈЈa
(m = 3) being the major component in the equilibrium 2ЈЈЈa
(m = 2) i 2ЈЈЈa (m = 3). Therefore we conclude that the
band with λmax = 622 nm corresponds to this state, which
Figure 4. a) UV/Vis/NIR absorption of 2a in CHCl3, with 2Јa as
the major component obtained by primary protonation and 2ЈЈЈa
(m = 3) obtained as the major component in the final protonation
(CHCl3/CF3COOH). b) UV/Vis/NIR absorption of 2c in CHCl3,
N-protonated carbinol 2ЈЈc, and methylium salt 2ЈЈЈc (m = 3) as
the major component after the final protonation with CF3COOH
(molar ratio 2c/CF3COOH, 1:200).
1
has already been described above in the analysis of the H
and 13C NMR spectroscopic data.
The carbinols 2b (λmax = 411 nm, ε = 155500 Lmolcm–1)
and 2c (λmax = 419 nm, ε = 277200 Lmolcm–1) show on
protonation a behavior that is quite different from that of
2a and 2e. The long-wavelength band is first blueshifted
from 411 to 360 nm and from 419 to 370 nm, respectively.
Figure 5. Immonium resonance structure of an unprotonated arm
of 2Ј and 2ЈЈЈ.
Further protonation decreases the intensity of the blue- methylium ions are formed [2b,c Ǟ 2ЈЈb,c (m = 2,3) Ǟ
shifted band and generates a new band at the Vis/NIR bor- 2ЈЈЈb,c (m = 2,3)]. Figure 4 (b) illustrates the protonation of
der at λmax = 732 (n = 2) and 783 nm (n = 3). We attribute 2c (n = 3) and the characteristic difference in the proton-
the blueshifted band to the protonated carbinols 2ЈЈb,c and ation of 2a (n = 1) shown in Figure 4 (a).
the finally generated band at the Vis/NIR border to the N-
The exact λmax values of 2ЈЈЈa–c depend to some extent
protonated methylium salts 2ЈЈЈb,c (Scheme 3). Compounds on the excess of CF3COOH. Although a 200-fold molar
2ЈЈb,c (m = 1) should give, on further careful protonation, excess of acid should favor 2ЈЈЈ (m = 3), 2ЈЈЈ (m = 2) as the
a methylium ion 2ЈЈЈb,c (m = 1) with λmax Ն1050 nm. We minor component cannot be excluded. A strict distinction
could not find such a species. Therefore we assume that the between m = 2 and m = 3 on the basis of a small variation
carbinols 2b,c are two- or three-fold protonated before the in λmax is not possible because we also observed such an
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S. Kim, H. Kalbitz, S. Hillmann, H. Meier
FULL PAPER
effect for the alkoxy-substituted ions 2Јe. We assume that type AD3. Consequently, the λmax values of 2ЈЈЈ are, for
the solvation of the ions or better of the ion pairs in CHCl3/ each value of n, lower than the λmax values of 8Ј. The un-
CF3COOH depends on the concentration of the acid. A protonated series 2a–c has, in contrast, for each value of n,
related solvation effect is discussed above for the NMR higher λmax values than 8a–c because dialkylamino groups
measurements of the electroneutral compound 7c in CDCl3/ are stronger donors than alkoxy groups.
CF3COOD.
In the light of these results, the tris(aminostilbenyl)meth-
Figure 6 gives an overview of the absorption maxima of ylium salts with λmax values of 952[12] and 1003 nm[11] pub-
2a–c, 2Јa, and 2ЈЈЈa–c and compares them with the hex- lished by Sengupta and Sadhukhan seem to be correct,
yloxy-substituted carbinols 8a–d (n = 1–4) and their meth- whereas the systems reported by Steele[9] and Screttas and
ylium ions 8Јa–d.[7]
Nunzi[8] and their co-workers, which have λmax values of
833 and 608 nm, respectively, are certainly polycations.
Stability
The tris(OPV)methylium dyes can be isolated in the solid
state as tetrafluoroborates. The dark-blue salts are highly
hygroscopic, hydrolyze rapidly (NMR control) in air or in
aqueous solvents and start to fade. The carbinols 2a–f are
thermally but not photochemically stable. Cross-linking by
the formation of C–C single bonds is a typical photoreac-
tion of stilbenoid compounds.[13] In particular, energy-rich
UV light, for example, λirr = 254 nm, leads to processes in
which the conjugated chromophores are slowly destroyed.
Stereoisomerization reactions (E) i (Z) are restricted to
stilbenes. Higher-conjugated stilbenoid systems do not
show this type of reaction because the bond order of the
olefinic double bonds is not sufficiently reduced in the exci-
tation of the ground state So to the first excited singlet state
S1.[13] Therefore compound 2a (n = 1) is by far the most
photosensitive compound in the series 2a–d. The model sys-
tem 2e behaves in the same way. Figure 7 demonstrates the
photoreactivity of 2e for monochromatic irradiation with
λirr = 366 nm. The long-wavelength band (λmax = 330 nm
in THF) is reduced and a new maximum at about 280 nm
is generated. The process looks clean because an isosbestic
point at λ = 274 is apparent. However, a 1H NMR study of
the probe after irradiation for 3 h revealed the presence of
small amounts of cross-linked oligomers, even for irradia-
tions at 366 nm. The major components during the entire
irradiation are the original system (E,E,E)-2e and its
(E,E,Z) and (E,Z,Z) isomers. For steric reasons only traces
Figure 6. Absorption maxima of the carbinols 2a–c and 8a–d in
CHCl3, the methylium dyes 2aЈ and 8Јa–d, and the protonated
methylium dyes 2ЈЈЈa–c in CHCl3/CF3COOH (7:3).
The carbinol series 2a–c and 8a–d are typical ba-
thochromic series, which means their λmax values are mo-
notonously redshifted with increasing numbers n of repeat
units and approach limiting values λϱ in accord with an
empirical exponential function.[14,18] Recently, semiempir-
ical and theoretically based algorithms were suggested for
such convergence problems.[19–21] Formation of the meth-
ylium salts causes a redshift that in series 8Јa–d is even more
pronounced than in 2ЈЈЈa–c and leads to a convergence limit
of λϱ at 879 nm. Compared with the carbinol series 2a–c
and 8a–d, 2ЈЈЈa–c and 8Јa–d have an extended conjugation,
Figure 7. Reaction spectra of (E,E,E)-2e in THF after 0, 1, 5, 20,
but only compounds 8Јa–d have a push–pull effect of the 40, 60, and 180 min of monochromatic irradiation (λirr = 366 nm).
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Tris[oligo(1,4-phenylenevinylene)]methylium Dyes
General Procedure for Preparation of the Carbinols 2a–f: Triphos-
phonate 3[7] (69.5 mg, 0.10 mmol) and aldehyde 4a–d,[25] 4e,[26] or
4f[27,28] (0.40 mmol) dissolved in dry THF (20 mL) were dropped
into a solution of KOC(CH3)3 (2.25 g, 20.0 mmol) in THF (40 mL).
The mixture was stirred at ambient temperature for 3–4 d and then
poured onto crushed ice (50 g). The extract (40 mL CH2Cl2) was
dried (MgSO4) and the solvents evaporated. The crude products 2a,
2b, and 2e were purified by filtration through silica gel (10ϫ13 cm,
toluene/CHCl3 gradient from 100:0 to 80:20). The products 2c, 2d,
and 2f were precipitated by the addition of ethanol or methanol to
the extract.
of (Z,Z,Z)-2e can be formed and detected (Scheme 4). The
(Z)-configured arms can be easily identified in the mixture
by their olefinic AB systems in the 1H NMR spectra, which
are shifted from δ = 7.0–7.1 (3J = 16 Hz) to 6.4–6.6 ppm
(3J = 10 Hz). The structures of the generated oligomers
were not studied.
all-(E)-Tris[4-(2-{4-[bis(2-hexyloctyl)amino]phenyl}vinyl)phenyl]-
methanol (2a): Yield 122 mg (68%); yellow, viscous oil. 1H NMR
(CD2Cl2): δ = 0.89 (m, 36 H, CH3), 1.16–1.33 (m, 120 H, CH2),
3
1.78–1.88 (m, 6 H, CH), 3.25 (d, J = 6.3 Hz, 12 H, NCH2), 6.65/
7.35 (AAЈBBЈ, 12 H, arom. H, outer benzene rings), 6.88/7.04 (AB,
3J = 16.2 Hz, 6 H, olefin. H), 7.27/7.43 (AAЈBBЈ, 12 H, arom. H,
inner benzene rings) ppm. 13C NMR (CDCl3): δ = 14.3 (CH3),
23.1, 27.0, 30.2, 30.3, 32.2, 32.4 (CH2, partly superimposed), 36.2
(CH), 57.2 (NCH2), 82.2 (COH), 113.4, 125.9, 128.0, 128.7 (arom.
CH), 123.4, 129.8 (olefin. CH), 125.0, 138.0, 145.9, 149.0 (arom.
Cq) ppm. MS (FD): m/z (%) = 1790 (100) [M]+·. UV (CHCl3): λmax
= 375 nm, ε = 84590 Lmol–1 cm–1. C127H205N3O (1790.1): calcd. C
85.22, H 11.54, N 2.35; found C 85.20, H 11.25, N 2.33.
all-(E)-Tris(4{2-[4-(2-{4-[bis(2-hexyloctyl)amino]phenyl}vinyl)phen-
yl]vinyl}phenyl)methanol (2b): Yield 101 mg (48%); yellow solid,
m.p. 55 °C. 1H NMR (CDCl3): δ = 0.87 (m, 36 H, CH3), 1.17–1.34
(m, 120 H, CH2), 1.78–1.88 (m, 6 H, CH), 3.21 (d, 3J = 6.3 Hz, 12
H, NCH2), 6.63/7.36 (AAЈBBЈ, 12 H, arom. H, outer benzene
rings), 6.87/7.04 (AB, 3J = 16.2 Hz, 6 H, olefin. H, outer double
bonds), 7.09 (ЈЈsЈЈ, 6 H, olefin. H, inner double bonds), 7.30/7.47
(AAЈBBЈ, 12 H, arom. H, inner benzene rings), 7.43–7.47 (m, 12
H, arom. H, middle benzene rings) ppm. 13C NMR (CDCl3): δ =
14.0 (CH3), 22.6, 26.4, 29.7, 31.7, 31.8 (CH2, partly superimposed),
35.5 (CH), 57.2 (NCH2), 81.7 (COH), 113.5, 126.0, 126.2, 126.8,
127.3, 128.2 (arom. CH), 123.6, 127.3, 128.9, 128.9 (olefin. CH),
125.9, 135.6, 136.6, 137.9, 145.9, 145.9 (arom. Cq) ppm. MS (FD):
m/z (%) = 2096 (100) [M]+·. UV/Vis (CHCl3): λmax = 411 nm, ε =
155500 L mol–1 cm–1. C151H223N3O (2096.5): calcd. C 86.51, H
10.72, N 2.00; found C 86.49, H 10.70, N 1.89.
Scheme 4. Photoreactions of 2e.
Conclusion and Outlook
Carbinols 2a–f with three OPV arms can be prepared by
the Wittig–Horner reaction and simultaneous autoxidation.
Compounds 2a–d with terminal dialkylamino groups exhi-
bit unexpected protonation behavior. The lowest member
2a (n = 1) first forms by O-protonation and elimination
of water the corresponding methylium salt 2Јa before N-
protonation to 2ЈЈЈa occurs. The higher members 2b,c (n =
2,3) are first N-protonated to the carbinols 2ЈЈb,c before the
N-protonated methylium ions 2ЈЈЈb,c are generated. This
distinction has a big effect on the long-wavelength electron
transition. The methylium ion 2Јa is a push–pull system
all-(E)-Tris{4-[2-(4-{2-[4-(2-{4-[bis(2-hexyloctyl)amino]phenyl}-
vinyl)phenyl]vinyl}phenyl)vinyl]phenyl}methanol (2c): Yield 108 mg
1
(45%); orange solid, m.p. 175 °C. H NMR (CDCl3): δ = 0.87 (m,
AD3 with an absorption far into the NIR region (λmax
=
36 H, CH3), 1.17–1.33 (m, 120 H, CH2), 1.81–1.90 (m, 6 H, CH),
3.24 (d, 3J = 6.4 Hz, 12 H, NCH2), 6.65/7.37 (AAЈBBЈ, 12 H, arom.
1100 nm),[22] whereas the tetracations 2ЈЈЈa–c have
absorption maxima in the visible region (λmax = 622, 740,
3
H, outer benzene rings), 6.87/7.07 (AB, J = 16.3 Hz, 6 H, olefin.
H, outer double bonds), 7.13–7.19 (m, 9 H, olefin. H), 7.29–7.57
(m, 39 H, arom. and olefin. H) ppm. 13C NMR (CD3SOCD3): δ =
14.3 (CH3), 23.1, 26.8, 30.1, 31.9, 32.2 (CH2, partly superimposed)
35.9 (CH), 57.0 (NCH2), 81.9 (COH), 113.0, 126.5, 126.5, 127.1,
127.2, 127.2, 127.9, 128.6 (arom. CH), 123.1, 127.6, 128.1, 128.7,
128.9, 129.4 (olefin. CH), 124.5, 135.9, 136.8, 136.8, 137.4, 138.3,
146.5, 148.6 (arom. Cq) ppm. MS (FD): m/z (%) = 2403 (3) [M]+·,
794 (19), 793 (49), 792 (100). UV/Vis (CHCl3): λmax = 419 nm, ε =
277200 L mol–1 cm–1. C175H241N3O (2402.9): calcd. C 87.48, H
10.11, N 1.75; found C 87.34, H 10.14, N 1.72.
and 790 nm). They represent
[λ(n + 1)Նλ(n)] for which a convergence limit at λϱ
827 nm can be predicted. The star-shaped molecules 2, 2Ј,
and 2ЈЈЈ promise as nanoparticles[23,24] interesting SHG and
TPA properties, although their photostability is limited
when they are irradiated with UV light.
a bathochromic series
=
Experimental Section
1
General Remarks: UV/Vis: Zeiss MCS 320/340. H and 13C NMR:
all-(E)-Tris[4-(2-{4-[2-(4-{2-[4-(2-{4-[bis(2-hexyloctyl)amino]phen-
yl}vinyl)phenyl]vinyl}phenyl)vinyl]phenyl}vinyl)phenyl]methanol (2d):
Yield 22 mg (8%); red-orange solid, m.p. Ͼ230 °C (decomp.). 1H
NMR ([D8]THF): δ = 0.79 (m, 36 H, CH3), 1.14–1.27 (m, 120 H,
CH2), 1.73–1.81 (m, 6 H, CH), 3.18 (d, J = 6.5 Hz, 12 H, NCH2),
6.58/7.39 (AAЈBBЈ, 12 H, arom. H, outer benzene rings), 6.81/6.98
Bruker AMX 400, Avance 600, CDCl3 as solvent, unless otherwise
stated; TMS as internal standard. MS (FD): Finnigan MAT 95.
Melting points: Büchi apparatus and Stuart Scientific SMP/3; un-
corrected. Elemental analyses: Microanalytical laboratory of the
Institute of Organic Chemistry, University of Mainz.
3
Eur. J. Org. Chem. 2009, 1976–1983
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1981

S. Kim, H. Kalbitz, S. Hillmann, H. Meier
FULL PAPER
3
(AB, J = 16.4 Hz, 6 H, olefin. H, outer double bonds), 7.06/7.09
20 mmol) gave 2.15 g (65%) of 7b. The colorless crystals melted
3
1
(AB, J = 16.4 Hz, 6 H, olefin. H), 7.05–7.12 (m, 6 H, olefin. H), after recrystallization from ethanol at 132 °C. H NMR (CDCl3):
7.20–7.47 (m, 54 H, arom. and olefin. H) ppm. 13C NMR ([D8]- δ = 0.87 (t, 9 H, CH3), 1.23–1.36 (m, 48 H, CH2), 1.42–1.47 (m, 6
THF): δ = 14.4 (CH3), 23.5, 27.3, 30.7, 32.4, 32.7 (CH2, partly H, CH2), 1.73–1.79 (m, 6 H, CH2), 3.95 (t, 6 H, OCH2), 5.51 (s, 1
superimposed), 36.5 (CH), 57.4 (NCH2), 81.5 (COH), 113.7, 123.9,
125.9, 126.5, 126.8, 127.4, 128.1, 128.3, 128.7, 128.9, 129.1, 129.2,
129.7 (olefin. and arom. CH, partly superimposed), 125.9, 136.6,
H, CH), 6.86/7.39 (AAЈBBЈ, 12 H, arom. H, outer benzene rings),
6.93/7.02 (AB, 3J = 16.3 Hz, 6 H, olefin. H), 7.10/7.39 (AAЈBBЈ,
12 H, arom. H, inner benzene rings) ppm. 13C NMR (CDCl3): δ
137.0, 137.6, 137.7, 137.8, 138.0, 138.8, 148.3, 148.9 (arom. = 14.1 (CH3), 22.7, 25.9, 29.2, 29.3, 29.5, 29.6, 31.9 (CH2, partly
Cq) ppm. MS (FD): m/z (%) = 2709 (3) [M]+·, 1815 (6), 998 (26), superimposed), 56.2 (CH), 68.2 (OCH2), 114.8, 126.0, 126.3, 127.7,
895 (100). Owing to the low yield, further characterizations and
studies of the compound have been omitted.
128.2, 129.7 (arom. and olefin. CH), 130.1, 136.0, 142.9, 159.0
(arom. Cq) ppm. MS (FD): m/z (%) = 1104 (100) [M + H]+.
C79H106O3 (1103.7): calcd. C 85.97, H 9.68; found C 85.92, H 9.35.
all-(E)-Tris(4-{2-[4-(hexyloxy)phenyl]vinyl}phenyl)methanol (2e):
1
Yield 61 mg (70%); almost colorless solid, m.p. 115 °C. H NMR
Generation of the Methylium Trifluoroacetates 2Јa, 2Јe, and 2ЈЈЈa–
c: Carbinol 2a (36 mg, 0.02 mmol) was dissolved in CH2Cl2 or
CHCl3 (1–2 mL) and treated with trifluoroacetic acid (10–40 mg,
0.1–0.4 mmol). The spontaneous formation of 2Јa as the major
component in the equilibrium 2a i 2Јa i 2ЈЈЈa (m = 1) was evident
by the color change from light-yellow to blue. The polycations
2ЈЈЈa–c (m = 3) i 2ЈЈЈa–c (m = 2) were obtained when 2a–c
(0.02 mmol) were dissolved in 7:3 mixtures of CHCl3/CF3COOH
or CH2Cl2/CF3COOH (1 mL). The molar ratio 2a–c/CF3COOH
amounts in these cases to 1:200. The latter procedure was also per-
formed for the generation of 2Јe.
(CDCl3): δ = 0.91 (t, 6 H, CH3), 1.30–1.40 (m, 12 H, CH2), 1.41–
3
1.53 (m, 6 H, CH2), 1.75–1.85 (m, 6 H, CH2), 3.95 (t, J = 6.6 Hz,
6 H, OCH2), 6.84/7.39 (AAЈBBЈ, 12 H, arom. H, outer benzene
rings), 6.92/7.02 (AB, 3J = 16.4 Hz, 6 H, olefin. H), 7.18/7.31
(AAЈBBЈ, 12 H, arom. H, inner benzene rings) ppm. 13C NMR
(CDCl3): δ = 14.0 (CH3), 22.6, 25.7, 29.3, 31.6 (CH2), 68.2 (OCH2),
81.8 (COH), 114.8, 125.9, 127.8, 128.3 (arom. CH), 126.0, 128.7
(olefin. CH), 130.0, 136.8, 145.7, 159.0 (arom. Cq) ppm. MS (FD):
m/z (%) = 866 (100) [M]+·. C61H70O4 (867.2): calcd. C 84.48, H
8.14; found C 84.39, H 8.11.
all-(E)-Tris(4-{2-[3,4-bis(hexyloxy)phenyl]vinyl}phenyl)methanol
(2f): Yield 76 mg (65%); almost colorless solid, m.p. 109 °C. 1H
NMR (CDCl3): δ = 0.89 (m, 18 H, CH3), 1.31–1.36 (m, 24 H,
CH2), 1.44–1.48 (m, 12 H, CH2), 1.77–1.86 (m, 12 H, CH2), 3.99
(t, 6 H, OCH2), 4.03 (t, 6 H, OCH2), 6.84/7.00/7.05 (ABC, 9 H,
all-(E)-Tris[4-(2-{4-[bis(2-hexyloctyl)ammonium]phenyl}vinyl)-
phenyl]methylium Tetra(trifluoroacetate) (2ЈЈЈa): H NMR (CDCl3/
1
CF3COOD, 7:3): δ = 0.86–0.95 (m, 36 H, CH3), 1.20–1.47 (m, 120
H, CH2), 1.55–1.64 (m, 6 H, CH), 3.60–3.68 (m, 12 H, NCH2),
7.53/7.75 (AB, 3J = 16.5 Hz, 6 H, olefin. H), 7.58/7.98 (AAЈBBЈ,
12 H, arom. H, outer benzene rings), 7.76/8.04 (AAЈBBЈ, 12 H,
arom. H, inner benzene rings) ppm. 13C NMR (CDCl3/ CF3COOD
7:3): δ = 13.7 (CH3), 22.8, 26.2, 29.5, 31.4, 31.9 (CH2, partly super-
imposed), 34.7 (CH), 66.2 (NCH2), 122.6, 129.0, 130.7, 142.0
(arom. CH), 130.6, 135.8 (olefin. CH), 137.9, 139.9, 140.0, 150.6
(arom. Cq), 198.2 (central C) ppm. Vis/NIR: λmax = 622 nm
(CHCl3/CF3COOH = 7:3).
3
arom. H, outer benzene rings), 6.93/7.02 (AB, J = 16.1 Hz, 6 H,
olefin. H), 7.27/7.42 (AAЈBBЈ, 10 H, arom. H, inner benzene
rings) ppm. 13C NMR (CDCl3): δ = 14.0 (CH3), 22.6, 22.6, 31.6,
31.6, 25.7, 25.8, 29.3, 29.4 (CH2), 69.5, 69.6 (OCH2), 81.8 (COH),
112.0, 114.1, 120.1 (arom. CH, outer benzene rings), 125.9, 128.2
(arom. CH, inner benzene rings), 126.2, 129.0 (olefin. CH), 130.6,
136.8, 145.8, 149.4, 149.5 (arom. Cq) ppm. MS (FD): m/z (%) =
1167 (100) [M]+·. C79H106O7 (1167.7): calcd. C 81.26, H 9.15; found
C 81.08, H 9.07.
all-(E)-Tris(4-{2-[4-(2-{4-[bis(2-hexyloctyl)ammonium]phenyl}vinyl)-
1
phenyl]vinyl}phenyl)methylium Tetra(trifluoroacetate) (2ЈЈЈb): H
all-(E)-Tris(4-{2-[4-(hexyloxy)phenyl]vinyl}phenyl)methane (7a):
Ethyl tris(p-tolyl)methyl ether (5)[6,29] and Schiff base 6a[28] were
prepared according to the literature. A mixture of KOC(CH3)3
(3.37 g, 30.0 mmol) and 6a (5.63 g, 20.0 mmol) in dry DMF
(100 mL) was degassed and purged with Ar before 5 (1.0 g,
3.0 mmol) in DMF (30 mL) was slowly added. After 1 h vigorous
stirring at 80 °C, the mixture was poured onto crushed ice (300 g)
and treated with 6  HCl (100 mL, 600 mmol) for about 1 h. Ex-
traction with CHCl3 (3ϫ50 mL) gave an organic phase that was
washed with water (2ϫ50 mL), dried (Na2SO4), and the solvents
evaporated. The residue was recrystallized from ethanol. Yield
1.66 g (65 %); colorless crystals, m.p. 121–122 °C. 1H NMR
(CDCl3): δ = 0.89 (t, 9 H, CH3), 1.31–1.34 (m, 12 H, CH2), 1.42–
1.46 (m, 6 H, CH2), 1.73–1.78 (m, 6 H, CH2), 3.95 (t, 6 H, OCH2),
5.51 (s, 1 H, CH), 6.86/7.40 (AAЈBBЈ, 12 H, arom. H, outer ben-
NMR (CDCl3/CF3COOD, 7:3): δ = 0.86–0.94 (m, 36 H, CH3),
1.22–1.50 (m, 120 H, CH2), 1.58–1.66 (m, 6 H, CH), 3.58–3.70 (m,
12 H, NCH2), 7.36/7.44 (AB, J = 16.5 Hz, 6 H, olefin. H), 7.40–
3
7.54 (m, 9 H, arom. and olefin. H), 7.72–7.85 (m, 21 H, arom. and
olefin. H), 7.89–7.94 (m, 6 H, arom. H), 8.01–8.06 (m, 6 H, arom.
H) ppm. 13C NMR (CDCl3/CF3COOD, 7:3): δ = 13.8 (CH3), 23.0,
26.5, 29.7, 31.9, 32.1 (CH2), 34.8 (CH), 66.4 (NCH2), 122.2, 127.6,
128.3, 128.7, 129.3, 129.8, 129.9, 132.8, 136.0, 139.1, 139.5, 141.6,
142.0 (arom. and olefin. CH and Cq, partly superimposed), 198.0
(central C) ppm. Vis/NIR: λmax = 740 nm (CHCl3/CF3COOH =
7:3).
all-(E)-Tris{4-[2-(4-{2-[4-(2-{4-[bis(2-hexyloctyl)ammonium]phen-
yl}vinyl)phenyl]vinyl}phenyl)vinyl]phenyl}methylium Tetra(trifluo-
roacetate) (2ЈЈЈc): Vis/NIR: λmax = 790 nm (CHCl3/CF3COOH =
1
7:3). The H and 13C NMR spectra exhibit broad overlapping sig-
3
zene rings), 6.89/7.02 (AB, J = 16.0 Hz, 6 H, olefin. H), 7.09/7.40
(AAЈBBЈ, 12 H, arom. H, inner benzene rings) ppm. 13C NMR
(CDCl3): δ = 14.0 (CH3), 22.6, 25.7, 29.3, 31.6 (CH2), 56.2 (CH),
68.2 (OCH2), 114.8, 126.3, 127.7, 129.8 (arom. CH), 126.2, 128.2
(olefin. CH), 130.1, 136.0, 143.0, 159.0 (arom. Cq) ppm. MS (FD):
m/z (%) = 851 (100) [M + H]+. C61H70O3 (851.2): calcd. C 86.07,
H 8.29; found C 85.99, H 8.35.
nals.
all-(E)-Tris(4-{2-[4-(hexyloxy)phenyl]vinyl}phenyl)methylium Tri-
fluoroacetate (2Јe): 1H NMR (CDCl3/CF3COOD, 7:3): δ = 0.88–
0.94 (m, 9 H, CH3), 1.33–1.40 (m, 12 H, CH2), 1.44–1.53 (m, 6 H,
CH2), 1.81–1.90 (m, 6 H, CH2), 4.14–4.21 (m, 6 H, OCH2), 7.06/
7.66 (AAЈBBЈ, 12 H, arom. H, outer benzene rings), 7.25/7.66 (AB,
3J = 16.1 Hz, 6 H, olefin. H), 7.66/7.89 (AAЈBBЈ, 12 H, inner ben-
zene rings) ppm. 13C NMR (CDCl3/CF3COOD, 7:3): δ = 13.1
(CH3), 22.2, 25.2, 28.7, 31.3 (CH2), 69.7 (OCH2), 116.0, 127.6,
all-(E)-Tris(4-{2-[4-(dodecyloxy)phenyl]vinyl}phenyl)methane (7b):
The procedure applied for 7a was also used for the preparation of
7b. Ether 5[6](1.0 g, 3.0 mmol) and Schiff base 6b[26] (7.31 g,
1982
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 1976–1983

Tris[oligo(1,4-phenylenevinylene)]methylium Dyes
[12] S. Sengupta, Tetrahedron Lett. 2003, 44, 307–310.
[13] H. Meier, Angew. Chem. 1992, 104, 1425–1446; Angew. Chem.
Int. Ed. Engl. 1992, 31, 1399–1420.
[14] H. Meier, Angew. Chem. 2005, 117, 2536–2561; Angew. Chem.
Int. Ed. 2005, 44, 2482–2506.
[15] The protonation/deuteriation of N,N-diethylaniline in CDCl3/
CF3COOD (7:3) serves here as an equivalent model. The ∆δ
values found for the CH2 groups and the ortho carbon atoms
for 2aǞ2ЈЈЈa amount to about 90% of the ∆δ values obtained
for diethyl(phenyl)ammonium trifluoroacetate. This value is a
clear indication that the tetracation 2ЈЈЈa (m = 3) is a major
component.
[16] Owing to the fast intra- and intermolecular proton exchange,
mediated by the trifluoroacetate anions, the trications 2ЈЈЈa
(m = 2) also have C3h symmetry.
129.8, 140.3 (arom. CH), 124.5, 138.1 (olefin. CH), 138.8, 150.9,
160.4, 191.0 (arom. Cq) ppm.
Isolation of the Dyes in the Solid State: The carbinols 2a–c,e
(0.02 mmol) were dissolved in CH2Cl2 (10 mL) and treated with
HBF4 (2 mL) and acetic anhydride (2 mL). The salts 2Јe and 2ЈЈЈa–
c precipitated as dark-blue solids and were purified by evaporation
of the volatile parts at 102 Pa. They are highly hygroscopic, attract
water, become sticky and start to fade.
Irradiation of Carbinol 2e:
A solution of (E,E,E)-2e (9 mg,
0.01 mmol) was irradiated in THF/[D8]THF (1 mL). (A saturated
solution of 2e in CH2Cl2/CD2Cl2 can be used as well.) An Osram
XBO-1000 W OFR lamp in an AMKO device was used. The
monochromator was adjusted to 366 nm, which is on the long-
wavelength end of the absorption. Thus, photocrosslinking could
be kept to a minimum. The isomerization process (Scheme 4) was
[17] Another drawback is the H/D exchange at the position ortho
to the dialkylamino group.
[18] H. Meier, U. Stalmach, H. Kolshorn, Acta Polym. 1997, 48,
1
followed by UV and H NMR measurements. Compound 2a was
379–384.
treated in a similar way.
[19] J. Gierschner, J. Cornil, H.-J. Egelhaaf, Adv. Mater. 2007, 19,
173–191.
[20] M. Bednarz, P. Reineker, E. Mena-Osteritz, P. Bäuerle, Chem.
Phys. 2007, 342, 191–200.
[21] A. C. Benniston, A. Harriman, D. B. Rewinska, S. Yong, Y.-G.
Zhi, Chem. Eur. J. 2007, 13, 10194–10203.
[22] The extended conjugation of the AD3 system causes such an
enormous bathochromic shift in comparison with tris(4-di-
Acknowledgments
We are grateful to the Deutsche Forschungsgemeinschaft (DFG),
the Fonds der Chemischen Industrie and the Centre of Materials
Science of the University of Mainz.
methylaminophenyl)methylium ions (Crystal Violet: λmax
=
590 nm).
[1] A. Noack, A. Schröder, H. Hartmann, Dyes Pigm. 2003, 57,
131–147, and references cited therein.
[23] Model considerations predict for 2c, with stretched saturated
chains, an extension of 7 nm. The real diameter in solution
should be somewhat smaller, as neutron-scattering experiments
[2] V. Nair, S. C. Mathew, K. G. Abhilash, Tetrahedron 2006, 62,
6731–6747, and references cited therein.
of related dendritic discs have revealed.[24]
.
[3] X. Vidal, J. R. Herance, J. Marquet, J. L. Bourdelande, J. Mar-
torell, Appl. Phys. Lett. 2007, 91, 081116/–081116/3.
[4] Y. A. Mikheev, L. N. Guseva, Y. A. Ershov, Russ. J. Phys.
Chem. A 2008, 82, 1580–1588.
[5] N. I. Myakima, I. L. Kothyarevskii, Bull. Acad. Sci. USSR Div.
Chem. Sci. (Engl. Transl.) 1973, 22, 1368–1370.
[6] D. Hellwinkel, H. Fritsch, Chem. Ber. 1989, 122, 2351–2360.
[7] H. Meier, S. Kim, Eur. J. Org. Chem. 2001, 1163–1167.
[8] C. Arbez-Gindre, C. G. Screttas, C. Fiorini, C. Schmidt, J.-M.
Nunzi, Tetrahedron Lett. 1999, 40, 7413–7416.
[24] S. Rosenfeldt, E. Karpuk, M. Lehmann, H. Meier, P. Lindner,
L. Harnau, M. Ballauff, ChemPhysChem 2006, 7, 2097–2104.
[25] H. Meier, J. Gerold, H. Kolshorn, B. Mühling, Chem. Eur. J.
2004, 10, 360–370.
[26] G. Zerban, H. Meier, Z. Naturforsch., Teil B 1993, 48, 171–
184.
[27] F. Kosteyn, G. Zerban, H. Meier, Chem. Ber. 1992, 125, 893–
897.
[28] T. Lifka, G. Zerban, P. Seus, A. Oehlhof, H. Meier, Tetrahedron
2008, 64, 6551–6560.
[9] C. Villalonga-Barber, B. R. Steele, V. Kovac, M. Micha-
Screttas, C. G. Screttas, J. Organomet. Chem. 2006, 691, 2785–
2792.
[29] NMR spectroscopic data for 5. 1H NMR (CDCl3): δ = 1.26 (t,
3 H, CH3), 2.35 (s, 9 H, CH3), 3.14 (q, 2 H, OCH3), 7.13/7.37
(AAЈBBЈ, 12 H, arom. H) ppm. 13C NMR (CDCl3): δ = 15.4
(CH3 of OC2H5), 21.1 (CH3), 59.3 (OCH2), 86.1 (CO), 128.5,
128.5 (arom. CH), 136.3, 142.0 (arom. Cq) ppm.
Received: November 25, 2008
[10] S. Sengupta, S. K. Sadhukhan, Ind. J. Chem., Sect. B 2003, 42,
858–862.
[11] S. Sengupta, S. K. Sadhukhan, J. Chem. Soc. Perkin Trans. 1
2000, 24, 4332–4334.
Published Online: February 26, 2009
Eur. J. Org. Chem. 2009, 1976–1983
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1983