Linear and Star-Shaped Extended Di- and Tristyrylbenzenes: Synthesis, Characterization and Optical Response to Acid and Metal Ions

Article abstract of DOI:10.1002/chem.202000893

Two linear 1,4-distyrylbenzenes and five star-shaped 1,3,5-tristyrylbenzene derivatives (L_2a and L_2b, Y₀–Y₃ and Y_NBu) were synthesized and spectroscopically characterized. The photophysical properties, optical response to acid and metal ions were investigated. Upon backbone extension of linear distyrylbenzenes or the introduction of dibutylanilines, the electronic spectra are redshifted. Incorporation of electron-deficient pyridyl units does not significantly affect the optical properties. Variation of the number of pyridine rings and substitution pattern tune the fluorescence response to acids and metal ions. The novel arenes discriminate Al³⁺, Mn²⁺, Fe³⁺, Fe²⁺, Cd²⁺, Ag⁺ and Hg²⁺.

Full text of DOI:10.1002/chem.202000893

A Journal of
Accepted Article
Title: Linear and Star-Shaped Extended Di- and Tristyrylbenzenes:
Synthesis, Characterization and Optical Response to Acid and
Metal Ions
Authors: Hao Zhang, Eugen A. Kotlear, Soh Kushida, Steffen Maier,
Frank Rominger, Jan Freudenberg, and Uwe Heiko Bunz
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To be cited as: Chem. Eur. J. 10.1002/chem.202000893
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Linear and Star-Shaped Extended Di- and Tristyrylbenzenes:
Synthesis, Characterization and Optical Response to Acid and
Metal Ions
Hao Zhang,[a] Eugen A. Kotlear,[a] Soh Kushida,[a] Steffen Maier,[a] Frank Rominger,[a] Jan
Freudenberg,*[a] and Uwe H. F. Bunz*[a]
Abstract: Two linear 1,4-distyrylbenzenes and five star-shaped
1,3,5-tristyrylbenzene derivatives (L2a-L2b, Y0-Y3 and YNBu) were
synthesized and spectroscopically characterized. The photophysical
skeleton (Y0) reported by Maier et al.,[5c] Y1-3 and YNBu are
obtained either by variation of the number of pyridine rings or the
introduction of electron-rich dibutylaniline groups, respectively
properties, optical response to acid and metal ions were investigated. (Scheme 1).
Upon backbone extension of linear distyrylbenzenes or the
introduction of dibutylanilines, the electronic spectra are red-shifted.
Incorporation of electron-deficient pyridyl units does not significantly
affect the optical properties. Variation of the number of pyridine rings
and substitution pattern tune the fluorescence response to acids and
1 was reacted with 1-bromohexane (K2CO3, anhydrous DMF)
to afford 2, which was transformed by a Bouveault reaction to
the monoaldehyde 3. Heck coupling between 3 and three
arylethylenes produced 4-6, which were in turn subjected to a
Horner reaction with triphosphonate 7 in the presence of sodium
metal ions. The novel arenes discriminate Al3+, Mn2+, Fe3+, Fe2+, Cd2+, hydride, thus, affording Y0 (77%), Y3 (33%) and YNBu (68%). As
Ag+ and Hg2+.
reference systems, distyrylbenzene L2a was obtained after Heck
reaction of 2 and 4-vinylpyridine (45%). To obtain π-extended
L2b, 8 was subjected to an Arbuzow reaction with triethyl
phosphite, followed by a Horner reaction with monoaldehyde 5.
L2b was isolated after column chromatography on silica gel
(82%). Y1 and Y2 were obtained via two one-pot procedures
starting from 7 with aldehydes 5 and 4. For Y1, the first Horner
reaction of 7 with monoaldehyde 5 (molar ratio: 1:1.1) afforded
10, which was subjected to a second Wittig-Horner reaction with
4 in situ (28% over two steps). By changing the stoichiometry of
7 and 5 (1:2.2), Y2 was isolated by a similar two-step routine with
a yield of 44%. It should be noted that potassium tert-butoxide
as a base did not work.[11]. L2a-L2b and Y0-Y3 are yellow or
orange solids, while YNBu is a yellow oil. All styrylbenzene
derivatives (SBs) are well soluble in common organic solvents.
We obtained single crystals for Y0 (from DCM/methanol), L2b
and Y3 (from DCM/n-hexane) and performed X-ray analysis.
Figure 1 depicts the structure and Table S1−S3 summarize the
corresponding data. As shown in Figure S1, all of derivatives are
almost planar and their vinylic linkers display E-configuration.
However, the packing patterns of L2b, Y0 and Y3 deviate
significantly from each other. L2b packs in parallel layer stacks
with some displacement. Y0 displays a 2-dimensional wall-like
arrangement and the orientation of molecular planes in adjacent
parallel walls is different. In Y3, a pattern of parallel planes was
observed, which extends in three directions.
Introduction
Functional π-conjugated chromophores with linear[1] or star-
shaped geometry[2] are relevant responsive materials.[3] 1,3,5-
Tristyrylbenzene[4] is an excellent core for dendritic molecules.[2c,
5]
Peripheral and core substitution allow tuning of
photoluminescence[6] and mesogenic behavior.[2b]
Manipulation of the substituents in X-shaped molecules leads
to disjunct frontier molecular orbitals and tunable optical
properties.[7] If pyridines or dialkylanilines are incorporated, they
become acidochromic.[8] Both size and symmetry of the
conjugated system affect the properties and performance in
9]
applications.[5c,
We describe the synthesis, photophysical
characterization, and acid/metal ion response of two linear 1,4-
distyryl (L2a and L2b) and five star-shaped styrylbenzene
derivatives (Y0-Y3 and YNBu).
Results and Discussion
Synthesis, X-ray crystallographic analyses and liquid
crystalline behavior
Similar to Maier’s star-shaped compounds, nematic liquid
crystalline phases from isotropic during cooling scans were
observed for Y0-2 as investigated by temperature-dependent
polarization optical micrographs (Figure S2).[5c] No liquid
crystalline behaviour was detected for oily YNBu at room
temperature.
L2a is a distyrylbenzene substituted with two pyridines. L2b was
designed as an analogue of L2a with a longer effective
conjugation length[10]. Y0 is a star-shaped and C3-symmetric π-
system bearing three identical arms. Based on this known
[a]
H. Zhang, Eugen A. Kotlear, Soh Kushida, Steffen Maier, Dr. F.
Rominger, Dr. J. Freudenberg, Prof. Dr. U. H. F. Bunz
Organisch-Chemisches Institut, Ruprecht-Karls-Universität
Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, FRG
E-mail: freudenberg@oci.uni-heidelberg.de,
uwe.bunz@oci.uni-heidelberg.de
Supporting information for this article is given via a link at the end of
the document.
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Scheme 1. Synthetic route to linear 1,4-distyrylbenzenes (L2a-L2b) and star-shaped 1,3,5-tristyrylbenzene derivatives (Y0-Y3 and YNBu).
centered at around 400 nm and a shoulder peak located at 326-
348 nm. It is mainly attributed to the extension of conjugation or
the electron-rich dibutylaniline groups.
In THF, the trend in the emission maxima (Figure 2b) follows
the order YNBu > L2b > L2a > Y3 > Y2 > Y1 > Y0. L2b exhibits a red-
shifted green emission with a vibronic structure relative to that of
L2a, owing to its longer conjugation length. Asymmetric Y1 and Y2
show similar emission maxima in comparison to symmetric Y3
while their maxima are redshifted by ca. 10 nm compared to
symmetric hydrocarbon Y0. The fluorescence maximum of YNBu
bathochromically shifted to 519 nm (Stokes shift of 4151 cm-1).
The large Stokes shift observed for YNBu is caused by its higher
dipole moment in its excited state stabilized in more polar
solvents.[12] L2a-2b and Y0-3 display quantum yields (Фf) varying
from 0.64 to 0.82, while YNBu exhibits a green fluorescence with
a quantum yield of 0.61. Although Y0-3 and Y4 have similar
conjugation skeletons, dibutylamine-containing Y4 shows lower
quantum yield, which might be attributed to the free
intramolecular rotation or the existence of photoelectron transfer
facilitated by the flexible dibutylamine groups.[13]
Density functional theory (DFT) calculations (B3LYP/6-
31++G**)[14] provide further insight into optoelectronics. The
calculated HOMO−LUMO energy gaps for L2a-L2b, Y0-Y3 and
YNBu are in the range from 2.56 to 3.06 eV (Figure S3). The
lower gaps of YNBu or L2b are a result of the extended
conjugation, resulting in distinct bathochromic shifts in the
electronic absorption spectra. These results, as well as the trend
of absorption maxima calculated by TDDFT methods (Figure S3)
Figure 1. Single crystal structures of L2b, Y0 and Y3.
Photophysical properties and theoretical calculations
The normalized absorption and emission spectra of the
compounds in dilute THF are shown in Figure 2. Table 1
summarizes the photophysical data. Due to the meta-
conjugation, absorption spectra of star-shaped series Y0-Y3 are
superimposable to that of L2a, with a maximum absorption
are
consistent
with
the
experiment.
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Figure 2. Normalized UV/vis absorption (a) and emission (b) spectra of SBs in THF.
Table 1. Photophysical data (in THF) and calculated energy gaps for SBs.
Compounds
λabs [nm]a
λmax,em [nm]
461
QYb
0.64
0.68
0.82
0.73
0.72
0.79
0.61
Ԏf [ns]
2.00
1.10
1.39
1.51
1.52
1.67
1.41
λst [nm]/∆ʋst [cm-1]c
61, 3308
calcd energy gap [eV, nm]
L2a
L2b
Y0
329 (2.37), 400 (2.88)
432 (7.31)
3.06, 405
2.56, 484
2.97, 417
2.86, 433
2.87, 432
2.96, 418
2.82, 440
485
53, 2529
329 (6.17), 401 (11.0)
330 (5.68), 403 (9.89)
331 (7.13), 405 (12.4)
348 (2.29), 401 (2.86)
326 (1.91), 427 (8.64)
447
46, 2566
Y1
454
51, 2787
Y2
456
51, 2761
Y3
457
56, 3118
YNBu
519
92, 4151
a Measured in THF and extinction coefficients (Ɛmax × 104 M-1·cm-1）are shown in parentheses. b QY = quantum yield. c ∆ʋst = 1/λabs-1/λem
.
slope of the fitting line for YNBu is highest, up to 9673 cm-1,
comparable to that of the X-shaped distyrylbenzenes,[16] which
further indicated its larger dipole moment changes between the
ground and excited states (μe-μg), leading to the pronounced
solvent sensitivity.[17]
Fluorochromicity
Optical response to protons
Pyridines or dibutylanilines are basic, all SBs (except Y0) and
display an acidochromic change of their absorption and
emission spectra (Figure 4). SBs with pyridine units experience
a red-shift, accompanied with a loss of fluorescence intensity.
Upon protonation the donor−acceptor character of these SBs
increases and therefore internal charge transfer is favored. The
addition of TFA to YNBu leads to strongly blue emissive species,
in which the dibutylamino groups are protonated and the HOMO
is stabilized by protonation, resulting in an increased HOMO-
LUMO gap. The color change is detected by eye. As expected,
Y3 is more sensitive to protonation compared to Y1 and Y2, as
there are three pyridine rings as interaction sites.
As shown in Figure 5, when -log [TFA] of approx. 1.30 is
reached (c = 50 mM), Y3 shows a red-shifted absorption (30 nm)
and a 100 nm red shift and distinct attenuation of its emission.
With excess acid (c = 500 mM, -log [TFA] < 1.0), the original
absorption band of YNBu at around 427 nm diminished and a new
distinct band formed at 338 nm. A blue shift in emission of Δλ = -
69 nm was observed.
Figure 3. Photograph of SBs in different solvents under a hand-held black
light with illumination at 365 nm.
Figure 3 shows the emission behaviors of SBs in solvents with
different polarity. Negligible changes are observed in the
emission color of L2a and Y1-3 with pyridine rings. L2b and YNBu
,
emit red-shifted with increasing solvent polarity.[12] The effect of
solvents on the emission features was evaluated by the Lippert–
Mataga plot[15] (Supporting Information). All of the SBs displayed
linear dependence of ∆ν on ∆푓 together with different slopes. L2b
and YNBu showed a much larger slope (Figure S5 and Table S5).
The
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and CuI) (Figure 6a). Only Hg2+ quenches luminescence of Y0.
Except for Zn2+, Cu2+, Ni2+, the addition of the remaining ten
metal ions leads to either quenching or a red shift in emission of
SBs with pyridine units (L2a, L2b and Y1-3). In the case of YNBu
,
Al3+, Mn2+, Fe3+, Fe2+, Cd2+, Ag+, and Hg2+ induce a blue shift in
emission, as expected for a coordination at the aniline nitrogen.
Al3+, Mn2+, Cd2+ and Co2+ are quenchers for Y1 and Y2, but they
less impact photoluminescence of Y3. Al3+, Mn2+, Fe3+, Fe2+, Cd2+,
Ag+ and Hg2+ can be easily distinguished from each other
through the responses of the SBs by the naked eye. It is
challenging to discriminate Cd2+ from Zn2+.[18] SBs with pyridine
or dibutylaniline groups display fluorescence response in the
presence of Cd2+ but no response with Zn2+.
Figure 4. Photograph of SBs in THF (c = 4 μg/mL) with increasing content of
TFA under a hand-held black light with illumination at 365 nm (inset data: the
number of equivalents of TFA).
푆퐵푠7
푆퐵푠1
2
2
)
+ 푔 −푔
푚
∑
(
푟
)
(
−푟
푚
푛
푛
√
(
)
흈
푚 푛
,
푟, 푔 =
(1)
3∗7
Statistical evaluation of differences in emission colors after
exposure to metal ions was performed. Figure 6b shows the
autocorrelation plot of their response. The brightness
independent color coordinates rg of the RAW data of the
photographs were determined and treated with MANOVA
statistics (eq. 1).[7c, 19] Zn2+, Cu2+ and Ni+ are hard to discern due
to their weak coordination and thus have similar color responses.
All of the other investigated metal ions are distinguished.
Conclusion
We have synthesized linear 1,4-distyryl and star-shaped 1,3,5-
tristyrylbenzene derivatives (L2a-L2b, Y0-Y3 and YNBu). These are
strongly fluorescent in dilute solutions. YNBu works as polarity
sensor due to its response to different solvents. Upon
protonation, all of the pyridine-containing L2a-L2b and Y0-Y3
compounds show a pronounced red shift, and the fluorophore
with dibutylaniline groups YNBu displays a blue shift in emission.
Ten metal ions such as Al3+, Mn2+, Fe3+, Fe2+, Cd2+, Ag+ and Hg2+
were well discriminated.
Figure 5. Normalized UV/vis absorption (left) and emission (right) spectra for
the titrations of Y3 (top) and YNBu (down) in THF with different concentration of
TFA.
Optical response to metal ions
Dilute solutions of all the SBs in DCM were exposed to an
excess of salts of 13 cations (Al3+, Zn2+, Cu2+, Cu+, Mn2+, Fe2+,
Fe3+, Co2+, Ni2+, Cd2+, Ag+, Pb2+ and Hg2+, added as perchlorates,
Figure 6. (a) Exposure of all the SBs (10 μM) to different metal cations in DCM. Photographs were taken under a hand-held black light (365 nm) with a digital
camera; (b) Autocorrelation plot (RAW rg values) of all the SBs in DCM after exposure to metal ions.
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(silica gel, PE/EA = 20:1, Rf = 0.50) afforded 6 as a yellow viscous oil
1
(582 mg, 1.10 mmol, 54%). H NMR (400 MHz, CDCl3) δ 10.42 (s, 1H),
7.41 (d, J = 8.7 Hz, 1H), 7.32 – 7.27 (m, 1H), 7.25 – 7.03 (m, 3H), 6.67 –
6.40 (m, 3H), 4.17 – 3.93 (m, 4H), 3.39 – 3.20 (m, 4H), 1.91 – 1.74 (m,
4H), 1.63 – 1.47 (m, 8H), 1.42 – 1.26 (m, 12H), 0.92 (m, 12H). 13C NMR
(100 MHz, CDCl3) δ 189.4, 189.2, 156.6, 155.8, 151.1, 150.5, 148.5,
147.7, 136.2, 135.9, 132.9, 132.8, 130.5, 128.5, 124.5, 123.9, 123.7,
123.4, 120.7, 117.6, 114.8, 111.7, 111.1, 110.2, 109.9, 109.7, 69.4, 69.3,
50.9, 31.7, 29.7, 29.4, 26.0, 22.8, 20.5, 14.2, 14.1. IR (cm−1): 2955, 2928,
2870, 1682, 1612, 1519, 1466, 1366, 1214, 1186, 811. HRMS (DART):
m/z [M+H]+ calcd for C35H54NO3 536.4098, found 536.4101.
Experimental Section
General Procedure 1 (GP1): Synthesis of intermediates 4-6 by Heck
reaction. The reaction was performed in a heat-gun-dried 50 mL Schlenk
tube under a nitrogen atmosphere. The brominated intermediate (1.0 eq)
and the vinyl compound (1.14 eq) were dissolved in dry DMF. Pd(OAc)2
(5 mol%), tris(o-tolyl)phosphine (0.1 eq) and dry triethylamine (0.8 mL)
were added and the mixture was stirred at 110 °C for 48 h. After the
reaction mixture was cooled to ambient temperature, it was poured into
water to give a suspension which was extracted with DCM. The
combined organic layers were washed with brine, dried over MgSO4 and
the solvents were removed under reduced pressure. The residues were
purified by column chromatography.
1,3,5-Tris((E)-2,5-bis(hexyloxy)-4-((E)-styryl)styryl)benzene
(Y0).
According to GP2 a solution of triphosphonate 7 (42.3 mg, 80.0 µmol) in
dry THF (8 mL) was treated with NaH (28.8 mg, 1.20 mmol) and
monoaldehyde 4 (105 mg, 256 µmol) was added. The crude product was
purified by column chromatography (silica gel, PE/EA = 20:1, Rf = 0.41)
to yield the desired compound Y0 as a yellow green powder (79.6 mg,
61.6 µmol, 77%). M.p.: 110-111 °C. 1H NMR (600 MHz, CDCl3) δ 7.66 –
7.49 (m, 15H), 7.39 (t, J = 7.6 Hz, 6H), 7.32 – 7.22 (m, 6H), 7.22 – 7.14
(m, 9H), 4.11 (dd, J = 15.1, 6.6 Hz, 12H), 1.99 – 1.85 (m, 12H), 1.59 (td,
J = 13.5, 7.0 Hz, 12H), 1.48 – 1.34 (m, 24H), 0.93 (dt, J = 25.7, 6.8 Hz,
18H). 13C NMR (150 MHz, CDCl3) δ 151.3, 151.2, 138.7, 138.1, 129.0,
128.9, 128.7, 127.5, 127.1, 126.6, 124.1, 123.6, 111.0, 110.8, 69.7, 31.7,
29.5, 26.1, 22.8, 14.2. IR (cm−1): 2926, 2856, 2360, 1419, 1199, 958, 750,
690, 598, 506. HRMS (MALDI): m/z [M]+ calcd for C91H114O6 1290.8615,
found 1290.947.
General Procedure 2 (GP2): Synthesis of symmetric Y0, Y3 and YNBu by
Wittig-Horner reaction. Under nitrogen atmosphere, the triphosphonate 7
(1.0 eq) was dissolved in dry THF and the solution was cooled to 0 °C.
NaH (15.0 eq) was added carefully and the mixture was stirred at 0 °C for
40 min before the monoaldehyde 4-6 (4.5 eq) was added slowly. The
reaction mixture was then allowed to warm to RT and further stirred for 3
days. After removing THF on a rotary evaporator, the residues were
purified on silica gel column.
4,4'-((1E,1'E)-(2,5-bis(hexyloxy)-1,4-phenylene)bis(ethene-2,1-
diyl))dipyridine (L2a). Under nitrogen atmosphere, a solution of 2 (218
mg, 500 μmol), 4-vinylpyridine (118 mg, 1.20 mmol), Pd(OAc)2 (11.2 mg,
50 μmol), tris(o-tolyl)phosphine (30.4 mg, 100 μmol) and triethylamine
(1.20 mL) in dry DMF (10 mL) was stirred at 110 °C for 48 h. After the
reaction mixture was cooled to ambient temperature, it was poured into
water to give a suspension which was extracted with DCM. The
combined organic layers were washed with brine dried over MgSO4 and
the solvents were removed under reduced pressure. The residues were
purified by column chromatography (silica gel, DCM/EE = 5:1, Rf = 0.21)
and afforded L2a as a yellow solid (110 mg, 225 μmol, 45%). M.p.: 135-
136 °C. 1H NMR (300 MHz, CDCl3) δ 8.58 (d, J = 6.0 Hz, 4H), 7.70 (s,
1H), 7.64 (s, 1H), 7.38 (d, J = 6.0 Hz, 4H), 7.18 – 7.08 (m, 3H), 7.05 (s,
1H), 4.08 (t, J = 6.5 Hz, 4H), 1.95 – 1.82 (m, 4H), 1.63 – 1.49 (m, 4H),
1.47 – 1.33 (m, 8H), 0.93 (t, J = 7.0 Hz, 6H). 13C NMR (100 MHz, CDCl3)
δ 151.7, 150.1, 149.8, 145.4, 129.7, 128.3, 128.2, 127.6, 126.9, 126.7,
126.5, 126.0, 123.6, 121.0, 114.6, 114.1, 111.2, 110.9, 69.7, 31.8, 29.5,
26.1, 22.8, 14.2. IR (cm−1): 2942, 2915, 2360, 1592, 1476, 1209, 1028,
968, 850, 803, 596, 525. HRMS (MALDI): m/z [M+H]+ calcd for
C32H41N2O2 485.3168, found 485.372.
1,3,5-Tris((E)-2,5-bis(hexyloxy)-4-((E)-2-(pyridin-4-
yl)vinyl)styryl)benzene (Y3). According to GP2
a
solution of
triphosphonate 7 (42.3 mg, 80.0 µmol) in dry THF (8 mL) was treated
with NaH (28.8 mg, 1.20 mmol) and monoaldehyde 5 (114.7 mg, 280
µmol) was added. The crude product was purified by column
chromatography (silica gel, DCM/MeOH = 50:1, Rf = 0.35) to yield the
desired compound Y3 as an orange solid (34.9 mg, 26.9 µmol, 33%).
M.p.: 122–123 °C. 1H NMR (600 MHz, CDCl3) δ 8.58 – 8.50 (d, J = 5.4
Hz, 6H), 7.71 – 7.39 (m, 12H), 7.23 – 6.63 (m, 15H), 4.01 – 3.93 (m,
12H), 1.91 – 1.83 (m, 12H), 1.58 (m, 12H), 1.39 – 1.27 (m, 24H), 0.96 –
0.89 (m, 18H). 13C NMR (150 MHz, CDCl3) δ 151.9, 151.5, 151.4, 150.8,
150.4, 149.9, 145.6, 139.0, 138.8, 130.4, 130.3, 129.9, 128.5, 128.3,
126.3, 126.2, 125.7, 125.6, 124.6 124.3, 124.2, 121.1, 115.9, 111.3,
111.0, 109.6, 69.9, 69.7, 68.8, 32.2, 31.9, 29.9, 29.7, 26.3, 26.2, 22.9,
14.4. IR (cm−1): 2925, 2856, 2320, 1591, 1498, 1416, 1204, 966, 803,
517. HRMS (MALDI): m/z [M+H]+ calcd for C87H112N3O6 1295.8629,
found 1295.8624.
4,4',4''-((1E,1'E,1''E)-(((1E,1'E,1''E)-benzene-1,3,5-triyltris(ethene-2,1-
diyl))tris(2,5-bis(hexyloxy)benzene-4,1-diyl))tris(ethene-2,1-
2,5-Bis(hexyloxy)-4-(2-(pyridin-4-yl)vinyl)benzaldehyde (5). According
to GP1 a solution of monoaldehyde 3 (385 mg, 1.00 mmol), 4-
vinylpyridine (214 mg, 1.14 mmol), Pd(OAc)2 (11.2 mg, 50.0 μmol), tris(o-
tolyl)phosphine (30.4 mg, 100 μmol) and triethylamine (0.7 mL) in DMF
(10 mL) was stirred at 110 °C for 48 h. Column chromatography (silica
gel, PE/EA = 5:1, Rf = 0.20) afforded 5 as a yellow viscous oil (343 mg,
840 μmol, 84%). 1H NMR (300 MHz, CDCl3) δ 10.59 (s, 1H), 8.73 (d, J =
5.2 Hz, 2H), 7.78 (d, J = 16.5 Hz, 1H), 7.52 (d, J = 5.6 Hz, 2H), 7.47 (s,
1H), 7.30 (t, J = 8.2 Hz, 2H), 4.24 (t, J = 6.5 Hz, 2H), 4.16 (t, J = 6.5 Hz,
2H), 2.11 – 1.90 (m, 4H), 1.72 – 1.27 (m, 14H), 1.05 (dd, J = 6.4, 4.4 Hz,
6H). 13C NMR (125 MHz, CDCl3) δ 189.1, 156.0, 151.1, 150.2, 144.7,
132.7, 129.4, 127.6, 125.1, 121.1, 111.3, 110.3, 69.3, 69.2, 31.6, 29.2,
25.9, 22.7, 14.1. IR (cm−1): 2928, 2857, 1676, 1601, 1422, 1206, 1018,
529. HRMS (DART): m/z [M+H]+ calcd for C26H36NO3 410.2690, found
410.2687.
diyl))tris(N,N-dibutylaniline) (YNBu). According to GP2 a solution of
triphosphonate 7 (42.3 mg, 80.0 µmol) in dry THF (8 mL) was treated
with NaH (28.8 mg, 1.20 mmol) and monoaldehyde 6 (137 mg, 256 µmol)
was added. The crude product was purified by column chromatography
(silica gel, PE/DCM = 2:1 + 2% triethylamine, Rf = 0.45) to yield the
desired compound YNBu as an orange viscous oil (90.9 mg, 54.3 µmol,
68%).1H NMR (600 MHz, CDCl3) δ 7.61 – 7.37 (m, 5H), 7.33 (d, J = 8.4
Hz, 4H), 7.26 – 7.03 (m, 11H), 7.03 – 6.89 (m, 4H), 6.82 – 6.65 (m, 1H),
6.62 – 6.15 (m, 7H), 4.16 – 3.60 (m, 12H), 3.18 (m, 12H), 1.92 – 1.63 (m,
12H), 1.48 (m, 24H), 1.41 – 1.26 (m, 24H), 1.25 – 1.07 (m, 12H), 0.95 –
0.73 (m, 36H). 13C NMR (150 MHz, CDCl3) δ 153.4, 151.4, 150.8, 147.8,
146.5, 138.9, 131.0, 130.3, 129.2, 128.6, 128.4, 128.3, 127.9, 127.7,
125.9, 125.8, 125.3, 124.3, 124.1, 118.4, 115.4, 114.0, 112.6, 112.0,
111.7, 111.2, 110.1, 69.8, 50.9, 31.8, 29.6, 27.8, 26.1, 22.8, 20.5, 16.0,
14.2. IR (cm−1): 2953, 2926, 2857, 1607, 1519, 1366, 1185, 1030, 962,
805, 523. HRMS (MALDI): m/z [M+H]+ calcd for C114H165N3O6 1673.2777,
found 1673.293. Elemental analysis calcd. (%) for C114H165N3O6: C
81.82; H 9.94; N 2.51; found: C 81.60, H 10.76, N 2.45.
4-(4-(Dibutylamino)styryl)-2,5-bis(hexyloxy)benzaldehyde
(6).
According to GP1 a solution of monoaldehyde 3 (771 mg, 2.00 mmol), 4-
dibutylaminostyrene (509 mg, 2.20 mmol), Pd(OAc)2 (22.4 mg, 100 μmol),
tris(o-tolyl)phosphine (60.9 mg, 200 μmol) and triethylamine (1.5 mL) in
DMF (20 mL) was stirred at 110 °C for 48 h. Column chromatography
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1,4-Bis((E)-2,5-bis(hexyloxy)-4-((E)-2-(pyridin-4-
CDCl3) δ 8.70 (d, J = 5.8 Hz, 4H), 7.81 (d, J = 16.4 Hz, 2H), 7.75 – 7.58
(m, 9H), 7.56 – 7.45 (m, 6H), 7.42 – 7.32 (m, 4H), 7.27 (m, 7H), 7.19 (d,
J = 16.4 Hz, 2H), 4.21 (m, 12H), 2.10 – 1.90 (m, 12H), 1.82 – 1.62 (m,
12H), 1.62 – 1.42 (m, 24H), 1.04 (m, 18H). 13C NMR (150 MHz, CDCl3) δ
151.7, 151.3, 151.2, 150.2, 145.4, 138.8, 138.6, 138.0, 129.7, 128.9,
128.8, 128.3, 128.2, 127.6, 127.2, 126.9, 126.6, 126.1, 125.6, 124.3,
124.1, 123.6, 120.9, 111.1, 110.8, 69.7, 31.7, 29.6, 26.1, 22.8, 14.2. IR
(cm−1): 2926, 2856, 2360, 1589, 1419, 1203, 962, 690, 527. HRMS
(MALDI): m/z [M+H]+ calcd for C88H113N2O6 1293.8599, found 1293.919.
yl)vinyl)styryl)benzene (L2b). Under
a nitrogen atmosphere, the
bisphosphonate 9 (45.4 mg, 120 µmol) was dissolved in dry THF (10 mL)
and the solution was cooled to 0 °C. NaH (28.8 mg, 1.20 mmol) was
added carefully and the mixture was stirred at 0 °C for 40 min before
monoaldehyde 5 (103 mg, 252 µmol) was added slowly. The reaction
mixture was then allowed to warm to RT and further stirred for 2 days.
After removing THF on a rotary evaporator, the residues were purified on
silica gel column (silica gel, PE/EA = 20:1, Rf = 0.19) to yield the desired
compound L2b as an orange solid (87.9 mg, 98.9 µmol, 82%). M.p.: 147-
148 °C. 1H NMR (600 MHz, CDCl3) δ 8.53 (m, 4H), 7.68 (d, J = 16.4 Hz,
2H), 7.61 – 7.42 (m, 6H), 7.38 (d, J = 6.0 Hz, 3H), 7.22 – 6.97 (m, 9H),
4.20 – 3.74 (m, 8H), 1.99 – 1.73 (m, 8H), 1.70 – 1.48 (m, 8H), 1.50 –
1.21 (m, 16H), 1.09 – 0.80 (m, 12H). 13C NMR (150 MHz, CDCl3) δ 151.7,
151.1, 150.2, 149.7, 145.4, 137.3, 129.2, 128.3, 128.2, 127.0, 126.0,
125.5, 124.1, 123.2, 120.9, 111.1, 110.5, 69.6, 31.7, 29.6, 29.5, 26.1,
22.8, 14.2. IR (cm−1): 2931, 2853, 1590, 1397, 1207, 1034, 961, 847, 726,
525. HRMS (MALDI): m/z [M]+ calcd for C60H76N2O4 888.5805, found
888.5835.
Crystallographic data: CCDC 1959608 (L2b), CCDC 1959609 (Y0), and
CCDC 1959610 (Y3) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge
Crystallographic
Data
Centre
via
https://www.ccdc.cam.ac.uk/structures/.
Acknowledgements
4-((E)-4-((E)-3,5-bis((E)-2,5-bis(hexyloxy)-4-((E)-styryl)styryl)styryl)-
2,5-bis(hexyloxy)styryl)pyridine (Y1). Under a nitrogen atmosphere, the
triphosphonate 7 (42.3 mg, 80 µmol) was dissolved in dry THF (10 mL)
and the solution was cooled to 0 °C. NaH (28.8 mg, 1.2 mmol) was
added carefully and the mixture was stirred at 0 °C for 40 min before
monoaldehyde 5 (35.4 mg, 86.8 µmol) was added slowly. The reaction
mixture was stirred overnight at room temperature. After removing THF in
vacuo, the residues containing 10 were dried and used in the next step
without further purification. To a solution of 10 in dry THF (8 mL) was
added NaH (28.8 mg, 1.20 mmol) at 0 °C. The mixture was stirred at 0 °C
for 40 min, and then another monoaldehyde 4 (71.9 mg, 176 µmol) was
added. The reaction mixture was then allowed to warm to RT and further
stirred for 2 days. After removing THF on a rotary evaporator, the crude
product was purified by column chromatography (silica gel, PE/EA = 1:1,
Rf = 0.49) to yield the desired compound Y1 as an orange solid (29.8 mg,
23.1 µmol, 28% over two steps). M.p.: 71–72 °C. 1H NMR (600 MHz,
CDCl3) δ 8.69 (d, J = 5.8 Hz, 2H), 7.82 (d, J = 16.4 Hz, 1H), 7.74 – 7.60
(m, 12H), 7.49 (m, 6H), 7.37 (dd, J = 16.3, 7.8 Hz, 4H), 7.34 – 7.23 (m,
9H), 7.19 (d, J = 16.4 Hz, 1H), 4.20 (dt, J = 10.9, 6.5 Hz, 12H), 2.07 –
1.98 (m, 12H), 1.74 – 1.66 (m, 12H), 1.57 – 1.47 (m, 24H), 1.08 – 0.99
(m, 18H). 13C NMR (150 MHz, CDCl3) δ 151.8, 151.2, 150.1, 145.5,
138.8, 138.5, 138.0, 129.8, 128.9, 128.7, 128.4, 128.31, 127.5, 127.0,
126.6, 125.9, 125.5, 124.3, 123.6, 120.9, 111.0, 110.7, 69.7, 31.7, 29.5,
26.1, 22.8, 14.2. IR (cm−1): 2925, 2856, 2359, 1590, 1420, 1202, 1029,
960, 690, 507. HRMS (MALDI): m/z [M+H]+ calcd for C89H114NO6
1292.8646, found 1292.963.
H. Z. is grateful to the CSC (Chinese Scholarship Council) for a
fellowship.
Keywords: Sensing • Tristyrylbenzene • Acidochromicity •
Optical Response • Metal Ions
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FULL PAPER
Hao Zhang, Soh Kushida, Gaozhan Xie,
Eugen A. Kotlear, Frank Rominger, Jan
Freudenberg* and Uwe H. F. Bunz*
Page No. – Page No.
Linear and Star-Shaped Extended Di-
and Tristyrylbenzenes: Synthesis,
Characterization
and
Optical
Response to Acid and Metal Ions
A series of extended star-shaped tristyrylbenzenes has been developed. Their optoelectronic properties can be tuned via the aryl
terminus, which make them useful sensors for protons or metal ions.
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