Synthesis, structures, redox and photophysical properties of benzodifuran-functionalised pyrene and anthracene fluorophores

Article abstract of DOI:10.1039/c1ob05778b

Benzodifuran-functionalised pyrene and anthracene fluorophores 1 and 2 were obtained in reasonable yields. Their single crystal structures, electrochemical, optical absorption, and fluorescence characteristics have been described. They show strong luminescence with high quantum yields of 0.53 for 1 and 0.48 for 2.

Full text of DOI:10.1039/c1ob05778b

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PAPER
Synthesis, structures, redox and photophysical properties of
benzodifuran-functionalised pyrene and anthracene fluorophores†
Stephan Keller,a Chenyi Yi,a Chen Li,a Shi-Xia Liu,*a Carmen Blum,a Gabriela Frei,a Olha Sereda,b
Antonia Neels,b Thomas Wandlowskia and Silvio Decurtinsa
Received 18th May 2011, Accepted 17th June 2011
DOI: 10.1039/c1ob05778b
Benzodifuran-functionalised pyrene and anthracene fluorophores 1 and 2 were obtained in reasonable
yields. Their single crystal structures, electrochemical, optical absorption, and fluorescence
characteristics have been described. They show strong luminescence with high quantum yields of 0.53
for 1 and 0.48 for 2.
leads to effective extension of the p–conjugation and a large
increase of fluorescence intensities even under aerated conditions.9
Taking these features into account, we herein report the syn-
thesis, photophysical properties and spectroelectrochemistry of
two new acetylene-linked benzodifuran-functionalised pyrene and
anthracene fluorophores.
The ability of the functionalised benzodifuran core to undergo
Suzuki, Heck and Sonogashira coupling reactions has been
demonstrated in the case of pyridyl substituents.1 Thereby, an
extended p-conjugated molecular platform is created, which allows
for photoinduced intramolecular charge-transfer processes to
occur. Therefore, as a part of a continuing research effort in the
development of new materials for molecular electronics, we herein
describe the synthesis of compounds 1 and 2 (Scheme 1), and their
characterisation in solution and in the solid state.
Introduction
This paper puts forward a study of largely extended p-conjugated
molecules, resulting from combining through ethynyl spacers a
recently developed redox-active chromophore, namely a benzodi-
furan (BDF) derivative,1 with two pending pyrene or anthracene
fluorophores, respectively. The motivation is triggered by the
fascinating features of these individual components.
Derivatives of benzofuran and benzodifuran show a wide range
of biological activities that put them within the focus of bioorganic
and medical research.2 Benzodifuran derivatives have also proven
to be excellent compounds in the field of molecular electronics,
especially for hole-transporting materials.3
Pyrene and anthracene, as strong p–p* emitters, have been
previously employed as fluorescent probes in many applications.
For example, anthracene chromophores can be used to signal
environmental effects that help to delineate inter/intramolecular
interactions.4 Pyrene is one of the most frequently used com-
pounds for oligonucleotide labelling.5 Pyrene-based fluorescent
probes are also used to monitor conformational changes by
virtue of their excimer fluorescence (for example in the case
of the natural iron chelator myo-inositol 1,2,3-triphosphate).6
Analogously, the face-to-face orientation excimer emission of
pyrene units is applied in chemosensor systems,7 or used for
reporting lipid-protein interactions in membranes.8 However, they
have serious drawbacks such as a relatively short absorption
wavelength, substantial fluorescence quenching in the presence
of oxygen and low fluorescence quantum yields. It has been found
that the introduction of alkynyl groups into pyrene/anthracene
Scheme 1 Synthesis of compounds 1–2.
aDepartement fu¨r Chemie und Biochemie, Universita¨t Bern, Freiestrasse
3, CH-3012, Bern, Switzerland. E-mail: liu@iac.unibe.ch; Fax: +41 31
6313995; Tel: +41 31 6314296
Results and discussion
bXRD Application LAB, CSEM Centre Suisse d’Electronique et de
Microtechnique SA, Jaquet-Droz 1, Case postale, CH-2002, Neuchaˆtel,
Switzerland
Synthesis
† Electronic supplementary information (ESI) available: Additional infor-
mation on the computational studies of compounds 1 and 2. See DOI:
10.1039/c1ob05778b
Our interest in malonitrile chemistry,10 recently led us to an
efficient synthetic approach to a fully functionalized benzodifuran
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molecule 3 (Scheme 1), which can readily undergo Suzuki,
Heck, and Sonogashira coupling reactions to afford extended
p-conjugated BDF derivatives with pyridine termini through
different spacers.1 As illustrated in Scheme 1, pyrene and an-
thracene fluorophores can be incorporated into the BDF core
via a Pd-catalyzed Sonogashira coupling reaction of 3 with the
corresponding 1-ethynylpyrene and 9-ethynylanthracene, leading
to the formation of compounds 1 and 2 in reasonable yields. 1-
Ethynylpyrene and 9-ethynylanthracene were accomplished ac-
cording to modified literature procedures, starting from iodo- or
bromo-substituted pyrene and anthracene through a Sonogashira
coupling and subsequent desilylation. In both cases, yields are
comparable to or even better than those reported.11,12
X-Ray studies
Slow evaporation of a saturated dichloromethane solution of 1
produced solvate-free orange needle-shaped crystals suitable for
X-ray diffraction. The compound crystallizes in the monoclinic
space group P21/c (No. 14) with one molecule per asymmet-
ric unit. The ORTEP diagram is illustrated in Fig. 1. The BDF
core is fairly planar; the rms deviation from the least-squares plane
Fig. 1 Solid state structure of 1. Thermal ellipsoids are set at the 50%
probability level and hydrogen atoms are omitted for clarity.
˚
through the heterocyclic BDF skeleton is 0.44 A. The dihedral
group P21/c (No. 14) with one half molecule per asymmetric unit;
the corresponding ORTEP diagrams are illustrated in Fig. 2. In
the solid state, a crystallographic inversion centre is located at
the central C6 ring for 2a and 2b. The BDF cores are nearly
planar; the rms deviations from the least-squares planes through
angles formed between the pyrene rings and the BDF unit are
19.3(2)◦ and 17.6(2)◦, respectively. Clearly, the orientation of the
pyrene units is such as to avoid close contacts with the nitrile
groups. There are no exceptional geometrical features, and all bond
lengths and angles are within the expected range; they compare
with the reported structures of BDF derivatives.1 In the crystal
lattice, the molecules show stacking along the crystallographic b-
axis. A p–p stacking is observed between alternating aromatic
BDF units and the pyrene parts. The shortest intermolecular
˚
˚
the heterocyclic BDF skeletons are 0.01 A and 0.03 A for 2a
and 2b, respectively. The dihedral angles formed between the
anthracene units and the BDF units are very different in the two
structures and have been calculated with 1.8(1)◦ (2a) and 28.45(1)◦
(2b). There are no exceptional geometrical features, and all bond
lengths and angles are within the expected range. They compare
with the reported structures of BDF derivatives.1
˚
distances related to these p–p interactions are found with 3.30 Afor
i
˚
C17 . . . C50 (symmetry operation i: -x, -y+1, -z) and 3.52 A for
C19 . . . C69ii (symmetry operation ii: -x+1, -y+1, -z), respectively.
Slow evaporation of a saturated dichloromethane solution of
2 produced a mixture of solvate-free orange rod-shaped (2a) and
block-shaped (2b) crystals suitable for X-ray diffraction. Com-
pound 2 crystallizes for both morphologies in the monoclinic space
In the crystal lattice of 2a, the molecules show a ladder like
stacking of alternating BDF and anthracene moieties in two
directions which results in an interwoven pattern. The smallest
carbon-carbon distance involved in the intermolecular stacking
i
˚
network was found with 3.27 A for C18 . . . C28 (symmetry
Fig. 2 Solid state structures of 2a (left) and 2b (right). Thermal ellipsoids are set at the 50% probability level and hydrogen atoms are omitted for clarity.
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operation i: -x+1, -y+2, -z). No special features have been
identified for 2b.
Electrochemistry
The electrochemical properties of 1–3 were investigated by cyclic
voltammetry in CH2Cl2 (Fig. 3). All compounds undergo one
1
reversible oxidation process with E1/2 = 0.85 V for 1, 0.86 V
for 2 and 0.97 V for 3, values that are characteristic for the
formation of the respective BDF radical cations.1,13 The first
oxidation potentials of 1 and 2 are quite similar and negatively
shifted when compared to 3. This finding can be attributed to
the stabilisation effect of the extended p-conjugation, which offers
the possibility of the free spin to be delocalised over the entire
conjugated p-system. The formation of the corresponding BDF
dication is represented clearly in a second reversible oxidation
Fig. 4 “Window-opening” cyclic voltammograms of 1 (1 ¥ 10-4 M) in
CH2Cl2 (0.1 M TBAPF6 (TBA = tetrabutylammonium)); platinum disk
working electrode; scan rate 100 mVs-1, with different positive potential
limits.
2
process for 3 with E1/2 = 1.23 V. In contrast, this process is not
electrochemically reversible in the cases of 1 and 2. Extending the
potential range to 1.4 V reveals for 1 a distorted anodic peak with
1
Epa = 1.18 V, and four successive cathodic peaks at Epc = 0.86 V,
2
3
4
Epc = 0.94 V, Epc = 1.05 V and Epc = 1.16 V. Compound 2 shows
an anodic peak at Epa = 1.26 V and a corresponding cathodic peak
at Epc = 1.06 V. To gain insight into the potential evolution of the
redox behaviour of 1, a “window-opening” CV experiment was
performed by extending the positive potential limit from 1.0 V to
1.5 V (Fig. 4). All cathodic peaks appear only upon the oxidation
of the BDF radical cation to dication species. Furthermore, it is
found that the charge consumption between the anodic and the
cathodic scans is not idential. These observations are indicative
of an electron-transfer reaction, most probably coupled with a
complex sequence of chemical follow-up processes.
Fig. 5 Molecular orbitals of 1.
extended over the whole molecule; in fact and as expected, they
are formed by symmetry-adapted linear combinations of the
respective HOMOs or LUMOs of the pending groups with the
HOMO or LUMO of BDF. The calculated HOMO–LUMO gap
results in a value for 1 of 2.7 eV (21800 cm-1) and for 2 of 2.5 eV
(20200 cm-1); both energies are comparable with those of the onsets
of the first absorption band of the optical spectra.
Fig. 3 Cyclic voltammograms of 1 (1 ¥ 10-4 M, black), 2 (5 ¥ 10-4 M, red)
and 3 (2 ¥ 10-4 M, blue) in CH2Cl2 (0.1 M TBAPF6 (TBA = tetrabutylam-
monium)); platinum disk working electrode; scan rate 100 mVs-1).
Electronic properties
The electronic spectra of the orange colored compounds
1 and 2, recorded in dichloromethane solution, show intense
optical absorptions over the UV-vis spectral part with absorption
onset energies at about 18400 cm-1 (543 nm) and 18100 cm-1
(552 nm), respectively (Fig. 7and8). As expected, both compounds
exhibit a quite similar absorption pattern. Based on the detailed
spectral analysis of the related BDF derivative with pending 4-
ethynylpyridine groups1 and on the comparison with the electronic
absorption spectra of the fragmental chromophoric moieties of
1 and 2, the main characteristics of the electronic transitions
can be explained. Firstly, at low wavelength a strong and broad
absorption band appears around 20400 cm-1 (490 nm) for 1
In order to evaluate the frontier molecular orbitals (MOs) for 1
and 2, ab initio quantum chemical calculations were performed,
employing density functional theory with the B3LYP functional
and the valence triple-z plus polarization basis set. The calcu-
lations were carried out with the TURBOMOLE V6.0 program
package.14 The ground-state optimized structures (see ESI†) of
both compounds (with NH2 instead of N(hexyl)2 groups) were
constrained to C2h symmetry. Some frontier molecular orbitals
are given in Fig. 5 and 6. The MO schemes appear analogous for
both compounds. The electron densities of the highest occupied
MO (HOMO) and the lowest unoccupied MO (LUMO) are
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Fig. 8 Electronic absorption (black solid line) and fluorescence emission
(dashed line) spectra of 2 in deaerated dichloromethane solution at
room temperature together with absorption spectra of the reference com-
pounds 9-ethynylanthracene (green line) and 2,6-bis(dihexylamino)-4,8-
diethynylbenzo[1,2-b:4,5-b¢]difuran-3,7-dicarbonitrile (red line).
are increasingly contributing to the overall absorption pattern.1
Furthermore, the chromophoric molecules 1 and 2 show strong
fluorescence emission in dichloromethane solution (Fig. 7 and 8)
at 18400 cm-1 (543 nm) and 17700 cm-1 (565 nm) with Stokes shifts
of nST = 2000 cm-1 and 2700 cm-1, respectively. The corresponding
luminescence quantum yields UF are quite high with values of 0.53
and 0.48, respectively.
Fig. 6 Molecular orbitals of 2.
Spin delocalisation as seen through spectroelectrochemical studies
Systematic changes in the optical spectra upon oxidation of the
neutral species 1–3 were examined by spectroelectrochemistry, as
shown in Fig. 9.
Fig. 9a shows the variation of the absorbance spectra of 1 at
seven consecutive applied potentials that lead to the monocationic
species 1∑+. As the potential shifts positively, it is observed that
the lowest-energy 20400 cm-1 (490 nm) peak gradually decreases
leading to an isosbestic point at 21500 cm-1 (465 nm) since a close
lying new absorption band appears. The higher energy intense
absorptions which bear strong BDF core character decrease
significantly, indicating the participation of the BDF central core
in the process. This result is in qualitative agreement with the
aforementioned interpretation of the electrochemical data. On the
other hand, in the wavelength range 18000–10000 cm-1 (555–1000
nm), four highly structured absorption bands (lmax = 610, 670, 760,
855 nm) appear. Importantly, all of the spectra shown in Fig. 9 have
this character; these bands are thus characteristic of the BDF p-
radical cation. Additionally, 1 shows one intense NIR absorption
band (lmax = 1130 nm, 8850 cm-1) upon the first oxidation, which
can probably be ascribed to the formation of the dimeric radical
cation species of the BDF cores (p-dimers) arising from strong
intermolecular p–p interactions.
Fig. 7 Electronic absorption (black solid line) and fluorescence emission
(dashed line) spectra of 1 in deaerated dichloromethane solution at
room temperature together with absorption spectra of the reference
compounds 1-ethynylpyrene (green line) and 2,6-bis(dihexylamino)-4,8-
diethynylbenzo[1,2-b:4,5-b¢]difuran-3,7-dicarbonitrile (red line).
and 20900 cm-1 (480 nm) for 2, which can only be observed
in such p–extended chromophores. Based on the vertical TD-
DFT calculation for the S0 → S1 electronic excitation observed
at 20800 cm-1 (481 nm) in case of the BDF(– –pyridine)2
analogue,1 one may predict that this lowest-energy band of 1
and 2 substantially corresponds to an excitation described by a
one-electron HOMO→LUMO promotion. Comparing it with the
frontier molecular orbitals one recognizes clearly that the involved
p–p* transition represents an electronic redistribution over the
whole molecule and there is no localisation on either the BDF
core or on the pending groups. Secondly, the intense absorptions
between 22000 cm-1 (455 nm) and 25000 cm-1 (400 nm) originate
to a larger extent from BDF-based p–p* transitions and thirdly,
at higher energies the p–p* transitions of the pending groups
Fig. 9b exhibits the absorption spectra of 2 taken at the indicated
potentials. Similar to 1, four well-defined absorption bands (lmax
=
620, 680, 775, 880 nm) and one broad band (lmax = 1250 nm,
8000 cm-1) appear upon the first oxidation. Significantly for 2, a
new strong absorption band at 19200 cm-1 (520 nm) accompanied
by an isosbestic point at 19800 cm-1 (505 nm) is observed. The
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cation states leading to intense optical absorbances over a wide
spectral range. The electrochemical oxidations of 1 and 2 lead to
the appearance of a broad absorption band in the NIR region
due to the significantly enhanced intermolecular p–p interactions
which originates from the fusion of pyrene and anthracene units
to the BDF core. The direct observation of such intermolecular
dimerizations in solution at room temperature is still quite
challenging as the intermolecular interactions are usually too
weak for a dimerization of the radical units to occur. A strong
fluorescence emission is also observed at 18400 cm-1 (543 nm) and
17700 cm-1 (565 nm) for 1 and 2, respectively, with large Stokes
shifts; quantum efficiencies being 0.53 for 1 and 0.48 for 2.
In search of an electrically triggered luminescence signal from a
molecular junction, p-extended BDF derivatives with two terminal
pyrene groups are expected to be very promising molecular
scaffolds due to their planarity and their strong fluorescence
with high quantum yields. Recently, Krupke et al. reported
the electroluminescence from a single nanotube - molecule -
nanotube junction.15 Therefore, tests of the electroluminescence
of the aforementioned p-conjugated systems 1 and 2 trapped
in nanogaps, such as between leads of carbon rods, will be of
particular interest.
Experimental section
Air and/or water-sensitive reactions were conducted un-
der N2 in dry, freshly distilled solvents. Unless stated
otherwise, all other reagents were purchased from com-
mercial sources and used without additional purifica-
tion. 2,6-Bis(dihexylamino)-4,8-diiodobenzo[1,2-b:4,5-b¢]difuran-
3,7-dicarbonitrile (3) was synthesized according to the literature.1
1-(Trimethylsilanylethynyl)pyrene, 1-ethynylpyrene, (anthracen-9-
ylethynyl)trimethylsilane and 9-ethynylanthracene were accom-
Fig. 9 UV-visible spectral changes of 1 (a), 2 (b) and the precursor 3 (c)
during the first oxidation in CH2Cl2, 0.1 M TBAPF6.
1
plished according to modified literature procedures.11,12 All H
NMR and 13C NMR spectra were measured at 300 and 75.5 MHz,
respectively. Chemical shifts (d) were calibrated against TMS as
an internal standard. UV-vis absorption and emission spectra
were recorded on a Perkin-Elmer Lambda 10 spectrometer, a
Perkin-Elmer Lambda 900 spectrometer and a Perkin-Elmer
Spectrophotometer LS50B. Mass spectra were recorded with an
LTQ Orbitrap XL spectrometer for the ESI ionisation mode.
Fluorescent quantum yields were referred to diphenylanthracene
in EtOH with a quantum yield of 0.916 for 1 and rhodamine 6G in
EtOH with a quantum yield of 0.9517 for 2.
Electrochemical UV/vis/NIR spectra were measured in a
commercial spectroelectrochemical cell (BAS, Inc) on a Perkin-
Elmer Lambda 900 spectrophotometer at room temperature. The
cell is the combination of a thin-layer electrochemical vessel and a
quartz cuvette (light path length 1 mm). The sample solutions were
dichloromethane (HPLC grade, Acros) containing 0.2 mM BDF
derivatives and 0.1 M TBAPF6 (tetrabutylammomium hexaflu-
orophosphate, electrochemical grade, Fluka) as the supporting
electrolyte. A gold minigrid was used as working electrode.
A platinum wire and a Ag/AgOx wire served as counter and
reference electrodes, respectively. The electrochemical potential
was controlled by a lab-built potentialstat.18 The electrochemical
environment was protected from oxygen by purging Ar moderately.
Blank solution was first measured as background. The potential
was initially stabilized in the potential region where BDFs
spectral evolution of the BDF precursor 3 during the first oxida-
tion is shown in Fig. 9c. As the oxidation proceeds, the original
lowest-energy absorption band at 25600 cm-1 (390 nm) decreases
and a new band at 23300 cm-1 (430 nm) raises. Importantly, as
mentioned above, the new and well structured absorption pattern
below 20000 cm-1 underpins clearly the signature of the newly
formed radical species.
Notably, there is not even a small rising from the baseline below
the 10000 cm-1 while forming the species 3∑+, as seen in Fig. 9c.
This finding indicates that the spontaneous self-association of
3∑+ to form a dimer does not take place. In contrast, both 1∑+
and 2∑+ show a strong tendency to undergo an intermolecular
p-dimerization owing to the stabilisation effect arising from the
strong p–p interactions. It can therefore be deduced that the
intermolecular p–p interactions are significantly enhanced via the
fusion of pyrene and anthracene units to the BDF core.
Conclusions
Benzodifuran-functionalised pyrene and anthracene fluorophores
1 and 2 were obtained in reasonable yields. An experimental
and computational study (MO schemes) on their electrochemical,
optical absorption, and fluorescence characteristics has been
described. The redox-active fluorophores 1 and 2 exhibit various
electronic charge-transfer transitions in both neutral and radical
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maintain their neutral states. The potential applied was adjusted
in steps of 0.05 V or 0.10 V towards more positive values, i.e. BDF
was oxidized to the radical cation. The UV/vis/NIR absorption
spectra were recorded ca. 2 min after each potential step. The
spectra show full reversibility with potential alteration.
piperidine (2 mL) in triethylamine (30 mL) was bubbled with N2
for 10 min., and then 1-ethynylpyrene (160 mg, 0.70 mmol) was
added. The resulting solution was heated at 110 ◦C overnight in an
inert atmosphere. The volatile was evaporated by rotavapor and
the residue was subjected to column chromatography on silica
gel, eluting initially with hexane, then with 1 : 1 hexane: CH2Cl2 to
yield an orange solid product (150 mg, 61%). 1H NMR (300 MHz,
CDCl3) d 8.72 (d, 2H, J = 6.0 Hz), 8.52 (d, 2H, J = 7.9 Hz), 8.11
(d, 4H, J = 8.1 Hz), 8.04–7.90 (m, 10H), 3.74 (t, 8H, J = 7.7 Hz),
1.85 (m, 8H), 1.45(m, 8H), 1.29 (m, 16H), 0.81 (t, 12H, J = 6.8
Hz). 13C NMR (75.4 MHz, CDCl3) d 163.2, 145.2, 131.6, 131.4,
131.2, 130.9, 130.0, 128.2, 128.1, 127.2, 126.0, 125.6, 125.5, 125.4,
124.8, 124.3, 123.1, 117.9, 116.8, 99.5, 96.3, 86.1, 62.9, 50.3, 31.7,
28.8, 26.4, 22.6, 14.0; ESI-MS Calc. for C72H70O2N4 1022.5499,
found 1022.5495.
Crystallography
Single crystals of 1 (0.50 ¥ 0.10 ¥ 0.05 mm), 2a (0.30 ¥
0.18 ¥ 0.08 mm) and 2b (0.10 ¥ 0.10 ¥ 0.05 mm) were used
for X-ray structure determinations, with diffraction data being
collected at low temperature (173 K) on a Stoe Mark II-Image
Plate Diffraction System19 with monochromated graphite Mo-Ka
˚
radiation, l = 0.71073 A.
Crystal data.
1
(CCDC 783323): C72H70N4O2, Mr
=
1023.32 gmol-1, monoclinic, space group P21/c, ◦a = 15.8530(13),
˚
b = 15.5929(15), c = 25.462(2) A, b = 115.951(6) , V = 5659.4(8)
(Anthracen-9-ylethynyl)trimethylsilane12.
A mixture of 9-
3
˚
A , Z = 2. 38921 reflection measured, 10102 unique (Rint = 0.3199).
The measured 2q range was 3.07–51.98◦ corresponding to dmax
–
bromanthracene (1.028 g, 4 mmol), trimethyl-silylacetylene
(1.4 mL, 10 mmol), Pd(PPh3)2Cl2 (300 mg, 0.43 mmol), CuI
(80 mg, 0.4 mmol) and piperidine (2 mL) in triethylamine (20 mL)
was bubbled with N2 for 10 min and then the resulting solution was
heated at 110 ◦C overnight in an inert atmosphere. The volatile was
evaporated by rotavapor and the residue was subjected to column
chromatography on silica gel, eluting with a mixture of CH2Cl2
and hexane (1/9) to afford a yellow solid (1.04 g, 95%). 1H NMR
(300 MHz, CDCl3) d 8.50–8.47 (dd, J = 8.7 Hz, J = 0.9 Hz, 2H),
8.35 (s, 1H), 7.92 (d, J = 8.4 Hz, 2H), 7.54–7.48 (ddd, J = 8.4 Hz,
J = 6.6 Hz, J = 1.3 Hz, 2H), 7.45–7.40 (ddd, J = 8.1 Hz, J = 6.6 Hz,
J = 1.1 Hz, 2H), 0.35 (s, 9H).
˚
dmin = 23.107–0.802 A. 2a (CCDC 783324): C68H70N4O2, Mr =
975.28 gmol-1, monoclinic, space group P21/c, a = 13.7947(9), b =
◦
3
˚
˚
9.0999(6), c = 22.2042(16) A, b = 105.631(5) , V = 2684.2(3) A ,
Z = 2. 15649 reflection measured, 4982 unique (Rint = 0.0867).
The measured 2q range was 3.07–51.98◦ corresponding to dmax
–
˚
dmin = 23.107–0.802 A. 2b (CCDC 783325): C68H70N4O2, Mr =
975.28 gmol-1, monoclinic, space group P21/c, a = 12.0856(10),
◦
˚
b = 17.2822(16), c = 16.4631(16) A, b = 129.164(6) , V = 2666.1(4)
3
˚
A , Z = 2. 13637 reflection measured, 4685 unique (Rint = 0.1203).
The measured 2q range was 3.07–51.98◦ corresponding to dmax
–
˚
dmin = 23.107–0.802 A. The structures were solved by direct
methods using the programme SHELXS-97.20 The refinement
and all further calculations were carried out using SHELXL-97.20
The H-atoms were included in calculated positions and treated as
riding atoms. The non-H atoms were refined anisotropically, using
weighted full-matrix least-squares on F2.
9-Ethynylanthracene12. To a solution of 9-((trimethylsilyl)-
ethynyl)anthracene (960 mg, 3.5 mmol) in THF (30 mL),
was added tetrabutylammonium fluoride trihydrate (1.66 g,
5.25 mmol). The mixture was stirred at r.t. for 30 min, then poured
into water (50 mL) and extracted with CH2Cl2 (3 ¥ 50 mL). The
solvent was removed under high vacuum to give a pale yellow solid
(728 mg, 97%).1H NMR (300 MHz, CDCl3) d 8.52–8.49 (dd, J =
8.8 Hz, J = 0.9 Hz, 2H), 8.39 (s, 1H), 7.93 (d, J = 8.4 Hz, 2H),
7.55–7.49 (ddd, J = 8.7 Hz, J = 6.6 Hz, J = 1.3 Hz, 2H), 7.46–7.41
(ddd, J = 8.1 Hz, J = 6.6 Hz, J = 1.3 Hz, 2H), 3.92 (s, 1H).
Synthesis
1-(Trimethylsilanylethynyl)pyrene11. A mixture of 1-bromo-
pyrene (560 mg, 2 mmol), Pd(PPh3)2Cl2 (175 mg, 0.25 mmol), CuI
(50 mg, 0.26 mmol) and piperidine (4 mL) in triethylamine (30 mL)
was bubbled with N2 for 10 min., and then trimethylsilylacetylene
(0.6 mL, 4.1 mmol) was added. The resulting solution was heated
at 110 ◦C overnight in an inert atmosphere. The volatile was
evaporated by rotavapor and the residue was subjected to column
chromatography on silica gel, eluting with hexane to yield a pale
yellow crystalline product (450 mg, 75%). It was characterized
Compound 2. A mixture of 3 (220 mg, 0.27 mmol), 9-
ethynylanthracene (161 mg, 0.8 mmol), Pd(PPh3)2Cl2 (70 mg,
0.1 mmol), CuI (20 mg, 0.1 mmol) and piperidine (2 mL) in
triethylamine (20 mL) was bubbled with◦N2 for 10 min and then
the resulting solution was heated at 110 C overnight in an inert
atmosphere. The volatile was evaporated by rotavapor and the
residue was subjected to column chromatography on silica gel,
eluting with a mixture of CH2Cl2 and hexane (1/1) to afford a
orange crystalline product (167.6 mg, 64%). 1H NMR (300 MHz,
CDCl3) d 8.90–8.87 (dd, J = 8.6 Hz, J = 0.9 Hz, 4H), 8.40 (s, 2H),
7.95 (d, J = 8.3 Hz, 4H), 7.58–7.52 (ddd, J = 8.7 Hz, J = 6.6 Hz,
J = 1.3 Hz, 4H), 7.48–7.43 (ddd, J = 8.3 Hz, J = 6.6 Hz, J = 1.1 Hz,
4H), 3.69 (t, J = 7.5 Hz, 8H), 1.72 (m, 8H), 1.15 (m, 24 H), 0.68 (t,
J = 7.1 Hz, 12H). 13C NMR (75.4 MHz, CDCl3) d 163.6, 146.3,
133.1, 131.4, 128.8, 128.4, 127.6, 126.8, 125.9, 123.3, 117.3, 116.7,
97.8, 96.8, 91.2, 63.4, 50.1, 31.6, 28.6, 26.3, 22.6, 14.0. ESI-MS
Calc. for C68H70O2N4 974.5493, found 974.5500.
1
by H NMR giving the same analytical data as reported in the
literature.
1-Ethynylpyrene11.
A mixture of 1-(trimethylsilyl)ethynyl-
pyrene (420 mg, 1.4 mmol) and tetrabutylammonium fluoride
trihydrate (620 mg, 2 mmol) in THF (15 mL) was stirred at room
temperature for 1h. The volatile was evaporated by rotavapor and
the residue was subjected to column chromatography on silica gel,
eluting with hexane to yield a white crystalline product (300 mg,
1
95%). H NMR (300 MHz, CDCl3) d 8.56 (d, 1H, J = 9 Hz),
8.22–8.03 (m, 8H), 3.62 (s, 1H).
Compound 1.
A mixture of 3 (200 mg, 0.25 mmol),
Pd(PPh3)2Cl2 (50 mg, 0.07 mmol), CuI (30 mg, 0.15 mmol) and
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8 Y. Li, H.-W. Li, L.-J. Ma, Y.-Q. Dang and Y. Wu, Chem. Commun.,
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(FUNMOLS FP7-212942-1).
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