Donor-acceptor substituted phenylethynyltriphenylenes - Excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

Article abstract of DOI:10.3762/bjoc.6.112

Several 2-(phenylethynyl)triphenylene derivatives bearing electron donor and acceptor substituents on the phenyl rings have been synthesized. The absorption and fluorescence emission properties of these molecules have been studied in solvents of different

Full text of DOI:10.3762/bjoc.6.112

Donor-acceptor substituted
phenylethynyltriphenylenes – excited state
intramolecular charge transfer, solvatochromic
absorption and fluorescence emission
Ritesh Nandy and Sethuraman Sankararaman*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2010, 6, 992–1001.
Department of Chemistry, Indian Institute of Technology Madras,
Chennai 600036, India
doi:10.3762/bjoc.6.112
Received: 08 June 2010
Accepted: 05 October 2010
Published: 18 October 2010
Email:
Sethuraman Sankararaman* - sanka@iitm.ac.in
* Corresponding author
Associate Editor: J. Murphy
Keywords:
© 2010 Nandy and Sankararaman; licensee Beilstein-Institut.
License and terms: see end of document.
charge transfer; fluorescence; solvatochromism; solvent effect;
triphenylene
Abstract
Several 2-(phenylethynyl)triphenylene derivatives bearing electron donor and acceptor substituents on the phenyl rings have been
synthesized. The absorption and fluorescence emission properties of these molecules have been studied in solvents of different
polarity. For a given derivative, solvent polarity had minimal effect on the absorption maxima. However, for a given solvent the
absorption maxima red shifted with increasing conjugation of the substituent. The fluorescence emission of these derivatives was
very sensitive to solvent polarity. In the presence of strongly electron withdrawing (–CN) and strongly electron donating (–NMe2)
substituents large Stokes shifts (up to 130 nm, 7828 cm−1) were observed in DMSO. In the presence of carbonyl substituents
(–COMe and –COPh), the largest Stokes shift (140 nm, 8163 cm−1) was observed in ethanol. Linear correlation was observed for
the Stokes shifts in a Lippert–Mataga plot. Linear correlation of Stokes shift was also observed with ET(30) scale for protic and
aprotic solvents but with different slopes. These results indicate that the fluorescence emission arises from excited state intramo-
lecular charge transfer in these molecules where the triphenylene chromophore acts either as a donor or as an acceptor depending
upon the nature of the substituent on the phenyl ring. HOMO–LUMO energy gaps have been estimated from the electrochemical
and spectral data for these derivatives. The HOMO and LUMO surfaces were obtained from DFT calculations.
Introduction
Fluorescent molecular probes that emit in the visible region and applications in chemistry, biology and environmental science
whose fluorescence emission is sensitive to environment and [1-4]. Considerable effort has been expended into shifting the
solvent polarity are of significant interest due to their versatile fluorescence emission of organic molecules into the visible
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Beilstein J. Org. Chem. 2010, 6, 992–1001.
region. The most commonly employed strategy for the Herein we report the synthesis of a series of 2-(phenyl-
bathochromic shifting of the emission wavelength is to extend ethynyl)triphenylene derivatives with donor and acceptor
the conjugation of the fluorophores with aryl, ethenyl and substituents on the phenyl ring (Scheme 1). The phenylethynyl
ethynyl groups. The addition of electron donating and with- group is used to extend the conjugation of the triphenylene
drawing substituents to these conjugation enhancing groups also chromophore and the substituents on the phenyl ring are used to
helps in shifting the emission wavelengths further into red enhance intramolecular charge transfer (ICT) in the excited
region. For example, boron-dipyrrolomethenes (BODIPYs) are state. We have studied the absorption and emission properties,
a class of molecules whose absorption and fluorescence emis- in particular the ICT based solvatochromic fluorescence emis-
sion have been fine tuned by suitable substituents [5-7]. Fluo- sion behavior and the correlation of the observed large Stokes
rophores emitting in the visible region are important especially shifts with orientation polarizibility (Δf) and solvent polarity
in the in vivo study of biological samples. Otherwise the back- (ET(30) scale). HOMO and LUMO surfaces of these deriva-
ground blue emission of the biological samples interferes with tives, obtained from DFT calculations, help in identifying the
the fluorescence sensing. The mechanism of fluorescence triphenylene chromophore acting as an acceptor when substi-
sensing often involves excited state intramolecular charge tuted with electron donating groups and as a donor when substi-
transfer (ICT) [8-11], photoinduced electron transfer [12-15] tuted with electron withdrawing groups on the phenyl ring.
and metal ion induced enhancement or quenching of fluores- HOMO–LUMO energy gaps have been estimated based on
cence [16-19]. Among these, fluorophores that exhibit excited electrochemical studies and compared with those obtained from
state ICT are very popular. In this context fluorescent donor-π absorption spectroscopy.
spacer-acceptor (d-π-a) type molecules are of considerable
interest and importance. In this class of molecule, the excited
state is generally highly polar compared to the ground state due
to intramolecular charge transfer from the donor to the acceptor
group. The intramolecular charge transfer results in a large
dipole moment in the excited state compared to that of the
ground state rendering its fluorescence emission sensitive to
environment and solvent polarity [20-22].
Pyrene is a prototypical example of a fluorophore and its mono-
mer emission occurs around 380 nm. It has been shifted to as
high as 600 nm by multiple substitution by groups that extend
the conjugation and also by substituting donor-acceptor groups
Scheme 1: Structures of 2-phenylethynyltriphenylene derivatives.
along the conjugation [23-25]. In addition, pyrene also exhibits
excimer emission at a longer wavelength compared to mono-
Results and Discussion
mer emission which can be used in sensing applications [26-
30]. The pyrene chromophore can act as a donor or as an Synthesis
acceptor depending upon the substituent. Pyrene- π spacer- 2-Ethynyltriphenylene (4) was synthesized by coupling 2-iodo-
donor and pyrene- π spacer-acceptor type molecules have been triphenylene (2) with 1,1-dimethylpropargyl alcohol followed
widely studied and they have been used in sensing, photo and by deprotection with KOH in refluxing toluene (Scheme 2).
electro-luminescence applications [31-36]. Unlike pyrene, the 2-Phenylethynyltriphenylene (1a) and those bearing electron
triphenylene chromophore has not been widely studied. In withdrawing substituent (1b–e) were synthesized by the
contrast to pyrene, triphenylene does not form an excimer in the Sonogashira coupling of 2-iodotriphenylene (2) with the corres-
excited state – emission from the excimer state is very rare for ponding phenylacetylene derivatives. Although 1f–g were also
triphenylene chromophore [37-39]. The fluorescence of tri- synthesized by this procedure, their purification proved diffi-
phenylene occurs around 348 nm, which is more blue shifted cult due to an inseparable minor product formed in these reac-
than pyrene monomer emission. Only a few reports on the tions. Therefore compounds 1f–g were synthesized via the
extension of conjugation of the triphenylene chromophore have Sonogashira coupling of 2-ethynyltriphenylene (4) and the
appeared. 2,3,6,7,10,11-Hexakis(ethynyl)triphenylene deriva- corresponding iodoarenes (Scheme 3). Compounds 1a–f were
tives have been used in photonics as organic light emitting obtained as colorless solids in good yields. Derivative 1g was
diode (OLED) materials [40-42]. Therefore, it is worthwhile to obtained as an orange solid in 58% yield. All compounds were
tune the fluorescence emission of the triphenylene chro- purified by column chromatography and thoroughly character-
mophore by the addition of suitable substituents.
ized by various spectroscopic methods and analytical data.
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Beilstein J. Org. Chem. 2010, 6, 992–1001.
absorption spectra of 1a–g in cyclohexane and acetonitrile are
shown in Figure 1. The lowest energy absorption of triphenyl-
ene is symmetry forbidden and appears at 330–340 nm [23].
Compared to triphenylene, the absorption bands of derivatives
1a–g are consistently red shifted and more intense (symmetry
allowed) due to extended conjugation with the phenylethynyl
group and loss of symmetry, respectively. Compared to 1a and
1b, the lowest energy absorption bands of 1c–g are further red
shifted in both cyclohexane and acetonitrile. Although there is
no significant solvent effect on the absorption bands of 1a–g in
these two solvents, the lowest energy absorption bands are red
shifted by 5–10 nm in cyclohexane compared to acetonitrile.
Moreover, the vibrational fine structure is more clearly seen in
cyclohexane than in acetonitrile where the bands are relatively
broadened, especially for 1g. These observations led to the
Scheme 2: Synthesis of 2-ethynyltriphenylene (4).
Scheme 3: Synthesis of phenylethynyltriphenylene derivatives 1a–g.
Absorption and fluorescence emission
studies
The UV–vis absorption spectra of 1a–g were recorded in
various solvents ranging from non-polar cyclohexane to dipolar
aprotic DMSO to polar protic ethanol and isopropanol. The
Figure 1: Absorption spectra of 1a–g in cyclohexane and acetonitrile
(10−5 M).
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Beilstein J. Org. Chem. 2010, 6, 992–1001.
conclusion that irrespective of the substituents on the phenyl phenylethynyltriphenylene chromophore and the band at 400
ring, the ground state of these molecules is relatively non-polar nm to ICT from the dimethylamino group to triphenylene
and devoid of significant solvent and substituent effects. By moiety [36]. In DMSO, the fluorescence emission of 1a–b
contrast, the fluorescence emission bands of 1a–g showed appeared at around 380 nm, arising from the local excited state
significant substituent and solvent effects.
of phenylethynyltriphenylene chromophore. The emission
maxima of all the other substrates (1c–g) were progressively red
The fluorescence emission spectra of 1a–g in cyclohexane, and shifted and highly dependent on the substituent present. The
DMSO are shown in Figure 2. In cyclohexane, 1a–f showed maximum red shift (499 nm) was observed in case of 1g where
emission maxima around 380 nm which is characteristic of the excited state ICT is expected to be efficient due to the strong
local excited state emission of the phenylethynyltriphenylene electron donating nature of the –NMe2 group. Compounds 1c–e
chromophore. The emission maximum was independent of the bearing electron withdrawing substituents also showed progres-
substituent, which implied that there was no significant ICT in sive red shifts (1c, 412 nm; 1d, 430 nm and 1e, 448 nm) of the
the excited state in cyclohexane. In the case of 1g, two emis- emission band due to ICT where charge transfer from triphenyl-
sion bands were observed at 381 and 400 nm. The 381 nm band ene moiety to the phenyl group bearing the electron with-
was assigned to emission from the local excited state of the drawing substituent occurred. In case of 1e, two emission bands
were observed at 394 and 448 nm due emission from local exci-
tation of the triphenylene chromophore and the ICT transition,
respectively. The fluorescence emission spectra of 1e and 1g
measured in various solvents are shown in Figure 3. These two
substrates, one with an electron withdrawing substituent (1e)
and the other with an electron donating substituent (1g) are
highlighted here because of the maximum Stokes shifts of the
ICT band observed with these two compounds. With increasing
solvent polarity the fluorescence maxima remained unchanged
in the cases of 1a and 1b, whereas in all the other cases a
progressive red shift of emission maxima was observed. The
emission maxima of compounds 1a (with no substituent in the
phenyl ring) and 1b (with a CF3 substituent ) were unaffected
by a change of solvent polarity, whereas in derivatives 1c–g the
substituent had a strong effect on the emission maxima with
increasing solvent polarity.
In cases of 1c and 1f–g, the maximum Stokes shift was
observed in DMSO where as in case of 1d–e the maximum
Stokes shift was observed in ethanol. Compounds 1d–e are car-
bonyl derivatives and the maximum shift in hydroxylic solvents
might be due to strong hydrogen bonding interactions between
the solvent and the carbonyl group in the excited state. In order
to probe further the effect of solvent polarity on the emission
maximum (solvatochromic fluorescence emission), the fluores-
cence spectrum of 1g was recorded in binary solvent mixtures
of cyclohexane and isopropyl alcohol. Initially in cyclohexane,
two emission bands were observed. With the addition of iso-
propyl alcohol the emission maximum shifted to longer wave-
lengths and the two bands merged. In an approximately 10%
isopropyl alcohol-cyclohexane mixture, the band that was
assigned to emission from a local excited state vanished and
only a band due to ICT was observed (Figure 4). With
increasing solvent polarity the emission intensity decreased due
Figure 2: Fluorescence emission spectra of 1a–g in cyclohexane and
DMSO (10−5 M), λex = 335 nm.
to competing excited electron transfer quenching of fluores-
cence.
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Beilstein J. Org. Chem. 2010, 6, 992–1001.
Figure 4: Effect of binary solvent system (cyclohexane-isopropyl
alcohol) on the fluorescence emission of 1g (10−5 M). CH – cyclo-
hexane, IPA – isopropyl alcohol, λex = 335 nm.
tronic excitation (μES − μGS) was estimated assuming the mole-
cular radius as the cavity radius [11]. The molecules under
consideration are non-spherical in nature. Hence, the above
assumption of substituting molecular radius for cavity radius is
only approximate. The molecular radii for 1c (8.8 Å), 1e (10.2
Å) and 1g (9.1 Å) were obtained from semi-empirical AM1
calculations [46]. The change in the dipole moments (Δμ) were,
25.7 D for 1c, 43.0 D for 1e and 40.0 D for 1g, respectively
(Table 1). The change in dipole moment for 1g is higher than
that of the corresponding pyrene derivative (30 D) [36].
Whenever there is an excited state charge transfer process,
Figure 3: Fluorescence emission spectra of 1e and 1g in various
solvents (10−5 M). CH – cyclohexane (λex = 334 nm (1e) and 345 nm
(1g)), BENZ – benzene (λex = 338 nm (1e) and 335 nm (1g)), DCM –
dichloromethane (λex = 336 nm (1e) and 357 nm (1g)), IPA – isopropyl
alcohol CH3CN (λex = 348 nm (1g)), DMSO (λex = 338 nm (1e) and
367 nm (1g). EtOH (λex = 335 nm (1e and 1g)), THF (λex = 356 nm
(1g)).
Correlation of Stokes shifts with solvent
polarity
Solvent induced spectral shifts are often interpreted in terms of
the Lippert–Mataga [43-45] equation, which describes Stokes
shifts in terms of the change in the dipole moment of the fluo-
rophore and the dependence of the energy of the dipole on the
dielectric constant and refractive index of the solvent. The
Lippert–Mataga equation accounts for the general solvent effect
and does not account for specific solvent–fluorophore interac-
tions, for example, through hydrogen bonding etc. The
Lippert–Mataga plot for 1c and 1g are shown in Figure 5 as
representative examples. From the slope of these plots the
change in the dipole moment (Δμ) of the fluorophore upon elec-
Figure 5: Lippert–Mataga plot showing Stokes shift as a function of
solvent orientation polarizibility (Δf).
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Beilstein J. Org. Chem. 2010, 6, 992–1001.
Table 1: Representative absorption, emission and fluorescence quantum yield data.
Substrate
Solventa
Absorption
Emission
Φfb
Δμ (D)c
λmax (nm)
λmax (nm)
1a
1b
1c
1d
1e
1f
CH
DMSO
334
336
370
371
0.20
0.28
CH
DMSO
334
337
368
373
0.17
0.35
CH
DMSO
349
353
362
412
0.60
0.54
25.7
29.5
43
CH
EtOH
351
353
383
434
—
0.32
CH
EtOH
354
350
381
490
—
0.11
CH
DMSO
343
348
365
421
0.58
0.43
28
1g
CH
DMSO
367
367
380
499
0.99
0.36
40
aCH = cyclohexane, bfluorescence quantum yield relative to quinine sulfate standard, cchange in dipole moment (μES − μGS) due to excited state ICT
calculated from Lippert–Mataga plot.
Reichardt–Dimroth’s ET(30) [47,48] scale is more useful to
correlate the solvent induced Stokes shift. Correlation using
ET(30) scale often follows two distinct lines, one for the non-
protic solvents and other for the protic solvents. The data points
corresponding to ethanol and isopropyl alcohol are indicated in
Figure 6. In protic solvents specific solvent–fluorophore inter-
action such as hydrogen bonding is possible and the extent of
this interaction would depend upon the functional groups
present in the fluorophore. In the case of 1e all the data points
of the correlation between Stokes shift and ET(30) lie on the
straight line with a correlation coefficient of 0.98. A similar
trend is observed in the case of 1d. However, in cases of 1c and
1g, the data points corresponding to the protic solvents do not
lie on the straight line since the observed Stokes shifts are much
lower than expected for these solvents. Derivative 1e is a car-
bonyl compound and stabilization due to hydrogen bonding
Figure 6: Correlation of Stokes shift with ET(30) scale.
interaction with protic solvents is expected both in the ground
and excited state. Such a specific solvent-fluorophore inter-
action might be weak in the case of other derivatives. Thus, the which did not show strong solvatochromic emission, the reverse
correlation of Stokes shift with ET(30) helps in identifying trend was observed. The quantum yield of fluorescence
specific solvent–fluorophore interactions.
increased in DMSO compared to cyclohexane. This might be
due to the increase in the viscosity of the medium which
quenches the non-radiative pathways. In the cases of the car-
bonyl derivatives 1d and 1e, the quantum yield of fluorescence
was measured in ethanol. The fluorescence quantum yields for
these derivatives in ethanol were low, presumably due to facile
electron transfer and hydrogen bonding interaction with the
solvent which enhances the non-radiative processes. In polar
solvents electron transfer from the aromatic moiety to the
benzophenone has been previously shown by time resolved
spectroscopy to result in the formation of a radical ion pair [52-
54].
Quantum yield of fluorescence
From Figure 3 and Figure 4 it is clear that with increasing
solvent polarity, the intensity of emission decreases along with
the bathochromic shift of the wavelength of emission. The fluo-
rescence intensity of molecular systems that undergo efficient
ICT upon photoexcitation decreases due to competing electron
transfer from the donor to the acceptor site that quenches the
fluorescence [49-51]. For compounds 1c, 1f and 1g, the fluores-
cence quantum yield decreased upon changing the solvent from
cyclohexane to DMSO (Table 1). For compounds 1a and 1b,
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HOMO and LUMO surfaces and energy gaps
Cyclic voltammograms of 1a–e and 1g were recorded in aceto-
nitrile in order to obtain the redox potentials, as well as to esti-
mate the HOMO–LUMO gap of these derivatives [31-35]. All
the compounds showed a single irreversible oxidation peak and
multiple reduction peaks. The HOMO–LUMO gap was esti-
mated from the CV data as the difference between the oxi-
dation peak potential and the reduction peak potential (Table 2)
and compared with the HOMO–LUMO gap estimated from the
onset of optical absorption from the UV–vis spectra in acetoni-
trile. The HOMO–LUMO gaps obtained by these two methods
are comparable considering the approximate nature of these
methods of estimation. The optimized structures, HOMO and
LUMO surfaces of 1c and 1g were obtained by DFT calcula-
tions [46]. In case of 1c, the molecule is planar whereas 1g is
twisted. The dihedral angle between the plane of the triphenyl-
ene ring and the plane of the phenyl ring is 96° for 1g. These
observations are comparable with the geometry of the corres-
ponding pyrene derivatives reported earlier [31,32]. The
HOMO and LUMO surfaces are shown in Figure 7. In case of
1g, the HOMO density is mainly located on the dimethylamino-
phenylethynyl moiety and the triphenylene moiety is devoid of
any HOMO density. The LUMO of 1g is mainly located on the
triphenylene moiety indicating that the dimethylaminophenyl-
ethynyl group is the donor and the triphenylene group the
acceptor. In case of 1c the situation is reversed, the HOMO
density is located mainly on the triphenylene moiety and the
LUMO density is on the cyanophenylethynyl group. This indi-
cates that there is role reversal of the triphenylene moiety either
as a donor or as an acceptor depending upon the nature of the
Table 2: HOMO-LUMO energy gap and change in dipole moment due
to ICT.
Substrate ΔE (eV)a Ep(ox) (V)b Ep(red) (V)b
ΔE (eV)c
1a
1b
1c
1d
1e
1f
3.42
3.41
3.30
3.27
3.20
3.19
2.97
+1.60
+1.65
+1.68
+1.66
+1.63
—
−2.14
−2.02
−1.85
−1.70
−1.63
—
3.74
3.67
3.53
3.36
3.26
—
1g
+0.76
−2.27
3.03
aHOMO–LUMO energy gap estimated on the basis of absorption data,
bat 0.1 Vs−1 scan rate, cHOMO–LUMO energy gap estimated on the
basis of electrochemical data.
Figure 7: HOMO and LUMO surfaces of 1c and 1g according to DFT
calculations.
functional group attached to the phenylethynyl unit. These find- Stokes shifts were correlated with solvent orientation polarizi-
ings are consistent with the earlier reports on the pyrene deriva- bility by the Lippert–Mataga equation and Reichardt’s ET(30)
tives [31].
solvent polarity scale. HOMO–LUMO gaps were calculated
from both optical and electrochemical data. HOMO and LUMO
surfaces based on DFT calculations show that the triphenylene
Conclusion
Several 2-phenylethynyltriphenylene derivatives bearing elec- chromophore can act either as an electron donor or as an elec-
tron donating and electron releasing groups on the phenyl ring tron acceptor in the ICT process, depending upon the nature of
were synthesized. Their absorption and fluorescence emission substituent on the phenyl ring. Derivatives 1e and 1g are poten-
were studied in several solvents. The absorption maximum of tial candidates for use as solvent polarity probes. However, their
these derivatives was not siginificantly altered by solvent performance is only comparable to those of the corresponding
polarity. However, the fluorescence emission maxima showed pyrene derivatives.
strong solvent polarity dependence and large Stokes shifts were
observed. These observations are explained on the basis of an Experimental
excited state intramolecular charge transfer (ICT) process. Synthesis of 2-methyl-4-(triphenylen-2-yl)but-3-yn-2-ol (3).
Derivative 1g, with dimethylamino substituent, showed the A Schlenk flask was charged with a mixture of 2-iodotripheny-
maximum solvent effect with a Stokes shift of nearly 130 nm lene and triphenylene (2.0 g, 45:55 by 1H NMR) (see
(7828 cm−1) in DMSO in comparison to that observed in cyclo- Supporting Information File 1), Pd(PPh3)2Cl2 (0.2 g, 0.3
hexane. Derivatives bearing carbonyl substituents (1d–e) mmol), PPh3 (0.15 g, 0.6 mmol), CuI (0.105 g, 0.6 mmol),
showed large Stokes shift in polar protic solvents such as degassed THF (30 mL) and diisopropylamine (30 mL). The
ethanol and isopropyl alcohol, presumeably due to the hydrogen mixture was stirred at room temperature for 15 min and
bonding stabilization of the excited state by these solvents. The 2-methyl-3-butyn-2-ol (0.32 g, 3.8 mmol) was added. Stirring
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Beilstein J. Org. Chem. 2010, 6, 992–1001.
was continued for 2 h at 60 °C after which time the solvent was 126.8, 123.5, 123.43, 123.41, 123.36, 123.31, 121.9, 90.2, 89.9
removed and the residue dissolved in dichloromethane (100 ppm; The mass spectrum was recorded as the silver ion adduct
mL). The solution was washed successively with 5% aq HCl (2 of 1a by adding silver triflate to a solution of 1a in acetonitrile
× 60 mL) and water (60 mL). The organic layer was dried over prior to measurement. ESI Q-TOF MS m/z 435 [M + Ag]+
anhydrous sodium sulfate and solvent removed under reduced along with the isotope peaks in the expected intensity ratios;
pressure. The crude product was purified by column chromato- HRMS calcd for C26H16Ag [M + Ag]+ 435.0303; found,
graphy on silica gel. Elution with hexane to remove unreacted 435.0298.
triphenylene followed by elution with a mixture of hexane and
ethyl acetate (9:1, v/v) gave 3 as a colorless solid (0.95 g, 78%), 2-(3-Trifluoromethylphenylethynyl)triphenylene (1b). The
mp 153–155 °C; IR (neat) 3331, 2978, 2212 cm−1; 1H NMR crude product was purified three times by column chromatogra-
(CDCl3, 400 MHz) δH = 8.71 (d, J = 1.2 Hz, 1H), 8.53–8.63 (m, phy with hexane as eluant to yield 1b as a colorless solid (0.654
5H), 7.63–7.67 (m, 5H), 2.24 (s, 1H), 1.72 (s, 6H) ppm. 13C g, 87%), mp 137–139 °C; IR (neat) 3069, 2213 cm−1; 1H NMR
NMR (CDCl3, 100 MHz) δc = 130.0, 129.9, 129.6, 129.5, (CDCl3, 500 MHz) δH = 8.80 (d, J = 1.5 Hz, 1H), 8.55–8.68 (m,
129.2, 129.0, 127.6, 127.5, 1273, 126.9, 123.5, 123.4, 123.38, 5H), 7.8 (m, 1H), 7.73–7.77 (m, 2H), 7.59–7.67 (m, 5H), 7.48-
123.31, 123.27, 121.3, 94.5, 82.5, 65.8, 31.6 ppm. ESI Q-TOF 7.51 (m, 1H) ppm; 13C NMR (CDCl3, 125 MHz) δc 134.7, 131
MS m/z 333 [M + Na]+, 293 [M − OH]+; HRMS calcd for (q, 2JC-F = 32.5 Hz), 130.1, 130.0, 129.9, 129.8, 129.7, 129.2,
C23H18ONa [M − Na]+ 333.1255; found, 333.1257.
129.0, 128.9, 128.5 (q, 3JC-F = 3.75 Hz), 127.7, 127.6, 127.41,
127.39, 127.0, 124.87 (q, 3JC-F = 3.75 Hz), 124.3, 123.5, 123.4,
Synthesis of 2-ethynyltriphenylene (4). To a degassed solu- 123.3, 122.7, 121.1, 91.4, 88.6 ppm; MALDI-TOF MS
tion of 3 (0.79 g, 2.5 mmol) in toluene (100 mL), KOH (0.57 g, C27H15F3 m/z (%) 396 (100) [M+], 397 (84) [M+ + 1], 398 (22)
10.2 mmol) was added and the reaction mixtureheated under [M+ + 2].
reflux for 2.5 h. Upon completion of the reaction, the hot reac-
tion mixture was filtered and the residue washed with toluene 4-(2-Triphenylenylethynyl)benzonitrile (1c). The crude pro-
(10 mL). The combined filtrate and washings were washed with duct was purified by column chromatography with a mixture of
water (2 × 60 mL). The organic layer was separated and dried hexane and dichloromethane (85:15, v/v) as eluant to yield 1c
over anhydrous sodium sulfate. The solvent was removed under as a colorless solid (0.529 g, 79%), mp 192–194 °C; IR (neat)
reduced pressure and the crude product purified by column 3059, 2221 cm−1; 1H NMR (CDCl3, 400 MHz) δH = 8.82 (d, J
chromatography on silica gel with hexane and dichloromethane = 1.2 Hz, 1H), 8.60–8.66 (m, 5H), 7.77 (dd, J = 1.2, 8.8 Hz,
(95:5, v/v) as eluant to give 4 as a colorless solid (0.508 g, 1H), 7.66–7.69 (m, 8H) ppm;13C NMR (CDCl3, 100 MHz) δc
79%); mp 149–151 °C; IR (neat) 3280, 2194 cm−1; 1H NMR 132.1, 130.2, 130.0, 129.8, 129.1, 128.9, 128.2, 127.9, 127.8,
(CDCl3, 400 MHz) δH = 8.80 (d, J = 1.2 Hz, 1H), 8.57–8.65 (m, 127.4, 127.2, 123.6, 123.5, 123.4, 123.37, 123.3, 120.8, 119.6,
5H), 7.74 (dd, J = 1.2, 8.8 Hz, 1H), 7.65–7.68 (m, 4H), 3.23 (s, 111.5, 94.3, 88.8 ppm; ESI Q-TOF MS C27H15N m/z 376 [M
1H) ppm; 13C NMR (CDCl3, 100 MHz) δc 130.2, 130.1, 129.9, +Na]+, 354 [M + H]+; HRMS calcd for C27H16N [M + H]+
129.1, 128.9, 127.7, 127.6, 127.5, 127.4, 127.3, 123.5, 123.4, 354.1283; found, 354.1287.
123.3, 120.6, 84.1, 77.9 ppm; MALDI-TOF MS m/z (%) 252
(72) [M+], 253 (100) [M+ + 1], 254 (22) [M+ + 2]; Anal. calcd. 4-(2-Triphenylenylethynyl)acetophenone (1d). The crude
for C20H12 C, 95.23; H, 4.75. Found C, 95.04, H 4.60.
product was purified by column chromatography with a mix-
ture of hexane and dichloromethane (4:1, v/v) as eluant to yield
General procedure for the synthesis of 1a–e. 1a–e were 1d as a colorless solid (0.506 g, 72%), mp 181–183 °C; IR
synthesized by coupling 2-iodotriphenylene (2 mmol) with the (neat) 3067, 2218, 1669 cm−1; 1H NMR (CDCl3, 400 MHz) δH
corresponding arylethyne (1.9 mmol) (see Scheme 3) according = 8.86 (d, J = 1.6 Hz, 1H), 8.62–8.68 (m, 5H), 7.97–8.0 (m,
to the procedure described above for the synthesis of 3.
2H), 7.80 (dd, J = 1.6, 8.8 Hz, 1H), 7.66–7.71 (m, 6H), 2.64 (s,
3H) ppm; 13C NMR (CDCl3, 100 MHz) δc 191.3, 136.6, 131.8,
2-(Phenylethynyl)triphenylene (1a). The crude product was 130.2, 130.0, 129.9, 129.8, 129.2, 129.0, 128.4, 128.2, 127.8,
purified by column chromatography with hexane as eluant to 127.7, 127.4, 127.1, 123.6, 123.4, 121.3, 93.2, 89.4, 26.6 ppm;
afford 1a as a colorless solid (0.495 g, 80%), mp 180–182 °C; ESI Q-TOF MS m/z 371 [M + H]+; HRMS calcd for C28H19O
IR (neat) 3069, 2217 cm−1; 1H NMR (CDCl3, 500 MHz) δH = [M + H]+ 371.1436; found, 371.1433.
8.80 (d, J = 1.5 Hz, 1H), 8.55–8.64 (m, 5H), 7.75 (dd, J = 1.5,
8.5 Hz, 1H), 7.61–7.66 (m, 6H), 7.36-7.40 (m, 3H) ppm; 13C 4-(2-Triphenylenylethynyl)benzophenone (1e). The crude
NMR (CDCl3, 125 MHz) δc 131.7, 130.1, 130.0, 129.9, 129.7, product was purified by column chromatography with a mix-
129.6, 129.3, 129.1, 128.5, 128.4, 127.59, 127.58, 127.4, 127.3, ture of hexane and dichloromethane (80:20, v/v) as eluant to
999

Beilstein J. Org. Chem. 2010, 6, 992–1001.
yield 1e as a colorless solid (0.517 g, 63%), mp 172–174 °C; IR 372 [M + H]+; HRMS calcd for C28H22N [M + H]+ 372.1752;
(neat) 3080, 2211, 1658 cm−1; 1H NMR (CDCl3, 400 MHz) δH found, 372.1759.
= 8.85 (d, J = 1.2 Hz, 1H), 8.61–8.66 (m, 5H), 7.79–7.86 (m,
5H), 7.59–7.73 (m, 7H), 7.49–7.53 (m, 2H) ppm; 13C NMR
Supporting Information
(CDCl3, 100 MHz) δc 196.0, 136.9, 132.6, 131.5, 130.20,
130.16, 130.06, 130.03, 129.9, 129.8, 128.4, 127.8, 127.7,
Supporting Information includes the NMR spectra of all
127.5, 127.1, 123.6, 123.5, 123.4, 121.4, 93.0, 89.5 ppm; ESI
compounds (1a–g, 2–4), UV–vis data in various solvents,
Q-TOF MS m/z 433 [M + H]+; HRMS calcd for C33H21O [M +
electrochemical data for 1a–g and calculated atomic
H]+ 433.1592; found, 433.1593.
coordinates for 1c and 1g.
Supporting Information File 1
General procedure for the synthesis of 1f–g. A Schlenk flask
was charged with the corresponding aryl iodide (0.6 mmol),
Pd(PPh3)2Cl2 (0.011 g, 0.015 mmol), PPh3 (0.008 g, 0.03
mmol), CuI (0.006 g, 0.03 mmol), degassed THF (30 mL) and
diisopropylamine (10 mL). The reaction mixture was stirred at
room temperature for 15 min and a solution of 2-ethynyltri-
Experimental data for compounds 1a–g and 2–4.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-6-112-S1.pdf]
phenylene (4) (0.5 mmol) in THF (3mL) added dropwise. Stir- Acknowledgements
ring was continued for 2.5 h. Removal of solvent and other We thank DST, New Delhi for financial support, IIT Madras for
volatile materials under reduced pressure gave the crude pro- a fellowship to RN, SAIF, the Department of Chemistry, IIT
duct which was purified by column chromatography on silica Madras for spectroscopic data and Prof. A. K. Mishra for useful
gel.
discussions.
References
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