Synthesis of monodisperse oligo(1,4-phenyleneethynylene-alt-1,4- triptycyleneethynylene)s

Article abstract of DOI:10.1021/jo9009744

(Chemical Equation Presented) The synthesis of monodisperse oligo(p-phenyleneethynylene)s 8a_n with alternating 2,5-dihexyl-1,4-phenylene and 6,14-di-tert-butyl-1,4-triptycylene units and orthogonally protected alkyne end groups is reported. Sta

Full text of DOI:10.1021/jo9009744

pubs.acs.org/joc
Synthesis of Monodisperse Oligo(1,4-phenyleneethynylene-alt-
1,4-triptycyleneethynylene)s
Daniela Maag, Tilman Kottke, Miriam Schulte, and Adelheid Godt*
€
Bielefeld University, Faculty of Chemistry, Universitatsstraße 25, D-33615 Bielefeld, Germany
godt@uni-bielefeld.de
Received May 10, 2009
The synthesis of monodisperse oligo(p-phenyleneethynylene)s 8an with alternating 2,5-dihexyl-1,4-
phenylene and 6,14-di-tert-butyl-1,4-triptycylene units and orthogonally protected alkyne end groups
is reported. Starting from 6,14-di-tert-butyl-1-(2-triisopropylsilylethynyl)-4-(2-trimethylsilylethynyl)-
triptycene (5a), 1,4-dihexyl-2,5-diiodobenzene (10), and 1,4-dihexyl-2-iodo-5-(3-hydroxyprop-1-ynyl)-
benzene (9), oligomers with up to four repeating units, i.e., eight phenyleneethynylene units, were
prepared through a partially divergent-convergent route with the alkynyl-aryl (Sonogashira-
Hagihara) coupling as the key reaction. The starting compound 5a was prepared from triptycenequinone
through a sequence of addition of 2-trialkylsilylethynyllithium, reduction and concomitant elimination
of water, conversion of the phenol into a triflate, and finally Pd/Cu-catalyzed coupling with trialk-
ylsilylethyne. A similar access to the key compound for a stringent divergent-convergent route,
6,14-di-tert-butyl-1-(3-hydroxybut-1-ynyl)-4-(2-triisopropylsilylethynyl)triptycene (6), is reported. The
optical properties of the oligomers 8an and the corresponding oligo(2,5-dihexyl-1,4-phenylene-
ethynylene)s in dilute solution are almost identical, whereas they differ significantly for the solid,
undiluted compounds.
Introduction
optoelectronic devices because of their electrooptical pro-
perties,1 especially their luminescence. Beyond that, they
serve as building blocks for nanoscopic molecules2,3 on
account of their rodlike structure together with their good
accessibility. In recent years, much time and effort has been
devoted to the development of strategies to retain the optical
Oligo- and poly(p-phenyleneethynylene)s (oligoPPEs,
polyPPEs) attract interest as materials for electronic and
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DOI: 10.1021/jo9009744
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Maag et al.
JOCArticle
properties of dilute solutions when going to the undiluted,
solid compounds.1f,4-8 One of the approaches uses the
bulkiness of iptycenes to keep the π-systems of polyPPEs
at a distance from each other: Benzene units were substituted
for triptycene and/or pentiptycene ones.5 Considering the
success of this concept, it is surprising that it was hardly
applied to oligomers.9,10 We know of only one report on a
series of oligomers with iptycene units.10 It describes the
synthesis and properties of “all-pentiptycene” oligoPPEs,
i.e., oligoPPEs with up to four repeating units in which all of
the benzene units are substituted for pentiptycene moieties
and with one alkoxy substituent at each of the two termini of
the oligomer backbone. Attempts to go beyond four repeat-
ing units were unsuccessful. Further fundamental studies on
the properties of polyconjugated molecules as well as their
use as construction units require an access to even longer,
monodisperse iptycene containing oligoPPEs with reactive
functional groups at their ends. Herein we describe a strategy
for the preparation of monodisperse oligoPPEs 8an in which
every second benzene unit is exchanged against a 1,4-tripty-
cene unit. All oligomers 8an have two orthogonally pro-
tected, terminal ethynyl groups.11 This allows for selective
deprotection and independent use of these two functional
groups in further derivatization, e.g., coupling with 1-al-
koxy-4-iodobenzene and alkyne dimerization (results not
shown).3a,12,13
SCHEME 1. Synthesis of the Key Iptycene Building Blocks 5a
and 6a
In the following section, first, the synthesis of the key
building block 5a, a 1,4-diethynyltriptycene with one TIPS
and one TMS protecting group, and the preparation of
triptycene-containing oligomers 8n are described. Second,
the key step toward a more rapid oligomer synthesis via
a strictly divergent-convergent synthesis with the prepara-
tion of triptycene 6 is presented. Triptycene 6 differs from
(4) (a) Frampton, M. J.; Anderson, H. L. Angew. Chem. 2007, 119, 1046–
1083. (b) Angew. Chem., Int. Ed. 2007, 46, 1028-1064. (c) Shi, Z.-F.; Wang,
L.-J.; Wang, H.; Cao, X.-P.; Zhang, H.-L. Org. Lett. 2007, 9, 595–598. (d) Zhao,
C.-H.; Wakamiya, A.; Yamaguchi, S. Macromolecules 2007, 40, 3898–3900.
(e) Englert, B. C.; Smith, M. D.; Hardcastle, K. I.; Bunz, U. H. F. Macromolecules
2004, 37, 8212–8221. (f) Masuo, S.; Yoshikawa, H.; Asahi, T.; Masuhara, H.;
Sato, T.; Jiang, D.-L.; Aida, T. J. Phys. Chem. B 2003, 107, 2471–2479. (g) Sato,
T.; Jiang, D.-L.; Aida, T. J. Am. Chem. Soc. 1999, 121, 10658–10659.
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C.; Rumbles, G.; Ryan, J. F.; Anderson, H. L. J. Chem. Soc., Perkin Trans. 1
1998, 2383–2398.
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J.; Swager, T. M. Macromolecules 2008, 41, 5559–5562. (c) Yang, J.-S.; Yan,
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Langmuir 2007, 23, 112–115. (e) Zhao, D.; Swager, T. M. Org. Lett. 2005,
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11864–11873. (h) Application to polymers with fluorene moieties in the main
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M. Macromolecules 2007, 40, 2380–2391. (b) Mikroyannidis, J. A. Macro-
molecules 2002, 35, 9289–9295. (c) Bao, Z.; Amundson, K. R.; Lovinger, A. J.
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3296–3301.
aFor simplicity, the compounds are shown as one distinct enantiomer or
diastereomer.
5a by the 3-hydroxybut-1-ynyl instead of the TMS-ethy-
nyl substituent. Finally, the optical properties of 8an in
solution and solid state are compared with those of the
corresponding iptycene-free oligo(2,5-dihexyl-1,4-phenylene-
ethynylene)s (11n).
(9) (a) Long, T. M.; Swager, T. M. J. Am. Chem. Soc. 2002, 124, 3826–
3827. (b) Long, T. M.; Swager, T. M. J. Mater. Chem. 2002, 12, 3407–3412.
(10) Yang, J.-S.; Yan, J.-L.; Hwang, C.-Y.; Chiou, S.-Y.; Liau, K.-L.;
Tsai, H.-H. G.; Lee, G.-H.; Peng, S.-M. J. Am. Chem. Soc. 2006, 128, 14109–
14119.
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Jeschke, G. J. Org. Chem. 2000, 65, 7575–7582.
Results and Discussion
Synthesis of the Key Building Block 1,4-Diethynyltripty-
cene 5a. The synthesis of diethynyltriptycene 5a (Scheme 1)
starts with a Diels-Alder reaction between 1,4-benzoqui-
none and 2,6-di-tert-butylanthracene. 1,4-Benzoquinone
acts additionally as an oxidant to provide triptycenequinone
(13) Ziener, U.; Godt, A. J. Org. Chem. 1997, 62, 6137–6143.
7734 J. Org. Chem. Vol. 74, No. 20, 2009

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1 directly.14 Triptycenequinone 1 turned out to be extremely
light sensitive. Even the short time needed to set up an
experiment is sufficient to produce photoreaction products
in amounts detectable by NMR spectroscopy and thin-layer
chromatography. The 1,2-addition of 2-trialkylsilylethynyl-
lithium to triptycenequinone 117 gave compounds 2 which
were converted into the phenols 3 through treatment with
zinc in acetic acid.10 The corresponding triflates 4, obtained
from the reaction of phenols 3 with triflic anhydride,18 were
coupled with trialkylsilylethyne under Pd/Cu catalysis to
yield the diethynyltriptycene 5a, the key building block for
the synthesis of the oligomers 8n.
conversionsinorder toavoidthe sidereactionis no solution to
this problem because the starting compound 4a and the
coupling product 5a are also very difficult to separate through
chromatography. Luckily, no such problem occurred in the
coupling of triflate 4b with TIPS-ethyne. The amount of side
products was much smaller, and side products as well as
residual starting compound, triflate 4b, could be removed
through chromatography. Thus, route B is clearly to be
preferred as compared to route A.
An attractive alternative to obtain 1,4-diethynyltriptycene
5a appears to be a reaction sequence in which first both
ethynyl substituents are introduced in one pot by two sub-
sequent 1,2-additions to quinone 1, followed by the reduc-
tion/water elimination procedure as described in the
literature for benzoquinone, naphthoquinone, and anthra-
quinone.17,22 The outcome of experiments to obtain 5a using
such a route is discouraging: The second 1,2-addition shows
very low conversion (<50%) and additionally the formation
of side products.
The reaction of 2-trimethylsilylethynyllithium or 2-triiso-
propylsilylethynyllithium with quinone 1 resulted in a mix-
ture of two diastereomers in a ratio of 1.0:2.3 and 1.0:2.5,
respectively. The ratios were constant throughout all of our
several experiments. The next step to obtain the phenols 3, the
reduction of the addition products 2 with concomitant elim-
ination of water, proceeded smoothly when zinc in acetic acid10
5g,19
Synthesis of the Triptycene-Containing Oligomers 8n.
Selective alkyne deprotection and Pd/Cu-catalyzed alky-
nyl-aryl coupling were used to assemble the oligomer series
8an (Scheme 2). The first member of this series, 8a1, was
obtained through coupling of aryliodide 9 with alkyne 5b, the
latter being the product of selective desilylation of 1,4-di-
ethynyltriptycene 5a. The syntheses of the longer oligomers
8an with n > 1 is based on alternating desilylation of 8an and
coupling of the resulting alkynes 8bn with iodo monomer 7.
Whereas our standard coupling conditions for oligoPPE
synthesis,11,13 i.e., Pd(PPh3)2Cl2 and CuI in piperidine and
THF at room temperature, worked well for the preparation of
8a1 (88%) and 8a2 (70%), they gave unsatisfying yields of 8a3
(40%). An influence of the length of oligoPPEs on the
conversion in coupling reactions had been found, too, in the
preparation of oligo(2,5-dihexyl-1,4-phenyleneethynylene)s
(11n).11 In that case, longer oligoPPEs were obtained in good
yields, when Pd(PPh3)2Cl2 was exchanged for Pd2(dba)3/PPh3.
For the triptycene-containing oligoPPEs improved yields
(89% of 8a2, 71% of 8a3, 77% of 8a4) were finally achieved
by using comparatively large amounts of the catalysts
Pd(PPh3)4 (10 mol %) and CuI (60 mol %) in diisopropyla-
mine and toluene at 60 °C similar to a procedure described by
Swager.5g Applying such large amounts of Pd(PPh3)4 is
not only costly but brings along separation problems: Very
was employed. Less successful was the use of SnCl2
in-
stead of Zn. In the case of 2b, hardly any phenol 3b was
obtained. Instead, 1-acetyl-6,14-di-tert-butyl-4-hydroxytrip-
tycene and 1-ethynyl-6,14-di-tert-butyl-4-hydroxytriptycene
were obtained together with minor amounts of unidentified
products. The former product must have been formed through
desilylation of 3b and subsequent addition of water. This is in
agreement with the findings from Fukaminato et al.20 who
reported that desilylation occurred when SnCl2 was used.
Desilylation was not reported in another publication where
SnCl2 was applied to similar compounds.5g The conversion of
the TIPS analogue 2a into phenol 3a with SnCl2 proceeded
cleanly, however, the workup was much more tedious than
when applying zinc.
The last step, the coupling of the triflates 4 with alkynes,
turned out to be a high hurdle. To find conditions which gave
acceptable to good conversion of the triflates 4a and 4b,
numerous experiments were necessary in which the type and
amount of Pd catalyst [Pd(PPh3)2Cl2, Pd(PPh3)4, Pd2(dba)3,
Pd(dba)2] the amount of CuI, the typeof base (Et3N, iPr2NH),
solvent (THF, DMF, toluene), and additives (Bu4NBr, Bu4-
NI, KI, PPh3), and the reaction temperature (60-110 °C)
were varied21 (Supporting Information, Table S2). Unfortu-
nately, when the reaction was driven to high conversion, the
coupling oftriflate4awithTMS-ethyneis accompanied by the
formation of a byproduct, probably a carbometalation pro-
duct as suggested by mass spectral data. Chromatographic
removal of this byproduct was unsuccessful. Accepting lower
careful column chromatography and in the case of 8a2
a
subsequent precipitation with methanol from a solution in
CH2Cl2 were required to obtain products free of triphenylpho-
sphane oxide.
The iodo monomer 7 was prepared through Pd/Cu-cata-
lyzed coupling of alkyne 5b with diiodobenzene 10. Despite
a huge excess of diiodobenzene 10 (7 molar equiv), dicou-
pling product (both iodo substituents of 10 coupled with
the alkyne 5b) was formed. The chromatographic separation
of 7 from diiodobenzene 10, dicoupling product, and the
oxidative alkyne dimerization (Glaser coupling) product
of alkyne 5b was facile because the di-tert-butyl-substituted
triptycylene unit influences the chromatographic beha-
vior drastically (Rf (10) = 0.68, Rf (7) = 0.49, Rf (disubstitu-
tion product and product of oxidative dimerization of alkyne
(14) (Slightly) different syntheses for triptycenequinone 1 were described
in refs 15 and 16.
(15) Long, T. M.; Swager, T. M. J. Am. Chem. Soc. 2003, 125, 14113–
14119.
(16) Nesterov, E. E.; Zhu, Z.; Swager, T. M. J. Am. Chem. Soc. 2005, 127,
10083–10088.
ꢀ
(17) (a) Lydon, D. P.; Porres, L.; Beeby, A.; Marder, T. B.; Low, P. J. New
J. Chem. 2005, 29, 972–976. (b) Sankararaman, S.; Srinivasan, M. Org.
Biomol. Chem. 2003, 1, 2388–2392.
(18) Bao, Z.; Chan, W. K.; Yu, L. J. Am. Chem. Soc. 1995, 117, 12426–
12435.
(19) Payne, M. M.; Parkin, S. R.; Anthony, J. E. J. Am. Chem. Soc. 2005,
127, 8028–8029.
(20) Fukaminato, T.; Sasaki, T.; Kawai, T.; Tamai, N.; Irie, M. J. Am.
Chem. Soc. 2004, 126, 14843–14849.
(21) (a) Powell, N. A.; Rychnovsky, S. D. Tetrahedron Lett. 1996, 37,
7901–7904. (b) Zhu, Z.; Swager, T. M. J. Am. Chem. Soc. 2002, 124, 9670–
9671. (c) Zhu, Z.; Swager, T. M. Org. Lett. 2001, 3, 3471–3474.
(22) de Meijere, A.; Zhao, L.; Belov, V. N.; Bossi, M.; Noltemeyer, M.;
Hell, S. W. Chem.;Eur. J. 2007, 13, 2503–2516.
J. Org. Chem. Vol. 74, No. 20, 2009 7735

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SCHEME 2. Syntheses of Oligomers 8an with Alternating 1,4-Phenylene and 1,4-Triptycylene Unitsa
aFor simplicity, the compounds are shown as one distinct enantiomer or diastereomer, and the oligomers 8an and 8bn are presented with only one specific
tacticity. All desilylations went to completion according to 1H NMR spectra. The yields of desilylation products are not given because the accompanying
trialkylsilyl compounds such as trialkylsilanol, hexaalkyldisiloxane, and trialkylsilyl fluoride were only partially removed.
5b) = 0.24 for n-pentane/Et2O 80:1, silica gel). This finding is
remarkable in light of our experience with oligoPPEs 11n. In
the latter case, two oligomers are (nearly) inseparable by
standard column chromatography, even if they differ by
several, e.g., four, repeating units.23
example of a triptycene with two differently protected ethy-
nyl substituents.5g,21b,c Selective removal of the TMS
group allows the two alkyne groups to be addressed inde-
pendently in subsequent reactions, e.g., for the formation
of the monodisperse oligomers 8an. However, the growth of
the oligomers 8an starting with diethynyltriptycene 5a is
slow: One repeating unit after the other is attached. For
much more rapid growth via a divergent-convergent
process, a 1,4-diethynyltriptycene with orthogonal alkyne
Synthesis of 1,4-Diethynyltriptycene 6 with Orthogonally
Protected Alkyne Groups. Diethynyltriptycene 5a is the first
(23) Ramezanian, N. Promotionsarbeit, Bielefeld University, 2007.
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FIGURE 1. (a) Structural formula of oligomer 119. (b) UV/vis (left) and fluorescence spectra (right) (excitation at 305 nm) of 8a4 in CHCl3
( - ) and in a pristine dropcast film (;) and of 119 in CHCl3 (---) and in a pristine dropcast film ( ).
3 3
3 3 3
protecting groups, such as triisopropyl and 1-hydroxyalkyl
(Scheme 1),11 is desired. We selected the 1-hydroxyethyl
group instead of the hydroxymethyl group because in com-
parison to the latter the 1-hydroxyethyl group inhibits or at
least drastically reduces the Pd-catalyzed addition of a
terminal alkyne to the ethynylene moiety.24,25 The 1-hydro-
xyethyl group can be removed as smoothly as the hydro-
xymethyl group using γ-MnO2/powdered KOH.25 Even
though the coupling of triflate 4a with but-3-yn-2-ol pro-
ceeded to completion and only a small amount of side
Comparison of Optical and Thermal Properties of Oligo-
mers 8an and OligoPPEs 11n. The UV/vis and fluorescence
spectra of diethynyltriptycene 5a and the oligomers 8an
(Figure S1 in the Supporting Information and Figure 1) in
dilute solution strongly resemble those of the corresponding
oligoPPEs 11n.11 The absorption bands of 5a and 8a1 show
distinct vibrational fine structures, the absorption bands of
the longer oligomers 8a2-4 are broad and featureless, and all
emission spectra exhibit vibrational fine structures. The
longer the backbone the more bathochromic the shift with
a linear relation between the absorption energy and the
reciprocal number of phenylene moieties (Figure S2 in the
Supporting Information).11,29
In order to investigate the effect of the di-tert-butyl-
substituted triptycene moiety on the intermolecular electro-
nic interaction, the optical spectra of solid films of iptycene
containing oligoPPE 8a4 and iptycene-free oligoPPE 119
were recorded (Figure 1). These two compounds have the
same end groups and have nearly the same length. The films
were drop-cast onto quartz from dilute solutions in chloro-
form and dried at room temperature. The transition of
oligoPPE 119 from a dilute solution into the solid state is
accompanied by drastic changes in the absorption and
emission spectra: A bathochromic shift of the absorption
maximum by 13 nm, an additional absorption band at 433
nm, and instead of the narrow emission band with vibra-
tional fine structure that was found for dissolved 119, a broad
emission band at long wavelengths (λmax = 499 nm). The
same type of changes was found for the structurally related
poly(2,5-didodecyl-1,4-phenyleneethynylene) (12)30 and
polyPPEs with other simple alkyl substituents:31 A bath-
ochromic shift of 26 nm, an additional absorption band
at 450 nm, and a broad emission band (λmax = 540 nm).
1
product was formed, as judged from the H NMR spec-
trum of the crude product, repeated chromatography was
needed to remove dibenzylideneacetone, the ligand of the
Pd catalyst, and two side products, most probably 6,14-di-
tert-butyl-1-(3-oxobut-1-enyl)-4-(2-triisopropylsilylethynyl)-
triptycene and 6,14-di-tert-butyl-1-(3-oxobut-1-ynyl)-4-
(2-triisopropylsilylethynyl)triptycene.26 For the formation
of the former, a base-induced isomerization of the 3-hydrox-
ybut-1-ynyl substituent is assumed.28 The difficulties in
isolation may have contributed to the disappointingly low
yield of 40% of isolated pure product 6.
(24) Such a side reaction was described for the Pd/Cu-catalyzed coupling
of 1,4-dihexyl-5-(3-hydroxyprop-1-ynyl)-2-iodobenzene with TIPS-ethyne
in ref 11.
(25) Schulte, M.; Sahoo, D.; Godt, A. Manuscript in preparation.
(26) Neither of these two side products were obtained as pure products.
Nevertheless, the following signals in the 1H NMR spectra from chromato-
graphic fractions containing these products give sufficient hints that these
side products were formed. The yields of these side products is estimated to be
below 5%. Characteristic signals of 6,14-di-tert-butyl-1-(3-oxobut-1-enyl)-
4-(2-triisopropylsilylethynyl)triptycene: 1H NMR (250 MHz, CDCl3) δ =
8.17 (d, J = 16.0 Hz, 1H, CHdCH-Ac), 7.20 and 7.11 (AB spinsystem, J =
8.4 Hz, 1H each, He), 6.71 (d, J = 16.0 Hz, 1H, CHdCH-Ac), 6.00 and 5.86
(2 s, 1 H each, Hd), 2.45 (s, 3 H, COCH3). Compare these data with the
reported NMR data for dibenzylideneacteone in ref 27. Characteristic signals of
6,14-di-tert-butyl-1-(3-oxobut-1-ynyl)-4-(2-triisopropylsilylethynyl)tripty-
cene: 1H NMR (250 MHz, CDCl3) δ = 7.11 and 7.07 (AB spinsystem, J =
8.1 Hz, 1H each, He), 5.93 and 5.79 (2 s, 1 H each, Hd), 2.56 (s, 3 H, COCH3).
(27) Iwata, M.; Emoto, S. Bull. Chem. Soc. Jpn. 1976, 49, 1369–1374.
(28) (a) Arcadi, A.; Cacchi, S.; Marinelli, F.; Misiti, D. Tetrahedron Lett.
1988, 29, 1457–1460. (b) Minn, K. Synlett 1991, 115–116. (c) Coelho, A.;
(29) (a) Tolbert, L. M. Acc. Chem. Res. 1992, 25, 561–568. (b) Kuhn, W.
Helv. Chim. Acta 1948, 106, 1780–1799. (c) Kuhn, W. J. Chem. Phys. 1949,
17, 1198–1212.
(30) Bunz, U. H. F.; Imhof, J. M.; Bly, R. K.; Bangcuyo, C. G.; Rozanski,
L.; Vanden Bout, D. A. Macromolecules 2005, 38, 5892–5896.
(31) Halkyard, C. E.; Rampey, M. E.; Kloppenburg, L.; Studer-Marti-
nez, S. L.; Bunz, U. H. F. Macromolecules 1998, 25, 8655–8659.
~
Sotelo, E.; Ravina, E. Tetrahedron 2003, 59, 2477–2484. (d) M€uller, T. J. J.;
Ansorge, M.; Aktah, D. Angew. Chem. 2000, 112, 1323-1326; (e) Angew.
Chem., Int. Ed. 2000, 39, 1253-1256.
J. Org. Chem. Vol. 74, No. 20, 2009 7737

Maag et al.
JOCArticle
Therefore, we consider the explanation for the optical
changes of the polymers to be valid for oligoPPE 119
and assign the additional absorption band of solid oligo-
PPE 119 to an increased planarization of the conjugated
backbone30,32 and the broad emission band to excimer
formation.30,33 Compared with oligoPPE 119, the iptycene-
containing oligoPPE 8a4 behaves quite differently. Upon
film formation from solution the absorption maximum is
red-shifted by only 4 nm, and no separated, additional
absorption band appears. The broadening of the absorption
band at the red edge which results in an absorption onset at
about 450 nm for the film (compare this with the onset at 430
nm for the solution) and the weakly developed shoulder at
around 430 nm indicate that upon film formation the con-
jugated backbone of 8a4 is planarized, however, to a much
smaller extent than that of 119. The emission spectra of both
oligomers 119 and 8a4 display a broad emission band at very
long wavelengths (λmax(8a4) = 487 nm; λmax(119) = 499 nm)
and, thus, disclose excimer formation for both compounds.
However, there is a striking difference between the emission
of 8a4 and 119. Whereas the red edge of the emission bands of
119 and 8a4 looks essentially identical, below 500 nm the
emission band of 8a4 is broader by about 30 nm. The
emission at shorter wavelengths may be the emission of
excimers of different structure, such as excimers with larger
intermolecular distances34 or with conformationally more
twisted backbones. It may also be interpreted as the emission
of individual oligomers. The missing of the 0f0 transition
for this emission would be explained with the reabsorption
effect in optically dense materials.
Obviously, the di-tert-butyltriptycene moieties profound-
ly influence the solid-state optical properties. They largely
inhibit packing induced planarization of the conjugated
backbone. How strong an influence they exert on the inter-
chain electronic interaction, especially in comparison to
unsubstituted triptycene and pentiptycene,5g,f cannot be
deduced from our study. Swager et al. concluded from a
comparative study on polyPPEs with alternating 2,5-dia-
lkoxy-1,4-phenylene and 1,4-triptycylene or 1,4-pentiptycy-
lene units that the iptycene moieties sequester the conjugated
backbones with pentiptycene being the much more effective
unit.5g,f Unfortunately, the optical data of those polymers
cannot be compared to the ones of oligomers 8n because the
thin film optical properties of polyPPEs with alkoxy side
chains and polyPPEs with alkyl side chains differ significan-
tly.1a,35 The “all-pentiptycene” oligoPPEs reported by Yang
et al.10 are not a good reference, either, because the end
groups play a distinctive role, too: Terminal, barely substi-
tuted benzene rings as in 8n can act as electronic mediators
between the individual molecules in solid state.10,37 Further
insight may be gained from oligomers such as 8n, but with
triptycene units at both ends.
FIGURE 2. UV/vis and fluorescence spectra (excitation at 305 nm)
of a drop-cast film of 8a4 before (;) and after (
at 300 °C.
- ) annealing
3 3 3 3
Bunz et al. showed that the annealing of the spin-cast film
of polymer 12 changes the intensity ratio of the two absorp-
tion maxima in favor of the “planarization” band at 450 nm,
i.e., increases the degree of coplanarity of the phenylene
moieties.30 Furthermore, annealing reduces the excimer
emission and leads to strong additional emission at shorter
wavelengths from individual chains.30 In contrast to these
findings,38 annealing a film of oligomer 8a4 at 300 °C (mp ∼
270 °C) resulted in minute changes (Figure 2): A blue-shift by
around 7 nm of the absorption and emission maxima and a
vanishing of the red edge shoulder of the absorption band.
Both features indicate that annealing leads to an increase of
twisted conformations at the expense of coplanar alignment
of the backbone forming phenylene units. A driving force for
this could be that a better space filling packing is gained. The
assumption of different packing in a pristine and an annealed
film is corroborated by the thermal behavior of oligomer 8a4.
Visual inspection reveals that the material sinters at 160 °C
(possibly the melting of the hexyl side chains) and melts at
267-270 °C. Corresponding endothermic transitions at 158,
260, and 267 °C were detected with DSC during the first
heating run. No thermal transition was detectable by DSC
during cooling or heating the same sample a second time.
However, the solid/fluid transition at around 270 °C could be
repeated several times with the same sample on a heating
stage. Most probably, upon cooling the melt, oligomer 8a4
forms a glass whose Tg stayed undetected by DSC because
there is too small a change in heat capacity at Tg. This
assumption fits the observation that the melt of 8a4 is highly
viscous, much more viscous than a melt of 119. In stark
contrast, DSC curves of oligoPPE 119 exhibit an easily
(38) A much better comparison would be with an annealed film of
oligoPPE 119, but this material in thin films decomposed when heated.
OligoPPE 119 shows a reproducible melting and crystallization transition in
subsequent DSC runs. Moreover, the 1H NMR spectrum of a sample that
had been used in three consecutive DSC runs, twice up to 200 °C and once up
to 300 °C, showed no indication of decomposition. However, annealing a
film of oligoPPE 99 at 200 °C overnight gave a brownish film which showed
very minute fluorescence and was only partially dissoluble in CHCl3.
Solution UV/vis and fluorescence spectra taken from the dissolved part bore
no resemblance to the spectra recorded from pristine material. In contrast to
this, the film of oligomer 8a4 proved to be thermally stable, even at much
higher temperature (300 vs 200 °C). The emission spectra of the dissolved
annealed film;the film was completely dissolvable;and of thermally
untreated material were identical.
(32) Miteva, T.; Palmer, L.; Klopenburg, L.; Neher, D.; Bunz, U. H. F.
Macromolecules 2000, 33, 652–654.
(33) Li, D.; Powell, D. R.; Firman, T. K.; West, R. Macromolecules 1998,
31, 1093–1098.
(34) Thomas, R.; Varghese, S.; Kulkarni, G. U. J. Mater. Chem. 2009, 19,
4401–4406.
(35) Compare data of oligo(2,5-dialkoxy-1,4-phenyleneethynylene)s (refs
10 and 36) and oligo(2,5-dialkyl-1,4-phenyleneethynylene)s (refs 30 and 31).
(36) Weder, C.; Wrighton, M. S. Macromolecules 1996, 29, 5157–5165.
(37) Pu, K.-Y.; Qi, X.-Y.; Yang, Y.-L.; Lu, X.-M.; Li, T.-C.; Fan, Q.-L.;
Wang, C.; Liu, B.; Chan, H. S. O.; Huang, W. Chem.;Eur. J. 2008, 14, 1205–
1215.
7738 J. Org. Chem. Vol. 74, No. 20, 2009

Maag et al.
JOCArticle
detectable melting and recrystallization peak, also when
repeating the heating/cooling cycle with the same sample.
It is not surprising that the bulky, conformationally rigid
di-tert-butyltriptycene units inhibit crystallization of the
oligomers 8n.
Conclusions and Outlook
A synthesis for monodisperse oligoPPEs with alternating
1,4-phenylene and 1,4-triptycylene units has been developed.
The two terminal ethynyl groups are orthogonally protected,
which allows for an independent derivatization of both
terminal groups. Additionally, a way to synthesize the ortho-
gonally protected 1,4-diethynyltriptycene 6 was found. In
combination with the diiodo compound 10 or 1,4-diiodo-
triptycene39 this 1,4-diethynyltriptycene 6 opens the door for
a stringent divergent-convergent synthesis of the oligomers
8an and “all triptycene” oligoPPEs, respectively, in analogy
to the synthesis of oligoPPEs 11n.11 The di-tert-butyltripty-
cene moieties hamper crystallization from the melt and
planarization of the conjugated backbone in solid films.
They also impact the electronic interaction between indivi-
dual oligomers.
FIGURE 3. Labeling of atoms for the assignment of NMR signals.
In this drawing, neither the possibility of isomers differing in their
tacticity nor other configurational isomerism is taken into account.
The NMR spectra give no hint that the proton or carbon resonances
are sensitive to the tacticity.
are assigned to the region int, ext-Si, and ext-OH. For quoting
the shifts of the protons He, which form an AB spinsystem, the
middle position between the two signals of A and the middle
position between the two signals of B is given despite the distinct
roof effect.
MALDI TOF mass spectra were recorded with a Voyager
DE Instrument mounted with a 1.2 m flight tube. Ionization
was achieved using a LSI nitrogen laser (337 nm beam wave-
length, 3 ns pulse width, 3 Hz repetition rate). Depending on
the mass range, the ions were accelerated with 15 to 20 kV.
If not mentioned differently, 2-[(2E)-3-(4-tert-butylphenyl)-
2-methylprop-2-enylidene]malononitrile41 was used as the mat-
rix and THF as solvent to prepare the samples. EI mass
spectra were recorded using an Autospec X magnetic sector
mass spectrometer with EBE geometry equipped with a
standard EI source (70 eV). Ions were accelerated by 8 kV. With
both MS-techniques, MALDI TOF, and EI, cations were
detected.
Experimental Section
General Methods. THF was dried over sodium/benzophe-
none. Piperidine was distilled from CaH2. Pyridine was pur-
chased from Merck in SeccoSolv quality and used as received.
γ-MnO2,40 1,4-dihexyl-2,5-diiodobenzene (10),11 and 1,4-dihex-
yl-2-(3-hydroxyprop-1-ynyl)-5-iodobenzene (9)11 were pre-
pared according to the literature.
If not mentioned otherwise, the reactions were carried out
under an argon atmosphere using the Schlenk technique. The
solvents or solutions were degassed through at least three free-
ze-pump-thaw cycles.
Thin-layer chromatography was performed with silica gel
coated aluminum foils (Merck, 60 F254). Spots were detected
using a UV lamp (λ = 254 nm and/or 366 nm). Chromatogra-
phy was carried out under slight pressure using silica gel (Merck,
40-63 μm, or Acros, 35-70 μm). If not mentioned otherwise,
the crude product was adsorbed onto a small quantity of silica
gel by dissolving it in CH2Cl2, adding silica gel to this solution,
and removing the solvent (40 °C, reduced pressure). The result-
ing fine, freely flowing powder was added on top of a silica gel
column through pouring it into the small amount of solvent
which overlaid the silica gel.
Solvents were removed at 40 °C and reduced pressure using a
rotary evaporator. Toward the end of solvent removal, most of
the materials form a voluminous solid foam abruptly. In most
cases, the material used for analytical purposes was freeze-dried
from benzene to remove residual solvent which was tenaciously
adhering to the compound.
The UV/vis spectra and emission spectra were obtained from
solutions in CHCl3 (5-6 μmol/L). For the recording of UV/vis
spectra of drop cast films on quartz an integrating sphere
(Ulbricht sphere) was used.
Synthesis of the Triptycene Building Blocks 5b and 6.
1,2-Adduct 2b. The glassware was flame-dried before use. A
solution of n-butyllithium in hexane (1.6 M, 22 mL, 35 mmol)
was added to a solution of trimethylsilylethyne (4.5 mL, 31
mmol) in THF (60 mL) at -78 °C. After the reaction mixture
was stirred at -78 °C for another 15 min, this solution of
trimethylsilylethynyllithium was added dropwise over a period
of 20 min to a solution of triptycenequinone 1 (10.4 g, 26.2
mmol) in THF (80 mL) at -78 °C. The color of the solution
changed immediately from orange to turquoise. After the reac-
tion mixture was stirred at -78 °C for 2 h, Et2O and water were
added to the cold reaction mixture, the phases were separated,
the aqueous phase was extracted with Et2O, and the combined
organic phases were washed with a saturated aqueous solution
of NH4Cl and dried over MgSO4. Removal of solvent gave a
beige-orange solid, which was dissolved in a minimum amount
of CH2Cl2. This solution was applied to a chromatography
column. Chromatography (solvent gradient CH2Cl2 f CH2Cl2/
Et2O 20:1f CH2Cl2/Et2O 10:1) gave first a mixture of
the starting quinone 1 and unidentified byproducts (2.17 g,
Rf(n-pentane/Et2O 5:2) = 0.58, 0.50), second the 1,2-adduct
2b (8.55 g, 66%; Rf(n-pentane/Et2O 5:2) = 0.27) as a
yellow-beige solid, and finally a mixture (1.13 g, Rf(n-pentane/
Et2O 5:2) = 0.27, 0.19) of the 1,2-adduct 2b and a product that
had resulted from a 1,2-addition of BuLi to starting compound
quinone 1. The product 2b consisted of two diastereomers D1
Melting points were determined in open capillaries and
are not corrected. The NMR spectra were recorded at 30 °C
(250 MHz instrument) and at 27 °C (500 MHz instrument) using
the solvent as an internal standard. Carbon multiplicity was
determined by a DEPT-135 experiment, and as mentioned with
the individual experiments, HMQC spectra were measured to
support signal assignment. For signal assignment, atoms are
labeled as shown in Figure 3. The atoms of compounds 1-6 are
labeled analogously. If a differentiation is possible, the atoms
(39) Ohira, A.; Swager, T. M. Macromolecules 2007, 40, 19–25.
(40) Burke, S. D., Danheiser, R. L., Eds. Handbook of Reagents for
Organic Synthesis, Oxidizing and Reducing Reagents; Wiley: Chichester,
2004; p 232.
(41) Ulmer, L.; Mattay, J.; Torres-Garcia, H. G.; Luftmann, H. Eur. J.
Mass Spectrom. 2000, 6, 49–52.
J. Org. Chem. Vol. 74, No. 20, 2009 7739

Maag et al.
JOCArticle
and D2 in a ratio of approximately 2:1. Analytical data of 1,2-
adduct 2b: 1H NMR (500 MHz, CD2Cl2) signals of diastereomer
D1: δ = 7.48 and 7.44 (2 d, 4J = 1.7 Hz, 1 H each, Ha), 7.332 (d, 3J
= 8 Hz, 1 H of D1, Hc of D1 and D2), 7.31 (d, 3J = 8 Hz, 1 H, Hc),
7.06 (dd, 3J =7.7Hz, 4J= 1.8Hz, 1 H, Hb), 7.03 (dd, 3J=7.7Hz,
4J = 1.8 Hz, 1 H of D1, Hb of D1 and D2), 6.68 (d, 3J = 9.9 Hz, 1
H, He), 6.01 (broadened d, 3J = 9.9 Hz, 1 H of D1, He of D1 and
D2), 5.70 (s, 1 HofD1, Hd of D1 and D2), 5.54 (s, 1 H, Hd), 2.52 (s,
1H of D1, OH of D1 and D2), 1.265 (1 s, 18 H, C(CH3)3), 0.18 (s, 9
H, Si(CH3)3); signals of diastereomer D2: δ = 7.46 and 7.43 (2 d,
4J = 1.7 Hz, 1 H each, Ha), 7.332 (d, 3J = 8 Hz, 1 H of D2, Hc of
D1 and D2), 7.326 (d, 3J = 8 Hz, 1 H, Hc), 7.08 (dd, 3J = 7.7 Hz,
4J = 1.8 Hz, 1 H, Hb), 7.03 (dd, 3J = 7.7 Hz, 4J = 1.8 Hz, 1 H of
(Ci or CkOTf), 143.8 (Ch para to tBu), 141.8 and 140.9 (Ch meta to
tBu), 138.7 (Ci or CkOTf), 130.1 (Ce ortho to CtC), 124.2 and
123.9 (Cc), 122.9 and 122.8 (Cb), 122.1 and 121.7 (Ca), 119.21
(CkCtCSiMe3), 119.16 (q, 1J = 321.0 Hz, CF3), 118.3 (Ce ortho
to OTf), 101.3 and 100.4 (CtC), 52.4 and 48.5 (Cd), 34.95 and
34.92 (CMe3), 31.6 (C(CH3)3), 0.1 (SiMe3); MS (EI) m/z = 610.16
(100) [M]þ, 595.13 (74). Anal. Calcd for C34H37F3O3SSi (610.813):
C, 66.86; H, 6.11. Found: C, 66.89; H, 6.13.
Diethynyltriptycene 5a Starting from Triflate 4b. To a de-
gassed yellowish solution of triflate 4b (4.01 g, 6.56 mmol)
and triisopropylsilylethyne (2.2 mL, 9.7 mmol) in (i-Pr)2NH
(100 mL) were added Pd(PPh3)4 (0.38 g, 0.33 mmol), CuI (1.25 g,
6.56 mmol), and n-Bu4NBr (6.35 g, 19.7 mmol). The brown
reaction mixture was stirred at 95 °C for 19 h, and then most of
the solvent (about 90 mL) was distilled off (125 °C, 1 atm) and
Et2O, CH2Cl2, and water were added to the residue. The phases
were separated, the aqueous phase was extracted with a mixture
of Et2O/CH2Cl2, and the combined organic phases were washed
with 2 N HCl and brine, and dried over MgSO4. Removal of the
solvent gave a brown solid containing the starting material
triflate 4b and diethynyltriptycene 5a in a ratio of 1.0:2.4 (1H
NMR spectroscopically determined). Column chromatography
(n-pentane/CH2Cl2 10:1) gave diethynyltriptycene 5a (2.39 g,
57%; Rf=0.39) and triflate 4b (1.14 g, 28%; RF=0.25), con-
taminated with a small amount of diethynyltriptycene 5a as
beige solids.
3
D2, Hb of D1 and D2), 6.69 (d, J = 9.9 Hz, 1 H, He), 6.01
(broadened d, 3J = 9.9Hz, 1 H of D2, He of D1 and D2), 5.70 (s, 1
H of D2, Hd of D1 and D2), 5.53 (s, 1H, Hd), 2.52 (s, 1H of D1,
OH of D1 and D2), 1.273 and 1.25 (2 s, 9 H each, C(CH3)3), 0.20
(s, 9 H, Si(CH3)3); HRMS (MALDI) m/z = 494.26348, calcd for
C33H38O2Si (494.26356). Anal. Calcd for C33H38O2Si (494.751):
C, 80.11; H, 7.74. Found: C, 79.90; H, 7.98.
Phenol 3b. To a solution of 1,2-adduct 2b (8.55 g, 17.3 mmol)
in THF (p.a., 120 mL) cooled with a NaCl/ice bath were added
zinc powder (5.66 g, 86.5 mmol) and glacial acetic acid (120 mL).
The resulting green-gray suspension was allowed to warm to
room temperature. After 17.2 h of stirring the reaction mixture
at room temperature, Et2O and water were added and residual
zinc was filtered off. The phases were separated, the aqueous
phase was extracted with Et2O, and the combined organic
phases were washed several times with a saturated aqueous
solution of NaHCO3 and dried over MgSO4. Removal of the
solvent yielded a slightly yellow solid. Column chromatography
(n-pentane/Et2O 3:2) yielded phenol 3b (7.0 g, 85%; Rf = 0.33)
as a slightly beige solid. Ahead of this product, a fraction
containing unidentified compounds (469 mg) was eluted: mp
138-140 °C; 1HNMR(250MHz, CD2Cl2) δ= 7.46 and 7.44 (2 d,
4J = 2.0 Hz, 1 H each, Ha), 7.33 (d with broadened signals, 3J=
7.8 Hz, 2 H, Hc), 7.051 and 7.048 (2 dd, 3J = 7.8 Hz, 4J = 2.0Hz, 1
H each, Hb), 6.98 and 6.44 (2 d, 3J = 8.4 Hz, 1 H each, He), 5.82
and 5.74 (2 s, 1 H each, Hd), 5.19 (s, 1 H, OH), 1.274 and 1.268 (2 s,
9 H each, C(CH3)3), 0.37 (s, 9 H, Si(CH3)3); 13C NMR (62.8 MHz,
CD2Cl2) δ = 150.94 and 150.88 (Ci ortho to CtC, CkOH), 149.1
and 149.0 (CtBu), 145.4 (Ch para to tBu), 142.6 (Ch meta to tBu),
132.2 (Ci ortho to OH), 129.7 (Ce ortho to CtC), 123.8 and 123.5
(Cc), 122.4 and 122.3 (Cb), 121.5 and 121.3 (Ca), 113.3 (Ce ortho to
OH), 111.7 (CkCtCSiMe3), 103.3 and 96.5 (CꢀC), 52.6 and 47.2
(Cd), 34.90 and 34.85 (CMe3), 31.63 and 31.62 (C(CH3)3), 0.3
(Si(CH3)3); MS (EI) m/z = 478.22 (100) [M]þ, 463.20 (65), 365.09
(16). Anal. Calcd for C33H38OSi (478.750): C, 82.79; H, 8.00.
Found: C, 82.62; H, 7.87.
Comment: Gaseous diisopropylamine was found to dissolve
the highly viscous silicon grease which was used to grease the
glass joints. To keep the sealing with silicon grease intact, either
a rather large flask or a flask with a long neck was used,
minimizing the contact between gaseous diisopropylamine and
silicon grease.
Analytical data: mp 116-117 °C; 1H NMR (250 MHz, CD2Cl2)
δ = 7.48 and 7.45 (2 d, 4J=1.8 Hz, 1 H each, Ha), 7.37 and 7.33 (2
d, 3J =7.9Hz, 1H each, Hc), 7.10 and 7.07 (2 m, 4 H, Hb, He), 5.97
and 5.87 (2 s, 1 H each, Hd), 1.30 (s, 30 H, C(CH3)3 and CH-
(CH3)2), 1.28 (s, 9 H, C(CH3)3), 0.41 (s, 9 H, Si(CH3)3); 13C NMR
(125.6 MHz, CD2Cl2) δ = 149.2 (CtBu), 148.6 and 148.3 (Ci),
145.0 and 144.9 (Ch para to tBu), 142.24 and 142.15 (Ch meta to
tBu), 128.1 and 128.0 (Ce), 123.8 and 123.7 (Cc), 122.6 and 122.5
(Cb), 121.5 and 121.4 (Ca), 119.1 and 118.7 (CkCtC), 104.7 and
96.3 (CtCTIPS), 102.7 and 100.0 (CtCTMS), 52.4 and 52.3 (Cd),
34.9 (CMe3), 31.61 and 31.58 (C(CH3)3), 19.0 (CH(CH3)2), 11.8
(CHMe2); 13C NMR signal assignment in agreement with
HMQC; MS (EI) m/z = 642.32 (78) [M]þ, 600.27 (56), 599.27
(100); UV/vis λ (ε [106 cm2 mol-1])=273 (sh, 29.59), 281 (49.12),
297 (61.88), 322 (5.00) nm. Anal. Calcd for C44H58Si2 (643.116):C,
82.18; H, 9.09. Found: C, 82.13; H, 8.96.
Diethynyltriptycene 5b. A suspension of diethynyltriptycene
5a (4.77 g, 7.43 mmol) and K2CO3 (1.24 g 8.97 mmol) in THF
(20 mL) and methanol (60 mL) was stirred at room temperature
for 1.5 h. Et2O and water were added, the phases were separated,
the aqueous phase was extracted with Et2O, and the combined
organic phases were washed with brine and dried over MgSO4.
Removal of the solvent gave a beige solid (4.25 g) containing
diethynyltriptycene 5b and TMSOH and/or TMS2O. The ma-
terial was used for the following reactions without further
purification. For analytical purposes, the accompanying TMS
containing products were removed from a sample through
freeze-drying from benzene: 1H NMR (250 MHz, CD2Cl2)
Triflate 4b. The glassware was flame-dried before use. Triflic
anhydride (3.2 mL, 18.9 mmol) was added dropwise over a
period of 30 min to a solution of phenol 3b (6.97 g, 14.5 mmol) in
pyridine (50 mL), which was cooled with an ice bath. The color
of the solution turned from yellow to orange. After the reaction
mixture was stirred for 19.5 h at room temperature, Et2O and
2 N HCl were added, the phases were separated, the aqueous
phase was extracted with Et2O, and the combined organic phases
were washed with 2 N HCl and brine and dried over MgSO4. Upon
solvent removal an orange solid was obtained. Column chroma-
tography (n-pentane/Et2O 3:2; Rf = 0.75) gave triflate 4b (8.08 g,
91%) as a slightly yellow solid: mp 107-109 °C; 1H NMR (250
MHz, CD2Cl2) δ = 7.49 and 7.47 (2 d, 4J = 1.9 Hz, 1 H each, Ha),
7.36 (slightly broadened d, 3J = 7.8 Hz, 2 H, Hc), 7.17 (d, 3J = 8.7
Hz, 1 H, He), 7.11 and 7.07 (2 dd, 3J=7.8 Hz, 4J = 1.9 Hz, 1 H
each, Hb), 6.90 (d, 3J = 8.7 Hz, 1 H, He), 5.89 and 5.72 (2 s, 1 H
each, Hd), 1.28 and 1.27 (2 s, 9 H each, C(CH3)3), 0.39 (s, 9 H,
Si(CH3)3); 13C NMR (125.6 MHz, CD2Cl2) δ = 152.0 (CkOTf
4
δ=7.49 and 7.42 (2 d, J=2.0 Hz, 1 H each, Ha), 7.36 and
7.30 (2 d, 3J = 7.8 Hz, 1 H each, Hc), 7.08 and 7.05 (2 m, 4 H, Hb,
He), 5.95 and 5.88 (s, 1 H each, Hd), 3.51 (s, 1 H, CtC-H), 1.274
and 1.271 and 1.25 (3 s, overall 39 H, CH(CH3)2)3, C(CH3)3);
MS (EI) m/z = 571.38 (39), 570.38 (76) [M]þ, 528.32 (47), 527.32
(100); C41H50Si (570.934).
Assembling of the Oligomers 8an and 8bn.
General Procedure for the Removal of the TIPS Group. A
t
or Ci), 149.59 and 149.55 (CtBu), 144.5 (Ch para to Bu), 144.3
7740 J. Org. Chem. Vol. 74, No. 20, 2009

Maag et al.
JOCArticle
solution of n-Bu4NF in THF (1 M, 2 equiv) was added to a
solution of the TIPS-protected alkyne in THF. After the reac-
tion mixture was stirred for 2.5-3.5 h at room temperature,
Et2O and water were added, the phases were separated, the
aqueous phase was extracted with Et2O, and the combined
organic layers were washed with brine and dried over MgSO4.
Removal of solvent gave the deprotected alkynes containing
Hd), 4.56 (d, 3J = 6.1 Hz, 2 H, CH2OH), 3.04 and 2.82 (2 t-like, 2
H each, ArCH2), 1.20-2.00 (m, 17 H, CH2, OH), 1.30 (s, 21 H,
CH(CH3)2), 1.29 and 1.28 (2 s, 9 H each, C(CH3)3), 0.94 and
0.87 (2 t-like, 3 H each, CH2CH3); HRMS (MALDI) m/z =
868.59696, calcd for C62H80OSi (868.59730); UV/vis λ (ε [106
cm2 mol-1]) = 316 (45.93), 328 (58.73), 333 (sh, 49.96), 351
(54.98) nm; emission (λexcitation = 305 nm) λ = 357, 375, 385
(sh), 406 (sh) nm. Anal. Calcd for C62H80OSi (869.407): C,
85.65; H, 9.28. Found: C, 85.61; H, 9.32.
Deprotected Monomer 8b1. Starting from protected monomer
8a1 (1.19 g, 1.37 mmol) in THF (40 mL), an orange solid (1.03 g)
was obtained containing deprotected monomer 8b1 and TIPS
derivatives: 1H NMR (250 MHz, CD2Cl2) δ = 7.51 (d, 4J = 1.9
Hz, 1 H, Ha,ext-OH), 7.49 (d, 4J = 1.9 Hz, 1 H, Ha,ext-H), 7.49 (s, 1
H, Hf), 7.39 (s, 1 H, Hg), 7.39 and 7.37 (2 d, 3J = 7.8 Hz, 1 H
each, Hc), 7.13 and 7.17 (AB spinsystem, 3J = 8.3 Hz, 2 H, He),
7.08 and 7.07 (2 dd, 3J = 7.9 Hz, 4J = 1.9 Hz, 1 H each, Hb), 5.95
and 5.91 (2 s, 1 H each, Hd), 4.55 (s, 2 H, CH2OH), 3.54 (s, 1 H,
CtCH), 3.01 and 2.80 (2 t-like, 2 H each, ArCH2), 1.20-2.00
(m, 17 H, CH2, OH), 1.28 and 1.27 (2 s, 9 H each, C(CH3)3), 0.92
and 0.84 (2 t-like, 3 H each, CH2CH3); MS (MALDI-TOF,
20 kV) m/z = 714.81 [M þ 2H]þ, 713.81 [M þ H]þ, 712.80 [M]þ;
C53H60O (713.069).
1
TIPSOH and/or TIPSF and/or TIPS2O, which give rise to H
NMR signals at 0.95-1.15 ppm in CDCl3. Freeze-drying from
benzene diminishes the amount of these products. The depro-
tected alkynes were used as obtained, i.e., without freeze-drying,
for further reactions. The quantities of deprotected oligomers
8bn used in the coupling reactions were calculated as if the
material consisted only of deprotected oligomers 8bn.
General Workup Procedure for the Alkynyl-Aryl Coupling
Reactions. Et2O and water were added, the phases were sepa-
rated, and the aqueous phase was extracted with Et2O. The
combined organic layers were washed with 2 N HCl and brine
and finally dried over MgSO4. The solvent was removed.
Iodo Monomer 7. To a degassed yellow solution of 1,4-
dihexyl-2,5-diiodobenzene (16.4 g, 32.9 mmol) and diethynyl-
triptycene 5b (2.76 g, max 4.84 mmol; the material contained
TMS derivatives) in THF (150 mL) and piperidine (30 mL) were
added Pd(PPh3)2Cl2 (34 mg, 0.05 mmol) and CuI (18 mg, 0.09
mmol). After the reaction mixture was stirred for 22 h at room
temperature, Et2O and water were added, the phases were
separated, the aqueous phase was extracted with Et2O, and
the combined organic layers were washed with 2 N HCl and
brine and finally dried over MgSO4. The solvent was removed.
Column chromatography (n-pentane/Et2O 100:1) of the yellow-
ish residue provided 1,4-dihexyl-2,5-diiodobenzene (13.7 g,
84%; Rf=0.68), iodo monomer 7 (2.57 g, 56%; Rf = 0.49) as
a colorless solid, and a mixture (1.15 g, Rf = 0.24) of the di-
substitution product and the Glaser coupling product (i.e., the
oxidative dimerization product) of diethynyltriptycene 5b was
obtained in a ratio of ca. 2:1 (1H NMR spectroscopically
determined). Analytical data of iodo monomer 7: mp 78 °C
(sintering), 100-103 °C (melting); 1H NMR (250 MHz,
CD2Cl2) δ=7.81 (s, 1H, Hg), 7.50 (d, 4J=1.8 Hz, 1 H, Ha,ext-I),
7.48 (s, 1 H, Hf), 7.46 (d, 4J = 1.8 Hz, 1 H, Ha,ext-Si), 7.37 and
7.34 (2 d, 3J = 8.2 Hz, 1 H each, Hc), 7.14 and 7.13 (AB
spinsystem, 3J=8.1 Hz, 2 H, He), 7.09 and 7.08 (2 dd, 3J=7.8
Hz, 4J = 1.9 Hz, 1 H each, Hb), 5.99 and 5.94 (2 s, 1 H each, Hd),
2.99 and 2.75 (2 t-like, 2 H each, ArCH2), 1.20-2.00 (m, 16 H,
CH2), 1.30 (s, 21 H, CH(CH3)2), 1.281 and 1.275 (2 s, 9 H each,
C(CH3)3), 0.84 and 0.86 (2 t-like, 3 H each, CH2CH3); HRMS
(MALDI) m/z = 940.48409; calcd for C59H77ISi (940.48337).
Anal. Calcd for C59H77ISi (941.256): C, 75.29; H, 8.25. Found:
C, 75.20; H, 8.34.
Protected Monomer 8a1. To a degassed solution of 1,4-
dihexyl-5-(3-hydroxyprop-1-ynyl)-2-iodobenzene (9) (990 mg,
2.32 mmol) and diethynyltriptycene 5b (1.42 g, 2.49 mmol) in
THF (60 mL) and piperidine (20 mL) were added Pd(PPh3)2Cl2
(16 mg, 0.02 mmol) and CuI (9 mg, 0.05 mmol). Fifteen minutes
later, a precipitate had formed. The reaction mixture was stirred
for 23 h at room temperature. Standard workup gave a beige
solid which was dissolved in a minimum amount of n-pentane/
CH2Cl2 (1:2). This solution was applied to a chromatography
column. Chromatography (n-pentane/CH2Cl2 1:2) gave pro-
tected monomer 8a1 (1.78 g, 88%, Rf=0.46) as a beige solid.
Ahead of the product, Glaser coupling product, i.e., the oxida-
tive dimer of diethynyltriptycene 5b, was eluted (Rf =0.75).
Analytical data of protected monomer 8a1: mp 121-124 °C; 1H
NMR (250 MHz, CD2Cl2) δ=7.51 (slightly broadened s, 2 H,
Hf, Ha,ext-OH), 7.47 (d, 4J = 1.9 Hz, 1 H, Ha,ext-Si), 7.40 (s, 1 H,
Hg), 7.39 and 7.35 (2 d, 3J = 7.8 Hz, 1 H each, Hc), 7.17 and 7.13
(AB spinsystem, 3J=8.1 Hz, 2 H, He), 7.10 and 7.08 (2 dd, 3J =
7.8 Hz, 4J=1.9 Hz, 1 H each, Hb), 6.00 and 5.96 (2 s, 1 H each,
Protected Dimer 8a2. Pd(PPh3)4 (132 mg, 0.114 mmol) and
CuI (137 mg, 0.72 mmol) were added to a degassed yellow
solution of iodo monomer 7 (1.08 g, 1.15 mmol) and deprotected
monomer 8b1 (950 mg, max 1.33 mmol; the material contained
TIPS derivatives) in (i-Pr)2NH (40 mL) and toluene (60 mL).
Upon addition of the catalyst, the color of the solution turned to
orange and a colorless solid formed. The suspension was heated
to 60 °C for 16 h. Standard workup yielded an orange solid
which was dissolved in a minimum amount of n-pentane/
CH2Cl2 (1:2). This solution was applied to a chromatography
column. Chromatography (n-pentane/CH2Cl2 1:2) gave pro-
tected dimer 8a2 (1.55 g, 89%; Rf = 0.55) as a yellow-orange
solid which contained a small amount of triphenylphosphane
1
oxide (identified through H NMR spectroscopy). This solid
was used in the following reactions without further purification.
For analytical purposes, protected dimer 8a2 (103 mg) was
dissolved in CH2Cl2 (0.5 mL), and methanol (1.5 mL) was
added. A yellow soft wax separated. The overlaying solution
was removed, and the residue was dissolved in CH2Cl2 (0.5 mL).
Upon addition of methanol (1.5 mL) again a second waxlike
phase formed, which was transformed into a fine-grained solid
by stirring the emulsion for 15 min. The suspension was filtered,
and the solid was washed with methanol and dried under
vacuum giving protected dimer 8a2 free of triphenylphosphane
oxide as a beige powder (91 mg, 79%; the calculation of the
yield takes into account that only a part of the obtained
material was treated as described): mp 170 °C (solid turns red),
172-174 °C (melting); 1H NMR (250 MHz, CD2Cl2) δ = 7.649
and 7.646 (2 s, 1 H each, Hg,int, Hf,int), 7.56, 7.55, and 7.54 (3 d,
4J = 1.9 Hz, 1 H each, Ha,int, Ha,ext-OH), 7.54 (s, 1 H, Hf,ext), 7.48
(d, 4J = 1.9 Hz, 1 H, Ha,ext-Si), 7.44 and 7.43 (2 d, 3J = 7.8 Hz,
1H and 2H, respectively, Hc,int, Hc,ext-OH), 7.41 (s, 1H, Hg,ext),
7.37 (d, 3J = 7.8 Hz, 1H, Hc,ext-Si), 7.27 and 7.24 (AB spinsystem,
3J = 8.3 Hz, 2 H, He,ext-OH, He,int), 7.21 and 7.16 (AB spinsystem,
3J = 8.1 Hz, 2H, He,ext-Si, He,int), 7.13, 7.12, 7.11, and 7.10 (4 dd,
3J = 7.8 Hz, 4J = 2.0 Hz, 1 H each, Hb), 6.04, 6.02, and 6.01 (3 s,
3
1H, 1H, and 2H, respectively, Hd), 4.57 (d, J = 6.2 Hz, 2 H,
CH2OH), 3.14, 3.06, and 2.83 (3 t-like, 4H, 2H, and 2H, respec-
tively, ArCH2), 1.05-2.05 (m, 32 H, CH2), 1.79 (t, 3J = 6.3 Hz,
1H, OH), 1.25-1.35 (m, 57 H, CH(CH3)2, C(CH3)3), 0.84-0.99
(m, 12 H, CH2CH3); MS (MALDI-TOF, 20 kV) m/z = 1526.59
[M þ H]þ, 1525.69 [M]þ; UV/vis λ (ε [106 cm2 mol-1]) = 358
(95.32) nm; emission (λexcitation = 305 nm) λ = 402, 425, 437 (sh)
nm. Anal. Calcd for C112H136OSi (1526.397): C, 88.13; H, 8.98.
Found: C, 87.81; H, 9.05.
J. Org. Chem. Vol. 74, No. 20, 2009 7741

Maag et al.
JOCArticle
Deprotected Dimer 8b2. Starting from protected dimer 8a2
(800 mg, 0.524 mmol) in THF (20 mL), an orange solid (778 mg)
was obtained containing deprotected dimer 8b2 and TIPS deri-
vatives: 1H NMR (250 MHz, CD2Cl2): 7.632 and 7.630 (2 s, 1 H
each, Hg,int, Hf,int), 7.55 (d, 4J = 1.8 Hz, 1 H, Ha,ext-OH), 7.52-
7.54 (m, 4 H, Ha,ext-H, Ha,int, Hf,ext), 7.44 7.43, and 7.41 (3 d, 3J=
7.8 Hz, 1 H, 2 H, and 1 H, respectively, Hc,int, Hc,ext-OH), 7.40 (s,
3J = 8.0 Hz, 2 H, He,int), 7.05-7.18 (m, 6 H, Hb), 6.04, 6.03, 6.00,
and 5.94 (4 s, 2 H, 1 H, 2 H, and 1 H, respectively, Hd), 4.56 (d,
3J = 6.1 Hz, 2 H, CH2OH), 3.56 (s, 1 H, CtC-H), 3.14, 3.05, and
2.82 (3 t-like, 8 H, 2 H, 2 H, respectively, ArCH2), 1.20-2.10 (m,
49 H, CH2, OH), 1.25-1.35 (m, 54 H, C(CH3)3), 0.80-1.00 (m,
18H, CH2CH3); MS (MALDI-TOF, 20 kV) m/z = 2026.61 [M þ
H]þ; C153H172O (2027.048).
3
1H, Hg,ext), 7.25 and 7.21 (AB spinsystem, J = 8.1 Hz, 2 H,
Protected Tetramer 8a4. Pd(PPh3)4 (13 mg, 0.01 mmol) and
CuI (13 mg, 0.07 mmol) were added to a degassed yellow
solution of iodo monomer 7 (103 mg, 0.109 mmol) and depro-
tected trimer 8b3 (282 mg, max. 0.139 mmol; the material
contained TIPS-derivatives) in (i-Pr)2NH (5 mL) and toluene
(9.5 mL). Upon addition of the catalyst, the color of the solution
turned orange and a colorless solid formed. The suspension was
heated to 60 °C for 14.5 h. Standard workup gave a yellow solid
which was dissolved in a minimum amount of n-pentane/
CH2Cl2 (1:1). This solution was applied to a chromatography
column. Chromatography (n-pentane/CH2Cl2 1:1) afforded
protected tetramer 8a4 (239 mg, 77%; Rf = 0.59) as a yellow
H
H
e,ext-OH,He,int), 7.21 and 7.16 (AB spinsystem, 3J = 8.1 Hz, 2 H,
e,ext-Si, He,int) 7.08-7.14 (m, 4 H, Hb), 6.02, 6.00, and 5.94 (3 s,
1 H, 2 H, and 1 H, respectively, Hd), 4.56 (d, 3J = 5.9 Hz, 2 H,
CH2OH), 3.55 (s, 1 H, CꢀC-H), 3.12, 3.04, and 2.82 (3 t-like,
4 H, 2 H, and 2 H, ArCH2), 1.25-1.35 (m, 33 H, CH2, OH),
1.25-1.32 (m, 36 H, C(CH3)3), 0.80-1.00 (m, 12 H, CH2CH3);
MS (MALDI-TOF, 20 kV) m/z = 1369.69 [M þ H]þ, C103H116
O
(1370.053).
Protected Trimer 8a3. Pd(PPh3)4 (53 mg, 0.05 mmol) and CuI
(55 mg, 0.29 mmol) were added to a degassed, orange solution of
iodo monomer 7 (430 mg, 0.457 mmol) and deprotected dimer
8b2 (725 mg, max. 0.529 mmol; the material contained TIPS
derivatives) in (i-Pr)2NH (20 mL) and toluene (30 mL). After
addition of the catalyst, a colorless solid formed. The suspension
was heated to 60 °C for 16 h. Standard workup gave an orange
solid, which was dissolved in a minimum amount of n-pentane/
CH2Cl2 (1:1). This solution was applied to a chromatography
column. Through chromatography (n-pentane/CH2Cl2 1:1)
protected trimer 8a3 (705 mg, 71%; Rf=0.47) was obtained as
a yellow solid: mp 150 °C (sintering), 182-185 °C (melting); 1H
NMR (250 MHz, CH2Cl2) δ = 7.68 and 7.67 (2 broadened s, 4
H, Hg,int, Hf,int), 7.52-7.63 (m, 6 H, Ha,int, Ha,ext-OH, Hf,ext),
7.41-7.52 (m, 7 H, Ha,ext-Si, Hc,int, Hc,ext-OH, Hg,ext), 7.38 (d,
3J = 7.8 Hz, 1H, Hc,ext-Si), 7.29 (apparent s, probably AB
spinsystem, 2 H, He,int), 7.27 and 7.25 (AB spinsystem, 3J =
8.2 Hz, 2 H, He,ext-OH, He,int), 7.23 and 7.16 (AB spinsystem,
3J=8.1 Hz, 2H, He,ext-Si, He,int), 7.07-7.18 (m, 6 H, Hb), 6.09,
6.07, and 6.03 (3s, 2 H, 1 H, and 3 H, respectively, Hd), 4.58 (d,
3J=6.2 Hz, 2 H, CH2OH), 3.18 and 3.08 and 2.85 (3 t-like, 8 H,
2 H, and 2 H, respectively, ArCH2), 1.20-2.20 (m, 49 H, CH2),
1.80 (t, J = 6.2 Hz, 1 H, OH), 1.25-1.37 (m, 75 H, CH(CH3)2,
C(CH3)3), 0.80-1.00 (m, 18 H, CH2CH3); MS (MALDI-TOF,
20 kV) m/z = 2182.65 [M þ H]þ; UV/vis λ (ε [106 cm2 mol-1])=
374 (147.34) nm; emission (λexcitation = 305 nm) λ = 414, 438
nm. Anal. Calcd for C162H192OSi (2183.391): C, 89.12; H, 8.86.
Found: C, 89.15; H, 8.83.
1
solid: mp 160 °C (sintering), 267-270 °C (melting); H NMR
(250 MHz, CD2Cl2) δ=7.70, 7.69, and 7.67 (3 s, the middle
one is slightly broadened, overall 6 H, Hg,int, Hf,int), 7.54-7.64
(m, 8 H, Ha,int, Ha,ext-OH, Hf,ext), 7.42-7.54 (m, 10 H, Ha,ext-Si
,
H
c,int, Hc,ext-OH, Hg,ext), 7.39 (d, 3J=7.8 Hz, 1H, Hc,ext-Si), 7.29
(apparent s, probably 2 AB spinsystems, 4 H, He,int, 7.26
(apparent s, probably AB spinsystem, 2 H, He,ext-OH, He,int),
7.08-7.23 (m, 10 H, Hb, He,ext-Si, He,int), 6.09 and 6.08 and 6.04
3
(4 s, 1 and 3 H, respectively, Hd), 4.58 (d, J = 6.1 Hz, 2 H,
CH2OH), 3.17 (m, 12H, ArCH2), 3.08 and 2.85 (2 t-like, 2 H
each, ArCH2), 1.22-2.10 (m, 65 H, CH2, OH), 1.22-1.38 (m, 93
H, CH(CH3)2, C(CH3)3), 0.80-1.05 (m, 24 H, CH2CH3); MS
(MALDI-TOF, 20 kV) m/z = 2838.89 [M þ H]þ; UV/vis λ
(ε [106 cm2 mol-1]) = 379 (194.79) nm; emission (λexcitation
=
305 nm) λ = 418, 443 nm. Anal. Calcd for C212H248OSi
(2840.386): C, 89.65; H, 8.80. Found: C, 89.40; H, 8.66.
Acknowledgment. We thank D. Sahoo for recording the
UV/vis and fluorescence spectra, A. Diekmann for perform-
ing the DSC measurements, and Prof. Dr. Koop for provid-
ing us access to the DSC equipment. This work was
supported by the DFG (SFB 613). D.M. thanks Bielefeld
University for a fellowship.
Supporting Information Available: Experimental procedures
for the synthesis of 2,6-di-tert-butylanthracene, triptycenequinone
1, diethynyltriptycene 5a via route A, and diethynyltriptycene 6
including the analytical data. 13C NMR data of iodo monomer 7
and the oligomers 8an. UV/vis and emission spectra of 5a and 8an.
1H and 13C NMR spectra of all compounds of which the synthesis
is described in this publication. This material is available free of
charge via the Internet at http://pubs.acs.org.
Deprotected Trimer 8b3. Starting from protected trimer 8a3
(300 mg, 0.137 mmol) in THF (10 mL), a yellow solid (312 mg)
was obtained containing deprotected trimer 8b3 and TIPS deri-
1
vatives: H NMR (250 MHz, CD2Cl2) δ=7.70-7.60 (m, 4 H,
Hg, int, Hf, int), 7.49-7.60 (m, overall 7 H, Ha,ext-OH, Ha,int, Ha,ext-
H, Hf,ext), 7.35-7.49 (m, 7 H, Hc, Hg,ext), 7.27 (apparent s,
probably AB spinsystem, 2 H, He,int), 7.25 and 7.22 (AB spinsys-
tem, 3J = 8.0 Hz, 2 H, He,ext-OH), 7.21 and 7.17 (AB spinsystem,
7742 J. Org. Chem. Vol. 74, No. 20, 2009