Synthesis and properties of conjugated oligoyne-centered π-extended tetrathiafulvalene analogues and related macromolecular systems

Article abstract of DOI:10.1021/jo2000447

Alkynyl-substituted phenyldithiafulvenes have been found to act as versatile building blocks for the construction of π-conjugated molecular rods, shape-persistent macrocycles (SPMs), and conducting polymers. Through Cu(I)-catalyzed alkynyl homocoupling, a

Full text of DOI:10.1021/jo2000447

ARTICLE
pubs.acs.org/joc
Synthesis and Properties of Conjugated Oligoyne-Centered
π-Extended Tetrathiafulvalene Analogues and Related
Macromolecular Systems
Guang Chen,† Ilias Mahmud,† Louise N. Dawe,† Lee M. Daniels,‡ and Yuming Zhao*,†
†Department of Chemistry, Memorial University of Newfoundland, St. John’s, Newfoundland A1B 3X7, Canada
‡Rigaku Americas Corporation, 9009 New Trails Drive, The Woodlands, Texas 77381, United States
S Supporting Information
b
ABSTRACT: Alkynyl-substituted phenyldithiafulvenes have
been found to act as versatile building blocks for the construc-
tion of π-conjugated molecular rods, shape-persistent macro-
cycles (SPMs), and conducting polymers. Through Cu(I)-
catalyzed alkynyl homocoupling, a series of linear-shaped π-
extended tetrathiafulvalene analogues (exTTFs) carrying con-
jugated oligoynes (ranging from diyne to hexayne) as the
central π-bridge were readily prepared. The solid-state proper-
ties and reactivities of diyne- and tetrayne-centered exTTFs
were characterized by X-ray crystallography and differential
scanning calorimetry (DSC), while the electronic properties of
the oligoyne-exTTFs were elucidated by UVꢀvis absorption spectroscopy and density functional theory (DFT) calculations. Cyclic
voltammetric analysis showed that the terminal phenyldithiafulvene groups of the oligyne-exTTFs could undergo oxidative coupling
to form tetrathiafulvalene vinylogue (TTFV)-linked polymer wires. Through a different synthetic route involving oxidative
dimerization and Pd/Cu-catalyzed alkynyl homocoupling, the acetylenic phenyldithiafulvene precursors led to shape-persistent
macrocycles where the formation of trimeric macrocycles was particularly favored due to the small ring strain incurred. Finally,
spectroelectrochemical studies on these oligoyne and TTF hybrid materials disclosed electrochromic and molecular redox-
controlled switching properties applicable to molecular electronic and optoelectronic devices.
’ INTRODUCTION
Conjugated oligoynes or polyynes constitute a class of quasi-
one-dimensional conjugated carbon chains and have been ex-
tensively investigated as versatile scaffoldings for functional
carbon-rich materials, owing to their rich optoelectronic
and electromagnetic properties and unique solid-state
reactivities.31ꢀ39 For instance, the nonlinear optical susceptibil-
ities of oligoynes were found to increase exponentially with
increasing number of acetylenic repeat units,40,41 while topo-
chemical polymerization of oligoynes tended to result in highly
conjugated polymer networks37,42ꢀ50 and ordered carbon-based
nanomaterials.51ꢀ54 Moreover, the “wire-like” sp carbon chains
(spCCs) of conjugated oligoynes or polyynes are the substruc-
tures of an intriguing carbon allotropeꢀcarbyne,55,56 while
debates over the nature of electronic delocalization in spCCs
have galvanized both experimental and theoretical invest-
igations.57ꢀ63 In particular, synthetic endeavors aiming at exten-
sion and functionalization of conjugated oligoynes have been
actively undertaken in recent years in order to realize suitable
models for unraveling the mystical characteristics of carbyne and
related polyyne materials.63ꢀ70
Tetrathiafulvalene (TTF) as an important organic electron
donor has found extensive uses in modern materials science.1,2
Ever since the seminal work by Wudl and co-workers on the
electrical conductivity of [TTF]•þClꢀ in the early 1970s,3,4 an
enormous array of TTF variants has been synthesized and appli-
ed as useful building blocks in the construction of advanced
molecular/supramolecular materials and devices, ranging from
organic conductors and superconductors,5ꢀ8 magnets,7ꢀ9 mo-
lecular switches and sensors,10ꢀ12 molecular machines,13,14
organic optoelectronics,15,16 and plastic solar cells,15,17,18 just
to name a few. In the development of functional TTF derivatives,
the strategy of increasing the π-conjugation of the TTF back-
bone has been widely employed to generate the so-called π-
extended tetrathiafulvalene analogues (exTTFs),11,15,19,20 In
current TTF chemistry, insertion of various π-conjugated
spacers such as quinoid,21ꢀ24 vinylogous,25ꢀ27 arylene,28 and
acetylene bridges29,30 between the two dithiole rings of TTF has
been proven effective at tuning the properties and functions of
exTTF derivatives to be applicable for device applications, such
as enhanced electron-donating ability, increased solid-state or-
dering and dimensionality, as well as controlled multistage redox
activities.
Received: January 12, 2011
Published: March 08, 2011
r
2011 American Chemical Society
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Figure 1. Examples of conjugated oligoyne-centered exTTFs reported in the literature.
Figure 2. Versatile reactivities of acetylenic phenyl-DTF.
Oligoyne-extended TTF analogues have been synthesized and
studied for more than two decades; however, they still remain a
rather small branch in the vast family of exTTF derivatives.71ꢀ74
In 1990, Gorgues and co-workers reported the synthesis of a
bis(dithiafulvenyl)-end-capped conjugated 1,3-butadiyne 1 (Fig-
ure 1) by a WittigꢀHorner reaction.75,76 The dithiafulvenyl
(DTF) moieties of 1 are in direct conjugation via a diyne π-
spacer (highlighted bold in Figure 1), presenting the first
example of a diyne-centered exTTF. The synthesis of 1,3,5,7-
octatetrayne-centered exTTF 2, which is a longer homologue of
exTTF 1, was, however, accomplished at a much later time. In
2004, Nielsen and co-workers used a Cu-catalyzed homocoupling
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Figure 3. Different macromolecular systems possibly derived from acetylenic phenyl-DTF 8.
reaction to construct tetrayne-exTTF 2 and investigated its redox
properties by electrochemical analysis.77 A similar series of diyne-
and tetrayne-centered exTTFs 3 and 4 have been prepared and
investigated by Diederich and Nielsen.78,79 In these compounds,
extended acetylenic units were appended to the exTTF backbones
in a cross-conjugated manner. Very recently, Diederich and co-
workers reported the synthesis of a diyne-centered exTTF 5 via
successive TTF/TCNE cycloadditions on a conjugated hexayne
precursor.80 In 2007, Nielsen and co-workers reported an exTTF
derivative 6 by oxidative alkynyl coupling reactions.81 The high-
lighted conjugation path of 6 shown in Figure 1 clearly reveals an
exTTF segment, in which two DTF groups are connected through a
linearly conjugated diyne-quinoid-diyne π-bridge. In addition to
diyne and tetrayne units, Nielsen and co-workers also successfully
prepared a hexayne-centered exTTF 7 in good yield via Hay
coupling.77 Although the chemical stability of hexayne 7 was not
mentioned in detail, the successful separation and spectroscopic
characterization of hexayne 7 were remarkable, given the relatively
poor stability of many hexayne species.82 The sufficient stability can
be attributed to the presence of bulky triisopropylsilyl (TIPS) end-
capping groups that prevent decomposition of the central hexayne
unit.63
Given the limited number of oligoyne-centered exTTFs in the
current literature, continued synthesis and characterization of
new oligoyne-exTTFs are indispensable and beneficial to better
understanding of the fundamental structureꢀproperty relation-
ships and potential applications of electroactive oligoynes in
synthetic and materials chemistry. Upon this consideration, we
set out to investigate a series of oligoyne-centered exTTFs 9
(Figure 2). The basic structure of 9 is akin to those of exTTFs 1
and 2; however, the incorporation of a phenyl ring between the
DTF and alkynyl groups in our designed structure not only
elongates π-conjugation but also adds versatile reactivity allow-
ing for the construction of highly conjugated macromolecular
systems. The DTF molecules have been known to undergo an
oxidative dimerization reaction to form tetrathiafulvalene viny-
logues (TTFVs).6,83ꢀ91 As illustrated in the mechanism in
Figure 2, the key step of this reaction involves the formation of
the DTF radical cation, which requires the assistance of a
neighboring group to gain sufficient stability for subsequent
dimerization.87,92 In general, DTF compounds that are mono-
substituted with aryl or electron-withdrawing groups are readily
subjected to oxidative dimerization reactions, whereas the alky-
nyl-substituted DTF species has not been known to undergo this
type of reaction. In studying the electrochemistry of an acceptor-
substituted acetylenic DTF, Nielsen and co-workers observed
the formation of a blue-colored thin film on the surface of the
working electrode.93 The authors suggested the thin film be an
insoluble cationic species; however, the possibility of electro-
polymerization cannot be simply ruled out and its occurrence still
remains unclear. In our design, the two phenyl-DTF units in
oligoyne-exTTF 9 serve as a pair of facile synthetic handles for
cross-linking through the oxidative coupling reaction to generate
some intriguing conjugated polymer materials.
A straightforward retro-synthetic analysis of oligoyne-exTTF
9 leads to a handy synthon, acetylenic phenyl-DTF 8, which in
turn can be used to make other varieties of TTFV-based macr-
omolecular structures through sequential DTF dimerization and
alkynyl coupling reactions. Of particular note is that the diphen-
yl-substituted TTFV unit shows redox-controlled conforma-
tional switching properties.86,87 In the neutral state, the two
phenyl groups are oriented in a cis, V-shaped conformation
governed by steric crowding, whereas upon oxidation the dica-
tion of phenyl-TTF assumes a trans conformation where the two
phenyl groups point outwardly in a linear fashion as a result of the
on-site Coulombic repulsion between the two cationic dithio-
lium rings.94ꢀ97 In this vein, it is conceivable that structural
extension based on synthon 8 would result in macromolecules of
very different conformations, depending on the synthetic sequences
and conditions. Taking the V-shape of neutral diphenyl-TTFV and
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Scheme 1. Synthesis Oligoyne-Centered exTTFs 16ꢀ18
the linear shape of oligoyne and dicationic [phenyl-TTFV]2þ units
into account, three major synthetic consequences are readily
perceived as illustrated in Figure 3, namely linear cationic polymer
chains, helical foldamers,98 and shape-persistent macrocycles
(SPMs).99ꢀ102 These oligoyne-TTFV-related macromolecules
have not been known in the literature prior to our work. In a recent
paper, we reported the synthesis and properties of a diyne-based
exTTF and related polymers and macrocycles.103 This paper
describes our further investigations of oligoyne-centered exTTFs,
ranging from diyne to hexayne analogues. In addition, related
oligoyne-TTFV polymers and SPMs were prepared and their
properties were characterized by spectroscopic and voltammetric
techniques.
the Hay coupling reaction, a considerably large excess of TMSA
(ca. 38 mol equiv) was added to ensure a satisfactory yield of
59%. With the acetylenic DTF precursors 13ꢀ15 in hand, a
straightforward oxidative homocoupling strategy was then im-
plemented to produce the desired oligoyne-centered exTTFs. As
shown in Scheme 1, desilylation of DTF 13 with K2CO3 followed
by oxidative homocoupling in the presence of the Hay catalyst
(CuI/TMEDA) afforded diyne-centered exTTF 16 in 66% yield.
Under the same conditions, the homocoupling of desilylated
diyne-DTF 14 proceeded more rapidly and efficiently, resulting
in tetrayne-centered exTTF 17 in a quantitative yield. Similarly,
the homocoupling of desilylated triyne-DTF 15 also resulted in a
high yield of hexayne-exTTF 18 in dilute solution as evidenced
by thin-layer chromatography (TLC). MALDI-TOF MS analysis
clearly showed the molecular ion at m/z = 709.9461 correspond-
ing to [18]þ (709.9487 calcd for C36H22S8), substantiating the
formation of hexayne-exTTF 18 during the homocoupling
reaction (see the Supporting Information). The isolation of
hexayne-exTTF 18 was, however, unsuccessful due to its ex-
tremely poor chemical stability in the solid state. Actually, upon
evaporation of the solvent under vacuum, the orange-colored
solution of 18 was instantaneously changed into a purplish
substance which was insoluble in any organic solvents. The
insolubility of the solid products hampered meaningful structural
elucidation. Previously, Tykwinski and co-workers synthesized a
diphenyl-end-capped hexayne which was isolated as a relatively
stable orange solid.40 In our case, the dramatically reduced stability
’ RESULTS AND DISCUSSION
Synthesis. The synthesis of oligoyne-centered exTTFs is
outlined in Scheme 1. Phosphonate 1130,103ꢀ106 was first treated
with n-BuLi in THF at low temperature to form the correspond-
ing ylide, which was immediately reacted with benzaldehyde 12
through a HornerꢀWadsworthꢀEmmons (HWE) reaction to
give acetylenic phenyl-DTF 13 in 80% yield. DTF 13 was desil-
ylated with K2CO3 affording a free alkyne intermediate, which
was subjected to Hay coupling107 with excess TMSA (ca. 14 mol
equiv) to form diyne-attached phenyl-DTF 14 in 82% yield.
Repetition of the same desilylation/Hay coupling sequence on
14 led to the formation of triyne-substituted phenyl-DTF 15. In
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Scheme 2. Synthesis of Shape-Persistent Macrocycles 21 and
22
was first attempted; however, these conditions resulted in very poor
yields for the macrocyclization reaction. After a number of trials, a
Cu(I)/Pd(II) cocatalyst system similar to the one employed in the
synthesis of TTF-based [18]annulenes reported by Iyoda et al.109
was found to give the best outcomes. In our work, desilylation of
TTFV 19 with K2CO3 followed by a Pd/Cu-catalyzed homocou-
pling reaction under dilute conditions (ca. 2.8 mM) in acetone
under reflux for 2 days afforded a series of macrocyclic products
ranging from trimer to pentamer, as evidenced by MALDI-TOF
MS analysis (Figure 4A). Flash column chromatography success-
fully isolated trimeric macrocycle 21 as the major product in 18%
yield, while other byproducts were not separable due to their trace
amounts.
In a similar manner, TTFV 20 was desilylated and then
subjected to macrocyclization reactions under the catalysis of
Pd/Cu in refluxing acetone for 5 days (see Scheme 2). MALDI-
TOF MS analysis clearly showed the formation of macrocycle 22
as the major product of the macrocyclization (see Figure 4B).
However, efforts to isolate pure 22 by flash column chromatog-
raphy failed because of the very similar Rf value of 22 to those of
some inextricable byproducts.
The two phenyl-DTF units in oligoyne-exTTFs 16 and 17
were expected to cross-link into “chain-like” oligomer and
polymer wires upon oxidative dimerization. The oxidative cou-
pling of DTF groups could be conducted by either chemical or
electrochemical means. Chemical polymerization was performed
by treating the solution of 16 or 17 with molecular iodine in
CH2Cl2 at ambient temperature for ca. 12 h (see Scheme 3).90,108
Afterward, the resulting polymers were reduced by Na2S2O3 to
afford neutral polymer products P1 and P2, respectively. Both P1
and P2 are orange solids and readily soluble in nonpolar organic
solvents such as CH2Cl2 and chloroform. MALDI-TOF MS
analysis on the samples of P1 and P2 revealed the presence of
oligomers of short chain lengths (m = 2ꢀ8 for P1 and m = 2ꢀ4
for P2, see the Supporting Information). The relatively low
degrees of polymerization observed are not surprising given the
moderate yields of the iodine-induced DTF coupling in the
solution phase. In addition, electrochemical polymerization of
oligoyne-exTTFs 16 and 17 could be readily achieved via
electrodeposition on conductive substrates under standard vol-
tammetric or electrolysis conditions.84,85 The electrochemically
polymerized products formed high-quality thin films on the
surface of the working electrode, which were not soluble in
common organic solvents. These results indicated that electro-
polymerization tended to induce much higher degrees of polym-
erization than did the chemical method. The detailed results of
the electrochemically induced polymerization of oligoyne-
exTTFs 16 and 17 will be elaborated in the latter section.
Structural and Solid-State Properties. Single crystals of
diyne-exTTF 16 and tetrayne-exTTF 17 were grown by slow
solvent evaporation methods at low temperature (ꢀ4 °C), and
their detailed molecular and solid-state structures were charac-
terized by single-crystal X-ray crystallography. Both diyne-
exTTF 16 and tetrayne-exTTF 17 show a nearly planar π-
conjugated backbone in the molecular structure (Figure 5A,
B), with the DTF rings slightly deviated from the plane of the
phenyl rings by ca. 15ꢀ20°. The X-ray structure of diyne 16 is in
good agreement with the optimized molecular geometries ob-
tained from density functional theory (DFT) calculations at the
B3LYP/6-31G* level of theory. For tetrayne 17, however, the
theoretically predicted triple bond distances appear to be slightly
longer than the crystallographic values by ca. 0.02 Å (see the
of hexayne 18 can be tentatively attributed to the end-capping DTF
groups that may induce optimal solid-state packing geometry via
strong SꢀS contacts to facilitate topochemical polymerization. On
the other hand, nucleophilic attack of the SMe substituents to the
hexayne moiety may also take place to a certain extent to destabilize
hexayne 18. The exact reason for the instability of 18 in the solid
state is unclear at this juncture and awaits further investigation.
Apart from the “rod-like” oligoyne-exTTF motifs, the con-
struction of shape-persistent macrocycles was also explored in
our synthetic work using the acetylenic phenyl-DTFs as pre-
cursors. As shown in Scheme 2, phenyl-DTFs 13 and 14 were
respectively subjected to an iodine-promoted oxidative dimer-
ization reaction,90,108 yielding cationic dimerized products which
were subsequently treated with Na2S2O3 to afford neutral acet-
ylenic phenyl-TTFVs 19 and 20 in the same yield of 60%. At this
juncture, a straightforward desilylation/homocoupling route
should furnish macrocyclic products. The use of Cu(I) species,
such as CuCl or CuI, as the metal-based catalyst for homocoupling
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Figure 4. (A) MALDI-TOF MS analysis of the crude reaction mixture of the synthesis of macrocycle 21. (B) MALDI-TOF mass spectrum of
macrocycle 22. The inset compares the experimentally determined isotope envelop of molecular ion [22]þ (pink color) against theoretically calculated
pattern (black color).
that of diyne 16, but a relatively smaller inclination angle φ =
48.8°. Of note is that the C10 to C4 distance (4.30 Å) is
considerably shorter than those of C10 to C2 and C10 to C6,
which implies a higher probability for topochemical polymeriza-
tion in a 1,4-addition fashion. In addition to the ordered alignment
of oligoyne moieties, intimate SꢀS interactions stand out as
another notable feature in the solid-state structure. In the crystal
of diyne-exTTF 16, the shortest SꢀS distances between adjacent
molecules are 3.51 Å, while for tetrayne-exTTF 17 the close SꢀS
contacts are 3.99 and 4.04 Å. Clearly, the DTF rings play an
important role in dictating the solid-state packing properties of
oligoyne-exTTFs, which in turn affect their solid-state reactivity.
The close SꢀS interactions are believed to be responsible for the
observed poor stability of hexayne-exTTF 18 in the solid state.
To further explore the solid-state thermal reactivities of
oligoyne-exTTFs 16 and 17, differential scanning calorimetry
(DSC) and thermogravimetric analysis (TGA) were undertaken.
As shown in Figure 6A, the DSC trace of diyne 16 shows a sharp
endothermic peak at 206.8 °C (ΔH = ꢀ40.3 kJ/mol) which is
attributed to the melting process. The melting is followed by a
conspicuous exotherm at 244.5 °C (ΔH = 171.4 kJ/mol), and
TGA measurement shows no significant weight loss at this tem-
perature (see the Supporting Information). These results suggest
that the exothermic process is due to the thermally induced
diacetylene polymerization reaction. Given the relatively broad peak
width and moderate reaction heat, the thermal polymerization very
likely took place in a random and disordered manner rather than
topochemical. The DSC trace of tetrayne 17 (Figure 6B) shows a
noticeable endothermic transition at 137 °C, the origin of which is
likely due to loss of the solvent molecules trapped in the crystal
lattice rather than melting. At 226.9 °C, an intense sharp exothermic
peak emerges (ΔH = 249.7 kJ/mol), while TGA data reveal a slight
weight loss (ca. 10%) at this temperature. Collectively, the thermal
data suggest that tetrayne 17 must have undergone an ordered
polymerization pathway in the solid state. According to the crystal-
lographic packing data (vide supra), the solid-state reaction quite
possibly proceeds through the 1,4-addition of tetraynes.
Scheme 3. Synthesis of Poly(oligoyne-TTFV)s P1 and P2 via
DTF Oxidative Coupling
Supporting Information). The discrepancy stems from the well-
known fact that the B3LYP method tends to overestimate the
degree of electron delocalization for some linearly conjugated
systems,110ꢀ112 and hence, predictions on the structural proper-
ties of higher conjugated oligoynes and polyynes by this method
should be treated with caution.
In the crystal lattice, molecules of diyne-exTTF 16 are closely
packed at a distance of d = 5.35 Å with an inclination angle φ =
57.2° between the axes of molecules and the packing axis (see
Figure 5C, E), while the distances between the nearest parallel
diyne chains (C10ꢀC2 4.79 Å, C10ꢀC4 4.59 Å) are beyond the
range of van der Waals contact (ca. 3.4 Å). Such packing
geometries are moderately deviated from the optimal arrange-
ments for diacetylene 1,4-addition (d = 3.5 Å, C10ꢀC4 = 3.5ꢀ4.0
Å, φ= 45°)37,44,46 polymerization and therefore suggest a
low probability for diyne 16 to react by topochemically con-
trolled polymerization in the solid state. The single crystals of
tetrayne-exTTF 17 show a packing distance d = 5.34 Å similar to
The structural properties of macrocycle 21 were investigated
by theoretical modeling studies. The relatively large molec
ular size prevented the use of sophisticated ab initio or DFT
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Figure 5. (A) ORTEP drawing of diyne-exTTF 16 (30% probability thermal ellipsoids). (B) ORTEP drawing of diyne-exTTF 17 (30% probability
thermal ellipsoids). (C) Crystal packing of 16 viewed perpendicular to the b-axis. (D) Crystal packing of 17 viewed perpendicular to the b-axis. (E)
Packing geometry of 16 in the solid state. (F) Packing geometry of 17 in the solid state.
Figure 7. Molecular models of macrocycle 21: (A) front view, (B) side
Figure 6. DSC traces of (A) diyne-exTTF 16 and (B) tetrayne exTTF
view, (C) side view showing the twist angle of TTFV moiety, and (D)
molecular model of phenyl-TTFV precursor. Structures are optimized at
17 acquired at a scan rate of 10 °C minꢀ1 in N2 atmosphere.
the RM1 level of theory, and the SMe groups were replaced by H atoms
to reduce computational expenses.
approaches; nevertheless, semiempirical calculations based on a
reparameterized AM1 method (RM1)113 were conducted at reason-
21 appears to be only slightly reduced by about 4°. The small degree
of structural reorganization suggests that the assembly of macrocycle
21 does not suffer from a substantial energetic penalty stemming
Figure 7A, macrocycle 21 assumes a triangular-shaped ring frame-
able computational expenses, and the results provided qualitative
understanding on its molecular structural properties. As shown in
from ring strain. The amount of strain energy gained is calculated to
be 31.3 kJ/mol (7.48 kcal/mol) by an isodesmic reaction (see the
Supporting Information). The reasonably small strain energy of
21 accounts well for its much higher yield than other larger-sized
macrocyclic oligomers in the one-pot macrocyclization reac-
tion (Scheme 2 and Figure 4). Nevertheless, TTFV-based cyclic
work. A side view of its optimized structure (Figure 7B) shows that
the phenyl-oliogyne segments are in a nearly planar arrangement
without significant distortion. The phenyl-TTFV units, however,
adopt a nonplanar conformation with a twist angle of 64.4° (see
Figure 7C). Compared with the optimized structure of its alkynyl
phenyl-TTFV precursor (Figure 7D), the twist angle of macrocycle
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oligomers larger than the trimer, although disfavored by sharply
increased ring strain, are not unprecedented for TTFV-based
macrocyclophanes. In a previous report, Lorcy and co-workers also
observed an inseparable mixture of tetrameric and pentameric
macrocycles resulting from electrolysis of a bis(dithiafulvenyl)ben-
zene monomer.87
Electronic Properties. The electronic absorption properties
of oligoyne-exTTFs 16ꢀ18 were investigated by UVꢀvis spec-
troscopy. For comparison purposes, the UVꢀvis spectra of
acetylenic DTF precursors 13ꢀ15 were also acquired, and
detailed spectroscopic results are given in Figure 8 and summar-
ized in Table 1.
The UVꢀvis absorption spectrum of diyne-exTTF 16 (see
Figure 8A) features a strong low-energy absorption band at
423 nm and a relatively weak band at 332 nm, which can be
assigned to the πfπ* transitions at the phenyl-DTF moiety. In
the spectrum of tetrayne-exTTF 17, the lowest energy absorp-
tion band (λmax = 467 nm) is notably red-shifted by ca. 40 nm
relative to that of diyne 16, as a result of extended π-conjugation.
Additionally, a relatively strong high-energy absorption peak
emerges at 307 nm in the spectrum of 17, the origin of which
is likely due to the πfπ* transitions at the phenyl-butadiyne-
phenyl framework.114 The UVꢀvis absorption spectrum of
hexayne-exTTF 18 was measured from the solution obtained
after a brief aqueous workup of the reaction solution. Since TLC
analysis showed that crude product solution contained only a
small amount of impurities, the spectrum was deemed trust-
worthy in offering a qualitative characterization of the electronic
absorption properties of hexayne-exTTF 18. In contrast to the
structureless low-energy profiles observed in the spectra of diyne
16 and tetrayne 17, the absorption of hexayne 18 gives rise to
spectral patterns with more distinctive fine structures. In the low
energy region, four absorption bands are discernible at 506, 467,
431, and 398 nm, and the intensities of these bands are relatively
weak in comparison to the bands in the high-energy range. The
spacings of the low energy peaks are determined to be 1650,
1788, and 1923 cmꢀ1, which are consistent with a vibrational
progression resulting from exciton coupling to the CdC and
CꢁC stretching modes.63,70,115 In the high energy region, fine
structures composed of a number of sharp absorption peaks are
also clearly seen at 343, 326, 303, 283, and 264 nm. The spacings
of these peaks are 1520, 2328, 2332, and 2543 cmꢀ1, respectively,
and such a spectral pattern can be assigned to the characteristic
vibrational modes of phenyl-end-capped hexayne moiety.63,70
From Figure 8A, the low-energy cutoff absorption wave-
lengths of oligoyne-exTTFs 16ꢀ18 are clearly seen to redshift
with increasing length of the oligoyne unit. A similar trend of
redshift can be observed in the spectra of acetylenic DTF pre-
cursors. As shown in Figure 8B, the lowest energy absorption
bands are steadily red-shifted from alkynyl-DTF 13 (λmax
=
383 nm) to diyne-DTF 14 (λmax = 404 nm) and triyne-DTF 15
(λmax = 423 nm) as a function of the number of acetylenic units
attached to the phenyl-DTF group. The UVꢀvis data indicate
that the optical bandgaps (Eg) of oligoyne-exTTFs are depen-
dent on the chain length of the central oligoyne moiety. DFT
calculations have provided rationalization for the observed
electronic absorption properties. Figure 9 shows the frontier
molecular orbital (FMOs) contour surfaces and energies for
oligoyne-exTTFs 16ꢀ18 calculated at the B3LYP/6-31G* level.
It can be seen that the highest occupied molecular orbitals
(HOMOs) are evenly distributed across the entire molecular
π-frameworks for 16ꢀ18, whereas their lowest unoccupied molec-
ular orbitals (LUMOs) appear to be more and more localized at the
central oligoyne segment as the oligoyne chain length increases.
Empirically, the longer the oligoyne is, the stronger its electron acce-
pting ability. In this sense, the increasing chain length would
enhance the electron “pushꢀpull” effect between DTF (donor) and
oligoyne (acceptor), which in principle should result in red-shifted
electronic absorption. Quantitatively, the LUMO energy is seen to
decrease more significantly than the HOMO energy, rendering a
declining trend for the energy gap between HOMO and LUMO as a
function of oligoyne chain length. The calculated HOMOꢀLUMO
gaps for the oligoyne-exTTFs are in good agreement with the
optical gaps obtained from their UVꢀvis spectra (see Table 1).
Figure 8. Normalized UVꢀvis spectra of (A) oligyne-exTTFs 16ꢀ18
and (B) acetylenic DTFs 13ꢀ15 measured in CHCl3 at room
temperature.
Table 1. Summary of Electronic Properties of Oligoyne-exTTFs 16ꢀ18
entry
λabs, nm (ε, 104 Mꢀ1 cmꢀ1
)
EHOMO (eV)
ELUMO (eV)
ΔEHꢀLa (eV)
Egb (eV)
16
17
18
423 (6.69), 332 (2.23)
467 (8.39), 307 (6.58)
506, 467, 458, 431, 346, 326, 303, 283(sh), 264(sh)
ꢀ5.08
ꢀ5.08
ꢀ5.21
ꢀ2.04
ꢀ2.33
ꢀ2.71
3.04
2.75
2.50
2.61
2.39
2.25
a Energy gap between HOMO and LUMO. b Optical energy gap obtained from the intersection between the tangential line and the baseline of the lowest
energy absorption profile.
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state to form foldamers as depicted in Figure 3, since such a
helical orientation would attenuate the electronic communica-
tion between each conjugated repeat segments in the polymer
backbone to an extent similar to macrocycle 21. The UVꢀvis
spectrum of P2 shows three absorption bands at 444, 348, and
304 nm. Compared with P1, the λmax value of P2 is red-shifted by
22 nm as a result of further elongated oligyne chain length. In
addition to the significant πfπ* features, the spectra of P1 and
P2 both show a weak long-wavelength hump in the visꢀNIR
region, peaking at 566 nm for P1 and 738 nm for P2. The origins
of these peaks can be attributed to trace amounts of cationic
TTFV moieties due to incomplete reduction during the polymer
preparation process. This assignment is corroborated by the
results of spectroelectrochemical analysis (vide infra).
Electrochemical and Electrochromic Properties. The elec-
trochemical redox properties of oligoyne-exTTFs and related
compounds were investigated by cyclic voltammetric (CV)
analysis, and the detailed voltammograms are given in Figure 11.
The CV profile of diyne-exTTF 16 (Figure 11A) shows an
anodic peak at Epa = þ0.75 V and a cathodic peak at Epc = þ0.55
V on the first scan cycle. The anodic wave originates from the
oxidation of the DTF moieties in 16 to [DTF]•þ. The cathodic
peak, however, is not due to a correlated reversible reduction
process of [DTF]•þ. Instead, it corresponds to the simultaneous
bielectronic reduction on [TTFV]2þ that results from a rapid
dimerization reaction of [DTF]•þ on the electrode surface. The
assignment is evidenced by the dramatically changed voltammo-
gram patterns observed on the second CV scan cycle, in which a
new anodic peak emerges at þ0.62 V, preceding the anodic peak
at þ0.75 V. Compared with the cyclic voltammogram of TTFV
precursor 19 (Figure 11C), the reversible couple at Epa = þ0.62
V and Epc = þ0.55 V can be reasonably assigned to the redox
processes taking place at TTFV units. In the succeeding scan
cycles, the cathodic peak due to [DTF]•þ formation (at ca.
þ0.75 V) shows a gradual decrease in intensity, whereas the
redox wave pairs related to the TTFV groups are seen to steadily
increase in intensity. This observation is indicative of electro-
polymerization of 16 on the surface of the working electrode to
form multiple layers of conductive polymers. Indeed, after a
number of CV scans, a smooth and uniform thin film was
observed to be deposited on the surface of the working electrode.
In Figure 11A, it is also notable that the redox wave pairs
associated with the TTFV moiety show gradually increased
quasi-reversible behavior with increasing number of CV scans.
Tetrayne-exTTF 17 gives CV patterns (see Figure 11B) very
similar to those of diyne-exTTF 16 and affords a high-quality
conductive polymer thin film on the working electrode surface
after successive CV scans. The voltammogram of macrocycle 21
shows a pair of quasi-reversible redox waves at Epa = þ0.82 V and
Epc = þ0.56 V (Figure 11D). Compared with the voltammogram
of TTFV 19, the redox potentials of 21 are shifted anodically by
ca. 0.1 V. The shift is due to the conformational constraint in
macrocycle 21 that prohibits the TTFV moiety from stretching
into a trans TTFV dication upon oxidation. Similar effects have
been observed in a series of poly(ethylene glycol)-tethered
TTFV macrocycles reported by Lorcy and co-workers.89
Figure 9. Plots and energies of frontier molecular orbitals (FMOs) for
(A) diyne-exTTF 16, (B) tetrayne-exTTF 17, and (C) hexayne-exTTF
18. Geometry optimization and single-point energy calculations were
both undertaken at the B3LYP/6-31G* level, and the SMe groups were
replaced by SH groups to reduce computational expenses.
Figure 10. Normalized UVꢀvis spectra of compounds 19, 21, and
polymers P1 and P2 measured in CHCl3 at room temperature.
The UVꢀvis absorption properties of TTFV-based macro-
cycle 21, polymers P1 and P1, and their TTFV precursor 19 are
compared in Figure 10. The absorption spectrum of macrocycle
21 shows three πfπ* bands at 400, 335, and 260 nm. The lowest
energy band is red-shifted by ca. 20 nm relative to that of TTFV
precursor 19 (λmax = 380 nm) as a result of extended π-con-
jugation. The spectrum of polymers P1, which is structurally the
acyclic analogue of macrocycle 21, shows three absorption bands
at 422, 331, and 298 nm, and the lowest energy absorption peak
of P1 is red-shifted by 22 nm in comparison with 21. It is
interesting to note that the low-energy cutoff edges of 21 and P1
are nearly superimposable, which is indicative of the same optical
band gap energy for the two species and suggests an insignificant
degree of electronic delocalization across the acyclic π-frame-
work of P1. It is therefore reasonable to assume that the TTFV
units of P1 predominately take cis conformation in the neutral
Clearly, the CV results show that both diyne-exTTF 16 and
tetrayne-exTTF 17 are excellent precursors for preparation of
conductive polymer thin film devices by electrodeposition
methods.85 To further explore this potential, we then performed
electropolymerization of 16 and 17 on indium tin oxide (ITO)-
coated glass substrates by means of multicycle CV scans (100
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Figure 11. Cyclic voltammograms of (A) diyne-exTTF 16 (10ꢀ3 M), scan rate: 200 mV sꢀ1, working electrode: glassy carbon; (B) tetrayne-exTTF 17
(10ꢀ3 M), scan rate: 200 mV sꢀ1, working electrode: glassy carbon; (C) TTFV 19 (10ꢀ3 M), scan rate: 50 mV sꢀ1, working electrode: glassy carbon;
(D) macrocycle 21 (10ꢀ3 M), scan rate: 50 mV sꢀ1, working electrode: glassy carbon; (E) poly[16] thin film, scan rate: 50 mV sꢀ1, working electrode:
ITO glass; (F) poly[17] thin film, scan rate: 50 mV sꢀ1, working electrode: ITO glass. Experimental conditions: supporting electrolyte: Bu4NBF4 (0.1
M); solvent: CH2Cl2; counter electrode: Pt; reference electrode: Ag/AgCl. The arrows indicate the initial potential scan direction.
cycles at a scan rate of 50 mV sꢀ1 in the presence of ca. 10ꢀ3 M pre-
cursor in Bu4NBF4 solution). Polymer thin films of good quality
were obtained, and they exhibited good electrical conductivities
and TTFV-related electroactivities as manifested in their cyclic
voltammetric measurements (see Figure 11E, F). The cyclic
voltammograms of both poly[16] and poly[17] include a pair of
quasi-reversible redox waves resembling the CV profile of TTFV
precursor 19, indicating that TTFV moieties are the key compo-
nents contributing to the redox activity of the polymers. It is also
worth noting that the electrochemically prepared thin films of
poly[16] and poly[17] were found to completely lose electrical
conductivity and electroactivity after being stored in the neutral
state for more than two weeks. Nevertheless, the conductivity
and electroactivity could be readily reactivated by subjecting the
thin films to a positive potential at þ0.9 V for a few seconds. This
behavior suggests that the doping effect plays a key role in dictating
the conducting and redox active properties of the polymer thin films.
In addition to voltammetric properties, UVꢀvis spectroelec-
trochemical analysis on the exTTFs and related TTFV macro-
molecules was also conducted in order to probe their optical
responses to electrochemical redox processes. In our experi-
ments, each UVꢀvis spectral scan was performed after the electr-
olysis of an analyte at a controlled voltage for at least 90 s to
ensure the electric current attained a constant value. As such, the
systems examined by UVꢀvis spectroscopy can be deemed as
having arrived at equilibrium.
of 16 is similar to that of TTFV precursor 19 (Figure 12C), hence
corroborating the formation of TTFV species in the process of
electrochemical oxidation of diyne-exTTF 16. For tetrayne-
exTTF 17, a substantial decrease of the absorption peak at 647 nm
along with an increasing broad band at 668 nm can be observed from
the spectroelectrochemical measurements (Figure 12B). The trend is
similar to that of diyne 16, indicating the electrochemical polymeriza-
tion through the formation of TTFV units. Unlike the spectroelec-
trochemical data for diyne 16, the UVꢀvis absorption profile of
tetrayne 17 shows three sharp bands at 347, 377, and 408 nm when a
high degree of oxidation is reached. The spacings between these bands
are 2293 and 2015 cmꢀ1, which are consistent with a vibronic
progression arising from the CꢁC stretching mode. The vibrational
spectral pattern is also clearly discernible in the UVꢀvis absorption
spectrum of oxidized (cationic) poly[17] thin film, where three sharp
bands can be seen at 353, 383, and 415 nm, respectively. The fine
vibrational spectral features imply that oxidized (cationic) poly[17]
possess more rigid polymeric backbone than its neutral form.
The spectroelectrochemical data for macrocycle 21 is shown
in Figure 12D. As oxidation progresses, the lowest energy band at
ca. 422 nm drops in intensity along with a moderate degree of
redshift, while the absorption in the high-energy region (ca.
322 nm) is increased slightly. The most notable spectral varia-
tion, however, is the substantial rise of a broad absorption tail
from ca. 500 to 750 nm with a barely distinguishable peak at
600 nm. This pattern is markedly different from those of acyclic
TTFV species 16, 17, and 19. The pronounced low-energy tail in
the spectrum of oxidized macrocycle 21 is correlated to the
electronic absorptions of [TTFV]2þ. Given the unique confor-
mational constraint in macrocycle 21, the TTFV moieties must
retain cis-conformation even after being oxidized into [TTFV]2þ
dications. In this sense, macrocycle 21 offers a convenient model
Upon increasing oxidation, the lowest energy absorption band
of diyne-exTTF 16 at 423 nm decreases steadily and a new broad
band appears at 660 nm with relatively weak intensity (see
Figure 12A). The new long-wavelength band is assigned to the
characteristic absorption of [TTFV]2þ 89,116
.
The trend of
UVꢀvis spectral changes in the spectroelectrochemical analysis
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Figure 12. UVꢀvis spectroelectrochemistry of (A) diyne-exTTF 16 (10ꢀ4 M), (B) tetrayne-exTTF 17 (10ꢀ4 M), (C) TTFV 19 (10ꢀ4 M), and (D)
macrocycle 21 (10ꢀ4 M). Experimental conditions: supporting electrolyte: Bu4NBF4 (0.1 M); solvent: CH2Cl2; working electrode: Pt mesh; counter
electrode: Pt; reference electrode: Ag/AgCl. (E) UVꢀvis absorption spectra of poly[16] on ITO glass in the neutral (blue trace) and cationic (red trace)
states. (F) UVꢀvis absorption spectra of poly[17] on ITO glass in the neutral (blue trace) and cationic (red trace) states.
to unravel the unique electronic absorption properties of
cis-[TTFV]2þ 89
As shown in Figure 12E, the thin film of poly[16] shows
a strongly absorbing πfπ* transition band at 441 nm. In
addition, a weak absorption tail is observed in the range of ca.
500ꢀ700 nm, which likely arises from trace amounts of un-
reduced [TTFV]2þ moieties (doping) in the polymer film. After
being subjected to electrolysis at þ0.9 V for 1 min, the thin film of
poly[16] was observed to gradually change color from pale
yellow to dark green. The UVꢀvis spectrum of oxidized poly[16]
shows a strong broad low-energy band covering the spectral
range of 500 to 850 nm and peaking at 670 nm (Figure 12E).
Meanwhile the absorption peak at 441 nm is greatly attenuated.
In the UVꢀvis spectrum of neutral poly[17] thin film
(Figure 12F), a strong absorption band at 464 nm and a long
absorption tail extending from ca. 550 to 800 nm are observed.
Upon oxidation, the peak at 464 nm disappears, while a broad
.
The solution-phase UVꢀvis spectroscopic studies have re-
vealed that in the neutral state the synthesized TTFV-containing
compounds are electronic transparent in the visꢀNIR region of
the spectrum (500ꢀ800 nm), whereas they become quite
absorbing in this spectral range after being oxidized. In addition,
the oxidation and reduction processes on the TTFV moieties are
chemically reversible. Collectively, these spectral and electro-
chemical properties point to potential applications in electro-
chromism and electrochromic devices.117ꢀ121 To further
investigate the electrochromic properties in the solid state, the
UVꢀvis absorption spectra of polymer films prepared by elec-
trodeposition of diyne-exTTF 16 and tetrayne-exTTF 17 on
ITO glass were characterized in both neutral and oxidized states.
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band appears in the visꢀNIR region (ranging from 550 to
900 nm and peaking at 691 nm) together with three distinctive
vibronic bands at 415, 383, and 353 nm are observed. The fine
vibrational structures observed in the high-energy region are
consistent with the signature vibrational mode of tetrayne and
indicate that the tetrayne moieties in poly[17] remain intact in
the solid state during redox cycles.
setup. Spectroelectrochemistry was investigated through the following
protocol: In a 1 mm quartz cuvette were placed a Pt mesh as working
electrode, a Ag/AgCl reference electrode, and a Pt wire as counter
electrode. The applied potential (V) was increased in steps through
controlled potential electrolysis. In each potential step, the electrolysis
was first performed for ca. 1.5 min until the electrical current remained
constant, then a UVꢀvis spectrum was determined. Quantum chemical
calculations were performed using the density functional theory (DFT)
and semiempirical (RM1) methods implemented in the Spartan’06
software package (Wavefunction, Inc.).
’ CONCLUSIONS
The redox-controlled conformational switching behavior of
phenyl-substituted TTFV is the key to the versatile synthesis of
extended π-conjugated molecular/macromolecular structures
with different topologies and structural dimensions, ranging from
“rod-like” oligoyne-exTTFs to TTFV-containing shape-persistent
macrocycles and conducting polymer wires. The optical gaps of
oligoyne-exTTFs show a reducing trend and do not converge as the
oligoyne chain length increases from diyne to hexayne. X-ray structural
analysis shows that the terminal DTF groups in oligoyne-exTTFs
facilitate tight parallel packing of the oligoyne chains through SꢀS
contacts, exacting a toll on the kinetic stability of higher oligoyne
species. The oligoyne-exTTFs can be efficiently polymerized through
DTF oxidative coupling reactions and the polymer thin films resulting
from electropolymerization show intriguing conductivity and redox
activities. Furthermore, the polymer films exhibit redox-switchable
coloration in the Vis-NIR region of the spectrum, suggesting potential
applications in electrochromic devices. The synthetic access to TTFV-
oligoyne shape-persistent macrocycles 21 and 22 has not only added
new members to the family of phenylacetylene-based cyclophanes but
also provided useful models for better understanding the effect
of conformational constraint on the electronic properties of TTFV-
embedded macromolecular systems. It is also envisaged that the nearly
flat arrangement of the acetylene-rich ring framework of 21 could
render it a unique supramolecular host for certain metal ions and
aromatic molecular guests. Investigations toward this direction are
currently underway. Finally, solid-state structural and thermal analyses
have shown that tetrayne-exTTF 17 can undergo topochemical
polymerization more readily than diyne-exTTF 16. This finding hints
that macrocycle 22 and electrochemically induced poly[17], if taking
the folding conformation as proposed in Figure 3, may be further
cross-linked through solid-state polymerization reactions of tetraynes
to form well-defined and organized 3-dimensional polymer networks
such as “nanotubes”. Thisappealingaspectawaitsfurtherstudiesinour
future work.
Synthesis of DTF 13. To a solution of phosphonate 11 (900 mg,
2.96 mmol) in THF (60 mL) cooled by a dry ice bath was added n-BuLi
(1.50 mL, 2.5 M in THF, 3.75 mmol). The mixture was stirred for 20 min
and then 4-(trimethylsilylethynyl)benzaldehyde (12) (530 mg, 2.62
mmol) in THF (20 mL) was added. The mixture was allowed to be
slowly warmed up to rt and stirred overnight. The resulting dark brown
yellow solution was diluted with Et2O, washed with H2O, and dried over
MgSO4. After concentration under vacuum, the residue was subjected to
column chromatography (10% CH2Cl2 in hexanes) affording com-
pound 13 (800 mg, 2.12 mmol, 80%) as a light yellow liquid, which
slowly solidified into a yellow solid in a refrigerator: mp 90ꢀ91 °C; IR
(KBr) 2954, 2920, 2149, 1563, 1540, 1499, 1247 cmꢀ1; 1H NMR (500
MHz, CDCl3) δ 7.45 (d, J = 8.3 Hz, 2H), 7.13 (d, J = 8.4 Hz, 2H), 6.43
(s, 1H), 2.44 (s, 3H), 2.43 (s, 3H), 0.29(s, 9H); 13C NMR (125 MHz,
CDCl3) δ 136.7, 134.2, 132.5, 128.1, 126.9, 124.7, 120.5, 114.3, 105.8,
95.1, 19.5, 19.3, 0.5; HRMS (MALDI-TOF, þeV) m/z calcd for
C17H21S4Si 381.0295, found 381.0306 [M]þ.
Synthesis of Diyne-DTF 14. To a solution of DTF 13 (95 mg,
0.25 mmol) in 20 mL of THF/MeOH (1:1) was added K2CO3 (200 mg,
1.45 mmol). The mixture was stirred at rt for 30 min. The mixture was
diluted with CH2Cl2, washed with H2O, dried over MgSO4, and
concentrated to 1 mL in vacuo. The residue was diluted with CH2Cl2
(20 mL), and to this solution were then added TMSA (0.50 mL, 3.4 ꢂ
mmol) and a solution of CuI (90 mg, 0.47 mmol) and TMEDA
(0.10 mL) in CH2Cl2 (3 mL). The mixture was stirred at rt under air
for 3 h, and then it was washed with H2O, dried over MgSO4, and
column chromatographed to give DTF 14 (0.83 mg, 0.21 mmol, 82%) as
a yellow solid: mp 85ꢀ86 °C; IR (KBr) 2923, 2854, 2199, 2102, 1564,
1385 cmꢀ1; 1H NMR (CDCl3, 500 MHz) δ 7.44 (d, J = 8.5 Hz, 2H),
7.12 (d, J = 8.5 Hz, 2H), 6.43 (s, 1H), 2.43 (s, 3H), 2.42 (s, 3H), 0.22(s,
9H); 13C NMR (CDCl3, 125 MHz) δ 137.3, 135.1, 133.1, 128.0, 126.7,
124.7, 118.2, 113.8, 91.2, 88.2, 77.3, 74.9, 19.2, 19.1, ꢀ0.2; HRMS (EI,
þeV) m/z calcd for C19H20S4Si 405.0295, found 405.0299 [M]þ.
Synthesis of Triyne-DFT 15. To a solution of diyne-DTF 14 (220
mg, 0.55 mmol) in THF/MeOH (1:1, 30 mL) was added K2CO3 (200
mg, 1.45 mmol). The mixture was stirred at rt for 20 min. The mixture
was diluted with Et2O, washed with H2O, and dried over MgSO4. After
vacuum evaporation, the residue was redissolved in CH2Cl2 (20 mL). In
the meantime, a solution of CuI (300 mg, 1.57 mmol) and TMEDA
(0.30 mL) in CH2Cl2 (27 mL) was prepared. To this mixture was slowly
added a premixed solution of desilylated DTF diyne 14 and TMSA
(3.00 mL, 20.7 mmol) at rt under air over a period of 4 h, and then the
reaction mixture was stirred for another 0.5 h, washed with H2O, dried
over MgSO4, and column chromatographed (10% CH2Cl2 in hexanes)
to afford triyne-DTF 15 (138 mg, 0.324 mmol, 59%) as a yellow solid:
’ EXPERIMENTAL SECTION
General Methods. Chemicals and reagents were purchased from
commercial suppliers and used directly without purification. All reac-
tions were conducted in standard and dry glassware unless otherwise
noted. Evaporation and concentration were carried out with a water-
aspirator. Flash column chromatography was performed using 240ꢀ400
mesh silica gel. Thin-layer chromatography (TLC) was carried out with
silica gel 60 F254 covered on plastic sheets and visualized by UV light. 1H
and 13C NMR spectra were measured on a 500 MHz spectrometer and
chemical shifts are reported in ppm downfield from the signal of the
internal reference SiMe4. Coupling constants (J) are given in Hz. Positive-
mode high-resolution mass spectra (HRMS) were measured on a mass
spectrometer equipped with an electron-impact ionization (EI) ion
source or a hybrid quadrupole/TOF mass spectrometer equipped with
an o-MALDI ion source. All samples for thermal analyses (DSC and
TGA) were measured under a nitrogen atmosphere. Cyclic voltam-
metric (CV) analyses were carried out in a standard three-electrode
mp 117ꢀ118 °C; IR (KBr) 2957, 2916, 2163, 2072, 1595, 1566 cmꢀ1
;
1H NMR (500 MHz, CDCl3) δ 7.51 (d, J = 8.0 Hz, 2H), 7.17 (d, J = 8.5
Hz, 2H), 6.47 (s, 1H), 2.47 (s, 3H), 2.46 (s, 3H), 0.25(s, 9H); 13C NMR
(125 MHz, CDCl3) δ 137.9, 135.7, 133.7, 128.3, 127.0, 125.0, 117.6,
113.7, 89.6, 88.5, 75.4, 67.6, 62.2, 19.4, 19.3; HRMS (EI, þeV) m/z calcd
for C21H20S4Si 428.0217 found 428.0215 [M]þ.
Synthesis of Diyne-exTTF 16. To a solution of DTF 13 (107 mg,
0.283 mmol) in THF/MeOH (1:1, 30 mL) was added K2CO3 (200 mg,
1.45 mmol). The mixture was stirred at rt for 30 min, diluted with
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CH2Cl2, washed with H2O, dried over MgSO4, and concentrated in
vacuo to ca. 2 mL. The residue was redissolved in CH2Cl2 (30 mL), and
to the resulting yellow solution was added a solution of CuI (200 mg,
1.05 mmol) and TMEDA (0.20 mL) in CH2Cl2 (3 mL). The mixture
was stirred at rt under air for 3 h, washed with H2O, dried over MgSO4,
and concentrated in vacuo. The residue was subjected to silica flash
column chromatography (10% CH2Cl2 in hexanes) to give diyne-exTTF 16
(57 mg, 0.093 mmol, 66%) as a yellow solid: mp >170 °C dec; IR (KBr) 2923,
2856, 1653, 1621, 1385 cmꢀ1;1H NMR (500 MHz, CDCl3) δ7.51(d,J=8.2
Hz, 4H), 7.18 (d, J= 8.2 Hz, 4H), 6.48 (s, 2H), 2.47 (s, 6H), 2.46 (s, 6H); 13C
NMR (125 MHz, CDCl3) δ 137.3, 135.3, 133.1, 128.3, 127.0, 125.0, 119.0,
114.2, 83.0, 75.4, 19.5, 19.3; HRMS (MALDI-TOF, þeV) m/z calcd for
C28H23S8 614.9565, found 614.9566 [M þ H]þ.
to ca. 2 mL. The residue was redissolved in CH2Cl2/acetone (1:1, 30 mL).
To the resulting yellow solution was sequentially added a solution of CuI
(60 mg, 0.31 mmol) and TMEDA (0.10 mL) followed by PdCl2(PPh3)2
(10 mg, 0.015 mmol) in CH2Cl2 (2 mL). The mixture was refluxed under
air for 5 days, washed with H2O, dried over MgSO4, and concentrated in
vacuo. The residue was dissolved in CS2 (2 mL) and subjected silica flash
column chromatography (40% CH2Cl2 in hexanes) to afford compound
21 (9.0 mg, 0.0049 mmol, 18%) as a yellow solid: mp 210 °C dec; IR
1
(neat) 2921, 2253, 1522, 1430, 905, 730 cmꢀ1; H NMR (500 MHz,
CDCl3) δ 7.34ꢀ7.28 (m, 24 H), 2.45 (s, 18 H), 2.44 (s, 18 H); 13C NMR
(125 MHz, CDCl3) δ 138.1, 133.0, 128.4, 126.7, 125.6, 123.8, 120.3, 82.8,
75.3, 19.1 (one alkenyl signal and one SCH3 signal were not observed due
to coincidental overlap); HRMS (MALDI-TOF, þeV) m/z calcd for
C84H60S24 1835.7992, found 1835.8222 [M]þ.
Synthesis of Tetrayne-exTTF 17. To a solution of diyne-DTF 14
(71 mg, 0.18 mmol) in THF/MeOH (1:1, 20 mL) was added K2CO3
(200 mg, 1.45 mmol). The mixture was stirred at rt for 30 min, diluted
with Et2O, washed with H2O, and dried over MgSO4. After vacuum
evaporation, the residue was redissolved in CH2Cl2 (20 mL). To the
solution was then added a solution of CuI (60 mg, 0.31 mmol) and
TMEDA (0.10 mL) in CH2Cl2 (3 mL). The mixture was stirred at rt
under air for 3 h. Another portion of CH2Cl2 (130 mL) was added to
dissolve all the solids formed during the reaction. The solution was
washed with H2O, dried over MgSO4, and filtered through a short silica
plug to afford pure tetrayne-exTTF 17 (58 mg, 0.88 mmol, 100%) as a
golden flake: mp 200 °C dec; IR (KBr) 2959, 2925, 2854, 2195, 1637,
1618, 1385 cmꢀ1; 1H NMR (500 MHz, CDCl3) δ7.50 (d, J = 8.0 Hz,
4H), 7.15 (d, J = 8.0 Hz, 4H), 6.45 (s, 2H), 2.45 (s, 6H), 2.44 (s, 6H);
13C NMR (125 MHz, CDCl3) δ 137.7, 136.2, 133.5, 128.2, 126.6, 125.0,
117.1, 113.6, 78.8, 76.0, 68.6, 64.9, 19.1, 19.0; HRMS (MALDI-TOF,
þeV) m/z calcd for C32H22S8 661.9487, found 661.9519 [M]þ.
Synthesis of TTFV 19. To a solution of DTF 13 (107 mg, 0.283
mmol) in CH2Cl2 (20 mL) was added I2 (260 mg, 1.02 mmol). The
resulting black greenish mixture, after being stirred at rt overnight, was
quenched with satd Na2S2O3 aq solution (20 mL). The contents were
kept under stirring for another 1 h, then the yellow organic layer was
separated, washed with H2O, dried over MgSO4, and concentrated in
vacuo. The residue was dissolved in CS2 (2 mL) and then subjected to
flash column chromatography (15% CH2Cl2 in hexanes) to give
compound 19 (64 mg, 0.085 mmol, 60%) as a yellow liquid, which
solidified into a yellow solid in the refrigerator: mp 180ꢀ181 °C; IR
(neat) 2919, 2849, 2153, 1523, 1425, 1247, 839, 861 cmꢀ1; 1H NMR
(500 MHz, CDCl3) δ 7.38 (d, J = 8.4 Hz, 4 H), 7.30 (d, J = 8.4 Hz, 4 H),
2.42 (s, 6 H), 2.37 (s, 6 H), 0.23 (s, 18H); 13C NMR (125 MHz, CDCl3)
δ 138.0, 137.2, 132.5, 128.7, 126.7, 126.5, 123.8, 121.4, 105.3, 95.2, 19.13,
19.07, 0.2; HRMS (MALDI-TOF, þeV) m/z calcd for C34H38S8Si2
758.0278, found 758.0272 [M]þ.
Synthesis of Macrocycle 22. To a solution of TTFV 20 (31 mg,
0.039 mmol) in THF/MeOH (1:1, 20 mL) was added K2CO3 (200 mg,
1.45 mmol). The mixture was stirred at rt for 20 min, diluted with CH2Cl2
(20 mL), washed with H2O, dried over MgSO4, and concentrated in vacuo to
ca.3mL.TheresiduewasredissolvedinCH2Cl2/acetone (1:1, 40 mL), and to
the resulting solution was added a solution of CuI (60 mg, 0.31 mmol) and
TMEDA (0.10 mL) in CH2Cl2 (3 mL). Then PdCl2(PPh3)2 (10 mg, 0.15
mmol) was added. The mixture was refluxed under air for 5 days. The mixture
was diluted with CH2Cl2,washedwithsatdNH4Cl (aq) and H2O sequentially,
and then dried over MgSO4. After vacuum evaporation, the residue was
subjected to silica flash column chromatography (35% CH2Cl2 in hexanes) to
afford crude product of 22. The presence of some inextricable oligomer
byproducts thwarted its complete purification.
Synthesis of Poly(diyne-TTFV)s P1. To a solution of diyne 16
(43 mg, 0.070 mmol) in CH2Cl2 (50 mL) was added I2 (46 mg, 0.18
mmol). The mixture was stirred at rt overnight, resulting in a pale yellow
solution with dark green precipitates. To this mixture was added satd
Na2S2O3 solution (aq 20 mL), and the content was kept under stirring
for 1 h. The resulting yellow organic layer was separated, washed with
H2O, and dried over MgSO4. Filtration followed by evaporation under
vacuum afforded P1 as a yellow solid (39 mg, crude yield 91%): HRMS
(MALDI-TOF, þeV) m/z found 1225.9014 (m = 2), 1837.8391 (m =
3), 2450.7645 (m = 4), 3063.6956 (m = 5), 3681.4704 (m = 6),
4902.6271 (m = 8).
Synthesis of Poly(tetrayne-TTFV)s P2. To a solution of TTF
tetrayne 17 (26 mg, 0.040 mmol) in CH2Cl2 (40 mL) was added I2 (30
mg, 0.12 mmol). The mixture was stirred at rt overnight, and then satd
Na2S2O3 solution was added. The mixture was stirred for another 1.5 h,
washed with H2O, dried over MgSO4, and evaporated in vacuo to afford
P2 (24 mg, crude yield 80%) as an orange solid: HRMS (MALDI-TOF,
þeV) m/z found 1321.8988 (m = 2), 1983.8686 (m = 3), 2643.7519 (m =4).
’ ASSOCIATED CONTENT
Synthesis of TTFV 20. To a solution of diyne-DTF 14 (56 mg, 0.14
mmol) in CH2Cl2 (30 mL) was added I2 (137 mg, 0.54 mmol). The
mixture was stirred at rt under air overnight, and then a satd Na2S2O3 aq
solution (20 mL) was added. The mixture was stirred for another 1 h.
The organic layer was separated, washed with H2O, dried over MgSO4,
and concentrated in vacuo. The residue was subjected to silica column
chromatography (20% CH2Cl2 in hexanes) to afford compound 20 as a
yellow solid (32 mg, 0.040 mmol, 60%): mp 125ꢀ127 °C; IR (KBr):
2959, 2921, 2200, 2101, 1596, 1520, 1503 cmꢀ1; 1H NMR (500 MHz,
CDCl3) δ7.41 (d, J=8.0Hz, 2H), 7.32(d, J= 8.0 Hz, 2H), 2.43 (s, 3H), 2.37
(s, 3H), 0.23(s, 9H); 13C NMR (125 MHz, CDCl3) δ 139.5, 137.7, 133.3,
129.1, 126.4, 125.5, 123.2, 119.4, 91.3, 88.2, 77.1, 75.0, 19.2, 19.1,-0.2; HRMS
(MALDI-TOF, þeV) m/z calcd for C38H38S8Si2 for 806.0278, found
806.0280 [M]þ.
Supporting Information. 1H and 13C NMR spectro-
S
b
scopic characterizations for all new compounds, mass spectro-
metric data for 18, P1, and P2, computational details for
oligoyne-exTTFs 16ꢀ18 and macrocycle 21, and X-ray crystal-
lographic data for 16 and 17. This material is available free of
charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: yuming@mun.ca.
Synthesis of Macrocycle 21. To a solution of TTFV 19 (64 mg,
0.085 mmol) in THF/MeOH (1:1, 30 mL) was added K2CO3 (300 mg,
2.17 mmol). The mixture was stirred at rt for 20 min, diluted with
CH2Cl2, washed with H2O, dried over MgSO4, and concentrated in vacuo
’ ACKNOWLEDGMENT
We thank the Natural Sciences and Engineering Research
Council (NSERC) of Canada, Canadian Foundation for Innovation
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The Journal of Organic Chemistry
ARTICLE
ꢃ
(CFI), and Memorial University of Newfoundland for financial
support.
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