α,ω-Bis(thioacetyl)oligophenylenevinylene Chromophores from Thioanisol Precursors

Article abstract of DOI:10.1021/jo035664g

The selective cleavage of arylmethyl thioethers provides a convenient protocol for the synthesis of all-E isomers of α,ω -bis(thioacetyl)oligophenyenevinylene molecules (OPVs). The S-methyl group is tolerant of Wittig-type and Heck-type reactions for form

Full text of DOI:10.1021/jo035664g

r,ω-Bis(th ioa cetyl)oligop h en ylen evin ylen e Ch r om op h or es fr om
Th ioa n isol P r ecu r sor s
Dwight S. Seferos,† David A. Banach,‡ Norma A. Alcantar,§, J acob N. Israelachvili,§ and
Guillermo C. Bazan*,†,‡
Departments of Chemistry and Biochemistry, Materials, and Chemical Engineering, Institute for Polymers
and Organic Solids, University of California, Santa Barbara, California 93106
bazan@chem.ucsb.edu
Received November 11, 2003
The selective cleavage of arylmethyl thioethers provides a convenient protocol for the synthesis of
all-E isomers of R,ω-bis(thioacetyl)oligophenyenevinylene molecules (OPVs). The S-methyl group
is tolerant of Wittig-type and Heck-type reactions for forming OPV structures and can be converted
to the S-acetyl group by treatment with sodium thiomethoxide and acetyl chloride. The thermal
conditions of the deprotection/reprotection step concurrently isomerize the conjugated chromophore
to the all-E isomer, regardless of the stereochemistry of the starting olefins. This approach is
demonstrated for a variety of linear and [2.2]paracyclophane containing OPVs, which have been
characterized by electrochemical and spectroscopic techniques. Additionally, these S-acetyl-
terminated OPVs self-assemble on gold surfaces. Monolayers containing these molecules were
characterized by water contact angle measurements, ellipsometry, and X-ray photoelectron
spectroscopy.
In tr od u ction
conjugated thiol is functionalized by an electron-with-
drawing group.8
Self-assembled monolayers (SAMs) formed by organic
thiols on gold surfaces are an area of intense scientific
investigation.1,2 SAMs of alkane-thiolates on gold form
spontaneously from solution and are of particular interest
because they are ordered, densely packed, and have
dimensions which are consistent with a single molecular
layer. SAMs of aromatic-thiolates have also been inves-
tigated.3 Experimental evidence suggests that they are
more stable toward oxidation4 but form less quickly5 and
with less order6 when compared to their aliphatic coun-
terparts. Also, electronic conjugation between the ad-
sorbed thiolate and aromatic substituents has been
shown to influence the binding to the surface, and the
molecular dipole of the resultant adsorbed species.7 For
example, adsorption to the surface is slowed when a
Thiol (and dithiol)-functionalized molecules that con-
tain a molecular fragment with a conjugated electronic
structure are attractive because they allow for the
attachment of well-defined organic semiconducting ma-
terials onto a metallic surface and are often referred to
as molecular wires. Additionally, these rigid, functional
molecules may be used as a template to assemble higher
order structures. Previously, these concepts have been
demonstrated by the fabrication and electronic charac-
terization of metal-molecule junctions9 and through the
formation of surface-nanoparticle10 or nanoparticle-
nanoparticle11 assemblies. Molecular structures that have
been used in this respect are typically thiol- or thioacetyl-
(8) Liao, S.; Shnidman, Y.; Ulman, A. J . Am. Chem. Soc. 2000, 122,
3688.
(9) (a) Reed, M. A.; Zhou, C.; Muller, C. J .; Burgin, T. P.; Tour, J .
M. Science 1997, 278, 252. (b) Chen, J .; Reed, M. A.; Rawlett, A. M.;
Tour, J . M. Science 1999, 286, 1550. (c) Cui, X. D.; Primak, A.; Zarate,
X.; Torfohr, J .; Sankey, O. F.; Moore, A. L.; Moore, T. A.; Gust, D.;
Harris, G.; Lindsey, S. M. Science 2001, 294, 571. (d) Ramachandran,
G. K.; Hopson, T. J .; Rawlett, A. M.; Nagahara, L. A.; Primak, A.;
Lindsey, S. A. Science 2003, 300, 1413. (e) Wold, D. J .; Frisbie, C. D.
J . Am. Chem. Soc. 2001, 123, 5549. (f) Kushmerick, J . G.; Holt, D. B.;
Yang, J . C.; Naciri, J .; Moore, M. H.; Shashidhar, R. Phys. Rev. Lett.
2002, 89, 086802-1. (g) Holmlin, R. E.; Hagg, R.; Chabinyc, M. L.;
Imagilov, R. F.; Cohen, A. E.; Terfort, A.; Rampi, M. A.; Whitesides,
G. M. J . Am. Chem. Soc. 2001, 123, 5075.
† Department of Chemistry and Biochemistry.
‡ Department of Materials.
§ Department of Chemical Engineering.
Current address: Department of Chemical Engineering, Univer-
sity of South Florida, Tampa, FL 33620.
(1) Selected reviews on self-assembled monolayers: (a) Ulman, A.
Introduction to Ultrathin Organic Films; Academic Press Inc: New
York, 1991. (b) Dubois, L. H.; Nuzzo, R. G. Annu Rev. Phys. Chem.
1992, 43, 437. (c) Ulman, A. Chem. Rev. 1996, 96, 1533. (d) Schreiber,
F. Prog. Surf. Sci. 2000, 65, 151.
(2) Bain, C. D.; Troughton, E. B.; Tao, Y.-T.; Evall, J .; Whitesides,
G. M.; Nuzzo, R. G. J . Am. Chem. Soc. 1989, 111, 321.
(3) (a) Sabatani, E.; Cohen-Boulakia, J .; Bruening, M.; Rubinstein,
I. Langmuir 1993, 9, 2974. (b) Chang, S.-C.; Chao, I.; Tao, Y.-T. J .
Am. Chem. Soc. 1994, 116, 6792.
(4) Kolega, R. R.; Shlenoff, J . B. Langmuir 1998, 14, 5469.
(5) Garg, N.; Friedman, J . M.; Lee, T. R. Langmuir 2000, 16, 4266.
(6) Tao, Y.-T.; Wu, C.-C.; Eu, J .-Y.; Lin, W.-L. Langmuir 1997, 13,
4018.
(10) (a) Andres, R. P.; Bein, T.; Dorogi, M.; Feng, S.; Henderson, J .
I.; Kubiak, C. P.; Mahoney, W. J .; Osifchin, R. G.; Reifenberger, R.
Science 1996, 272, 1323. (b) Brust, M.; Bethell, D.; Kiely, C. J .;
Schiffrin, D. J . Langmuir 1998, 14, 5425.
(11) (a) Andres, R. P.; Bielefeld, J . D.; Henderson, J . I.; J anes, D.
B.; Kolagunta, V. R.; Kubiak, C. P.; Mahoney, W. J .; Osifchin, R. G.
Science 1996, 273, 1690. (b) Novak, J . P.; Feldheim, D. L. J . Am. Chem.
Soc. 2000, 122, 3979. (c) J avier, A.; Yun, C. S.; Sorena, J .; Strouse, G.
F. J . Phys. Chem. B 2003, 107, 435. (d) Ouyang, M.; Awschalom, D.
D. Science 2003, 301, 1074.
(7) Ulman, A. Acc. Chem. Res. 2001, 34, 855.
10.1021/jo035664g CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/20/2004
1110
J . Org. Chem. 2004, 69, 1110-1119

R,ω-Bis(thioacetyl)oligophenylenevinylene Chromophores
SCHEME 1. Dith ioa cetyl OP Vs 1-7
terminated oligomers of polyphenylene12 (OP) and poly-
phenylenethynylene13 (OPE) because their synthesis and
self-assembly have been well established. Thioacetyl
groups are often the preferred terminal functionality for
these structures because they behave much like thiols
but are not as susceptible to oxidation. When exposed to
gold surfaces thioacetyl groups are cleaved in situ to form
gold thiolate monolayers identical with those formed from
organic thiols.14
mophore dimers that incorporate a [2.2]paracyclophane
unit as a point of attachment. The molecular structure
of these paracyclophane chromophores can serve to study
how a well-defined through-space delocalized unit influ-
ences electronic communication between a pair of elec-
troactive organic units.18 This property should prove
significant when examining the fabrication of molecular-
scale junctions19 and devices.20
In this contribution we report a general and straight-
forward synthetic route to a variety of thioacetyl-
terminated oligo(phenylenevinylene)s (OPVs). The OPV
backbone is a superior semiconducting organic structure,
relative to OP and OPE, because of its high degree of
planarity and highly tunable optical properties.15 Few
synthetic protocols that lead to thiol- or thioacetyl-
terminated OPVs have been reported. Chidsey et al.16
reported a synthetic route to benzylthiol-terminated
OPVs. However, the methylene spacer in the benzyl
system introduces a point of saturation in an otherwise
fully conjugated organic thiol system; this disrupts
electronic delocalization from the OPV π-system to the
thiol, and ultimately to the surface. Recently, the syn-
thesis of thioacetyl-terminated stilbenes and distrylben-
zenes was reported by Bjørnholm et al.17 In this effort,
the synthetic intermediates were S-tert-butyl derivatives,
which are not commercially available, and in many cases
conversion to the corresponding S-acetyl-protected target
compounds is difficult to achieve.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . The synthetic
challenge in building thiol-terminated OPVs lies in the
incorporation of the highly reactive thiol terminus, or
termini, into the growing molecular backbone. Although
previous synthetic strategies employ protecting the thiol
as an S-acetyl21 or S-tert-butyl17 derivative, we chose a
more general procedure. Several considerations led us to
incorporate S-methyl derivatives. First, many derivatives
are commercially available, allowing this route to be
widely applicable. Second, S-acetyl derivatives are less
tolerant of synthetic manipulations that require nucleo-
philic bases, such as trialkylamines. As a result, S-acetyl
derivatives are difficult to use in palladium-mediated
cross-coupling protocols, such as Heck-type reactions.
Third, a general method is available for the selective
dealkylation of methylaryl thioethers.22
The reaction of methylaryl thioethers with sodium
thiomethoxide in polar solvent leads to the selective
cleavage of the S-CH3 bond.22 Under these conditions,
nucleophilic attack by sodium thiomethoxide on the
terminal methyl group of the thioether produces dimethyl
sulfide and generates an aryl sulfur anion. Although
typical protocols involve acidic workup, we demonstrate
that workup with acetyl chloride installs the acetyl group
at the sulfur terminus, and that these S-acetyl deriva-
The molecular structures reported in this contribution
are shown in Scheme 1. In addition to the detailed
synthetic protocol, we report on the electronic character-
ization of these molecules, and demonstrate the formation
of self-assembled monolayers on gold surfaces. Our
molecular building blocks include OPVs up to six and a
half repeat units in length, which are soluble in common
organic solvents. Furthermore, we include OPV chro-
(17) Stuhr-Hansen, N.; Chrisensen, J . B.; Harrit, N.; Bjørnholm, T.
J . Org. Chem. 2003, 68, 1275.
(18) Bartholomew, G. P.; Bazan, G. C. Acc. Chem. Res. 2001, 34,
30.
(19) Nitzan, A.; Ratner, M. A. Science 2003, 300, 1384.
(20) Tour, J . M. Acc. Chem. Res. 2000, 33, 791.
(21) Hsung, R. P.; Babcock, J . R.; Chidsey, C. E. D.; Sita, L. R.
Tetrahedron Lett. 1995, 36, 4525.
(12) Azzam, W.; Wehner, B. I.; Fischer, R. A.; Terfort, A.; Woll, C.
Langmuir 2002, 18, 7766.
(13) Tour, J . M.; J ones, L., II; Pearson, D. L.; Lamba, J . J . S.; Burgin,
T. P.; Whitesides, G. M.; Allara, D. L.; Parikh, A. N.; Atre, S. V. J .
Am. Chem. Soc. 1995, 117, 9529.
(14) Wasserman, S. R.; Biebuyck, H.; Whitesides, G. M. J . Mater.
Res. 1989, 4, 886.
(15) Sherf, U. Top. Curr. Chem. 1999, 201, 163.
(16) Dudek, S. P.; Sikes, H. D.; Chidsey, C. E. D. J . Am. Chem. Soc.
2001, 123, 8033.
(22) (a) Tiecco, M.; Tingoli, M.; Testiferri, L.; Chianelli, D.; Maiolo,
F. Synthesis 1982, 478. (b) Testaferri, L.; Tiecco, M.; Tingoli, M.;
Chianelli, D.; Montanucci, M. Synthesis 1983, 751.
J . Org. Chem, Vol. 69, No. 4, 2004 1111

Seferos et al.
tives are much more soluble than the corresponding
S-methyl or S-H counterparts. This additional stability
is significant because it allows the final, surface-reactive
compounds to be purified by standard chromatographic
techniques.
in 61% yield. 1,4-Bis[2′,5′-dihexyloxy-4′-(4′′-(4′′′-(meth-
ylthio)styryl)styryl)styryl]benzene (3a ) was obtained after
coupling of 1,4-bis[methyl(triphenyl)phosphonium bro-
mide]benzene and 2 equiv of 10. Finally, 3a was con-
verted to the S-acetyl-terminated derivative 3 in the
same manner described above for 1.
Additionally, the thermal conditions of the deprotec-
tion/reprotection step yield exclusively the all-E isomer,
eliminating the need for a subsequent isomerization step,
regardless of the stereochemistry of the starting material.
Because they are more linear, and thus more fully
conjugated, the all-E isomers of OPVs are the most
desirable structures. It should be noted that the isomer-
ization of the final conjugated targets often complicates
the synthesis of OPV-type molecules. In our efforts, many
of the methylated precursors can only be obtained as a
mixture of E/Z isomers. However, the concurrent isomer-
ization process during the final conversion to the thio-
acetyl product allows one to use all isomers obtained in
the previous manipulations to maximize overall yields
and avoid tedious chromatographic separations.
The synthetic route to alkoxy-substituted OPV-SAc
molecules is shown in Scheme 2. In the first example,
commercially available 4-(methylthio)benzaldehyde and
1,4-bis[(methyl)triphenylphosphonium chloride]-2,5-di-
hexyloxybenzene were reacted under Wittig-type condi-
tions23 to form the distyrylbenzene derivative 1,4-
dihexyloxy-2,5-bis[4′-(methylthio)styryl]benzene (1a ) in
93% yield. The S-methyl groups were cleaved by treat-
ment with sodium thiomethoxide to form a dianionic
intermediate, which was quenched in situ with acetyl
chloride. After standard workup and routine chromatog-
raphy, 1,4-dihexyloxy-2,5-bis[4′-(acetylthio)styryl]ben-
zene (1) was isolated in 39% yield. We note that the
temperature (140 °C) of this deprotection/reprotection
step provides the all-E isomer, as determined by using
absorption and NMR (1H and 13C) spectroscopies.
For the synthesis of 1,4-dihexyloxy-2,5-bis[4′-(4′′-
(acetylthio)styryl)styryl]benzene (2), which contains an
OPV structure with five aromatic rings and four olefinic
linkages, 4-(methylthio)benzaldehyde was extended by
one repeat unit to 4-(4′-(methylthio)styryl)benzaldehyde
(8). This conversion is readily accomplished by the
Horner-Emmons-Wadsworth reaction24 of 4-(methyl-
thio)benzaldehyde with diethyl 4-(4,4,5,5-tetramethyl-
1,3-dioxolan-2-yl)benzylphosphonate, followed by hydrol-
ysis of the terminal acetal with dilute hydrochloric acid
to provide 8 in 82% yield. Compound 8 reacts under
similar conditions as in the synthesis of 1 to yield 1,4-
dihexyloxy-2,5-bis[4′-(4′′-(methylthio)styryl)styryl]ben-
zene (2a ) in 61% yield. Subsequent deprotection/acylation
provided 2 in 87% yield.
The synthesis of the paracyclophane derivatives and
the unsubstituted distyrylbenzenes, shown in Scheme 3,
adopts a simple two-step protocol. In the first step, the
methyl derivatives were formed and isolated after either
Heck or Wittig-type reactions. Then, in the one-pot
deprotection/reprotection procedure described for 1-3,
the methyl group was cleaved, and the anion was
acylated. For example, 4,12-bis[4′-(acetylthio)styryl][2.2]-
paracyclophane (6) was made available after Heck cou-
pling of 4-(methylthio)styrene with pseudo-p-dibromo-
[2.2]paracyclophane, which provides 4,12-bis[4′-(meth-
ylthio)styryl][2.2]paracyclophane (6a ) in 37% yield,fol-
lowed by deprotection/reprotection to form 6 in 78% yield.
2,5-Bis[4′-(acetylthio)styryl]benzene (4) was prepared by
(1) a Horner-Wittig reaction of 4-(methylthio)benzalde-
hyde and 1,4-bis[methyldiethylphosphonate]benzene to
form 2,5-bis[4′-(methylthio)styryl]benzene (4a ), followed
by (2) deprotection/reprotecton to form the S-acyl-
terminated product 4, in 65% and 49% yield, receptively.
In this example a 49% yield of the deprotection/repro-
tection step was achieved on a multiple gram scale. 4,7,-
12,15-Tetra[4′-(acetylthio)styryl][2.2]paracyclophane (5)
and 4,4′-bis[4-(acetylthio)styryl]-1,1′-dibenzene (7) were
afforded in an analogous sequence to 4 in 77% and 76%
overall yield, starting from 4,7,12,15-tetra[(methyl)-
diethylphosphonate][2.2]paracyclophane and 4,4′-bis-
[(methyl)triphenylphosphonium bromide]-1,1′-dibenzene,
respectively.
In the synthesis of 1-7, the solubility of the methyl
derivatives 1a -7a is substantially lower, relative to that
of the S-acetyl compounds. Solubility is further dimin-
ished after isomerization to the all-E isomers, which was
necessary for spectral assignment of the 1H and 13C NMR
resonances. As a result of this low solubility, 13C NMR
spectroscopy assignments of S-methyl derivatives are
reported only for 1a , 5a , and 6a , the most soluble
intermediates. Compounds 4a and 7a were the least
soluble S-methyl-terminated OPVs, and could only be
isolated by trituration. In the case of 7a , no 1H NMR data
1
are available, and only the H NMR data are given for
the final target compound 7. The low solubility of the
intermediates highlights the efficiency of the deprotec-
tion/reprotection step.
Spectr oscopy an d Electr och em ical Measu r em en ts.
Spectroscopic data for 1-7 and electrochemical measure-
ments of 1a -6a are summarized in Table 1. For the
electrochemical measurements, we chose to work with
all S-methyl derivatives, instead of the S-acetyl coun-
terparts, to rule out adsorption onto the electrode sur-
faces and avoid reduction of the carbonyl functionality.
It is assumed that the carbonyl does not contribute to
the OPV π-system and that it is removed once the
molecule is self-assembled onto a surface.26 In the case
of 7a , no electrochemical data could be obtained due to
low solubility.
The synthesis of 1,4-bis[2′,5′-dihexyloxy-4′-(4′′-(4′′′-
(acetylthio)styryl)styryl)styryl]benzene (3) was accom-
plished in four steps. First, 4-(methylthio)benzaldehyde
was converted to 4-(4′-(methylthio)styryl)styrene (9) in
32% yield by a Horner-Emmons-Wadsworth reaction
with diethyl-4-(vinyl)benzylphosphonate. Next, Pd cata-
lyzed coupling with 4-iodo-2,5-dihexyloxybenzaldehyde
under phosphine-free conditions25 afforded 2,5-dihexyl-
oxy-4-(4′-(4′′-(methylthio)styryl)styryl)benzaldehyde (10)
(23) Maercker, A. Org. React. 1965, 14, 270.
(24) Wadsworth, W. S. Org. React. 1977, 25, 73.
(25) Heck, R. F. Org. React. 1982, 27, 345.
(26) Price, D. W., J r.; Dirk, S. M.; Rawlett, A. M.; Chen, J .; Wang,
W.; Reed, M. A.; Zacarias, A. G.; Seminario, J . M.; Tour, J . M. Mater.
Res. Soc. Proc. 2001, 660, J J 9.4.1/D7.4.1.
1112 J . Org. Chem., Vol. 69, No. 4, 2004

R,ω-Bis(thioacetyl)oligophenylenevinylene Chromophores
SCHEME 2. Syn th etic Rou te to OP Vs 1-3a
a
Reagents and conditions: (i) NaH, THF. (ii) (1) NaH, toluene; (2) HCl (aq), THF. (iii) NaH, THF. (iv) Pd(OAc)2, Et3N, DMF. (v)
1,4-Bis[(methyl)triphenylphosphonium chloride]benzene, NaH, THF. (vi) (1) NaSCH3, DMF; (2) AcCl.
Examination of the absorption and fluorescence spectra
of 1-3 reveals a red shift as the conjugation length is
systematically increased. The λmax ) 447 nm for 3 is close
to the saturation maximum (λmax ≈ 460 nm) observed for
OPVs with eight aryl rings and seven double bonds.28
Compound 1 is red-shifted compared to the unsubstituted
distyrylbenzene derivative 4, which is attributed to the
donating properties of alkoxy substituents.29 The linear
spectra of compounds 4 and 7 are nearly identical,
(27) Cervini, R.; Li, X.-C.; Spencer, G. W. C.; Holmes, A. B.; Moratti,
S. C.; Friend, R. H. Synth. Met. 1997, 84, 359.
(28) Maddux, T.; Li, W.; Yu, L. J . Am. Chem. Soc. 1997, 119, 844.
(29) Dottinger, S. E.; Hohloch, M.; Segura, J . L.; Steinhuber, E.;
Hanack, M.; Tompert, A.; Oelkrug, D. Adv. Mater. 1997, 9, 223.
J . Org. Chem, Vol. 69, No. 4, 2004 1113

Seferos et al.
SCHEME 3. Syn th etic Rou te to OP Vs 4-7a
a
Reagents and conditions: (i) 1,4-Bis[(methyl)triphenylphosphonium chloride]benzene, NaH, THF. (ii) 4,7,12,15-Tetra[(methyl)-
diethylphosphonate][2.2]paracyclophane, KOt-Bu, DMF. (iii) Methyltriphenylphosphonium bromide, NaH, THF. (iv) Psuedo-p-
dibromo[2.2]paracyclophane, Pd(OAc)2, tri-o-tolylphosphine, Et3N, DMF. (v) 1,1′-Bis[(methyl)triphenylphosphonium brominde]-4,4′-
dibenzene, KH, THF. (vi) (1) NaSCH3,DMF; (2) AcCl.
TABLE 1. Electr och em ica l a n d Sp ectr oscop ic Da ta for
the [2.2]paracyclophane-containing chromophores. The
large stokes shift of 90 nm in 6 is attributed to internal
conversion from the excited “stilbene like” chromophore
to the inter-ring excited state centered on the [2.2]-
paracyclophane core, which has a very low oscillator
strength.30 Compound 5 can be viewed as a dimer of 4.
When comparing 5 to 4, a red shift in both the absorption
and fluorescence is observed, and thus the S1 state differs
in the two molecules. The lower energy of the S0 f S1
transition in 5 is attributed to a mixed excited state that
has contributions from through-space as well as through-
bond delocalization.31
OP Vs 1-7
compda λmaxb (nm) PLb (nm) Egc (eV) IPd (eV) EAe (eV)
1
2
3
4
5
6
7
402
428
447
365
408
336
359
460
489
505
423
467
425
427
2.75
2.58
2.48
3.06
2.56
3.22
3.08
5.19
5.25
5.02
5.32
5.13
5.28
2.44
2.67
2.54
2.23
2.57
2.06
a
b
The structures are given in Scheme 1. Measured in DCM.
c Refers to the optical band-gap measured from the absorption edge
at 10% maximum intensity. Refers to the ionization potential
d
Self-Assem bly a n d Ch a r a cter iza tion of Mon ola y-
er s. Examples of S-acetyl-terminated organic molecules
and their reactivity with gold surfaces are numerous.
Whitesides et al. observed that S-acetyl-terminated
molecules have the same binding energy as thiols when
allowed to react with gold surfaces and that the structure
determined from the first anodic wave, referenced internally to
ferrocene, then the absolute value was calculated.27 e Refers to the
electron affinity calculated from the ionization potential and
optical band-gap.
indicating little contribution from the added aryl ring in
the biphenyl, instead of the phenyl, core.
By examining the absorption and fluorescence spectra
of 4-6, insight can be gained into the contributions from
through-space and through-bond delocalization within
(30) Oldham, W. J ., J r.; Miao, Y.-J .; Lachicotte, R. J .; Bazan, G. C.
J . Am. Chem. Soc. 1998, 120, 419.
(31) Wang, S.; Bazan, G. C.; Tretiak, S.; Mukamel, S. J . Am. Chem.
Soc. 2000, 122, 1289.
1114 J . Org. Chem., Vol. 69, No. 4, 2004

R,ω-Bis(thioacetyl)oligophenylenevinylene Chromophores
TABLE 2. Ad va n cin g a n d Reced in g Wa ter Con ta ct
An gle a n d La yer Th ick n ess Da ta for Tr ea ted Gold
Su bstr a tes
substrates treated with 4-7 ranged from 48° to 56°.
When the substrate treated with 4 was treated with
concentrated ammonium hydroxide and rinsed with
water, the advancing water contact angle decreased by
3°, and the receding water contact angle decreased by
24°, indicating further derivatization of the surface.
Because a decrease in the water contact angle indicates
more hydrophilic surface groups,36 the hydrolysis of the
protruding thioacetate esters to thiophenol termini upon
exposure to aqueous base is likely to cause this change.
In previous studies involving thioacetyl-terminated con-
jugated molecules, ammonium hydroxide has been shown
to completely hydrolyze the thioacetate group.13 Sub-
strates treated with 1-3 gave water contact angles
ranging from 81° to 83° and 62° to 57° for advancing and
receding drops, respectively. These higher values, relative
to 4-7, may be attributed to the more hydrophobic
character of the hexyloxy side chains contained within
these molecules. Although the side chains are not surface
groups, disorder on the surface and/or poor packing
within these monolayers could make contributions from
these side chains more significant.
thickness (Å)
samplea
ODT
1
2
ΦAc (deg)
ΦRd (deg)
calcde
obsdf
110 ( 1
84 ( 1
82 ( 2
81 ( 2
71 ( 1
68 ( 7
71 ( 1
73 ( 2
72 ( 4
97 ( 2
59 ( 2
62 ( 1
57 ( 2
48 ( 3
24 ( 3
51 ( 2
52 ( 4
56 ( 3
22
19 ( 1
3 ( 0
19.8-22.5
32.5-37.2
43.2-49.5
19.8-22.5
8 ( 3
3
4
12 ( 4
12 ( 1
4 + NH4OHb
5
6
7
14.3-20.8
21.2-24.2
24.8-28.4
11 ( 2
7 ( 2
22 ( 1
a
Refers to a gold substrate treated with a solution of the
corresponding compounds (structures are given in Scheme 1). ODT
was adsorbed from absolute ethanol, all other samples from DCM.
b
Measured after the 4-treated surface was immersed in concen-
trated NH4OH for 2 min. c Advancing water contact angle. Reced-
d
ing water contact angle. e Calculated from the Au surface to the
farthest hydrogen atom of the molecule, optimized by MMFF
calculations (see the Experimental Section). f Measured by ellip-
sometry assuming a refractive index of 1.55 for the adsorbed layer.
Ellipsometry measurements suggest that compounds
4, 5, and 7 form the most complete layers, where the
observed thickness is closest to the calculated range for
the three molecules. The calculated range refers to an
orientation where the molecule coincides with the surface
normal, or is tilted up to 30° from the surface normal,
although some investigators have reported a more tilted
geometry for aromatic thiols.6 Further, we note that a
systematic error in observed monolayer thickness due to
advantageous contamination on untreated substrates
could be responsible for some discrepancies, as previously
observed,2 and confirmed experimentally (vide infra). We
emphasize that none of the layers appear to be as ordered
or dense as the alkane thiol example ODT. Substrates
treated with 1-3, whose structures contain hexyloxy side
chains, generally gave low observed thicknesses, although
there is a correlation between thickness and the molec-
ular dimension. A thickness of 11 Å for the substrate
treated with 5 suggests that this molecule is oriented in
an upright fashion, relative to the plane of the gold
surface, despite the fact that coordination of three thi-
olates, resulting in a less upright orientation, is also
possible when considering the structure of this tetra-
(thioacetyl) molecule. The substrate treated with 6, whose
thickness is 7 Å, appears to be less dense than the layers
that contain the more linear structures 4 and 7.
The atomic concentrations derived from the XPS
survey scans for the different compounds are given in
Table 3. Evidence of a thin contamination layer (∼5 Å)
is provided by the existence of ∼22% carbon on the gold
surface prior to treatment. For a dense monolayer, one
would expect an increase in the carbon concentration
compared to the untreated gold since the XPS spectra
survey the top 1-5 nm of the surface, which is on the
order of the monolayer thickness. A significant (26%)
increase in the carbon content was observed after treat-
ing the substrate with a solution of ODT, indicating the
presence of a dense monolayer. Smaller, but significant
(5-16%) increases in carbon concentration compared to
of the adsorbed species was indistinguishable from that
obtained with the corresponding free thiols.14 It was also
noted that the acetate group was no longer present in
the adsorbed layer. Later, Frisbie et al. observed this
reaction in similar experiments, and again noted the
similarity of the monolayers formed from both thiol- and
thioacetate-containing molecules.32 The reactivity of other
organic protected thiols toward gold surfaces has also
been examined.33
The examination of gold surfaces after treatment with
organic thiols typically relies on contact angle measure-
ments, ellipsometry, reflectance Fourier transform in-
frared spectroscopy (FTIR), electrochemistry, X-ray pho-
toelectron spectroscopy (XPS), scanning tunneling mi-
croscopy (STM), and atomic force microscopy (AFM).34 For
our analysis we used water drop contact angle measure-
ments, ellipsometry, and XPS to determine monolayer
quality. Also, we used AFM to examine surface roughness
before and after treatment with a solution of surface-
active compound. For comparison with the new molecules
reported here, and to test the accuracy of the measure-
ments, octadecane thiol (ODT) was used because it has
been demonstrated to form dense, ordered monolayers.35
Table 2 contains the water contact angle measure-
ments and ellipsometry data for gold substrates after
treatment in 0.1 mM solutions of 1-7 in dichloromethane
(DCM) for 24 h, followed by rinsing. Substrates treated
with 4-7 gave advancing water contact angles ranging
from 71° to 73°, in agreement with the literature value
of 70° for monolayers formed from ω-S-acetyl-function-
alized thiols.2 The receding water contact angle for
(32) Skulason, H.; Frisbie, C. D. J . Am. Chem. Soc. 2000, 122, 9750.
(33) Gryko, D. T.; Clausen, C.; Lindsey, J . S. J . Org. Chem. 1999,
64, 8635.
(34) (a) Porter, M. D.; Bright, T. B.; Allara, D. L.; Chidsey, C. E. D.
J . Am. Chem. Soc. 1987, 109, 3559. (b) Nuzzo, R. G.; Dubois, L. H.;
Allara, D. L. J . Am. Chem. Soc. 1990, 112, 558. (c) Liu, G.-Y.; Fenter,
P.; Chidsey, C. E. D.; Ogletree, D. F.; Eisenberger, P.; Salmeron, M. J .
Chem. Phys. 1994, 101, 4301. (d) Caldwell, W. B.; Campbell, D. J .;
Chen, K.; Herr, B. R.; Mirken, C. A.; Malik, A.; Durbin, M. K.; Dutta,
P.; Huang, K. G. J . Am. Chem. Soc. 1995, 117, 6071.
(35) For a recent paper containing wettablility, ellipsometry, elec-
trochemical measurements, FTIR, and SPM data of this SAM see: Ron,
H.; Matlis, S.; Rubinstein, I. Langmuir 1998, 14, 1116.
(36) J ohnson, R. E., J r.; Dettre, R. H.; Brandreth, D. A. J . Colloid
Interface Sci. 1977, 62, 205.
J . Org. Chem, Vol. 69, No. 4, 2004 1115

Seferos et al.
TABLE 3. Elem en ta l Com p osition of Tr ea ted Gold
Su bstr a tes Deter m in ed by XP S
TABLE 4. High -Resolu tion XP S Decon volu tion of th e
Ar om a tic a n d Alip h a tic Con tr ibu tion s to th e C1s P ea k s
Obser ved in Gold Su bstr a tes
samplea
C (%)
Au (%)
O (%)
S (%)
samplea
aromaticb (%)
18.8
aliphaticb (%)
untreated
ODT
21.8
47.8
27.7
30.7
25.6
36.8
32.4
27.8
38.9
26.3
35.2
26.5
47.2
38.1
45.9
25.7
27.4
27.0
51.9
14.6
45.8
19.6
36.3
14.1
40.3
43.8
32.4
2.4
2.5
untreated
61
1
2
3
4
5
6
7
ODT
4
93.6
43.5
39.2
a
Refers to a gold substrate treated with a solution of the
3.1
1.5
1.0
1.7
corresponding compounds (structures are given in Scheme 1).
Untreated samples were cleaned and handled exactly as treated
samples (see the Experimental Section). ODT was adsorbed from
b
absolute ethanol, 4 from DCM. Abundance determined by de-
a
Refers to a gold substrate treated with a solution of the
corresponding compounds (structures are given in Scheme 1).
Untreated samples were cleaned and handled exactly as treated
samples (see the Experimental Section). ODT was adsorbed from
absolute ethanol, all other samples from DCM.
convolution of the C1s peaks (see the Experimental Section).
TABLE 5. Su r fa ce Rou gh n ess of Gold Su bstr a tes a fter
Tr ea tm en t in Va r iou s Con cen tr a tion s of 4
samplea
rmsb
Ra
c
untreated
0.1 mM
1.0 mM
10 mM
0.385
0.930
0.841
0.900
0.076
0.276
0.595
0.193
a
Untreated samples measured immediately after evaporation.
0.1, 1.0, and 10 mM refer to the concentration of 4 in DCM that
b
the substrate was treated with. Refers to the root-mean-square
surface roughness obtained from AFM measurements. c Refers to
the average surface roughness obtained from AFM measurements.
observed in the untreated gold sample, which was most
likely due to adsorbed aromatic contaminants. A signifi-
cantly larger aromatic component (39.2%) was seen in
the sample treated with 4, signifying the presence of
aromatic species in the monolayer. No evidence of
aromatic carbon was observed in sample treated with
ODT. The enhancement of the aromatic component of the
C1s peak in the sample treated with 4 was also ac-
companied by a decrease in aliphatic components by the
same magnitude.
F IGURE 1. High-resolution XPS spectra showing the C1s
peaks for a substrate treated with a solution containing 4 (a),
ODT (b), and the substrate prior to treatment (c). The vertical
line is at 284.7 eV.
Surface analyses of gold substrates before and after
treatment with 4 were measured by AFM. For this
experiment the surfaces were immersed for 24 h in DCM
solutions of 4 with concentrations varying from 0.1 to 10
mM. From the section analysis of the AFM images the
surface roughness values were obtained and are given
in Table 5. In all cases, surface roughness increased after
deposition of 4. The morphology of the untreated sample
was essentially featureless, substrates treated in 0.1 and
1.0 mM solutions showed slightly more surface features,
while the sample obtained from the 10 mM solution had
large, smooth features within the 1 µm × 1 µm image
(see the Supporting Information). Examination of the
sectional analysis of the plane images reveals the height
of the features in each sample. Untreated substrates had
features with heights that were less than the calculated
height of the SAM of 4, substrates treated with both 0.1
and 1.0 mM solutions of 4 had features that were
commensurate with the molecular dimensions of the
SAM, and substrates treated with 10 mM solutions of 4
had features that were significantly larger than the
molecular dimensions of the SAM (see the Supporting
Information). These data suggest over-deposition of
organic material at higher concentrations.
the original gold surface were observed for samples
treated with compounds 1-7. Additionally, the increase
in the carbon signal correlated with the presence of
sulfur, which was detected using the S2p peak located at
162.3 eV. This peak was assigned as the metal-thiolate
species.37 Substrates treated with 4-7 generally gave
higher abundances of carbon and sulfur than those
treated with 1-3.
High-resolution spectra of the C1s peaks from untreated
gold substrates and substrates treated with ODT and 4
were taken and curve-fitted after referencing to Au(4f7/2
)
at 84.0 eV and are presented in Figure 1. At 20 eV pass
energy, the main component of the C1s peak was too broad
(fwhm ) 1.85 eV) to be considered a single component
and was fitted by using the following assignments:
aromatic; aliphatic; C R to carbonyl; C-O (alcohols,
ethers, carboxylic acids); and carbonyl acids at 284.4,
284.7, 285.8, 287.2, and 289 eV, respectively.2,38 Although
all components were used to deconvolute the C1s peaks,
contributions from the aliphatic and aromatic compo-
nents were the most significant, and are tabulated
in Table 4. A small aromatic component (18.8%) was
(37) Zharnikov, M.; Frey, S.; Heister, K.; Grunze, M. Langmuir 2000,
16, 2697
(38) (a) Briggs, D. Surface analysis of polymers by XPS and static
SIMS; Cambridge University Press: Cambridge, U.K., 1998. (b)
Cumpston, B. H.; J ensen, K. F. J . Appl. Polym. Sci. 1998, 69, 2451.
Su m m a r y a n d Con clu sion
We have demonstrated a facile synthetic approach for
the synthesis of R,ω-bis(thioacetyl)phenylenevinylene
1116 J . Org. Chem., Vol. 69, No. 4, 2004

R,ω-Bis(thioacetyl)oligophenylenevinylene Chromophores
The crude product was purified by column chromatography
eluting with 50% dichloromethane in hexanes to yield 0.448 g
(93%) of green, florescent powder, which contained all three
isomers of the title compound. For spectroscopic analysis the
product was converted to the all-E isomer by degassing and
refluxing in toluene with a few crystals of iodine. 1H NMR
oligomers. In this method, the S-acetyl group is masked
as an S-methyl derivative. Most significantly, from a
molecular structure elaboration point of view, the S-
methyl-terminated aryl group can be used in Heck and
Wittig or Horner-Wittig-type reactions, which are often
used for building OPV structures. We have also shown
how the S-methyl terminus or termini can be converted
to the corresponding S-acetyl derivative, while concur-
rently thermally isomerizing the olefinic linkages to
produce solely all-E products. The methodology was
demonstrated by creating a series of new thioacetyl-
terminated OPVs. In addition to the more classic linear
OPV systems, examples of chromophore dimers with [2.2]-
paracyclophane points of attachment were also synthe-
sized and examined.
Spectroscopic and electrochemical measurements were
performed. We note the unique optical properties of
molecules that contain the [2.2]paracyclophane core that
exhibit through-space, as well as through-bond, delocal-
ization. Finally, we demonstrate the utility of these
molecules to chemically adsorb on gold surfaces. Mol-
ecules with linear hexyloxy-substituted OPV structures
1-3 form disordered SAMs. The [2.2]paracyclophane-
containing OPVs 5 and 6 form significantly better SAMs
than examples with side groups, and to our knowledge
these are the first examples of surface-bound [2.2]-
paracyclophane-containing molecules. The best struc-
tures for obtaining a monolayer are the unsubstituted
OPVs 4 and 7, but appear to be less complete than SAMs
prepared from ODT, an alkane thiol of approximately the
same molecular dimension. Given the ease of prepara-
tion, interesting electronic properties, and reactivity
toward gold surfaces, these compounds are promising
surface-modifying reagents and molecular-wire candi-
dates.
3
3
(CDCl3) δ 7.463 (d, J ) 8.37 Hz, 4H), 7.447 (d, J trans ) 16.75
Hz, 2H), 7.251 (d, 4H), 7.116 (s, 2H), 7.093 (d, 2H), 4.057 (t,
3J ) 6.42 Hz, 4H), 2.52 (s, 6H), 1.879 (m, 4H), 1.559 (m, 4H),
3
1.399 (m, 8H), 0.937 (t, J ) 6.98 Hz, 6 H). 13C NMR (CDCl3)
δ 151.3, 137.7, 135.2, 128.3, 127.1, 127.0, 126.9, 123.061, 110.7,
69.8, 31.8 29.7, 26.2, 22.9, 16.1, 14.3. HRMS-EI 574.2920,
∆ ) 3.4 ppm.
1,4-Dih exyloxy-2,5-bis[4′-(acetylth io)styr yl]ben zen e (1).
In an inert atmosphere glovebox, a 10-mL round-bottom flask
fitted with a magnetic stir-bar and needle valve was charged
with 1a (200 mg, 0.35 mmol) and sodium thiomethoxide (60
mg, 0.86 mmol). The apparatus was attached onto a Schlenck
line, 3 mL of DMF was added, and the reaction was heated to
140 °C, at which time the solution became dark red. The
reaction was stirred at 140 °C for 20 h. Upon cooling to 0 °C,
excess acetyl chloride (0.25 mL, 3.5 mmol) was added all at
once, the ice bath was removed, and the mixture was stirred
for an additional hour. The solution was diluted with chloro-
form (100 mL), washed with three portions of brine, dried, and
concentrated. Column chromatography eluting with chloroform
afforded 87 mg (39%) of the title compound as a pale green
1
solid, with only the all-E isomer present. H NMR (CDCl3) δ
7.570 (d, 3J ) 8.37, 4H), 7.532 (d, 3J trans ) 16.47 Hz, 2H), 7.410
(d, 4H), 7.146 (d, 2H), 7.127 (s, 2H), 4.068 (t, 3J ) 6.42 Hz,
4H), 2.448 (s, 6H), 1.887 (m, 4H), 1.570 (m, 4H), 1.406 (m, 8H),
3
0.942 (t, J ) 7.26 Hz, 6H). 13C NMR (CDCl3) δ 194.5, 151.4,
139.4, 134.9, 128.1, 127.4, 127.0, 126.6, 125.215, 110.8, 69.7,
31.8, 30.4, 29.639, 26.2, 22.9, 14.3. HRMS-EI 630.2848, ∆ )
1.6 ppm.
4-(4′-(Meth ylth io)styr yl)ben zld eh yd e (8). To a 50-mL
round-bottom flask fitted with a magnetic stir-bar was added
4-(methylthio)benzaldehyde (380 mg, 2.4 mmol), diethyl
4-(4,4,5,5-tetramethyl-1,3-dioxolan-2-yl)benzylphosphonate (1.00
g, 2.8 mmol), and toluene (30 mL) under an argon atmosphere.
Sodium hydride (240 mg, 10.0 mmol) was added at 0 °C, and
the reaction was stirred at 65 °C for 16 h. After cooling, the
contents of the flask were rinsed into toluene (80 mL), washed
with water, dried, and concentrated to give a white powder.
The crude product was taken up in a solution of THF (50 mL)
and aqueous hydrochloric acid (10%, 100 mL) and stirred at
60 °C for 1 h. The THF was evaporated, and the remaining
aqueous solution was extracted with three portions of DCM,
dried, and concentrated. The crude solid was passed through
a short silica plug (DCM elutent) to yield 520 mg (82%) of the
Exp er im en ta l Section
Su bstr a te P r ep a r a tion . For contact angle measurements,
ellipsometry, and XPS, 1500 Å of gold (99.999%) was E-beam
evaporated on heavily doped (n+) silicon wafers with 2000 Å
of thermal SiO2 and a 20 Å titanium adhesion layer. After
evaporation, the samples were annealed for 1 h in a vacuum
oven at 260 °C and stored under absolute ethanol until use.
For AFM measurements, 50 Å of gold (99.999%) was E-beam
evaporated on freshly cleaved mica with a 20 Å chromium
adhesion layer.
P r ep a r a tion of Mon ola yer s on Gold . Working in a
laminar flow cabinet, a gold substrate was irradiated in a UVO
cleaner (20 m), then immersed in absolute ethanol (20 m) to
remove any transient oxide. The substrate was then rinsed
with ethanol, blown dry with a stream of nitrogen, and
immersed in a 0.1 mM solution of the acetylthiol in DCM. After
the formation of a monolayer (24 h), the sample was removed,
rinsed with DCM and absolute ethanol, and stored under
absolute ethanol. Prior to analysis, the sample was removed
and blown dry with nitrogen.
1,4-Dih exyloxy-2,5-b is[4′-(m et h ylt h io)st yr yl]b en zen e
(1a ). To a two-neck round-bottom flask equipped with a needle
valve and a magnetic stir-bar was added 4-(methylthio)-
benaldehyde (0.25 mL, 1.87 mmol), 1,4-bis[(methyl)triphen-
ylphosphonium chloride]-2,5-dihexyloxybenzene (750 mg, 0.83
mmol), and THF (15 mL) under an atmosphere of argon. The
mixture was cooled to 0 °C, sodium hydride (45 mg, 1.87 mmol)
was added under an argon purge, and the reaction was allowed
to warm to room temperature and stirred overnight. The
reaction was quenched with water, rinsed into ether (100 mL),
washed with three portions of brine, dried, and concentrated.
1
title compound as a white solid. H NMR (CDCl3) δ 9.987 (s,
1H), 7.879 (d, 2H), 7.633 (d, 2H), 7.465 (d, 2H), 7.253 (d, 2H),
7.152 (d, 2H), 2.512 (s, 3H). 13C NMR (CDCl3) δ 191.8, 143.6,
139.5, 135.4, 133.5, 131.7, 130.4, 127.5, 127.0, 126.7, 126.6,
15.7. HRMS-EI 254.0767, ∆ ) 0.6 ppm.
1,4-Dih exyloxy-2,5-bis[4′-(4′′-(m eth ylth io)styr yl)styr yl]-
ben zen e (2a ). 8 (400 mg, 1.57 mmol) and 1,4-bis[(methyl)-
triphenylphosphonium chloride]-2,5-dihexyloxybenzene (635
mg, 0.71 mmol) were reacted, worked up, and purified in the
same manner described above. Chromatography afforded 340
mg (61%) of the title compound as a yellow, florescent powder.
1H NMR (CDCl3) δ 7.516 (m, 12H), 7.461 (d, 3J ) 8.37 Hz,
3
4H), 7.256 (d, 4H), 7.146 (s, 2H), 7.089 (s, 4H), 4.080 (t, J )
6.42 Hz, 4H), 2.523 (s, 6H), 1.900 (m, 4H), 1.580 (m, 4H), 1.415
(m, 8H), 0.951 (t, 3J ) 7.25 Hz, 6H). HRMS-EI 778.33908,
∆ ) 3.8 ppm.
1,4-Dih exyloxy-2,5-bis[4′-(4′′-(a cetylth io)styr yl)styr yl]-
ben zen e (2). 2a (150 mg, 0.19 mmol) and sodium thiomethox-
ide (32 mg, 0.46 mmol) were reacted, quenched with excess
acetyl chloride, worked up, and purified in the same manner
as described above. Chromatography afforded 138 mg (87%)
of the title compound as a yellow, florescent powder. 1H NMR
J . Org. Chem, Vol. 69, No. 4, 2004 1117

Seferos et al.
3
(CDCl3) δ 7.541 (m, 14H), 7.413 (d, J ) 8.37 Hz, 4H), 7.150
washed with water, and collected by filtration. This procedure
was repeated a total of three times to afford 244 mg (65%) of
the title compound as a pale-yellow powder. Repeating on a
20-mmol scale afforded 3.183 g (37%). 1H NMR (CDCl3) δ 7.519
(d, 3J ) 8.93 Hz, 4H), 7.502 (s, 4H), 7.232 (d, 4H), 7.082 (s,
4H), 2.522 (s, 6H). Anal. Calcd for C24H22S2: C, 76.96; H, 5.92.
Found: C, 76.12; H, 6.06. HRMS-EI 374.1155, ∆ ) 2.0 ppm.
2,5-Bis[4′-(a cetylth io)styr yl]ben zen e (4).17 4a (2.50 g,
6.68 mmol) and sodium thiomethoxide (1.12 g, 16.63 mmol)
were reacted in DMF (100 mL) and quenched with excess
acetyl chloride in the manner previously described. The
contents of the flask were precipitated into 150 mL of
methanol, filtered, and spun onto silica gel. Column chroma-
tography eluting with chloroform afforded 1.42 g (49%) of the
title compound. 1H NMR (CDCl3) δ 7.564 (d, 3J ) 8.37 Hz, 4H),
7.535 (s, 4H), 7.415 (d, 4H), 7.149 (m, 4H), 2.448 (s, 6H). 13C
NMR (CDCl3) δ 194.4, 138.7, 136.8, 134.9, 129.9, 127.924,
127.4, 127.3, 127.0, 30.3. Anal. Calcd for C26H22O2S2: C, 72.52;
H, 5.15. Found: C, 72.52; 5.22. HRMS-EI 430.1063, ∆ )
0.4 ppm.
3
(m, 8H), 4.083 (t, J ) 6.42 Hz, 4H), 2.448 (s, 6H), 1.804 (m,
4H), 1.583 (m, 4H), 1.420 (m, 8H), 0.954 (t, 3J ) 7.26). 13C
NMR (CDCl3) δ 194.4, 151.4, 138.8, 138.0, 136.2, 134.9, 130.1,
128.5, 127.5, 127.4, 127.2, 127.1, 126.9, 123.8, 110.7, 69.7, 31.9,
30.4, 29.7, 26.2, 22.9, 14.3. LRMS-FAB calcd 834, found 834.
4-(4′-(Meth ylth io)styr yl)styr en e (9). A round-bottom flask
fitted with a gas inlet tube and a magnetic stir-bar was
charged with 4-(methylthio)benzaldehyde (1.00 g, 7.15 mmol),
diethyl-4-(vinyl)benzylphosphonate (2.00 g, 7.87 mmol), so-
dium hydride (240 mg, 10.00 mmol), and toluene (50 mL)
under an argon atmosphere. The reaction was heated at
65 °C for 2.5 h. Upon cooling, the mixture was diluted with
toluene (150 mL), washed with water, dried, and concentrated
to yield an orange powder. The crude material was passed
through a silica plug and recrystallized in a solution of 50%
benzene in petroleum ether to afford 580 mg (32%) of the title
compound. 1H NMR (CDCl3) δ 7.477 (d, 3J ) 8.37 Hz, 2H),
7.448 (d, 3J ) 8.37 Hz, 2H), 7.411 (d, 2H), 7.250 (d, 2H), 6.726
3
3
2
(dd, J cis ) 10.89 Hz, J trans ) 17.56 Hz, 1H), 5.777 (dd, J )
0.84 Hz, 1H), 5.261 (dd, 1H), 2.518 (s, 3H). 13C NMR (CDCl3)
δ 138.1, 137.081, 137.0, 136.7, 134.5, 128.2, 127.8, 127.1, 126.9,
126.8, 126.8, 113.9, 16.0. HRMS-EI 252.0961, ∆ ) 4.6 ppm.
4,7,12,15-Tet r a [4′-(m et h ylt h io)st yr yl][2.2]p a r a cyclo-
p h a n e (5a ). A 50-mL round-bottom flask fitted with a rubber
septa and a magnetic stir-bar was back-filled with argon and
charged with 4,7,12,15-tetra[(methyl)diethylphosphonate][2.2]-
paracyclophane (500 mg, 0.62 mmol), 4-(methylthio)benzal-
dehyde (0.5 mL, 3.72 mmol), and DMF (40 mL). A separate
suspension of potassium tert-butoxide (347 mg, 3.1 mmol) in
DMF was prepared and added to the flask at 0 °C. Upon
addition of the base, there was an immediate color change to
dark blue, and the reaction was allowed to warm to room
temperature and stirred overnight. The contents of the flask
were then dissolved in chloroform (700 mL), washed with
brine, dried, and concentrated. Column chromatography on
silica gel eluting with chloroform afforded 450 mg (91%) of the
title compound. 1H NMR (CDCl3) δ 7.409 (d, 3J ) 8.30 Hz, 8H),
7.288 (d, 8H), 7.174 (d, 3J trans ) 16.04, 4H), 6.983 (s, 4H), 6.865
(d, 4H), 3.576 (m, 4H), 2.877 (m, 4H), 2.568 (s, 12H). 13C NMR
(CDCl3) δ 138.2, 138.0, 136.8, 134.8, 128.23, 128.15, 127.2,
127.0, 124.9, 33.3, 16.1. LRMS-FAB calcd 800, found 800.
4,7,12,15-Te t r a [4′-(a ce t ylt h io)st yr yl][2.2]p a r a cyclo-
p h a n e (5). 5a (275 mg, 0.34 mmol) and sodium thiomethoxide
(119 mg, 1.7 mmol) were reacted, quenched with excess acetyl
chloride, worked up, and purified in the same manner as
previously described. Chromatography afforded 263 mg (85%)
2,5-Dih exyloxy-4-(4′-(4′′-(m eth ylth io)styr yl)styr yl)ben z-
a ld eh yd e (10). In an inert atmosphere glovebox, a two-neck
round-bottom flask fitted with a reflux condenser, needle valve,
and magnetic stir-bar was charged with 2,5-dihexyloxy-4-
iodobenzaldehyde (0.99 g, 2.3 mmol), 9 (0.69 g, 2.7 mmol), and
palladium(II) acetate (0.01 g, 0.046 mmol). The apparatus was
attached to a Schlenk line and triethylamine (0.39 mL,
2.8 mmol) and DMF (5 mL) were added. The reaction was
heated to 100 °C for 24 h with vigorous stirring. Upon cooling,
the mixture was diluted with ether (500 mL), washed with
water, dried, and concentrated. Column chromatography on
silica eluting with DCM afforded 0.77 g (61%) of the title
1
compound. H NMR (CDCl3) δ 10.462 (s, 1H), 7.533 (m, 4H),
7.468 (m, 3H), 7.339 (s, 1H), 7.254 (m, 3H), 7.188 (s, 1H), 7.094
(m, 2H), 4.124 (t, 2H), 4.085 (t, 2H), 2.519 (s, 3H), 1.870 (m,
4H), 1.576 (br s, 4H), 1.385 (br s, 8H), 0.937 (t, 6H). 13C NMR
(CDCl3) δ 189.4, 156.4, 150.9, 138.3, 137.5, 136.7, 134.5, 134.3,
132.0, 127.7, 127.5, 127.1, 127.0, 126.8, 124.4, 122.9, 110.6,
110.3, 69.4, 69.3, 31.8, 29.43, 29.41, 26.1, 26.0, 22.84, 22.81,
16.0, 14.3. HRMS-EI 556.30096, ∆ ) 0.3 ppm.
1,4-Bis[2′,5′-d ih exyloxy-4′-(4′′-(4′′′-(m eth ylth io)styr yl)-
styr yl)styr yl]ben zen e (3a ). 10 (40 mg, 0.065 mmol), 1,4-bis-
[(methyl)triphenylphosphonium chloride]benzene (22.6 mg,
0.032 mmol), and sodium hydride (1.8 mg, 0.078 mmol) were
reacted and worked up in the manner previously described.
Column chromatography on silica gel eluting with 50% DCM
in hexanes afforded 26 mg (70%) of the title compound. 1H
NMR (CDCl3) δ 7.518 (br m, 16H), 7.462 (d, 3J ) 8.37 Hz, 4H),
7.258 (d, 4H), 7.153 (m, 8H), 7.091 (s, 4H), 4.85 (t, 8H), 2.524
(s, 6H), 1.905 (m, 8H), 1.570 (m, 8H), 1.421 (m, 16H), 0.955
(t, 12H). MALDI-TOFMS calcd 1183, found 1183.
1
3
of the title compound. H NMR (CDCl3) δ 7.492 (d, J ) 8.37
3
Hz, 8H), 7.443 (d, 8H), 7.263 (d, J trans ) 15.91 Hz, 4H), 6.975
(s, 4H), 6.887 (d, 4H), 3.58 (m, 4H), 2.88 (m, 4H), 2.480 (s, 12H).
13C NMR (CDCl3) δ 194.4, 138.879, 138.3, 136.9, 135.0, 128.7,
128.1, 127.5, 127.1, 126.7, 33.3, 30.5. LRMS-FAB calcd 912,
found 912.
4-(Meth ylth io)styr en e.39 To a flame-dried three-neck round-
bottom flask fitted with a magnetic stir-bar and back-filled
with argon was added 4-(methylthio)benzaldehyde (5.72 g,
37.58 mmol), methyltriphenylphosphonium bromide (16.11 g,
45.10 mmol), and THF (300 mL). Sodium hydride (1.08 g, 45.10
mmol) was added under argon purge at 0 °C. The reaction
mixture warmed to room temperature overnight with stirring.
Volatile substances were removed under reduced pressure, and
the remaining crude material was diluted with chloroform (300
mL), washed with brine (3 × 100 mL), and concentrated.
Distillation under reduced pressure (75-80 °C) afforded 5.58
g (99%) of pure product. 1H NMR (CDCl3) δ 7.346 (d, 3J )
1,4-Bis[2′,5′-d ih exyloxy-4′-(4′′-(4′′′-(a cet ylt h io)st yr yl)-
styr yl)styr yl]ben zen e (3). 3a (9 mg, 7.6 µmol) and sodium
thiomethoxide (1.3 mg, 18.24 µmol) were reacted, quenched
with excess acetyl chloride, worked up, and purified in the
same manner as previously described. Chromatography af-
forded 5.5 mg (58%) of the title compound. 1H NMR (CDCl3) δ
3
7.545 (m, 20H), 7.415 (d, J ) 8.37 Hz, 4H), 7.157 (m, 12H),
4.088 (t, 8H), 2.449 (s, 6H), 1.907 (m, 8H), 1.586 (m, 8H), 1.421
(m, 16H), 0.955 (t, 12H). MALDI-TOFMS calcd 1239, found
1239.
3
3
8.652, 2H), 7.222 (d, 2H), 6.679 (dd, J cis ) 10.89 Hz, J trans
)
17.59 Hz, 1H), 5.720 (d, 1H), 5.221 (d, 1H), 2.498 (s, 3H). 13C
NMR (CDCl3) δ 138.2, 136.4, 134.7, 126.8, 126.8, 113.4, 16.0.
LRMS-EI calcd 150, found 150.
2,5-Bis[4′-(m eth ylth io)styr yl]ben zen e (4a ). To a flame-
dried three-neck flask fitted with a needle valve and magnetic
stir-bar was added 1,4-bis[(methyl)dethylphosphonate]benzene
(378 mg, 1.0 mmol), 4-(methylthio)benzaldehyde, and toluene
(10 mL) under an argon atmosphere. The suspension was
cooled to 0 °C, sodium hydride was added, and the reaction
was heated to 65 °C for 24 h. Upon cooling, the solids were
suspended in a solution of hexanes and chloroform (1:1),
4,12-Bis[4′-(m eth ylth io)styr yl][2.2]par acycloph an e (6a).
In an inert atmosphere glovebox, a 1-neck round-bottom flask
(39) For an alternative preparation with additional spectroscopic
characterization see: Hirao, A.; Shione, H.; Ishizone, T.; Nakahama,
S. Macromolecules 1997, 30, 3728.
1118 J . Org. Chem., Vol. 69, No. 4, 2004

R,ω-Bis(thioacetyl)oligophenylenevinylene Chromophores
fitted with a needle valve and a magnetic stir-bar was charged
with 4,12-dibromo[2.2]paracyclophane (250 mg, 0.68 mmol),
4-(methylthio)styrene (225 mg, 1.5 mmol), palladium(II) ac-
etate (20 mmg, 0.09 mmol), tri-o-tolylphosphine (50 mg, 0.16
mmol), and DMF (5 mL). The apparatus was attached to a
Schlenck line, and triethylamine (0.21 mL, 1.5 mmol) was
added and the resulting mixture was degassed by 3 freeze-
pump-thaw cycles and heated to 100 °C for 40 h under rapid
stirring. Upon cooling, the contents of the flask were rinsed
into chloroform (25 mL) and washed with brine (3 × 25 mL).
Column chromatography, eluting with 50% chloroform in
hexanes, afforded 126 mg (37%) of the title compound. 1H NMR
DCM, and at an analyte concentration of 0.5 mg/mL. Scans
were measured nominally from 0 to 1.1 to 0 V vs Pt wire, at
200 mV/s, and referenced internally to Fc/Fc+.
Wa ter Con ta ct An gle Mea su r em en ts. Advancing and
receding contact angles were obtained at room temperature
and humidity on a Gaertaer Scientific Corporation Goniometer,
using MilliQ purified water. Each sample substrate was
measured three times and averaged.
Ellip som etr y. Layer thickness measurements were pre-
formed on a Rudolf Auto EL instrument with a 632.8 nm light
source at 70° angle of incidence. Measurements of the analyzer
and polarizer angles of the substrate were made immediately
before and after deposition in the thiol-containing solutions.
The change in sample thickness was calculated assuming
values of 1.55 and 0 for the n and k optical constants of the
organic layer, respectively. Each sample substrate was mea-
sured 2-3 times before and after treatment, and averaged.
The calculated thickness range was determined assuming a
mean S-Au distance of 2 Å,1 and also that the molecules lie
normal to the surface or have an average tilt of 30° from the
surface normal. Molecular dimensions were minimized (MMFF)
and measured with the Spartan software package.
XP S. Surface chemical analysis was performed with a
Kratos Axis Ultra photoelectron spectrometer with a mono-
chromatic Al KR source at 1486.6 eV. A charge neutralizer was
used for all samples. Survey scans were measured with a 160
eV pass energy at 0.5 eV intervals, 225 W electron beam power,
and 700 µm by 300 µm spherical spot size. The data acquisition
time for the survey scans was 5 min. All spectra were
calibrated by using the Au(4f7/2) peak referenced at 84.0 eV.
Peak areas from the survey scans were converted into atomic
concentration percentages by using elemental sensitivity fac-
tors. High-resolution scans of the C1s peak were taken with
use of 20 eV pass energy at 0.05 eV intervals, 300 W electron
beam power, and 700 µm by 300 µm spherical spot size. The
data acquisition time for the high-resolution scans was 4 min.
The C1s peaks were curve-fitted with 70% Gaussian/30%
Lorentzian peak shapes of variable widths with use of XPS
data analysis software. The takeoff angle for all scans was 90°.
AF M. Images of the gold substrates (1 × 1 µm scan size)
were obtain by using a Digital Instruments Dimension 3000
microscope operating in tapping mode. Images were plane-fit
and flattened.
3
(CDCl3) δ 7.523 (d, J ) 8.37 Hz, 4H), 7.261 (d, 4H), 7.198 (d,
4
3J trans ) 16.19 Hz, 2H), 6.856 (d, 2H), 6.689 (d, J ) 1.68 Hz,
2H), 6.665 (dd, 3J ) 7.82 Hz, 2H), 6.423 (d, 2H), 3.606 (m, 2H),
3.168-2.895 (complex, 6H), 2.550 (s, 6H). 13C NMR (CDCl3) δ
139.7, 138.3, 137.9, 137.6, 135.1, 133.8, 130.3, 129.6, 128.8,
127.08, 127.06, 126.6, 34.7, 33.6, 13.2. HRMS-EI 504.19337,
∆ ) 2.3 ppm.
4,12-Bis[4′-(a cetylth io)styr yl][2.2]p a r a cyclop h a n e (6).
6a (80 mg, 0.158 mmol) and sodium thiomethoxide (27 mg,
0.38 mmol) were mixed in DMF (2 mL), quenched with excess
acetyl chloride, worked up, and purified in the same manner
as previously described. After chromatography, 69 mg (78%)
1
of the title compound was isolated. H NMR (CDCl3) δ 7.629
3
3
(d, J ) 8.37 Hz, 4H), 7.462 (d, 4H), 7.280 (d, J trans ) 16.19
4
Hz, 2H), 6.901 (d, 2H), 6.712 (d, J ) 1.68 Hz, 2H), 6.667 (dd,
3J ) 7.82 Hz, 2H), 6.436 (d, 2H), 3.600 (m, 2H), 3.2-2.9
(complex, 6H), 2.474 (s, 6H). 13C NMR (CDCl3) δ 194.5, 139.7,
139.3, 138.7, 137.2, 135.0, 133.8, 130.5, 130.1, 128.7, 128.5,
127.4, 126.8, 34.7, 33.6, 30.5. HREI-MS 560.183444, ∆ )
1.7 ppm.
4,4′-Bis[4-(m eth ylth io)styr yl]-1,1′-d iben zen e (7a ). To a
three-neck round-bottom flask equipped with a needle valve
and a magnetic stir-bar was added 4-(methylthio)benzaldehyde
(0.2 mL, 1.5 mmol), 4,4′-bis[(methyl)triphenylphosphonium
bromide]-1,1′-dibenzene (432 mg, 0.5 mmol), and THF (25 mL)
under an argon atmosphere. Potassium hydride (60 mg, 1.5
mmol) was added at 0 °C, and the reaction was allowed to
warm to room temperature overnight with constant stirring.
The suspension was poured into hexanes (100 mL), washed
with water, then collected by filtration to afford 209 mg (93%)
of pale yellow solid, which was used in the next step without
further purification.
4,4′-Bis[4-(a cetylth io)styr yl]-1,1′-d iben zen e (7). 7a (200
mg, 0.49 mmol) and sodium thiomethoxide (123 mg, 1.76
mmol) were reacted in DMF (7 mL), quenched with excess
acetyl chloride, worked up, and purified in the same manner
as previously described. After chromatography, 182 mg (82%)
Ack n ow led gm en t. Financial support form the Na-
tional Science Foundation (DMR 0097611), the Office
of Naval Research, and the Mitsubishi Chemical Center
for Advanced Materials is gratefully acknowledged.
AFM and XPS results were obtained at the MRL (Ma-
terials Research Laboratory at UCSB) Central Facilities
supported by the National Science Foundation (DMR
96-32716).
1
of the title compound was isolated. H NMR (CDCl3) δ 7.638
3
(m, 8H), 7.585 (d, J ) 8.37 Hz, 4H), 7.424 (d, 4H), 7.185 (m,
4H), 2.452 (s, 6H). Anal. Calcd for C32H26O2S2: C, 75.86;
H, 5.17. Found: C, 75.01; H, 5.46. HREI-MS 506.13905, ∆ )
3.2 ppm.
Cyclic Volta m m etr y Mea su r em en ts. Electrochemical
measurements were obtained by using a standard three-
electrode cell cyclic voltammetry setup with a Pt disk, Ag wire,
and Pt wire for the working, auxiliary, and reference elec-
trodes, respectively. Measurements were made in solutions of
0.1 M tetrabutlyamonium phosphorushexafloride, in degassed
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal methods, including references to OPV precursors, and AFM
images: plane view and section analysis. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O035664G
J . Org. Chem, Vol. 69, No. 4, 2004 1119