Syntheses of new functionalized azobenzenes for potential molecular electronic devices

Article abstract of DOI:10.1016/j.tet.2006.08.069

New non-symmetrical azobenzene derivatives have been synthesized as potential molecular electronic switching device candidates. The Oxone mediated oxidation of anilines provided nitroso-functionalized arenes, which were then condensed with substituted anilines to provide a series of azobenzene derivatives that could be further converted into oligo(phenylene ethynylene)s or diazonium salts. The resulting thiolacetates, thiols, or diazonium salts are capable of forming molecular layers on the surface of gold or silicon, thereby paving the way for molecular electronics testing.

Full text of DOI:10.1016/j.tet.2006.08.069

Tetrahedron 62 (2006) 10303–10310
Syntheses of new functionalized azobenzenes for potential
molecular electronic devices
Byung-Chan Yu,a,y Yasuhiro Shiraib and James M. Tourb,
*
aDepartment of Chemistry, Mokwon University, Daejon 302-729, Republic of Korea
bDepartment of Chemistry and The Smalley Institute for Nanoscale Science and Technology, MS 222, Rice University,
6100 Main Street, Houston, TX 77005, USA
Received 18 May 2006; revised 14 August 2006; accepted 21 August 2006
Available online 15 September 2006
Abstract—New non-symmetrical azobenzene derivatives have been synthesized as potential molecular electronic switching device candi-
dates. The OxoneÒ mediated oxidation of anilines provided nitroso-functionalized arenes, which were then condensed with substituted
anilines to provide a series of azobenzene derivatives that could be further converted into oligo(phenylene ethynylene)s or diazonium salts.
The resulting thiolacetates, thiols, or diazonium salts are capable of forming molecular layers on the surface of gold or silicon, thereby paving
the way for molecular electronics testing.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
storage and molecular recognition applications.3 Azobenz-
ene derivatives are interesting molecular device candidates
that have been widely investigated due to their non-degrada-
tive reversible trans–cis photoisomerization during repeated
switching cycles; azobenzenes also possess useful electro-
chemical activity.4 Accordingly, the isomerization of azo-
benzene derivatives has been observed under the influence
of an external electric field at the single molecule level.5
Molecular electronics is a promising area of research that
focuses on a bottom-up strategy to fabricate nanoscopic
electronic devices based on self-assembled monolayers
(SAMs) of organic molecules on surfaces.1 One of the clas-
ses of compounds we have concentrated on is a series of
oligo(phenylene ethynylene) (OPE) derivatives that have
enabled the study of molecular switching processes in elec-
tronic devices.1,2
Previously we have shown that symmetrical azobenzene
OPEs bearing protected thiol end groups form SAMs on
metal surfaces.2e We envisioned that the synthesis of non-
symmetrical azobenzene derivatives could be realized by
changing the substituents (R1 and R2 in A, Fig. 1) of
Alternatively, the self-assembly of photo-responsive mole-
cules onto the substrates creates the possibility of using
switching devices as photo-responsive components in optical
N
N
R2
R1
A
R2 = I
R2 = NO2 or NH2
Pd/Cu catalyzed
coupling
reduction/diazonium
formation
-
N2+BF4
N
N
SR
N
N
R1
R1
B
R = Ac or H
C
grafted molecular layers
on Si
SAMs on gold
Figure 1. Synthesis of azobenzene derivatives B (for self-assembly on gold) or C (for grafting of molecular layers on silicon) from disubstituted azobenzene A.
* Corresponding author. Tel.: +1 713 348 6246; fax: +1 713 348 6250; e-mail: tour@rice.edu
While on sabbatical leave to Rice University.
y
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.08.069

10304
B.-C. Yu et al. / Tetrahedron 62 (2006) 10303–10310
-
N
N2+BF4
N
SR2
F3C
N
R1
N
7
1, R1 = H, R2 = Ac
2, R1 = H, R2 = H
3, R1 = CF3, R2 = Ac
4, R1 = CF3, R2 = H
5, R1 = NO2, R2 = Ac
-
N
N
N2+BF4
8
N
O
SH
N
6
Figure 2. The structures of the type B azobenzene OPEs 1–5, azobenzene alkanethiol 6 and type C azobenzene diazonium salts 7 and 8 synthesized in this work.
a disubstituted azobenzene. The resulting products would
lead to an azobenzene OPE thiol/thioacetate that could
form SAMs on many metal surfaces through compound
on the substituent at the para position of the azobenzene
moieties comprising the SAM.9 Therefore para-substituted
azobenzene OPEs 3–5 were prepared. It was expected that
the SAMs formed from 3 or 4 would show changes in wet-
tability depending on whether the molecules were in their
trans (hydrophobic) or cis (hydrophilic) forms. Since the
trans and cis isomers also have different dipole moments,10
it is possible that isomerization of the molecules in the
SAMs could change the electrical properties of the SAM.
With that in mind, we prepared 3 and 4 (Scheme 1). Com-
mercially available 4-trifluoroaniline 9b was smoothly oxi-
dized using OxoneÒ to afford the nitrosobenzene 10b,
which was subsequently condensed with 11 in acetic acid
to give the iodoazobenzene 12b. Coupling to 13 gave 3,
which was converted to the corresponding thiol 4 as previ-
ously described.
B
grafting of molecular layers on semiconductor surfaces
1,2 or alternatively to an azobenzene diazonium salt C for
(Fig. 2).6
2. Results
2.1. Syntheses of azobenzene derivatives of type B
Functionalized azobenzene OPEs bearing free thiol or pro-
tected thiol end groups are preferred for formation of
SAMs on gold substrates. Therefore the azobenzene OPEs
1–5 were prepared. After some preliminary experiments,
the OxoneÒ mediated oxidation of anilines 9b,c to provide
nitrosoarenes 10a–c,7 followed by condensation with iodo-
aniline 11, was found to be an efficient path to prepare a
series of azobenzene derivatives. For example, the nitroso-
benzene 10a (Scheme 1, prepared from aniline7) was treated
with 11 in acetic acid to afford the iodoazobenzene 12a. This
was coupled with thioacetate 131,8 to give the protected azo-
benzene OPE 1. The thioacetate 1 was carefully treated with
aqueous potassium hydroxide in ethanol under an oxygen-
free atmosphere (to minimize the oxidative coupling of the
thiol) to provide the azobenzene OPE thiol 2 in 61% yield.
In a similar fashion, the nitro-substituted azobenzene OPE 5,
which might show enhanced switching characteristics due to
the electron-withdrawing nature of the nitro group, was pre-
pared by oxidation of 9c to 10c using OxoneÒ, followed by
condensation with 11 to give 12c. The OxoneÒ mediated
oxidation is noteworthy because nitrosobenzenes containing
electron-withdrawing groups at the para position are diffi-
cult to prepare on a large scale.7 Compound 12c was sub-
sequently coupled with the thioacetate 13 to afford the
nitroazobenzene OPE 5. Compounds 3–5 are currently being
tested by our collaborators using scanning tunneling micros-
copy (STM) to detect switching effects at the single molec-
ular level.2f–g
It is known that the relative order of the formed SAMs and
the photo responsiveness of the molecules are dependent
H
SAc
H2N
I
N
I
O
13
PdCl2(PPh3)2, CuI
Oxone
CH2Cl2/H2O
11
R1
NH2
R1
N
R1
N
AcOH
9b, R1 = CF3
9c, R1 = NO2
12a, R1 = H: 85%
12b, R1 = CF3: 40% (two steps)
12c, R1 = NO2: 51% (two steps)
10a, R1 = H
10b, R1 = CF3
10c, R1 = NO2
N
SR2
R1
N
1, R1 = H, R2 = Ac: 73%
2, R1 = H, R2 = H
KOH, EtO/H2O, 61%
KOH, EtO/H2O, 67%
3, R1 = CF3, R2 = Ac: 71%
4, R1 = CF3, R2 = H
5, R1 = NO2, R2 = Ac: 62%
Scheme 1. Synthesis of the azobenzene OPEs 1–5.

B.-C. Yu et al. / Tetrahedron 62 (2006) 10303–10310
10305
Azobenzenes bearing an alkanethiol functional group have
been used to study molecular photo-switching at the nano-
scale in SAMs.4 To test single molecular switching by
STM we prepared the azobenzene alkanethiol 6. Compound
10a was condensed with hydroxyethyl aniline (14) in acetic
acid. The resulting alcohol was alkylated using dibromo-
butane in the presence of excess NaH in DMF. The alkyl-
ation, which was sluggish at room temperature, afforded
the bromide 16. Subsequent conversion of the bromide
into the thiol 6 was accomplished by addition of thiourea fol-
lowed by treatment with aqueous potassium hydroxide
(Scheme 2).
4-nitronitrosobenzene 20. Without purification the labile
nitroso compound was directly submitted to an acetic acid
mediated condensation reaction with 4-tritylaniline (21) to
provide 4-tritylnitroazobenzene (22) in 82% yield over two
steps. Reduction of the nitro group to the corresponding
amine 23 in the presence of the diazo moiety was accom-
plished by treatment with sodium sulfide in a mixture of
refluxing dioxane, ethanol and water.12 The amine 23 was
subsequently converted into the air stable diazonium salt 8
upon the treatment with boron triflouride-diethyl etherate
and tert-butylnitrite.
Additional examples of the synthesis of disubstituted azo-
benzenes are shown in Table 1. Oxidation of 4-substituted
anilines by OxoneÒ followed by condensation of the result-
ing nitrosobenzenes with 4-substituted anilines provides
4,40-disubstituted azobenzenes in 40–93% yields. The excel-
lent yield of 40-bromo-4-iodoazobenzene (entry 8) is partic-
ularly noteworthy because the compound could be useful for
non-symmetric azobenzene OPE synthesis.13 The azobenz-
enes formed were generally insoluble in acetic acid; a differ-
ent work-up procedure was used for those products that were
soluble (see Section 4). Formation of the corresponding
nitrosobenzene from 4-trimethylsilylethynylaniline fol-
lowed by coupling with 11 to provide the corresponding
40-trimethylsilyliodoazobenzene could be useful for more
advanced azobenzene OPE oligomers (entry 9).
2.2. Syntheses of azobenzene derivatives of type C
The formation of grafted molecular layers on silicon is
important due to the possibility of integrating molecular
electronics into existing silicon microelectronic architec-
tures.11 The Si–C bond is both thermodynamically and
kinetically stable due to the high bond strength and low
polarity of the bond.11a Covalent attachment of arenes via
aryldiazonium salts to hydride-passivated SiC111D and
SiC100D has been successfully demonstrated.6 Until now
few methods concerning the preparation of azobenzene
molecular layers on silicon surfaces have been reported.11b
Therefore we synthesized new functionalized azobenzene
diazonium salts for grafting azobenzene derivatives onto Si
substrates.
4-Trifluoromethylnitrosobenzene (10b) was condensed with
p-phenylenediamine to afford 18. The resultant amine was
converted into the desired diazonium salt 7 upon treatment
with boron triflouride-diethyl etherate and tert-butylnitrite
(Scheme 3).
3. Summary
In summary, the methodology detailed here provides versa-
tile synthetic pathways to azobenzene derivatives that could
be used as potential molecular electronic or photo-respon-
sive nanoscale devices. Work is currently underway to eval-
uate these photo-responsive azobenzene derivatives for their
effectiveness as molecular switches integrated in nanoscale
devices.
The tritylazobenzene diazonium salt 8 was prepared in
a similar manner (Scheme 4). Commercially available
4-nitroaniline 19 was oxidized with OxoneÒ to afford
OH
N
Br
H2N
O
Br
OH
N
14
N
NaH, DMF
36%
AcOH
10a
15, 44% (over two steps
from aniline)
1) thiourea, ethanol
N
O
N
O
SH
Br
2) KOH, water
70%
N
N
16
6
Scheme 2. Synthesis of the azobenzene alkanethiol 6.
H2N
NH2
N
NH2
O
BF3 OEt2
17
AcOH
F3C
N
F3C
N
t-BuONO
THF
18, 43% from 9b
10b
95%
-
N
N2+BF4
F3C
N
7
Scheme 3. Synthesis of the trifluoromethyldiazobenzene diazonium salt 7.

10306
B.-C. Yu et al. / Tetrahedron 62 (2006) 10303–10310
NH2
O
Oxone
CH2Cl2/H2O
21
H2N
NO2
N
NO2
AcOH
19
20
N
N
NH2
N
N
O2
BF3 OEt2
Na2S
N
t-BuONO
85%
dioxane
ethanol
water
23
22, 82% over 2 steps
81%
-
N
N2+BF4
N
8
Scheme 4. Synthesis of the trityldiazobenzene diazonium salt 8.
Table 1. Synthesis of the para-disubstituted azobenzenes
the Rice University or University of South Carolina Mass
Spectroscopy Laboratory. Melting point values are uncor-
rected. Compounds were named using the Struct¼Name
algorithm in ChemDraw 9.0 developed by CambridgeSoft.
N
R2
R1
N
Entry
Product
R1
R2
Yield (%)a
4.2. General procedure for the coupling of a terminal
alkyne with an aryl halide utilizing a palladium–copper
cross-coupling (Castro–Stephens/Sonogashira
protocol)8
1
2
3
4
5
6
7
8
9
10
12a
12b
12c
15
18
22
24
25
26
27
H
I
I
I
85
40
51
44
43
82
74
93
35
72
CF3
NO2
H
CF3
NO2
Br
Br
TMS
NO2
(CH2)2OH
NH2
Trityl
H
To a screw cap tube or a round-bottom flask were added the
aryl halide, bis(triphenylphosphine)palladium(II) dichloride
(5 mol % based on aryl halide), and copper(I) iodide
(10 mol % based on aryl halide). The vessel was sealed
with a rubber septum, evacuated, and backfilled with nitro-
gen (3ꢀ). A cosolvent of THF was added followed by the
amine base. The terminal alkyne was then added followed
by replacing the septum with a screw cap when a tube was
used and the reaction was heated if necessary. TLC was
used to follow the progress of the reaction, and when com-
plete, the reaction vessel was cooled to room temperature.
The mixture was quenched with water or a saturated solution
of NH4Cl. The organic layer was diluted with organic sol-
vent and washed with brine (3ꢀ). The combined aqueous
layers were extracted with organic solvent (3ꢀ), and the
combined organic layers were dried over anhydrous
MgSO4. The slurry was filtered, and the solvent was
removed from the filtrate in vacuo, followed by further puri-
fication of the residue as indicated.
I
I
(CH2)2OH
a
All yields are based on the two-step reaction sequence from the aniline
except entry 1.
4. Experimental
4.1. General synthetic methods
Unless stated otherwise, reactions were performed in oven-
dried, nitrogen flushed glassware equipped with a magnetic
stir bar using freshly distilled solvents. Reagent grade tetra-
hydrofuran (THF) was distilled from sodium benzophenone
ketyl. Triethylamine (TEA) was distilled from calcium
hydride. Trimethylsilylacetylene (TMSA) was donated by
FAR Research Inc. and Petra Chemical. Compound 13 was
prepared as described previously.1 All other commercially
available reagents were used as received. Unless otherwise
noted, reactions were magnetically stirred and monitored
by thin-layer chromatography (TLC) using E. Merck silica
gel 60 F254 precoated plates (0.25 mm). Flash chromato-
graphy was performed with the indicated solvent systems
using silica gel grade 60 (230–400 mesh). NMR chemical
shifts are reported in parts per million downfield from tetra-
methylsilane (TMS) or relative to the known value of resi-
dual solvent signal. Mass spectroscopy was performed at
4.3. General synthesis of para-disubstituted
azobenzenes7
To a solution of the substituted aniline in CH2Cl2 was added
OxoneÒ (2.00 equiv) dissolved in water. The mixture was
stirred under nitrogen at room temperature until TLC mon-
itoring indicated complete consumption of the starting mate-
rial (2–24 h). The color of the solution generally turned to
green as the corresponding nitrosoarene formed. After sepa-
ration of the layers, the aqueous layer was extracted with

B.-C. Yu et al. / Tetrahedron 62 (2006) 10303–10310
10307
CH2Cl2 (3ꢀ). The combined organic layers were washed
with 1 N HCl, saturated sodium bicarbonate solution, water,
brine and dried with MgSO4. After filtration, removal of the
solvent from the filtrate in vacuo yielded the corresponding
labile nitrosoarene, which was submitted to the next conden-
sation step without further purification. To the nitrosoarene
dissolved in acetic acid was added the substituted aniline
(1.00 equiv). The resulting mixture was stirred at room tem-
perature for 24–48 h. The precipitate was separated by filtra-
tion and the collected solid was washed with acetic acid and
water and dried in a desiccator over P2O5 under reduced
pressure. The compound was further purified by chromato-
graphy as necessary. For the acetic acid-soluble azobenz-
enes, saturated NaHCO3 was added slowly to precipitate
the product. The mixture was extracted with CH2Cl2 (3ꢀ).
The combined extracts were dried with magnesium sulfate.
After filtration the solvent was removed from the filtrate
and the residue was chromatographed on silica gel.
1495, 1398, 1301 cmꢂ1
;
1H NMR (400 MHz, CDCl3)
d 7.96–7.93 (m, 4H), 7.68 (d, J¼8.6 Hz, 2H), 7.55–7.46
(m, 3H), 7.36 (d, J¼8.4 Hz, 2H), 7.25 (d, J¼8.4 Hz, 2H),
3.54 (s, 1H); 13C NMR (100 MHz, CDCl3) d 152.9, 152.0,
132.6 (2C), 132.5 (2C), 132.4, 131.5, 129.4 (2C), 129.2
(2C), 126.1, 123.18 (2C), 123.17 (2C), 120.3, 91.6, 89.8;
HRMS calcd for C22H22N2S 314.8777, found 314.8779.
4.3.4. (E)-1-(4-Iodophenyl)-2-(4-(trifluoromethyl)phe-
nyl)diazene (12b). Following the general synthesis of
azobenzenes procedure, to a solution of 9b (1.50 g,
9.31 mmol) in CH2Cl2 (20 mL) was added a solution of
OxoneÒ (11.5 g, 18.6 mmol) in H2O (20 mL). The crude
product (2.0 g) was dissolved in acetic acid (50 mL) and
11 (2.00 g, 9.31 mmol) was added. The resulting product
12b was isolated as an orange solid (1.40 g, 40%):
mp 150–151 ꢁC; FTIR (KBr) 3076, 1942, 1577, 1476,
1336 cmꢂ1
;
1H NMR (400 MHz, CDCl3) d 8.01 (d,
J¼8.2 Hz, 2H), 7.91 (d, J¼8.6 Hz, 2H), 7.79 (d, J¼8.2 Hz,
2H), 7.69 (d, J¼8.6 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d 154.4, 151.9, 138.7 (2C), 132.7 (q, 2JCF¼32.5 Hz), 126.6
(2C, q, 3JCF¼3.7 Hz), 124.9 (2C), 124.1 (q, 1JCF¼272.4 Hz),
123.3 (2C), 99.0; HRMS calcd for C13H8F3IN2 375.9682,
found 375.9684.
4.3.1. (E)-2-(4-Iodophenyl)-1-phenyldiazene (12a). Fol-
lowing the general azobenzene synthesis procedure, a solu-
tion of nitrosobenzene 10a (510 mg, 4.76 mmol) and
4-iodoaniline 11 (935 mg, 4.33 mmol) in acetic acid (30 mL)
was stirred for 24 h. The product 12a (1.13 g, 85%) was
a yellow solid: mp 89–90 ꢁC; FTIR (KBr) 3064, 1950,
1561, 1472 cmꢂ1; 1H NMR (400 MHz, CDCl3) d 7.93 (dd,
J¼7.8, 1.7 Hz, 2H), 7.88 (d, J¼8.4 Hz, 2H), 7.66 (d,
J¼8.4 Hz, 2H), 7.54–7.47 (m, 3H); 13C NMR (100 MHz,
CDCl3) d 152.7, 152.2, 138.6 (2C), 131.6, 129.4 (2C),
124.7 (2C), 123.2 (2C), 97.9; HRMS calcd for C12H9IN2
307.9810, found 307.9805.
4.3.5. (E)-S-4-((4-((4-(Trifluoromethyl)phenyl)diazenyl)-
phenyl)ethynyl)phenyl ethanethioate (3). Following the
general coupling procedure, the iodoazobenzene 12b
(250 mg, 0.665 mmol) was coupled to 13 (129 mg,
0.731 mmol) using PdCl2(PPh3)2 (19 mg, 0.027 mmol),
CuI (10 mg, 0.053 mmol), TEA (1 mL), and THF (5 mL).
The crude product was purified using column chromato-
graphy on silica gel (50% CH2Cl2 in hexanes) to afford 3
(201 mg, 71%) as an orange solid: mp 184–187 ꢁC; FTIR
(KBr) 3103, 2920, 2843, 2206, 1918, 1705, 1588, 1499,
4.3.2. (E)-S-4-((4-(Phenyldiazenyl)phenyl)ethynyl)-
phenyl ethanethioate (1). Following the general coupling
procedure, 12a (259 mg, 0.841 mmol) was coupled to 131
(163 mg, 0.925 mmol) using PdCl2(PPh3)2 (23 mg,
0.034 mmol), CuI (13 mg, 0.067 mmol), TEA (1 mL), and
THF (5 mL). Column chromatography of the crude product
on silica gel (40% CH2Cl2 in hexanes) afforded 1 as a yellow
solid (219 mg, 73%): mp 185–186 ꢁC; FTIR (KBr) 3064,
2924, 2202, 1926, 1689, 1592, 1491, 1437, 1351, 1297,
1
1406, 1316 cmꢂ1; H NMR (500 MHz, CDCl3) d 8.03 (d,
J¼8.2 Hz, 2H), 7.97 (d, J¼8.7 Hz, 2H), 7.80 (d, J¼8.2 Hz,
2H), 7.71 (d, J¼8.7 Hz, 2H), 7.60 (d, J¼8.5 Hz, 2H), 7.44
(d, J¼8.5 Hz, 2H), 2.46 (s, 3H); 13C NMR (125 MHz,
CDCl3) d 193.6, 154.6, 151.9, 134.5 (2C), 132.8 (2C),
3
132.5 (2C), 128.8, 126.7, 126.6 (2C, q, JCF¼3.8 Hz),
1
1
1106 cmꢂ1; H NMR (400 MHz, CDCl3) d 7.94–7.91 (m,
124.2, 124.1 (q, JCF¼272.4 Hz), 123.5 (2C), 123.3 (2C),
4H), 7.67 (d, J¼8.4 Hz, 2H), 7.58 (d, J¼8.1 Hz, 2H),
7.54–7.46 (m, 3H), 7.41 (d, J¼8.1 Hz, 2H), 2.44 (s, 3H);
13C NMR (100 MHz, CDCl3) d 193.4, 152.6, 152.0, 134.3
(2C), 132.5 (2C), 132.2 (2C), 131.3, 129.1 (2C), 128.5,
125.5, 124.2, 123.0 (4C), 91.1, 90.8, 30.3; HRMS calcd
for C24H24N2OS 356.0983, found 356.0972.
91.8, 90.8, 30.6 (2JCF coupling of the aromatic carbon at
the ipso-position from CF3 group was not clearly observed
due to the low intensity of the corresponding quartet signal);
HRMS calcd for C23H15F3N2OS 424.0857, found 424.0857.
4.3.6. (E)-4-((4-((4-(Trifluoromethyl)phenyl)diazenyl)-
phenyl)ethynyl)benzenethiol (4). A solution of ethanol
(2 mL) and water (2 mL) was purged with N2 for 30 min
and KOH (66 mg, 1.2 mmol) was added. The solution was
purged with N2 for 20 min. The thioacetate 3 (90 mg,
0.236 mmol) was added and the solution was purged again
with N2 for 10 min. It was then heated at reflux under N2
for 30 min. The reaction mixture was carefully neutralized
with 1 N HCl under N2. The yellow solid was filtered,
washed repeatedly with water under N2, and dried in a desic-
cator in vacuo to afford the thiol 4 (60 mg, 67%) as an orange
solid: mp 184–187 ꢁC; FTIR (KBr) 3289, 3044, 2919, 1953,
1736, 1605, 1443, 1301 cmꢂ1; 1H NMR (500 MHz, CDCl3)
d 8.02 (d, J¼8.2 Hz, 2H), 7.96 (d, J¼8.5 Hz, 2H), 7.80 (d,
J¼8.2 Hz, 2H), 7.68 (d, J¼8.5 Hz, 2H), 7.44 (d, J¼8.3 Hz,
2H), 7.27 (d, J¼8.3 Hz, 2H), 3.56 (s, 1H); 13C NMR
4.3.3. (E)-4-((4-(Phenyldiazenyl)phenyl)ethynyl)benz-
enethiol (2). A solution of ethanol (2 mL) and water
(2 mL) was purged with N2 for 40 min and then KOH
(47 mg, 0.842 mmol) was added. The solution was purged
again with N2 for 20 min. The thioacetate 1 (90 mg,
0.252 mmol) was added and the solution was purged again
with N2 for 10 min. The reaction mixture was heated at re-
flux under N2 for 30 min, and then was carefully neutralized
with 1 N HCl under N2. The orange solid was filtered,
washed repeatedly with water under N2 and dried in vacuo.
Purification on silica gel using 40% CH2Cl2 in hexanes
afforded the thiol 2 (48 mg, 61%) as an orange solid: mp
161–195 ꢁC (broad range likely due to oxidative decomposi-
tion); FTIR (KBr) 3437, 3060, 2924, 2559, 2206, 1584,

10308
B.-C. Yu et al. / Tetrahedron 62 (2006) 10303–10310
(125 MHz, CDCl3) d 154.6, 151.7, 132.8 (2C), 132.6, 132.5
(2C), 129.1 (2C), 127.0, 126.6 (2C, q, 3JCF¼3.8 Hz), 123.5
(2C), 123.3 (2C), 120.1, 92.2, 89.7; (Carbon signals with
1JCF and 2JCF couplings were not observed due to the low in-
tensity of the quartet signals caused by limited solubility of
the product.) HRMS calcd for C21H13F3N2S 382.0753,
found 382.0751.
azobenzene ethanol 15 (600 mg, 2.65 mmol). NaI (40 mg,
0.26 mmol) and dibromobutane (2.30 g, 10.7 mmol) were
then added to the solution. The reaction mixture was stirred
for 32 h at room temperature. Since a significant amount of
the starting alcohol was present in the mixture by TLC
analysis, additional portions of NaH (212 mg, 5.30 mmol),
dibromobutane (1.72 g, 7.96 mmol), and DMF (3 mL) were
added to the solution. The reaction mixture was further
stirred at room temperature for 20 h. Water was carefully
added to quench the excess NaH after cooling the mixture
to 0 ꢁC. The aqueous layer was separated and extracted
with CH2Cl2 (3ꢀ). The extracts were washed with brine,
dried over MgSO4, filtered, and the filtrate was concentrated
in vacuo. The residue was chromatographed on silica gel.
Elution with 10% EtOAc in hexanes gave the bromide 16
(352 mg, 36%) as an orange semi-solid: FTIR (KBr) 3049,
4.3.7. (E)-1-(4-Iodophenyl)-2-(4-nitrophenyl)diazene
(12c). Following the general procedure for synthesis of
azobenzenes, to a solution of 4-nitroaniline 9c (2.00 g,
14.5 mmol) in CH2Cl2 (40 mL) was added a solution of
OxoneÒ (17.8 g, 29.0 mmol) in H2O (150 mL). The crude
intermediate was dissolved in acetic acid (50 mL) and then
4-iodoaniline (3.18 g, 14.5 mmol) was added. Purification
of the product on silica gel (50% CH2Cl2 in hexanes) gave
12c (2.60 g, 51%) as an orange solid containing a small
amount of cis isomer (<5%) according to the 1H NMR anal-
ysis: mp 237–243 ꢁC; FTIR (KBr) 3099, 2928, 1926, 1596,
1515, 1468, 1332 cmꢂ1; 1H NMR (400 MHz, CDCl3) d 8.40
(d, J¼9.1 Hz, 2H), 8.05 (d, J¼9.1 Hz, 2H), 7.93 (d,
J¼8.7 Hz, 2H), 7.71 (d, J¼8.7 Hz, 2H); 13C NMR
(100 MHz, CDCl3) d 155.7, 151.9, 149.1, 138.9 (2C),
125.1 (2C), 125.0 (2C), 123.8 (2C), 99.9; HRMS calcd for
C12H8IN3O2 352.9661, found 352.9664.
2932, 2850, 1950, 1600, 1478, 1433, 1347, 1243 cmꢂ1
;
1H NMR (400 MHz, CDCl3) d 7.92 (d, J¼8.2 Hz, 2H),
7.87 (d, J¼8.3 Hz, 2H), 7.53–7.47 (m, 3H), 7.38 (d,
J¼8.3 Hz, 2H), 3.69 (t, J¼7.0 Hz, 2H), 3.49 (t, J¼6.2 Hz,
2H), 3.43 (t, J¼6.7 Hz, 2H), 2.97 (t, J¼7.0 Hz, 2H), 1.94
(m, 2H), 1.73 (m, 2H); 13C NMR (100 MHz, CDCl3)
d 152.9, 151.5, 142.9, 131.0, 129.8 (2C), 129.3 (2C), 123.1
(2C), 123.0 (2C), 71.6, 70.2, 36.5, 34.0, 29.9, 28.4; HRMS
calcd for C18H21BrN2O 360.0830, found 360.0837.
4.3.8. (E)-4-((4-((4-Nitrophenyl)diazenyl)phenyl)ethy-
nyl)benzenethiol (5). Following the general coupling proce-
dure, 12c (96 mg, 0.26 mmol) was coupled to 13 (55 mg,
0.31 mmol) using PdCl2(PPh3)2 (17 mg, 0.025 mmol), CuI
(8 mg, 0.042 mmol), TEA (1 mL), and THF (5 mL). Column
chromatography of the crude product on silica gel (50%
CH2Cl2 in hexanes) afforded 5 as an orange solid (66 mg,
62%): mp 184–185 ꢁC; FTIR (KBr) 3103, 2924, 2854,
4.3.11. (E)-4-(4-(Phenyldiazenyl)phenethoxy)butane-1-
thiol (6). A solution of the azobenzene bromide 16
(209 mg, 0.578 mmol) and thiourea (220 mg, 2.89 mmol)
in ethanol (10 mL) was heated at reflux for 12 h. The solvent
was evaporated under reduced pressure. To the concentrated
mixture was added KOH (194 mg, 3.47 mmol) in nitrogen
purged water (10 mL). The reaction mixture was heated at
reflux for 1.5 h and then acidified with 1 N HCl. The aqueous
mixture was extracted with CH2Cl2 (3ꢀ). The extracts were
washed with brine, dried over MgSO4, filtered, and the fil-
trate was concentrated in vacuo. The residue was chromato-
graphed on silica gel. Elution with 20% EtOAc in hexanes
gave the thiol 6 (127 mg, 70%) as an orange solid: mp 31–
33 ꢁC; FTIR (KBr) 3425, 3054, 2947, 2851, 2794, 2558,
1
2214, 1709, 1522, 1491, 1340 cmꢂ1; H NMR (400 MHz,
CDCl3) d 8.40 (d, J¼8.9 Hz, 2H), 8.06 (d, J¼8.9 Hz, 2H),
7.98 (d, J¼8.5 Hz, 2H), 7.71 (d, J¼8.5 Hz, 2H), 7.60 (d,
J¼8.3 Hz, 2H), 7.43 (d, J¼8.3 Hz, 2H), 2.45 (s, 3H); 13C
NMR (100 MHz, CDCl3) d 193.5, 155.9, 151.8, 149.1,
134.5 (2C), 132.9 (2C), 132.5 (2C), 129.0, 127.4, 125.0
(2C), 124.1, 123.8 (4C), 92.3, 90.7, 30.6; HRMS calcd for
C22H15N3O3S 401.0822, found 401.0834.
1955, 1598, 1480, 1434, 1366, 1302 cmꢂ1 1H NMR
;
(400 MHz, CDCl3) d 7.90 (m, 2H), 7.85 (d, J¼8.4 Hz,
2H), 7.52–7.42 (m, 3H), 7.36 (d, J¼8.4 Hz, 2H), 3.65 (t,
J¼7.0 Hz, 2H), 3.43 (t, J¼5.7 Hz, 2H), 2.94 (t, J¼7.0 Hz,
2H), 2.51 (m, 2H), 1.64 (m, 4H), 1.32 (t, J¼7.8 Hz, 1H);
13C NMR (100 MHz, CDCl3) d 153.1, 151.7, 143.1, 131.0,
130.1 (2C), 129.5 (2C), 123.6 (2C), 123.3 (2C), 71.8, 70.8,
36.7, 31.0, 28.8, 24.9; HRMS calcd for C18H22N2OS
314.1449, found 314.1453.
4.3.9. (E)-2-(4-(Phenyldiazenyl)phenyl)ethanol (15). Fol-
lowing the general azobenzene procedure, to a solution of
aniline (1.05 g, 11.3 mmol) in CH2Cl2 (20 mL) was added
a solution of OxoneÒ (13.9 g, 22.6 mmol) in H2O
(100 mL). The crude product was dissolved in acetic acid
(100 mL) and 4-(hydroxyethyl)aniline (14) (1.55 g,
11.3 mmol) was added. After purification on silica gel
(30% EtOAc in hexane), isolation of the product gave 15
(1.15 g, 44%) as an orange solid: mp 81–83 ꢁC; FTIR
(KBr) 3303, 3051, 2933, 2857, 1486, 1443, 1590, 1519,
4.3.12. (E)-4-((4-(Trifluoromethyl)phenyl)diazenyl)benz-
eneamine (18). Following the general azobenzene proce-
dure, to a solution of 9b (1.50 g, 9.31 mmol) in CH2Cl2
(20 mL) was added a solution of OxoneÒ (11.5 g,
18.6 mmol) in H2O (20 mL). The crude product was dis-
solved in acetic acid (60 mL) and p-phenylenediamine
(17) (1.00 g, 9.31 mmol) was added. After workup, the crude
product was purified on silica gel using CH2Cl2 to give 18
(1.05 g, 43%) as an orange solid: mp 134–136 ꢁC; FTIR
(KBr) 3503, 3410, 3056, 2920, 1938, 1592, 1499, 1425,
1
1341 cmꢂ1; H NMR (400 MHz, CDCl3) d 7.93–7.88 (m,
4H), 7.53–7.48 (m, 3H), 7.40 (d, J¼8.5 Hz, 2H), 3.94 (t,
J¼6.5 Hz, 2H), 2.97 (t, J¼6.5 Hz, 2H), 1.60 (br s, 1H);
13C NMR (100 MHz, CDCl3) d 152.9, 151.7, 142.2, 131.1,
130.0 (2C), 129.3 (2C), 123.3 (2C), 123.0 (2C), 63.7, 39.3;
HRMS calcd for C14H14N2O 401.0822, found 401.0834.
4.3.10. (E)-1-(4-(2-(4-Bromobutoxy)ethyl)phenyl)-2-phe-
nyldiazene (16). To a suspension of NaH (60% dispersion in
mineral oil) in 7 mL of DMF was added dropwise at 0 ꢁC the
1394, 1316, 1289 cmꢂ1 1H NMR (500 MHz, CD3CN)
;
d 7.92 (d, J¼9.0 Hz, 2H), 7.81 (d, J¼9.0 Hz, 2H), 7.77 (d,
J¼8.8 Hz, 2H), 6.76 (d, J¼8.8 Hz, 2H), 4.96 (br s, 2H);

B.-C. Yu et al. / Tetrahedron 62 (2006) 10303–10310
10309
13C NMR (125 MHz, CD3CN) d 156.5, 154.1, 145.6, 131.3
(q, 2JCF¼32.1 Hz), 127.7 (2C, q, 3JCF¼3.9 Hz), 127.0 (2C),
4.3.16. (E)-4-((4-Tritylphenyl)diazenyl)benzendiazo-
nium tetrafluoroborate (8). In a 100 mL round-bottom
flask was placed boron trifluoride-diethyl etherate
(0.432 mL, 3.41 mmol). The flask was submerged into
a dry ice bath to control the temperature at ꢂ40 ꢁC. The di-
azobenzeneamine 23 (500 mg, 1.14 mmol) in THF (15 mL)
was added dropwise. The reaction mixture was stirred for
10 min and then tert-butylnitrite (0.273 mL, 2.28 mmol)
was added dropwise. The reaction mixture was allowed to
warm to room temperature and then anhydrous ether was
added to precipitate the diazonium salt. The mixture was
filtered and the solid was washed with excess ether to afford
the pure diazonium salt 8 (520 mg, 85%): FTIR (KBr)
3348, 3111, 3045, 2272, 1957, 1817, 1577, 1487, 1413,
1
125.7 (q, JCF¼271.1 Hz), 123.7 (2C), 115.3 (2C); HRMS
calcd for C13H10F3N3 265.0827, found 265.0824.
4.3.13. (E)-4-((4-(Trifluoromethyl)phenyl)diazenyl)benz-
endiazonium tetrafluoroborate (7). In a 100 mL round-
bottom flask was placed boron trifluoride-diethyl etherate
(0.143 mL, 1.13 mmol). The flask was submerged into
a dry ice bath to control the temperature at ꢂ40 ꢁC. The di-
azobenzeneamine 18 (100 mg, 0.377 mmol) in THF (4 mL)
was added dropwise. The reaction mixture was stirred for
10 min and then tert-butylnitrite (0.090 mL, 0.75 mmol)
was added dropwise. The reaction mixture was allowed to
warm to room temperature and then anhydrous ether was
added to precipitate the diazonium salt. The mixture was fil-
tered and the solid washed with excess ether to afford the
diazonium salt 7 (130 mg, 95%): FTIR (KBr) 3363, 3212,
3107, 2291, 1938, 1802, 1577, 1475, 1456, 1332 cmꢂ1; 1H
NMR (400 MHz, acetone-d6) d 9.13 (d, J¼9.1 Hz, 2H),
8.51 (d, J¼9.1 Hz, 2H), 8.26 (d, J¼8.2 Hz, 2H), 8.06
(d, J¼8.2 Hz, 2H); 13C NMR (125 MHz, acetone-d6)
d 159.2, 155.1, 135.9 (2C), 134.6 (q, 2JCF¼32.6 Hz), 127.8
1317 cmꢂ1
;
1H NMR (400 MHz, CDCl3) d 8.76 (d,
J¼8.2 Hz, 2H), 8.29 (d, J¼8.2 Hz, 2H), 7.99 (d,
J¼7.5 Hz, 2H), 7.65 (d, J¼7.5 Hz, 2H), 7.42–7.33 (m,
15H); 13C NMR (100 MHz, CDCl3) d 159.6, 154.3,
150.9, 146.8 (3C), 135.0 (2C), 132.6 (2C), 131.2
(6C), 128.5 (6C), 126.8 (3C), 125.6 (2C), 123.8 (2C),
114.9, 65.9.
4.3.17. (E)-1-(4-Bromophenyl)-2-phenyldiazene (24).14
Following the general azobenzene procedure, to a solution
of 4-bromoaniline (2.50 g, 14.9 mmol) in CH2Cl2 (45 mL)
was added a solution of OxoneÒ (17.9 g, 29.8 mmol) in
H2O (180 mL). The crude product (2.78 g) was >90%
pure by 1H NMR. A portion (500 mg, 2.70 mmol) was dis-
solved in acetic acid (30 mL) and was condensed with ani-
line (210 mg, 2.25 mmol). Purification on silica gel using
5% CH2Cl2 in hexanes gave the 24 (520 mg, 74%) as an
orange solid: mp 89–90 ꢁC; FTIR (KBr) 3084, 1573,
3
(2C, q, JCF¼3.8 Hz), 126.1 (2C), 125.2 (2C), 124.8
(q, 1JCF¼271.8 Hz), 117.8.
4.3.14. (E)-1-(4-Nitrophenyl)-2-(4-tritylphenyl)diazene
(22). Following the general azobenzene procedure, to a solu-
tion of 19 (1.00 g, 7.24 mmol) in CH2Cl2 (20 mL) was added
a solution of OxoneÒ (8.90 g, 14.5 mmol) in H2O (80 mL).
After workup, the crude product was dissolved in acetic
acid (50 mL) and 4-tritylaniline 21 (2.43 g, 7.24 mmol)
was added to give a product that was recrystallized from hex-
anes to afford 22 (2.79 g, 82%) as an orange solid: mp 301–
302 ꢁC; FTIR (KBr) 3052, 2443, 1957, 1592, 1515, 1492,
1480 cmꢂ1
;
1H NMR (400 MHz, CDCl3) d 7.92 (d,
J¼8.1 Hz, 2H), 7.80 (d, J¼8.5 Hz, 2H), 7.65 (d, J¼8.5 Hz,
2H), 7.55–7.47 (m, 3H).
1437, 1350, 1312 cmꢂ1 1H NMR (400 MHz, CDCl3)
;
d 8.38 (d, J¼9.1 Hz, 2H), 8.01 (d, J¼9.1 Hz, 2H), 7.87 (d,
J¼8.8 Hz, 2H), 7.46 (d, J¼8.8 Hz, 2H), 7.30–7.23 (m,
15H); 13C NMR (100 MHz, CDCl3) d 156.1, 152.1, 150.6,
148.9, 146.4 (3C), 132.3 (2C), 131.3 (6C), 128.0 (6C),
126.4 (3C), 125.0 (2C), 123.6 (2C), 122.8 (2C), 65.4;
HRMS calcd for C31H23N3O2 469.1787, found 469.1790.
4.3.18. (E)-1-(4-Bromophenyl)-2-(4-iodophenyl)diazene
(25). A portion of the crude 4-bromonitrosobenzene
(500 mg, 2.70 mmol) from the preparation of 24 was dis-
solved in acetic acid (30 mL) and 11 (493 mg, 2.25 mmol)
was added. Workup provided 25 (810 mg, 93%) as an orange
solid: mp 209–212 ꢁC; FTIR (KBr) 3068, 1907, 1561, 1472,
1
1394, 1336 cmꢂ1; H NMR (400 MHz, CDCl3) d 7.88 (d,
4.3.15. (E)-4-((4-Tritylphenyl)diazenyl)benzeneamine
(23). To 22 (1.50 g, 3.19 mmol) in a solution of dioxane
(80 mL), ethanol (20 mL), and water (5 mL) was added
sodium sulfide (2.30 g, 9.58 mmol). The mixture was heated
at 80 ꢁC for 1.5 h. The solvents were partly evaporated and
the residue was dissolved in CH2Cl2. The solution was
washed with 1 N HCl followed by saturated NaHCO3. The
organic layer was dried over MgSO4, filtered, and the filtrate
was concentrated in vacuo. The residue was chromato-
graphed on silica gel using 60% CH2Cl2 in hexanes to give
23 (1.14 g, 81%): mp 230–231 ꢁC; FTIR (KBr) 3476,
3379, 3056, 3025, 1957, 1619, 1503, 1445, 1417,
J¼8.7 Hz, 2H), 7.80 (d, J¼8.8 Hz, 2H), 7.66 (d, J¼8.8 Hz,
2H), 7.65 (d, J¼8.7 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d 152.0, 151.4, 138.7 (2C), 132.6 (2C), 126.0, 124.74
(2C), 124.67 (2C), 98.3; HRMS calcd for C12H8BrIN2
385.8916, found 385.8915.
4.3.19. (E)-1-(4-Iodophenyl)-2-(4-((trimethylsilyl)ethy-
nyl)phenyl)diazene (26). Following the general azobenzene
procedure, to a solution of 4-((trimethylsilyl)ethynyl)ani-
line15 (250 mg, 1.32 mmol) in CH2Cl2 (2.5 mL) was added
a solution of OxoneÒ (1.63 g, 2.62 mmol) in H2O (20 mL).
The crude product was dissolved in acetic acid (20 mL)
and 11 (289 mg, 1.32 mmol) was added. Workup and chro-
matography using 5% CH2Cl2 in hexane on silica gel gave
26 (185 mg, 35%) as an orange solid: mp 143–144 ꢁC;
FTIR (KBr) 2948, 2155, 1926, 1565, 1468, 1398,
1
1289 cmꢂ1; H NMR (500 MHz, CDCl3) d 7.80 (d, J¼
8.7 Hz, 2H), 7.73 (d, J¼8.7 Hz, 2H), 7.36 (d, J¼8.7 Hz,
2H), 7.30–7.20 (m, 15H), 6.75 (d, J¼8.7 Hz, 2H), 4.11
(br s, 2H); 13C NMR (125 MHz, CDCl3) d 151.0,
149.8, 148.9, 146.7 (3C), 145.8, 132.0 (2C), 131.3 (6C),
127.8 (6C), 126.2 (3C), 125.3 (2C), 121.5 (2C), 114.9
(2C), 65.2; HRMS calcd for C31H25N3 439.2048, found
439.2048.
1250 cmꢂ1
;
1H NMR (400 MHz, CDCl3) d 7.88 (d,
J¼8.7 Hz, 2H), 7.87 (d, J¼8.7 Hz, 2H), 7.66 (d, J¼8.7 Hz,
2H), 7.61 (d, J¼8.7 Hz, 2H), 0.29 (s, 9H); 13C NMR
(100 MHz, CDCl3) d 152.1, 151.9, 138.6 (2C), 133.1 (2C),

10310
B.-C. Yu et al. / Tetrahedron 62 (2006) 10303–10310
3. Astrand, P. O.; Ramanujam, P. S.; Hvilsted, S.; Bak, K.; Sauer
Stephan, P. A. J. Am. Chem. Soc. 2000, 122, 3482–3487.
4. (a) Evans, S. D.; Johnson, S. R.; Ringsdorf, H.; Williams, L. M.;
Wolf, H. Langmuir 1998, 14, 6436–6440; (b) Stiller, B.;
Knochenhauer, G.; Markava, E.; Gustina, D.; Muzikante, I.;
Karageorgiev, P.; Brehmer, L. Mater. Sci. Eng. 1999, C8-9,
385–389; (c) Landraud, N.; Peretti, J.; Chaput, F.; Lampel,
G.; Boilot, J.-P.; Lahlil, K.; Safarov, V. Appl. Phys. Lett.
2001, 79, 4562–4564; (d) Matsumoto, M.; Miyazaki, D.;
Tanaka, M.; Azumi, R.; Manda, E.; Kondo, Y.; Yoshino, N.;
Tachibana, H. J. Am. Chem. Soc. 1998, 120, 1479–1484; (e)
Tamada, K.; Akiyama, H.; Wei, X. Langmuir 2002, 18,
5239–5246; (f) Jaschke, M.; Schonherr, H.; Wolf, H.; Butt,
H. J.; Bamberg, E.; Besocke, M. K.; Ringsdorf, H. J. Phys.
Chem. 1996, 100, 2290–2301; (g) Ichimura, K.; Oh, S.-K.;
Nakagawa, M. Science 2000, 288, 1624–1626; (h) Hugel, T.;
Bolland, N.; Cattani, A.; Moroder, L.; Sitz, M.; Gaub, H.
Science 2002, 296, 1103–1106; (i) Kajikawa, K.; Anzai, T.;
Takezoe, H.; Fukuda, A. Thin Solid Films 1994, 243, 587–591.
5. Yasuda, S.; Nakamura, T.; Matsumoto, M.; Shigekawa, H.
J. Am. Chem. Soc. 2003, 125, 16430–16433.
126.4, 124.7 (2C), 123.1 (2C), 104.8, 98.3, 97.6, 0.1
(3C); HRMS calcd for C17H17IN2Si 404.0213, found
404.0206.
4.3.20. (E)-2-(4-((4-Nitrophenyl)diazenyl)phenyl)ethanol
(27). Following the general azobenzene procedure, to a solu-
tion of 4-nitroaniline (19) (1.20 g, 8.69 mmol) in CH2Cl2
(20 mL) was added a solution of OxoneÒ (10.7 g,
17.4 mmol) in H2O (80 mL). The crude product was dis-
solved in acetic acid (150 mL) and 4-(hydroxyethyl)aniline
(14) (1.90 g, 8.69 mmol) was added. After workup the resi-
due was chromatographed on silica gel using 30% EtOAc in
hexane to give 27 (1.69 g, 72%) as an orange solid: mp 149–
152 ꢁC; FTIR (KBr) 3522, 3402, 3103, 2940, 1915, 1653,
1584, 1522, 1495, 1340, 1207, 1099, 1036 cmꢂ1; 1H NMR
(400 MHz, CDCl3) d 8.39 (d, J¼9.1 Hz, 2H), 8.03 (d,
J¼9.1 Hz, 2H), 7.94 (d, J¼8.4 Hz, 2H), 7.44 (d, J¼8.4 Hz,
2H), 3.96 (t, J¼6.5 Hz, 2H), 2.99 (t, J¼6.5 Hz, 2H), 1.53
(s, 1H); 13C NMR (100 MHz, CDCl3) d 156.0, 151.4,
148.8, 144.0, 130.2 (2C), 124.9 (2C), 123.9 (2C), 123.6
(2C), 63.5, 39.3; HRMS calcd for C14H13N3O3 271.0959,
found 271.0957.
6. Stewart, M. P.; Maya, F.; Kosynkin, D. V.; Dirk, S. M.;
Stapleton, J. J.; McGuiness, C. L.; Allara, D. L.; Tour, J. M.
J. Am. Chem. Soc. 2004, 126, 370–378.
€
7. Priewisch, B.; Ruck-Braun, K. J. Org. Chem. 2005, 70, 2350–
Acknowledgements
2352.
8. Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 16, 4467–4470.
9. Akiyama, H.; Tamada, K.; Nagasawa, J.; Abe, K.; Tamaki, T.
J. Phys. Chem. B 2003, 107, 130–135.
We thank DARPA and the AFOSR for funding this research.
B.-C.Y. thanks Mokwon University for funding during sab-
batical leave in 2005.
10. (a) Maya, F.; Chanteau, S. H.; Cheng, L.; Stewart, M. P.; Tour,
J. M. Chem. Mater. 2005, 17, 1331–1345; (b) Radugc, C.;
Papastavrou, D. G.; Kurth, D. G.; Motschmann, H. Eur. Phys.
J. E 2003, 10, 103–114; (c) Vanoppen, P.; Grim, P. C. M.;
R€ucker, M.; De Feyter, M. S.; Moessner, G.; Valiyaveettil, S.;
References and notes
1. Tour, J. M. Molecular Electronics: Commercial Insights,
Chemistry, Devices, Architecture and Programming; World
Scientific: River Edge, NJ, 2003.
€
Mullen, K.; De Schryver, F. C. J. Phys. Chem. 1996, 100,
2. (a) Hwang, J.-J.; Tour, J. M. Tetrahedron 2002, 58, 10387–
10405; (b) Dirk, S. M.; Tour, J. M. Tetrahedron 2003, 59,
287–293; (c) Price, D. W.; Dirk, S. M.; Maya, F.; Tour, J. M.
Tetrahedron 2003, 59, 2497–2518; (d) Price, D. W., Jr.; Tour,
J. M. Tetrahedron 2003, 59, 3131–3156; (e) Flatt, A. K.;
Dirk, S. D.; Henderson, J. C.; Shen, D. E.; Su, J.; Reed,
M. A.; Tour, J. M. Tetrahedron 2003, 59, 8555–8570;
(f) Dameron, A. A.; Ciszek, J. W.; Tour, J. M.; Weiss, P. S.
J. Phys. Chem. B 2004, 108, 16761–16767; (g) Lewis, P. A.;
Inman, C. E.; Maya, F.; Tour, J. M.; Hutchison, J. E.; Weiss,
P. S. J. Am. Chem. Soc. 2005, 127, 17421–17426; (h) Choi,
B.-Y.; Kahng, S.-J.; Kim, S.; Kim, H.; Kim, H. W.; Song,
Y. J.; Ihm, J.; Kuk, Y. Phys. Rev. Lett. 2006, 96, 156106-1–
156106-4.
19636–19641; (d) Matsumoto, K.; Kubota, M.; Matsuoka, H.;
Yamaoka, H. Macromolecules 1999, 32, 7122–7127.
11. (a) Buriak, J. M. Chem. Rev. 2002, 102, 1271–1308; (b)
Delorme, N.; Bardeau, J.-F.; Bulou, A.; Poncin-Epaillard, F.
Langmuir 2005, 21, 12278–12282; (c) He, J.; Chen, B.; Flatt,
A. K.; Stephenson, J. J.; Doyle, C. D.; Tour, J. M. Nat.
Mater. 2006, 5, 63–68.
12. Matsui, M. J. Fluorine Chem. 1999, 96, 65–69.
13. Humphrey, J.; Lott, K. M.; Wright, M. E.; Kuciauskas, D.
J. Phys. Chem. B 2005, 109, 21496–21498.
14. Denonne, F.; Seiler, P.; Diederich, F. Helv. Chim. Acta 2003,
86, 3096–3117.
15. Chang, J. Y.; Rhee, S. B.; Cheong, S.; Yoon, M. Macro-
molecules 1992, 25, 2666–2670.