Preparation of azobenzenealkanethiols for self-assembled monolayers with photoswitchable properties

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CSIRO PUBLISHING

www.publish.csiro.au/journals/ajc

Aust. J. Chem. 2010, 63, 303–314

Preparation of Azobenzenealkanethiols for Self-Assembled

Monolayers with Photoswitchable Properties

Simone Krakert^Aand Andreas Terfort^A,B

^APhilipps-Universität Marburg, Fachbereich Chemie, Hans-Meerwein-Strasse,

35032 Marburg, Germany.

^BCorresponding author. Email: aterfort@chemie.uni-marburg.de

A series of azobenzenealkanethiol compounds with the structure p-RC₆H₄N=NC₆H₄(CH₂)_nSH (n = 3, 4) was synthesized

using a divergent strategy with the two anilines H₂NC₆H₄(CH₂)_nSAc as central compounds. This strategy provides fast

access to a broad variety of the respective azobenzenethiols without (note!) an oxygen atom in the alkyl chain, thus

permitting the self-assembly of these compounds onto gold in a predictable conformation, also taking advantage of the

previously found odd–even effect in aromatic–aliphatic hybrid systems. Initial experiments indicate that all of these

molecules indeed form dense monolayers, in which the orientation of the azobenzene unit is determined by the number

of methylene groups in the aliphatic part of the molecules.

Manuscript received: 27 May 2009.

Manuscript accepted: 13 September 2009.

Introduction

determines the structure and the structural quality within these

monolayers. If azobenzenes are introduced as aryl head groups,

we expect to observe a similarly predictable orientation for both

the cis- and the trans-configuration as shown in Fig. 2.

Self-assembled monolayers (SAMs), in particular of thiols

on gold, are useful tools for the adjustment of surface

properties.^[1–3]Although most systems used, for example, in

material science or biochemistry have to be viewed as static in

their properties, a number of applications, such as data storage,

require surfaces that are temporally and locally switchable.

Azobenzenes are probably the best-known photoswitchable

moieties^[4–8]and therefore have been intensively studied in

connection with SAMs, e.g. for optical information storage,

optoelectronics, non-linear optics,^[4,9,10]and even for the photo-

chemical switching of biochemical interactions.^[11–15]The

reversibleswitchingbetweenthethermodynamicallymorestable

trans- (360 nm) and the cis-configuration (450 nm)^[16–19]causes

not only the change in optical properties, but also a change in

the orientation of the head group,^[20]and therefore, depending

on the R group, also a change in the surface dipole moment

(Fig. 1).^[5,21]

This change of dipole moment can be determined as a

variation of the surface potential in well-ordered SAMs.^[21–24]

As 4-hydroxyazobenzenes are easily accessible via azo-

coupling,^[25]almost exclusively alkoxy-azobenzene derivatives

have been attached to surfaces.^[26,27]The problem with oxygen

atoms within these chains is that owing to steric and electronic

effects of the non-binding electron pairs (lone pairs) of the oxy-

gen atom, distortions from the all-trans conformation occur

(Scheme 1).

As different applications might require different head groups,

we were looking to develop a strategy that would permit effi-

cient access to this class of substances. This can be achieved by

a divergent strategy with the node compound being as close to

the final products as possible. We decided to use two node com-

poundstoobtainentrytothetwoclassesofcompoundswiththree

(1b) and four methylene groups (1a), respectively (Scheme 2).

These compounds should consist of the carbon backbone and

carry the sulfur atom as well, although in protected form. The

azobenzene unit should be formed from an amino group already

present in the node compounds by reaction with a variety of

nitroso benzenes.^[18,34–40]The late introduction of the azoben-

zene group is also advantageous regarding the handling of the

compounds, because azobenzenes are often sensitive to elevated

temperatures, light, and many reagents.

After deprotection, the different azobenzene thiols should be

used for monolayer formation, followed by a first characteriza-

tion of the completeness of layer formation and the properties

of the newly formed surfaces.

Results and Discussion

Synthetic Route

As the central compounds should already carry the sulfur atom

necessary for binding to the gold substrate, and nitroso com-

pounds readily react with free thiol groups, forming a variety of

non-specific products,^[41–45]we had to protect the thiol group.

Thioestersarepopularprotectivegroupsforthispurposebecause

both the introduction and the removal of the acyl group proceed

cleanly and with high yields. However, amino compounds are

frequently used to achieve this deprotection,^[46–50]so we needed

to make sure that the free amino group in our desired node

Another factor known to significantly influence the orien-

tation of the head groups in monolayers is the number (odd or

even) of methylene groups: owing to the binding angle at the car-

bon atom (104^◦) and a preferred dihedral angle of 180^◦within

n-alkane chains, the orientation of the head group of an aryl-

terminated alkanethiol is predictable for monolayers on gold

and silver substrates, because the binding angles at the sulfur

atoms at these substrates are fixed.^[28–33]This parity effect also

10.1071/CH09308

0004-9425/10/020303

304

S. Krakert and A. Terfort

Distortion due to lone pairs

R

N

R

N

R

N

SH

Head group

N

O

SH

R

N

Scheme 1. Most azobenzene thiols published until now contain an oxygen

atom between the alkyl chain and the azobenzene unit (right). This oxygen

atom results in bond distortion, whereas a heteroatom-free alkyl chain can

adopt an all-trans conformation.

Spacer

Anchoring group

S

Gold

compounds would not interfere with the protection chemistry.

Our assumption that anilines are too weakly basic to achieve

the deprotection of aliphatic thioesters was supported by ini-

tial experiments, in which we treated dodecanethioacetate with

equimolar amounts of p-toluidine in THF for a prolonged time.

NMR and TLC proved that no reaction between these com-

pounds takes place, thus suggesting the compatibility of these

two functionalities in one molecule. As the coupling reaction

between nitroso benzenes and anilines is best performed in acetic

acid,^[34–40]thecompatibilityofthealiphaticthioesterandtheani-

line was also tested in this solvent without and with addition of

4-methylnitrosobenzene: the thioester was not altered in either

case and the formation of the azobenzene proceeded cleanly both

at room temperature and when heated to reflux.

ϳ450 nm

ϳ360 nm

N

R

S

Gold

With these positive results, we were confident enough to

pursue the synthesis of the two node compounds 1a, b. The

synthesis of both could be achieved from the respective ω-(4-

nitrophenyl)alcohols 2a, b, which themselves had to be obtained

by different routes. While 3-(4-nitrophenyl)propenol 2b was

obtained by the reduction of trans-4-nitrocinnamaldehyde,^[51]

the ω-(4-nitrophenyl)butanol 2a was synthesized in a two-step

manner from 4-phenylbutyric acid via nitration^[52]and reduction

with borane.^[53]

Fig. 1. Basic principle of a photoswitchable azobenzene-terminated self-

assembled monolayer on gold: if the molecules carry a suitable head group

R, the effective surface dipole moment can be changed (blue arrow).

R

N

R

N

Both compounds were converted to the ω-(4-aminophenyl)

alkanols 3a, b by catalytic hydrogenation.^[53]Because these

amino compounds are light-, oxygen-, and temperature-

sensitive, and to permit the subsequent chemistry for the attach-

ment of the sulfur atom, the amino groups were protected as

tert-butoxycarbamates (BOC) using di-tert-butyl dicarbonate in

THF at 80^◦C, generating compounds 4a, b.^[54]The introduc-

tion of the sulfur atom took place in a two-step reaction. First,

the alcohol functions were converted quantitatively to the mesy-

lates 5a, b, which were obtained as crystalline solids; 5b yielded

crystals suitable for X-ray diffraction.^[55]The mesylates were

transformed to the respective thioacetates 6a, b by means of

potassium thioacetate. Because reactions involving thioacetate

almost always result in a variety of coloured side-products with

different polarity, the purification of these compounds required

careful investigation. Although 6a and 6b are crystalline com-

pounds, neither recrystallization nor sublimation under reduced

pressure yielded pure products. After screening a wide variety

of conditions, we found that apparently only chromatography on

silica gel with a mixture of toluene and dichloromethane (some-

times twice) was able to solve the purification problems. These

two compounds were then used as stock materials because at

−20^◦C, they were stable for a prolonged time.

N

R

S

Gold

R

N

S

The deprotection of these compounds to obtain the node com-

pounds 1a, b turned out to be surprisingly difficult. Although in

general the BOC group can efficiently be removed using triflu-

oroacetic acid (TFA), for example in methylene chloride, in this

caseTFA alone was not enough.After several attempts, a mixture

Gold

Fig. 2. The orientation of the molecules, and thus their exact switch-

ing behaviour, should depend on the parity of the number (odd-even) of

methylene groups in the alkane chain.

Self-Assembled Monolayers with Photoswitchable Properties

305

O

NO₂

NH₂

NO₂

HN

O

CH₃SO₂Cl

NEt₃

S^ϪK^ϩ

Boc₂O

THF

H₂/Pd/C

or

DMF

n

O

OH

O

S

O

S

OH

2b

OH

2a

O

5a, b

3a, b

4a, b

6a, b

R

N

R

a n ϭ 3

b n ϭ 2

HCl

or

K₂CO₃

or

NH₂

R

N

7, 16, 25 R ϭ CH₃

8, 17, 26 R ϭ OCF₃

9, 18, 27 R ϭ CF₃

10, 19, 28 R ϭ H

11, 20, 29 R ϭ F

12, 21, 30 R ϭ Cl

13, 22, 31 R ϭ Br

14, 23, 32 R ϭ COOMe

15, 24, 33 R ϭ CN

N

ON

TFA/HBF₄

CH₂Cl₂

7–15

LiAlH₄

or

HNMe₂

CH₃COOH

n

S

O

n

S

O

SH

1a, b

16–24a, b

25–33a, b

Scheme 2. Synthetic route to the library of azobenzenealkanethiols with three and four methylene groups in the alkyl chain. The central

building blocks are the thioacetates 1a and 1b, from which the final thiols could be obtained in two steps.

ofTFA and HBF₄turned out to be suitable, but the optimal reac-

tion times and temperatures needed to be adjusted every time by

following the reaction with, for example, TLC.

depending on the head group. Nevertheless, both systems also

showed their problems: while the acidic system sometimes did

not yield 100% conversion, the alkaline system often resulted in

too many side-products. A striking example is the partial solvo-

lysis (under alkaline conditions!) of the cyano group in 24a or b

that resulted in the formation of small amounts of 23a, b, which

could not be separated from the final products.

In general, the compounds 23a, b and 24a, b turned out to

be the most problematic because, even under acidic conditions

and exclusion of air, the deprotection of the SAc group resulted

in the formation of significant amounts of disulfides (in some

cases, complete conversion took place). In contrast to this, thiol

32b was obtained during chromatography of thioester 23b on

Al₂O₃.

The amines 1a and 1b obtained this way turned out to be

quite sensitive to light and air and therefore could not be purified

by chromatography. Instead, they were directly reacted with the

nitrosobenzenes 7–15 to yield the different azobenzenealkane

thioacetate species 16a, b–24a, b.^[40]The required nitrosoben-

zenes 7–15 could be obtained in good to very good yields by

the oxidation of the respective anilines with hydrogen peroxide

in the presence of a catalytic amount of ammonium molybdate

tetrahydrate.^[56]To remove side-products (in particular the nitro

compound), chromatography on silica was performed. Owing to

the high volatility of the nitrosobenzenes, it is highly advised to

use pentane for this purification step. In most cases, the purifi-

cation of these compounds could be skipped and the products

7–15 used directly. The side-products were then eliminated after

the coupling step by chromatography.

As with the thioacetates, some of the thiols also had the ten-

dency to crystallize on the column during chromatography, thus

hampering their purification.As a result, many of the compounds

had to be chromatographed several times.

Presumably because both coupling partners (amines 1a, b,

and the nitrosobenzenes 7–15) had to be used as crude materi-

als, a number of impurities showed up after the coupling step,

the removal of which turned out to be tedious. Because the

molecules 16a, b–24a, b are very sensitive to elevated temper-

atures, recrystallization and sublimation were not suitable for

purification, although some of the compounds (in particular 24a

and b) showed a strong tendency to crystallize in the chromato-

graphy column. Only in the case of compounds 24a, b could this

behaviour be exploited for purification by vapour crystallization,

although this had to be repeated several times.

The choice of the best reagent for the deprotection of the

thiol group depended on the head-group substituent. Certain

reagents such as dimethylamine or the frequently used LiAlH₄

were suitable in some cases, but often resulted in too many side-

products. For the deprotection of most of the thioacetates, the

best choice turned out to be either HCl/MeOH or K₂CO₃/MeOH,

Nevertheless, with the exception of compounds 30b and 33b,

which were obtained either mainly or exclusively as disulfides,

all azobenzene thiols could finally be attained in very good

purity.

Attempts at the Synthesis of Alkoxy-Terminated

Azobenzene Thiols

Although a broad variety of substituted azobenzene thiols could

be attained by the nitrosobenzene–aniline coupling reaction, the

electron-rich alkoxy azobenzenes were not accessible in this

manner. This already started with surprising difficulties during

the oxidation of 4-methoxyaniline (p-anisidine) to the respective

nitrosobenzene 34, which could only be obtained in low yield

(∼30%). Furthermore, this nitroso compound did not react with

the amines 1a, b to yield the azobenzenes, presumably owing to

a too-high electron density at the nitroso group.

306

S. Krakert and A. Terfort

NH₂

N₂^ϩ

ONO

/TFA

•

ϩ

2 RS

N

•

ϩ

N

2 H

CH₂Cl₂

n

h␯

S

O

S

O

1a, b

h␯

N

ϩ

HN

ϩ

2 RSH

(RS)₂

OH

N

OR

N

NH

h␯

OH

N

NEt₃

ϩ

2 RSH

N

n

S

SH

O

Scheme 4. The observed light-induced reaction and two proposed path-

ways.

35a, b

Scheme 3. Attempted access route to the alkoxy derivatives via an azo-

coupling reaction. 35a was obtained in a too small yield to make this route

feasible.

groups changed the situation.This assumption was confirmed by

experiments, in which NMR spectra of an equimolar mixture of

non-substituted azobenzene (Ph–N=N–Ph) with dodecanethiol

(C₁₂H₂₅SH) were recorded after different time-spans. Only the

samples exposed to light showed similar signals to the ones

mentioned before. With these simpler molecules, it was also

possible to identify the reaction products: obviously a light-

driven redox reaction occurs with the transfer of hydrogen atoms,

resulting in the formation of hydrazobenzene and dodecyldisul-

fide, as indicated by the appearance of signals at δ 7.16 and

6.84 (hydrazobenzene) and 2.68 (disulfide). The brutto reaction

shown in Scheme 4 (centre) turned out to be compatible with all

the observations.

Two possible pathways for this reaction exist. The first is

the light-induced, homolytic cleavage of the S–H bond with

formation of hydrogen and sulfyl radicals, with the first being

scavenged by the azobenzene, while the latter dimerizes. It is

also imaginable that the azobenzene is switched into the cis-

form, which is then the better oxidant,^[57,58]thus consuming the

thiol.

We therefore decided to attempt to access this class of

compounds by the aforementioned azo-coupling with phenol,

followed by the etherification of the hydroxy group (Scheme 3).

For this, the amines 1a, b were converted to the respective

diazonium compounds under anhydrous conditions (to avoid the

hydrolysis of the thioacetate) and reacted with phenol.

First results on the synthesis of 4-[4-((4-hydroxyphenyl)

diazenyl)phenyl]butylethanethioate 35a showed that the desired

product could only be obtained in a limited yield (<30%) and

its purification turned out to be tedious. As the alkoxy deriva-

tives were not crucial for our investigations of surface-bound

molecular switches, we decided to shift the synthesis of these

compounds to the future.

Light Sensitivity

During our experiments, we often were surprised that NMR

spectra of seemingly pure thiols (as determined for example by

TLC) showed extra peaks, in particular in the aromatic range.

The impurities causing these signals could not be removed by

repeated chromatography and – even worse – became some-

times stronger after purification. A careful evaluation resulted

in the observation that the disulfide content of the samples cor-

related well with the amount of ‘impurities’ in the aromatic

range and that these two effects roughly correlated with the

waiting time in the NMR queue, suggesting a decomposition

reaction either mediated by the acidity of the solvent (CDCl₃

releases small amounts of DCl over time) or by daylight. The

substitution of CDCl₃by C₆D₆reduced the effect, but did not

completely suppress it, hinting at the minor role of acid traces.

As the interaction of light with azobenzenes usually at most

results in isomerization at the –N=N– double bond but not in

further reactions, we suspected that the presence of free thiol

Within the current project, the consequence of this observa-

tion was that all spectra of the thiols were then recorded in C₆D₆

as solvent, using brown NMR tubes. These measures completely

eliminated this undesired reaction.

Initial Monolayer Characterization

For further studies, it is important to show that the molecules

indeed form dense monolayers on gold. A suitable characteriza-

tion method is ellipsometry, which permits the determination of

the thickness of very thin layers. As the molecules contain both,

aliphatic and aromatic parts, an intermediate refractive index of

1.50 (at λ = 632 nm) was assumed for all molecules. The data

shown in Table 1 indeed speak for the formation of dense mono-

layers in which the molecules adopt a tilt angle of ∼20–30^◦

with respect to the surface normal. This tilting has been found in

many systems.^[59–62]A peculiarity is the systematically higher

Self-Assembled Monolayers with Photoswitchable Properties

307

Table 1. Layer thickness and wetting properties (advancing contact angle of water) of the respective

self-assembled monolayers on gold

Head group

CH₃

No. of CH₂groups

Compound

Layer thickness [Å]

Contact angle [^◦]

4

3

4

3

4

3

4

3

4

3

4

3

4

3

4

3

4

3

25a

25b

26a

26b

27a

27b

28a

28b

29a

29b

30a

30b

31a

31b

32a

32b

33a

33b

18.3 0.5

19.6 1.2

17.8 0.3

18.7 1.3

16.5 0.2

18.7 0.1

16.3 0.6

17.8 0.6

16.0 0.8

18.1 0.6

15.8 0.8

20.2 1.3

18.4 0.4

21.8 0.9

21.0 0.4

21.1 0.8

19.1 1.0

18.3 0.5

96

98

100

2

1

OCF₃

CF₃

H

110 0.5

95

98 0.5

1

83

86

1

F

92 0.5

93 0.5

Cl

87

94 0.5

85

90 0.5

1

Br

2

COOMe

CN

61

62

55

56

2

1

2

thickness of the thiols bearing a propylene chain (three CH₂

groups, derivatives 25–33b) compared with the ones with the

longer butylene chain (four CH₂groups, derivatives 25–33a).

While this thickness decrease of ∼2 Å seems to be in contra-

diction with the additional methylene unit, it is fully consistent

with previous results in the araliphatic series, as mentioned in

the Introduction.^[28–33]

Alkane chains with an even number of methylene units force

the stiff aromatic part into a higher tilt angle, thus rendering

these layers effectively thinner (Fig. 2). The only exceptions are

the layers of 33a and 33b, where, in the latter case not the thiol,

but the respective disulfide was used for the layer formation.

Although, according to the literature, this change should not

have any influence on the final monolayers, in this case a clear

reversal of the trend is visible.

groups, a portfolio of deprotection reactions had to be used, with

an optimal one for each thiol.

In contrast to previous studies, no oxygen atoms were used as

linkers between the azobenzene unit and the alkane chain. While

this made the development of a new synthetic strategy necessary,

the monolayers formed by these thiols behaved quite predictably

and in accord with previously studied aromatic–aliphatic hybrid

systems, in particular regarding the odd–even effect imposed by

the configuration of the alkane chain.

These works provide a solid basis for the study of the

photoresponse of these systems. In the next steps, we are plan-

ning to investigate the structure of the systems before and after

irradiation with different wavelength using several microscopic

and spectroscopic methods.

A very sensitive tool for the outermost chemistry of mono-

layers is the contact angle of liquids. The typical sensitivities

for the respective head groups could be found with water

droplets: the ester and the cyano group turned out to be the most

hydrophilic, while the fluorine-terminated monolayers were the

most hydrophobic. On top of this general trend, it can be seen

that the contact angles for the shorter-chained derivatives 25–

33b were in all cases higher than the ones measured for the

layers of the (CH₂)₄derivatives 25–33a, hinting again at layers

in which the surface dipole moments are almost perpendicularly

oriented to the surfaces.

Experimental

Substrates

Phenylbutyric acid was purchased from Acros Organics.

p-Toluidine was obtained from Merck whereas 4-bromoaniline,

4-fluoroaniline, and 4-aminobenzonitrile were obtained from

Aldrich. 4-Aminobenzotrifluoride and 4-(trifluoromethoxy)

aniline were purchased from Apollo Scientific, and

4-chloroaniline and methyl 4-aminobenzoate were obtained

fromAlfaAesar. Commercially available thioacetic acid (Merck)

was distilled and kept under N₂.

All these results suggest the formation of very dense and

highly ordered monolayers, at least of the trans-azobenzene

thiols.

NMR Measurements

¹H, ¹⁹F, and ¹³C NMR spectra were obtained on Avance 300 or

DRX 400 Bruker spectrometers. Furthermore, some ¹H and ¹³

C

NMR spectra were recorded on a DRX 500 Bruker spectrometer.

IR spectra were carried out on a Bruker IFS 88 spectrometer.

Mass spectra were recorded on Finnigan MAT TSQ 700 or

MAT 95S spectrometers. Elemental analyses were recorded on

an EA 1108 CHNS-O from Carlo Erba Instruments in the chem-

istry department at the University of Hamburg. Melting points

were determined on a Dr Tottoli apparatus (Büchi) and are

uncorrected.

Conclusions

In conclusion, we were able to develop a divergent route to a

family of azobenzene alkanethiols with different alkyl chain

lengths and a variety of head groups, with a central building

block for each alkyl series. The attachment of the head groups

is based on an N–N-coupling forming the desired azobenzene

units. Owing to the different chemical behaviour of the head

308

S. Krakert and A. Terfort

Monolayers

4.98. Calc. for C₁₄H₂₁NO₃: C 66.91, H 8.42, N 5.57%.)

ν_max(KBr)/cm⁻¹3350, 3321, 2977 (ν_–CH3), 2935 (ν_–CH2), 2858

(ν_–CH2), 1700 (ν_–HNCO–), 1597 (ν_C–Car), 1526 (δ_–NH, ν_N–C=O),

1454 (δ_–CH2, δ_–CH3), 1412 (δ_–CH2, δ_–CH3), 1316, 1245, 1163,

For ellipsometry, 200 nm of gold with chromium as adhesion

promoter were deposited onto (100) silicon wafers (used as

delivered, Wacker Siltronic AG).

The Au substrates were prepared by first evaporating 5 nm of

titanium and subsequently 100 nm of gold onto Si(100) wafers

in a recipient with a residual gas pressure of 10⁻⁵Pa. The

adsorption of the organothiolate monolayers was carried out by

immersing the substrates into ethanolic solutions of the thiols

for 24 h. In the case of azobenzene alkanethiols, 1 mM solutions

were used.

3

1056, 832 (δ_C–Har). δ_H(500 MHz, CDCl₃) 7.26 (d, J_HH8.1,

3

2H, H₂), 7.10 (d, J_HH8.4, 2H, H₃), 6.49 (s, 1H, NH),

3

3.65 (t, J_HH6.4, 2H, CH₂CH₂CH₂OH), 2.65 (t, J_HH7.7,

2H, CH₂CH₂CH₂OH), 1.89–1.81 (m, 2H, CH₂CH₂CH₂OH),

1.51 (s, 9H, NHCOOC(CH₃)₃). δ_C(125 MHz, CDCl₃) 152.90

(NHCOOC(CH₃)₃), 136.51 (C₄), 136.17 (C₁), 128.84 (C₃),

118.82 (C₂), 80.35 (NHCOOC(CH₃)₃), 62.14 (CH₂CH₂CH₂

OH), 34.24 (CH₂CH₂CH₂OH), 31.32 (CH₂CH₂CH₂OH), 28.33

(NHCOOC(CH₃)₃). m/z (EI) 251 (11%, M⁺), 195 (43%, M⁺

– C₄H₈), 177 (14%), 151 (31%, C₉H₁₃NO), 132 (20%), 106

(100%, C₆H₆N₂or C₇H₈N⁺), 57 (46%, C₄H₉⁺), 41 (25%,

C₃H⁺₅).

Contact Angle

Contact angle measurements (sessile drop method) were per-

formed using a Multiskop (Optrel GBR, Germany). The water

droplets images were captured with a charge-coupled device

camera before the included software calculated their shape and

the respective contact angles. In all cases, the advancing angle

was determined.

4-[4-(tert-Butoxycarbonylamino)phenyl]butyl

Methanesulfonate 5a; Typical Procedure

To a solution of tert-butyl 4-(4-hydroxybutyl)phenylcarbamate

4a (25.2 g, 95 mmol) in dry dichloromethane (220 mL) was

added triethylamine (21 mL) before the mixture was cooled

down to −20^◦C. Then methanesulfonyl chloride was added.

The solution was kept at −30^◦C for a couple of minutes.

Then the mixture was stirred for 20 minutes without cool-

ing. The solution was washed with water (2 × 100 mL). The

organic phase was evaporated under vacuum. A small amount

(6.3 g) was purified by chromatography on silica gel using

dichloromethane/diethyl ether (1% → 5%) as eluent to yield

4-[4-(tert-butoxycarbonylamino)phenyl]butylmethanesulfonate

5a as a white solid (6 g) for further analysis.

Ellipsometry

The thicknesses of the films were determined using an ellipso-

meter SE 400 (Sentech Instruments GmbH) under an incidence

angle of 70^◦at a wavelength of 633 nm. The substrates were

cleaned using a hydrogen plasma before determination of the

substrate parameters ∆ and Ψ.^[63]For the organic layers, a

refractive index of n = 1.50 was assumed.

Preparation of tert-Butyl 4-(4-Hydroxybutyl)

phenylcarbamate 4a; Typical Procedure

4-(p-Aminophenyl)butanol 3a (14.8 g, 89 mmol) was dissolved

in THF (150 mL). To the solution, di-tert-butyldicarbonate

(23.3 g, 107 mmol) was added. The mixture was heated to 80^◦C

under nitrogen for 24 h. The solvent was removed under vac-

uum and the residue extracted with dichloromethane and water.

The organic phase was evaporated to dryness. A small amount

of the product (1.0 g) was purified by chromatography on silica

gel using light petroleum/ethyl acetate 7:3 → 3:7 as eluent for

analysis.

Yield: 26.3 g (99 mmol, 111%, contaminated by di-tert-

butyl-dicarbonate), yellow-beige solid. Mp 74–76^◦C (Found:

C 67.90, H 8.74, N 5.24. Calc. for C₁₅H₂₃NO₃: C 67.90, H

8.74, N 5.28%.) ν_max(KBr)/cm⁻¹3360, 3358, 2984 (ν_–CH3),

2937 (ν_–CH2), 2860 (ν_–CH2), 1809 (ν_C–O), 1758 (ν_C=O), 1695

(ν_–HNCO–), 1615 (ν_C–Car), 1593 (ν_C–Car), 1520 (δ_–NH, ν_N–C=O),

1462 (δ_–CH2, δ_–CH3), 1412, 1316, 1240, 1162, 1057, 825

Yield:32.1 g(93 mmol, 99%), lightbrownsolid. Mp52–54^◦C

(Found: C 55.70, H 7.29, N 4.07, S 8.94. Calc. for C₁₆H₂₅NO₅S:

C 55.96, H 7.34, N 4.08, S 9.34%.) ν_max(KBr)/cm⁻¹3370

(ν_N–H), 2979 (ν_–CH3), 2937 (ν_–CH2), 2868 (ν_–CH2), 1703 (ν_C=O),

1593 (ν_C–Car), 1528 (δ_–HNCO–), 1467 (δ_–CH2, δ_–CH3), 1352,

3

1171, 825 (δ_C–Har). δ_H(400 MHz, CDCl₃) 7.27 (d, J_HH

3

8.4, 2H, H₂), 7.07 (d, J_HH8.4, 2H, H₃), 6.52 (s, 1H,

3

NH), 4.21 (t, J_HH6.2, 2H, CH₂CH₂CH₂CH₂OSO₂CH₃),

3

2.97 (s, 3H, CH₂CH₂CH₂CH₂OSO₂CH₃), 2.59 (t, J_HH

7.2, 2H, CH₂CH₂CH₂CH₂OSO₂CH₃), 1.78–1.60 (m, 4H,

CH₂CH₂CH₂CH₂OSO₂CH₃), 1.50 (s, 9H, NHCOOC(CH₃)₃).

δ_C(100 MHz, CDCl₃) 152.90 (NHCOOC(CH₃)₃), 136.37 (C₄),

136.21(C₁), 128.84(C₃), 118.82(C₂), 80.38(NHCOOC(CH₃)₃),

69.88 (CH₂CH₂CH₂CH₂OSO₂CH₃), 37.36 (CH₂CH₂CH₂CH₂

OSO₂CH₃), 34.44 (CH₂CH₂CH₂CH₂OSO₂CH₃), 28.52 (CH₂

CH₂CH₂CH₂OSO₂CH₃), 28.35 (NHCOOC(CH₃)₃), 27.21

(CH₂CH₂CH₂CH₂OSO₂CH₃). m/z (EI) 343 (12%, M⁺), 287

(42%, M⁺− C₄H₈), 243 (32%, C₁₁H₁₇NO₃S), 163 (21%), 132

(15%), 106 (100%, C₆H₆N₂or C₇H₈N⁺), 79 (10%, CH₃SO₂⁺),

57 (72%, C₄H⁺₉).

3

(δ_C–Har). δ_H(400 MHz, CDCl₃) 7.25 (d, J_HH8.4, 2H, H₂),

3

7.10 (d, J_HH8.4, 2H, H₃), 6.61 (s, 1H, NH), 3.62 (t,

³J_HH6.4, 2H, CH₂CH₂CH₂CH₂OH), 2.57 (t, J_HH7.4, 2H,

3

CH₂CH₂CH₂CH₂OH), 2.01 (s, 1H, CH₂CH₂CH₂CH₂OH),

1.68–1.52 (m, 4H, CH₂CH₂CH₂CH₂OH), 1.50 (s, 9H,

NHCOOC(CH₃)₃). δ_C(100 MHz, CDCl₃) 152.94 (NHCOOC

(CH₃)₃), 136.99 (C₄), 135.99 (C₁), 128.73 (C₃), 118.69 (C₂),

80.24 (NHCOOC(CH₃)₃), 62.60 (CH₂CH₂CH₂CH₂OH), 34.82

(CH₂CH₂CH₂CH₂OH), 32.10 (CH₂CH₂CH₂CH₂OH), 28.28

(CH₂CH₂CH₂CH₂OH), 27.52 (NHCOOC(CH₃)₃). m/z (EI) 265

(24%, M⁺), 209(100%, M⁺− C₄H₈), 150(38%, C₁₀H₁₄O), 132

(10%), 106 (62%, C₆H₆N₂or C₇H₈N⁺), 57 (85%, C₄H₉⁺).

3-[4-(tert-Butoxycarbonylamino)phenyl]propyl

Methanesulfonate 5b

Yield: 61.9 g (188 mmol, 99%), colourless solid. Mp 79–

81^◦C (Found: C 54.69, H 7.15, N 4.19, S 9.89. Calc.

for C₁₅H₂₃NO₅S: C 54.69, H 7.04, N 4.25, S 9.73%.)

ν_max(KBr)/cm⁻¹3381 (ν_N–H), 2983 (ν_–CH3), 2939 (ν_–CH2),

1702 (ν_C=O), 1593 (ν_C–Car), 1524 (δ_–HNCO–), 1460 (δ_–CH2

,

tert-Butyl 4-(3-Hydroxypropyl)phenylcarbamate 4b

δ_–CH3), 1358, 1158, 838 (δ_C–Har). δ_H(500 MHz, CDCl₃) 7.28

3

Yield: 24.0 g (95.6 mmol, 101%, contaminated by di-tert-butyl-

dicarbonate), yellow-brown oil (Found: C 65.43, H 8.43, N

(d, J_HH8.1, 2H, H₂), 7.10 (d, J_HH8.4, 2H, H₃), 6.44 (s,

3

1H, NH), 4.20 (t, J_HH6.3, 2H, CH₂CH₂CH₂OSO₂CH₃),

Self-Assembled Monolayers with Photoswitchable Properties

309

3

2.98 (s, 3H, CH₂CH₂CH₂OSO₂CH₃), 2.70 (t, J_HH7.5,

2.63 (t, J_HH7.6, 2H, CH₂CH₂CH₂SCOCH₃, 2.33 (s, 3H,

CH₂CH₂CH₂SCOCH₃), 1.90–1.80 (m, 2H, CH₂CH₂CH₂SCO

CH₃), 1.51 (s, 9H, NHCOOC(CH₃)₃). δ_C(125 MHz, CDCl₃)

195.86 (CH₂CH₂CH₂SCOCH₃), 152.83 (NHCOOC(CH₃)₃),

136.28 (C₄), 135.79 (C₁), 128.88 (C₃), 118.73 (C₂), 80.37

(NHCOOC(CH₃)₃), 34.08 (CH₂CH₂CH₂SCOCH₃), 31.13

(CH₂CH₂CH₂SCOCH₃), 30.63 (CH₂CH₂CH₂SCOCH₃), 28.45

(CH₂CH₂CH₂SCOCH₃), 28.31 (NHCOOC(CH₃)₃). m/z (EI)

309 (10%, M⁺), 253 (43%, M⁺– C₄H₈), 209 (41%,

C₁₁H₁₅NOS), 132 (10%), 106 (100%, C₆H₆N₂or C₇H₈N⁺),

57 (81%, C₄H⁺₉), 43 (64%, C₂H₃O⁺or C₃H⁺₇).

2H, CH₂CH₂CH₂OSO₂CH₃), 2.30–1.90 (m, 2H, CH₂CH₂CH₂

OSO₂CH₃), 1.51 (s, 9H, NHCOOC(CH₃)₃). δ_C(125 MHz,

CDCl₃) 152.81 (NHCOOC(CH₃)₃), 136.60 (C₄), 134.89 (C₁),

128.91 (C₃), 118.88 (C₂), 80.47 (NHCOOC(CH₃)₃), 69.07

(CH₂CH₂CH₂OSO₂CH₃), 37.35 (CH₂CH₂CH₂OSO₂CH₃),

30.80 (CH₂CH₂CH₂OSO₂CH₃), 30.69 (CH₂CH₂CH₂OSO₂

CH₃), 28.33 (NHCOOC(CH₃)₃). m/z (EI) 329 (7%, M⁺), 273

(32%, M⁺− C₄H₈), 229 (67%, C₁₀H₁₅NO₃S), 132 (41%), 106

(100%, C₆H₆N₂or C₇H₈N⁺), 79 (12%, CH₃SO₂⁺), 57 (63%,

C₄H⁺₉), 44 (98%), 39 (76%), 28 (33%).

Removal of the tert-Butoxycarbonyl Function;

4-(4-Aminophenyl)butylethanethioate 1a;

Typical Procedure

4-[4-(tert-Butoxycarbonylamino)phenyl]butylethanethioate

6a; Typical Procedure

To a solution of potassium-tert-butanolate (17.1 g, 152 mmol) in

DMF (250 mL), thioacetic acid (23.7 g, 305 mmol) was added.

Then 4-[4-(tert-butoxycarbonylamino)phenyl]butylmethane-

sulfonate 5a (26.1 g, 76 mmol) in DMF (150 mL) was added.

The mixture was stirred at room temperature for 2 days. DMF

and thioacetic acid were removed under vacuum. The residue

was dissolved in water and extracted with dichloromethane.

The organic phase was evaporated under vacuum (32.2 g). For

purification, the residue was stirred in water for 15 min. The

product was isolated by decantation (this was repeated twice).

The residue was further purified by chromatography on sil-

ica gel using dichloromethane/light petroleum 3:7 → 7:3, only

dichloromethane (from the beginning on 1% diethyl ether),

dichloromethane/diethyl ether (1% → 10%) as eluent to yield

4-[4-(tert-butoxycarbonylamino)phenyl]butylethanethioate 6a

as a brown solid.

To a solution of 4-[4-(tert-butoxycarbonylamino)phenyl]butyl

ethanethioate 6a (7.5 g, 23.0 mmol) in dichloromethane (60 mL)

was added trifluoroacetic acid (3.2 mL, 46.6 mmol).The mixture

was stirred at 35^◦C for 24 h until HBF₄(2.3 mL, 17.9 mmol)

dissolved in diethyl ether was added. The mixture was stirred for

48 h at room temperature and another 24 h at 35^◦C. The acid was

quenched by adding saturated NaHCO₃solution. The organic

phase was separated and the solvent was removed under vacuum

to yield 2.1 g of compound 1a.

Yield: 2.1 g (9.4 mmol, 96%), light brown solid. Mp 67–

69^◦C ν_max(KBr)/cm⁻¹3399 (ν_NH2), 3317 (ν_NH2), 2955 (ν_–CH3),

2929 (ν_–CH2), 2856 (ν_–CH2), 1614 (ν_C=O), 1515, 1481 (δ_–NH2

,

δ_–NH3), 1472 (δ_–NH2, δ_–NH3), 1440 (δ_–CH2, δ_–CH3), 1256,

3

1049, 822 (δ_C–Har). δ_H(400 MHz, CDCl₃) 6.97 (d, J_HH

3

8.3, 2H, H₃), 6.68 (d, J_HH8.3, 2H, H₂), 3.96 (s, 2H,

3

NH₂), 2.88 (t, J_HH7.0, 2H, CH₂CH₂CH₂CH₂SCOCH₃),

Yield: 20.4 g (63 mmol, 83%), auburn solid. Mp 52–

54^◦C (Found: C 62.78, H 7.82, N 4.29, S 10.33. Calc.

for C₁₇H₂₅NO₃S: C 63.13, H 7.79, N 4.33, S 9.91%.)

ν_max(KBr)/cm⁻¹3362 (ν_N–H), 2976 (ν_–CH3), 2931 (ν_–CH2),

2858 (ν_–CH2), 1729 (ν_C=O), 1668 (ν_–HNCO–), 1593 (ν_C–Car),

1526 (δ_–HNCO–), 1455 (δ_–CH2, δ_–CH3), 1230, 1157, 833

3

2.52 (t, J_HH7.2, 2H, CH₂CH₂CH₂CH₂SCOCH₃), 2.32

(s, 3H, CH₂CH₂CH₂CH₂SCOCH₃), 1.72–1.52 (m, 4H,

CH₂CH₂CH₂CH₂SCOCH₃). δ_C(100 MHz, CDCl₃) 195.94

(CH₂CH₂CH₂CH₂SCOCH₃), 142.96 (C₁), 132.93 (C₄), 129.15

(C₃), 115.79 (C₂), 34.45 (CH₂CH₂CH₂CH₂SCOCH₃), 30.72

3

(CH₂CH₂CH₂CH₂SCOCH₃),

30.59

(CH₂CH₂CH₂CH₂

(δ_C–Har). δ_H(400 MHz, CDCl₃) 7.25 (d, J_HH8.5, 2H,

3

SCOCH₃), 28.99(CH₂CH₂CH₂CH₂SCOCH₃), 28.94(CH₂CH₂

CH₂CH₂SCOCH₃).

H₂), 7.08 (d, J_HH8.5, 2H, H₃), 6.44 (s, 1H, NH),

3

2.87 (t, J_HH6.9, 2H, CH₂CH₂CH₂CH₂SCOCH₃), 2.55

3

(t, J_HH7.1, 2H, CH₂CH₂CH₂CH₂SCOCH₃), 2.31 (s, 3H,

3-(4-Aminophenyl)propylethanethioate 1b

CH₂CH₂CH₂CH₂SCOCH₃), 1.67–1.55 (m, 4H, CH₂CH₂CH₂

CH₂SCOCH₃), 1.51 (s, 9H, NHCOOC(CH₃)₃). δ_C(100 MHz,

CDCl₃) 195.91 (CH₂CH₂CH₂CH₂SCOCH₃), 152.84 (NHCOO

C(CH₃)₃), 136.64 (C₄), 136.08 (C₁), 128.73 (C₃), 118.64 (C₂),

80.21 (NHCOOC(CH₃)₃), 34.55 (CH₂CH₂CH₂CH₂SCOCH₃),

30.55 (CH₂CH₂CH₂CH₂SCOCH₃), 30.46 (CH₂CH₂CH₂CH₂

SCOCH₃), 28.93(CH₂CH₂CH₂CH₂SCOCH₃), 28.83(CH₂CH₂

CH₂CH₂SCOCH₃), 28.28 (NHCOOC(CH₃)₃). m/z (EI) 323

(32%, M⁺), 267 (22%, M⁺− C₄H₈), 223 (83%, C₁₂H₁₇NOS),

132 (10%), 106 (100%, C₆H₆N₂or C₇H₈N⁺), 57 (99%, C₄H₉⁺),

43 (52%, C₂H₃O⁺or C₃H₇⁺).

Yield: 2.5 g (12 mmol, 100%), light-brown oil. δ_H(400 MHz,

3

CDCl₃) 6.96 (d, J_HH8.2, 2H, H₃), 6.62 (d, J_HH8.3, 2H,

3

H₂), 3.56 (s, 2H, NH₂), 2.87 (t, J_HH7.3, 2H, CH₂CH₂CH₂

3

SCOCH₃), 2.58 (t, J_HH7.6, 2H, CH₂CH₂CH₂SCOCH₃),

2.33 (s, 3H, CH₂CH₂CH₂SCOCH₃), 1.89–1.78 (m, 2H,

CH₂CH₂CH₂SCOCH₃). δ_C(100 MHz, CDCl₃) 195.91 (CH₂

CH₂CH₂SCOCH₃), 144.38 (C₁), 131.14 (C₄), 129.21 (C₃),

115.25 (C₂), 33.94 (CH₂CH₂CH₂SCOCH₃), 31.33 (CH₂CH₂

CH₂SCOCH₃), 30.64(CH₂CH₂CH₂SCOCH₃), 28.57(CH₂CH₂

CH₂SCOCH₃).

3-[4-(tert-Butoxycarbonylamino)phenyl]

propylethanethioate 6b

4-[4-((4-Hydroxyphenyl)diazenyl)phenyl]

butylethanethioate 35a

Yield: 55.6 g (179 mmol, 99%), red brown solid. Mp 65–

67^◦C (Found: C 62.21, H 7.57, N 4.49, S 10.03. Calc.

for C₁₆H₂₃NO₃S: C 62.11, H 7.49, N 4.53, S 10.36%.)

ν_max(KBr)/cm⁻¹3377 (ν_N–H), 2972 (ν_–CH3), 2928 (ν_–CH2), 1695

(ν_C=O), 1690 (ν_–HNCO–), 1590 (ν_C–Car), 1521 (δ_–HNCO–), 1453

(δ_–CH2, δ_–CH3), 1235, 1158, 829 (δ_C–Har). δ_H(500 MHz, CDCl₃)

To a solution of 4-(4-aminophenyl)butylethanethioate 1a (1.2 g,

5.0 mmol) in dry dichloromethane (40 mL) was added trifluo-

roacetic acid (0.9 g, 8.1 mmol) before the mixture was cooled to

−30^◦C. Then, isoamylnitrite was added (0.9 g, 8.0 mmol). The

solution was stirred at −20^◦C for 45 min until the addition of

phenol (1.7 g, 18.0 mmol) followed and the stirring was contin-

ued for another 20 min.While keeping the temperature at – 20^◦C,

the mixture was quenched by addition of triethylamine (6 mL).

3

7.26 (d, J_HH8.0, 2H, H₂), 7.08 (d, J_HH8.4, 2H, H₃), 6.44

3

(s, 1H, NH), 2.86 (t, J_HH7.3, 2H, CH₂CH₂CH₂SCOCH₃),

310

S. Krakert and A. Terfort

After a few minutes, the solution was acidified using a small

amount of hydrochloric acid and the addition of ammonium

chloride solution followed. The organic phase was washed with

water and dried under vacuum.The residue was purified by chro-

matography on silica gel first using dichloromethane/methanol

(1 and 2%), for the second chromatography using light

petroleum/diethyl ether (1:1) as eluent to yield 4-[4-((4-

hydroxyphenyl)diazenyl)phenyl]butylethanethioate 35a as an

orange-brown viscous semi-solid compound.

Yield: 0.45 g (1.4 mmol, 27%), orange-brown viscous semi-

solid compound (Found: C 64.64, H 6.28, N 8.22, S 11.15.

Calc. for C₁₈H₂₀N₂O₂S: C 65.83, H 6.14, N 8.53, S 9.76%.)

ν_max(KBr)/cm⁻¹3347 (ν_OH), 2926 (ν_–CH3, ν_–CH2), 2855

(75%, M⁺), 165 (32%, C₁₀H₁₃S⁺), 123 (38%), 91 (100%,

C₇H⁺₇), 65 (15%).

Deprotection of Azobenzenealkanethioate using

MeOH/HCl; 4-[4-((4-Triﬂuoromethoxyphenyl)diazenyl)

phenyl]butanethiol 26a; Typical Procedure

To a solution of 4-[4-((4-trifluoromethoxyphenyl)diazenyl)

phenyl]butylethanethioate17a (1.2 g, 3.4 mmol)indrymethanol

(60 mL) was added degassed hydrochloric acid (25%, 2.5 mL).

The mixture was refluxed for 24 h under a nitrogen atmo-

sphere (reaction status monitored by TLC). The solvent was

removed under vacuum and the residue was dissolved in

dichloromethane, washed with water and dried under vacuum.

The residue was purified by chromatography on silica gel using

light petroleum/diethyl ether (1%) as eluent to yield 4-[4-((4-

trifluoromethoxyphenyl)diazenyl)phenyl]butanethiol 26a as an

orange solid.

(ν_–CH2), 1687 (ν_C=O), 1664, 1589 (ν_C–Car), 1504, 1461 (δ_–CH2

,

δ_–CH3), 1437, 1411, 1273, 1227, 1139, 844 (δ_C–Har). δ_H

3

(400 MHz, CDCl₃) 7.88 (d, J_HH8.8, 2H, H₂), 7.81 (d, J_HH

3

8.3, 2H, H_2‘), 7.28 (d, J_HH8.3, 2H, H₃), 6.96 (d, J_HH8.8,

2H, H_3‘), 2.91 (t, J_HH7.1, 2H, CH₂CH₂CH₂CH₂SCOCH₃),

3

2.69 (t, J_HH7.5, 2H, CH₂CH₂CH₂CH₂SCOCH₃), 2.34

Yield: 0.7 g (2.0 mmol, 58% yield), orange solid. Mp

28–30^◦C (Found: C 57.88, H 4.92, N 7.86, S 9.08. Calc.

for C₁₇H₁₇F₃N₂OS: C 57.62, H 4.84, N 7.90, S 9.05%.)

ν_max(KBr)/cm⁻¹2930 (ν_–CH3, ν_–CH2), 2854 (ν_–CH2), 1594

(ν_C–Car), 1496, 1460 (δ_–CH2, δ_–CH3), 1417, 1273, 1170, 860

(s, 3H, CH₂CH₂CH₂CH₂SCOCH₃), 1.80–1.69 (m, 2H,

CH₂CH₂CH₂CH₂SCOCH₃), 1.69–1.57 (m, 2H, CH₂CH₂CH₂

CH₂SCOCH₃). δ_C(100 MHz, CDCl₃) 196.61 (CH₂CH₂CH₂

ꢀ

CH₂SCOCH₃), 159.11 (C₄), 150.45 (C₁), 146.60 (C₁), 145.05

ꢀ

(C₄), 129.09 (C₃), 125.25 (C₂), 122.57 (C₂), 115.99 (C₃), 35.20

(CH₂CH₂CH₂CH₂SCOCH₃), 30.63 (CH₂CH₂CH₂CH₂SCO

CH₃), 30.22 (CH₂CH₂CH₂CH₂SCOCH₃), 29.04 (CH₂CH₂CH₂

CH₂SCOCH₃), 28.91 (CH₂CH₂CH₂CH₂SCOCH₃). m/z (EI)

328 (73%, M⁺), 149 (11%, C₁₀H₁₅N), 123 (29%), 121 (61%,

C₆H₅N₂O⁺), 107 (44%, C₇H₉N⁺), 93 (100%, C₆H₇N), 65

(22%), 43 (42%, C₂H₃O⁺or C₃H₇⁺).

(δ_C–₃_Har). δ_H(500 MHz, C₆D₆) 7.99 (d, ³J_HH8.6, 2H, H₂), 7.77

3

ꢀ

(d, J_HH8.9, 2H, H₂), 7.02 (d, J_HH8.3, 2H, H₃), 6.90 (d,

3

ꢀ

J_HH8.2, 2H, H₃), 2.28 (t, J_HH7.5, 2H, CH₂CH₂CH₂CH₂SH),

2.11 (q, ³J_HH7.3, 2H, CH₂CH₂CH₂CH₂SH), 1.44–1.32 (m, 2H,

CH₂CH₂₃CH₂CH₂SH), 1.32–1.22(m, 2H, CH₂CH₂CH₂CH₂SH),

1.04 (t, J_HH7.8, 1H, CH₂CH₂CH₂CH₂SH). δ_C(125 MHz,

3

ꢀ

C₆D₆) 151.47 (C₁), 151.31 (C₁), 150.87 (d, J_CF1.5, F–C₄),

ꢀ

146.48 (C₄), 129.42 (C₃), 124.60 (C₂), 123.54 (C₂), 121.51

1

ꢀ

(C₃), 121.06 (q, J_CF257.6, CF₃), 35.35 (CH₂CH₂CH₂

CH₂SH), 33.65 (CH₂CH₂CH₂CH₂SH), 29.87 (CH₂CH₂

CH₂CH₂SH), 24.36 (CH₂CH₂CH₂CH₂SH). δ_F(300 MHz,

C₆D₆) −57.48. m/z (EI) 354 (69%, M⁺), 189 (28%,

C₆H₄F₃N₂O⁺), 165 (55%, C₁₀H₁₃S⁺), 161 (98%, C₇H₄F₃O⁺),

123 (100%), 95 (77%).

Deprotection of Azobenzenealkanethioate using LiAlH₄;

4-[4-(p-Tolyldiazenyl)phenyl]butanethiol 25a;

Typical Procedure

To a stirred suspension of lithium aluminium hydride (0.4 g,

10.8 mmol) in dry THF (20 mL), a solution of 4-[4-(p-

tolyldiazenyl)phenyl]butylethanethioate 16a (1.16 g, 3.6 mmol)

in dry THF (30 mL) was added dropwise. The reaction mixture

was stirred overnight at room temperature. Then, acidification

with hydrochloric acid (1 M, 15 mL) was followed by removal

of the solvent under reduced pressure. The residue was extracted

three times with dichloromethane. The solvent was removed

under vacuum and the residue was purified by chromatography

on silica gel using dichloromethane/light petroleum 1:4 → 7:3,

as eluent to yield 4-[4-(p-tolyldiazenyl)phenyl]butanethiol 25a

as an orange solid.

Methyl 4-[4-(4-Mercaptobutyl)phenyl]diazenyl

Benzoate 32a

The product was purified by chromatography using toluene/

dichloromethane (1%) as eluent.

Yield: 0.3 g (0.9 mmol, 70%), orange solid. Mp 78–80^◦C

(Found:C65.82, H6.26, N8.45, S9.57. Calc. forC₁₈H₂₀N₂O₂S:

C 65.83, H 6.14, N 8.53, S 9.76%.) ν_max(KBr)/cm⁻¹2930

(ν_–CH3, ν_–CH2), 2856 (ν_–CH2), 1716 (ν_C=O,COOCH3), 1601

(ν_C–Car), 1496, 1447 (δ_–CH2, δ_–CH3), 1432, 1281, 1221, 1192,

Yield: 0.8 g (2.8 mmol, 78%), orange solid. Mp 66–68^◦C

(Found: C 71.67, H 7.07, N 9.87, S 11.04. Calc. for C₁₇H₂₀N₂S:

C 71.79, H 7.09, N 9.85, S 11.27%.) ν_max(KBr)/cm⁻¹3021

(ν_C–Har), 2925 (ν_–CH3, ν_–CH2), 2852 (ν_–CH2), 1600 (ν_C–Car), 1579

(ν_C–Car), 1497, 1445 (δ_–CH2, δ_–CH3), 1414, 1153, 823 (δ_C–Har).

δ_H(300 MHz, C₆D₆) 8.07 (d, ³J_HH8.2, 2H, H₂), 8.04 (d, ³J_HH

3

1141, 1113, 862 (δ_C–Har). δ_H(500 MHz, C₆D₆) 8.15 (d, J_HH

3

ꢀ

8.7, 2H, H₃), 7.97 (d, J_HH8.3, 2H, H₂), 7.91 (d, J_HH

3

8.7, 2H, H₂), 7.01 (d, J_HH8.4, 2H, H₃), 3.50 (s, 3H,

3

COOCH₃), 2.28 (t, J_HH7.6, 2H, CH₂CH₂CH₂CH₂SH), 2.12

(q, J_HH7.3, 2H, CH₂CH₂CH₂CH₂SH), 1.43–1.32 (m, 2H,

3

ꢀ

7.7, 2H, H₂), 7.01 (d, J_HH8.5, 2H, H₃), 7.00 (d, J_HH8.1,

CH₂CH₂₃CH₂CH₂SH), 1.32–1.22(m, 2H, CH₂CH₂CH₂CH₂SH),

3

2H, H_3‘), 2.27 (t, J_HH7.4, 2H, CH₂CH₂CH₂CH₂SH), 2.10

(q, J_HH7.2, 2H, CH₂CH₂CH₂CH₂SH), 2.03 (s, 3H, CH₃ar),

1.43–1.15 (m, 4H, CH₂CH₂CH₂CH₂SH), 1.05 (t, J_HH7.9,

1.08 (t, J_HH7.8, 1H, CH₂CH₂CH₂CH₂SH). δ_C(125 MHz,

3

ꢀ

C₆D₆) 166.06 (COOCH3), 155.57 (C₁), 151.57 (C₁), 146.77

3

ꢀ

(C₄), 132.29 (C₄), 130.92 (C₃), 129.40 (C₃), 123.72 (C₂),

122.98 (C₂), 51.75 (COOCH₃), 35.37 (CH₂CH₂CH₂CH₂SH),

33.69 (CH₂CH₂CH₂CH₂SH), 29.83 (CH₂CH₂CH₂CH₂SH),

24.38 (CH₂CH₂CH₂CH₂SH). m/z (EI) 328 (68%, M⁺), 165

(81%, C₁₀H₁₃S⁺), 135 (50%, C₈H₇O₂), 123 (100%), 106 (20%,

C₆H₆N₂or C₇H₈N⁺).

1H, CH₂CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 151.81 (C₁),

ꢀ

151.55 (C₁), 145.59 (C₄), 141.32 (C₄), 130.01 (C₃), 129.32

ꢀ

(C₃), 123.39 (C₂), 123.33 (C₂), 35.33 (CH₂CH₂CH₂CH₂SH),

33.72 (CH₂CH₂CH₂CH₂SH), 29.92 (CH₂CH₂CH₂CH₂SH),

24.40 (CH₂CH₂CH₂CH₂SH), 21.26 (CH₃ar). m/z (EI) 284

Self-Assembled Monolayers with Photoswitchable Properties

311

4-[4-(4-Mercaptobutyl)phenyl]diazenyl Benzonitrile 33a

C₁₀H₁₃S⁺), 123 (78%), 106 (44%, C₆H₆N₂or C₇H₈N⁺), 77

(100%, C₆H⁺₅).

Yield: 0.6 g (2.0 mmol, 60%), orange solid. Mp 92–94^◦C (Found:

68.47, H 5.81, N 13.91, 10.74. Calc. for C₁₇H₁₇N₃S: C 69.12,

H 5.80, N 14.22, S 10.85%.) ν_max(KBr)/cm⁻¹3042 (ν_C–Har),

2932 (ν_–CH3, ν_–CH2), 2853 (ν_–CH2), 2226 (ν_–CN), 1599 (ν_C–Car),

4-[4-((4-Fluorophenyl)diazenyl)phenyl]butanethiol 29a

Yield: 1.0 g (3.5 mmol, 87%), orange solid. Mp 42–44^◦C (Found:

C 66.70, H 6.14, N 9.69, S 11.41. Calc. for C₁₆H₁₇FN₂S:

C 66.64, H 5.94, N 9.71, S 11.12%.) ν_max(KBr)/cm⁻¹2931

(ν_–CH3, ν_–CH2), 2855 (ν_–CH2), 1592 (ν_C–Car), 1494, 1460

(δ_–CH2, δ_–CH3), 1417, 1227, 1150, 1136, 1089, 847 (δ_C–Har).

1491, 1454 (δ_–CH2, δ_–CH3), 1413, 1303, 1221, 1156, 854 (δ_C–Har).

3

ꢀ

δ_H(300 MHz, C₆D₆) 7.94 (d, J_HH8.4, 2H, H₂), 7.56 (d,

3

ꢀ

J_HH8.6, 2H, H₂), 7.02 (d, J_HH8.3, 2H, H₃), 7.00 (d, J_HH

8.3, 2H, H₃), 2.27 (t, J_HH7.4, 2H, CH₂CH₂CH₂CH₂SH),

3

δ_H(300 MHz, C₆D₆) 7.98 (d, J_HH8.4, 2H, H₂), 7.88–

2.11 (q, J_HH7.2, 2H, CH₂CH₂CH₂CH₂₃SH), 1.45–1.18

3

ꢀ

7.77 (m, 2H, H₂), 7.01 (d, J_HH8.4, 2H, H₃), 6.84–6.71

(m, 4H, CH₂CH₂CH₂CH₂SH), 1.06 (t, J_HH7.9, 1H,

3

ꢀ

(m, 2H, H₃), 2.78 (t, J_HH7.4, 2H, CH₂CH₂CH₂CH₂SH),

CH₂CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 154.49 (C₁),

3

ꢀ

2.11 (q, J_HH7.1, 2H, CH₂CH₂CH₂CH₂₃SH), 1.44–1.19

151.37 (C₁), 147.38 (C₄), 133.10 (C₃), 129.50 (C₃), 123.77

ꢀ

(m, 4H, CH₂CH₂CH₂CH₂SH), 1.06 (t, J_HH7.9, 1H,

(C₂), 123.21 (C₂), 118.44 (CN), 114.31 (C₄), 35.38

(CH₂CH₂CH₂CH₂SH), 33.62 (CH₂CH₂CH₂CH₂SH), 29.78

(CH₂CH₂CH₂CH₂SH), 24.34 (CH₂CH₂CH₂CH₂SH). m/z (EI)

295 (49%, M⁺), 181 (27%, C₁₂H₉N⁺), 165 (58%, C₁₀H₁₄S⁺),

123 (100%), 118 (56%, C₇H₆N₂)², 106 (93%, C₆H₆N₂or

C₇H₈N⁺), 102 (46%, C₇H₅N⁺), 91 (34%, C₇H⁺₇), 77 (15%,

C₆H⁺₅).

1

CH₂CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 164.55 (d, J_CF

251.3, C₄), 151.47 (C₁), 149.69 (d, J_CF2.9, C₁), 146.01

4

ꢀ

3

ꢀ

(C₄), 129.35 (C₃), 125.13 (d, J_CF8.8, C₂), 123.41 (C₂),

116.14 (d, ²J_CF22.8, C₃), 35.34 (CH₂CH₂CH₂CH₂SH), 33.69

ꢀ

(CH₂CH₂CH₂CH₂SH), 29.89 (CH₂CH₂CH₂CH₂SH), 24.38

(CH₂CH₂CH₂CH₂SH). δ_F(300 MHz, C₆D₆) −109.47. m/z (EI)

288 (55%, M⁺), 165 (37%, C₁₀H₁₃S⁺), 123 (100%, C₆H₄FN⁺₂),

111 (37%, C₆H₆FN), 95 (82%, C₆H₄F⁺), 91 (21%, C₇H₇⁺), 77

(18%, C₆H⁺₅).

4-[4-(3-Mercaptopropyl)phenyl]diazenyl Benzonitrile 33b

Only the disulfide could be isolated. The product was purified

by vapour crystallization using chloroform as the solvent and

pentane as the non-solvent.

3-[4-((4-Fluorophenyl)diazenyl)phenyl]propanethiol 29b

Yield: 0.6 g (2.2 mmol, 69%), orange solid. Mp 43–45^◦C (Found:

C 65.70, H 5.70, N 10.11, S 11.73. Calc. for C₁₅H₁₅FN₂S:

C 65.67, H 5.51, N 10.21, S 11.69%.) ν_max(KBr)/cm⁻¹3026

(ν_C–Har), 2935 (ν_–CH3, ν_–CH2), 2853 (ν_–CH2), 1590 (ν_C–Car),

1492, 1455 (δ_–CH2, δ_–CH3), 1415, 1225, 1150, 1136, 1090, 844

Yield: 0.5 g (0.9 mmol, 47%), orange solid. Mp 126–128^◦C

(Found: 68.53, H 5.07, N 15.00, 11.09. Calc. for C₁₆H₁₅N₃S:

C 68.30, H 5.37, N 14.93, S 11.40%.) ν_max(KBr)/cm⁻¹3033

(ν_C–Har), 2928 (ν_–CH3, ν_–CH2), 2852 (ν_–CH2), 2234 (ν_–CN), 1600

(ν_C–Car), 1493, 1454 (δ_–CH2, δ_–CH3), 1413, 1288, 1222, 1156,

3

(δ_C–Har). δ_H(300 MHz, C₆D₆) 7.96 (d, J_HH8.4, 2H, H₂),

3

1109, 851 (δ_C–Har). δ_H(400 MHz, C₆D₆) 7.92 (d, J_HH8.3,

3

ꢀ

7.88–7.78 (m, 2H, H₂), 6.98 (d, J_HH8.5, 2H, H₃), 6.84–

3

ꢀ

2H, H₂), 7.55 (d, J_HH8.6, 2H, H₂), 7.00 (d, J_HH8.5, 4H,

3

ꢀ

6.72 (m, 2H, H₃), 2.35 (t, J_HH7.6, 2H, CH₂CH₂CH₂SH),

2.08 (q, J_HH7.4, 2H, CH₂CH₂CH₂SH), 1.59–1.45 (m, 2H,

H_{3 ,3}), 2.42 (q, ³J_HH7.3, 4H, CH₂CH₂CH₂S), 1.88–1.75 (m, 2H,

ꢀ

3

ꢀ

CH₂CH₂CH₂S). δ_C(100 MHz, C₆D₆) 154.41 (C₁), 151.47 (C₁),

3

CH₂CH₂CH₂SH), 1.05 (t, J_HH7.9, 1H, CH₂CH₂CH₂SH).

ꢀ

146.38 (C₄), 133.11 (C₃), 129.59 (C₃), 123.83 (C₂), 123.20

1

ꢀ

δ_C(75 MHz, C₆D₆) 164.57 (d, J_CF251.4, C₄), 151.53

ꢀ

(C₂), 118.37 (CN), 114.47 (C₄), 38.02 (CH₂CH₂CH₂S), 34.35

4

ꢀ

(C₁), 149.69 (d, J_CF3.1, C₁), 145.21 (C₄), 129.42 (C₃),

125.14 (d, J_CF8.9, C₂), 123.43 (C₂), 116.15 (d, J_CF22.8,

(CH₂CH₂CH₂S), 30.44 (CH₂CH₂CH₂S). m/z (EI) 281 (67%,

M⁺), 151 (100%, C₉H₁₁S⁺), 123 (24%), 118 (28%, C₇H₆N₂),

102 (83%, C₇H₅N⁺), 91 (25%, C₇H⁺₇).

3

2

ꢀ

C₃), 35.33 (CH₂CH₂CH₂SH), 34.29 (CH₂CH₂CH₂SH), 23.93

(CH₂CH₂CH₂SH). δ_F(300 MHz, C₆D₆) −109.40. m/z (EI) 274

(100%, M⁺), 151 (74%, C₉H₁₁S⁺), 123 (37%, C₆H₄FN⁺₂), 95

(83%, C₆H₄F⁺), 91 (17%, C₇H⁺₇).

4-[4-(Phenyldiazenyl)phenyl]butanethiol 28a

The mixture was refluxed for 1.5 h and stirred at room tem-

perature for another 1.5 h before the solvent was removed.

The product was purified by chromatography on silica gel

using dichloromethane/light petroleum 1:4 → 1:3 → 1:1 → 3:1

(+0.5% diethyl ether) as eluent.

Deprotection of Azobenzenealkanethioate using

Dimethylamine; 4-[4-((4-Triﬂuoromethylphenyl)diazenyl)

phenyl]butanethiol 27a; Typical Procedure

To

a solution of 4-[4-((4-trifluoromethylphenyl)diazenyl)

Yield: 0.7 g (2.6 mmol, 86%), orange liquid (Found: C

71.11, H 6.73, N 10.36, S 11.99. Calc. for C₁₆H₁₈N₂S: C

71.07, H 6.71, N 10.36, S 11.86%.) ν_max(KBr)/cm⁻¹2935

(ν_–CH3, ν_–CH2), 2853 (ν_–CH2), 2226, 1599 (ν_C–Car), 1501,

1490, 1455 (δ_–CH2, δ_–CH3), 1413, 1303, 1156, 1140, 854

phenyl]butylethanethioate 18a (0.6 g, 1.58 mmol) in dry

ethanol (30 mL) was added dimethylamine (0.2 g, 4.6 mmol).

The solution was stirred at room temperature for

3

days. The solvent was removed under vacuum and the

residue extracted with dichloromethane and water. The

organic phase was evaporated to dryness to yield 4-[4-

((4-trifluoromethylphenyl)diazenyl)phenyl]butanethiol 27 as an

orange solid. The crude product was used without further

purification.

ꢀ

(δ_C–Har). δ_H(300 MHz, C₆D₆) 8.09–8.00 (m, 4H, H_{2 ,2}), 7.24–

3

ꢀ

7.15 (m, 2H, H₃), 7.13–7.05 (m, 1H, H₄), 7.00 (d, J_HH

8.5, 2H, H₃), 2.26 (t, J_HH7.4, 2H, CH₂CH₂CH₂CH₂SH),

3

2.10 (q, J_HH7.2, 2H, CH₂CH₂CH₂CH₂₃SH), 1.43–1.18

(m, 4H, CH₂CH₂CH₂CH₂SH), 1.05 (t, J_HH7.9, 1H,

Yield: 0.5 g (1.57 mmol, 99%), orange solid. Mp 37–39^◦C

(Found: C 60.28, H 5.37, N 8.26, S 9.45. Calc. for C₁₇H₁₇F₃N₂S:

C 60.34, H 5.06, N 8.28, S 9.48%.) ν_max(KBr)/cm⁻¹2931

(ν_–CH3, ν_–CH2), 2859 (ν_–CH2), 1610 (ν_C–Car), 1503, 1461

ꢀ

CH₂CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 153.33 (C₁), 151.69

ꢀ

(C₁), 145.91 (C₄), 130.93 (C₄), 129.33 (C₃), 129.29 (C₃),

ꢀ

123.48 (C₂), 123.25 (C₂), 35.33 (CH₂CH₂CH₂CH₂SH), 33.69

(CH₂CH₂CH₂CH₂SH), 29.89 (CH₂CH₂CH₂CH₂SH), 24.39

(δ_–CH2, δ_–CH3), 1410, 1321, 1162, 1127, 1103, 849 (δ_C–Har).

3

(CH₂CH₂CH₂CH₂SH). m/z (EI) 270 (47%, M⁺), 165 (41%,

δ_H(300 MHz, C₆D₆) 7.98 (d, J_HH8.4, 2H, H₂), 7.77 (d,

ꢀ

312

3

S. Krakert and A. Terfort

3

ꢀ

J_HH8.5, 2H, H₂), 7.36 (d, J_HH8.5, 2H, H₃), 7.00 (d, J_HH

55.02, H 4.91, N 8.02, S 9.81.) ν_max(KBr)/cm⁻¹3043 (ν_C–Har),

2930 (ν_–CH3, ν_–CH2), 2854 (ν_–CH2), 1571 (ν_C–Car), 1476, 1456

(δ_–CH2, δ_–CH3), 1396, 1155, 1096, 1063, 1005, 837 (δ_C–Har).

3

8.3, 2H, H₃), 2.27 (t, J_HH7.4, 2H, CH₂CH₂CH₂CH₂SH),

3

2.11 (q, J_HH7.2, 2H, CH₂CH₂CH₂CH₂₃SH), 1.42–1.20

3

(m, 4H, CH₂CH₂CH₂CH₂SH), 1.05 (t, J_HH7.9, 1H,

δ_H(300 MHz, C₆D₆) 7.96 (d, J_HH8.3, 2H, H₂), 7.66 (d,

3

ꢀ

CH₂CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 154.85 (C₁), 151.45

(C₁), 146.99 (C₄), 129.46 (d, J_CF2.2, F–C₄), 126.47 (C₃),

126.46 (q, J_CF3.7, C₃), 124.64 (q, J_CF272.3, CF₃),

123.75 (C₂), 123.25 (C₂), 35.37 (CH₂CH₂CH₂CH₂SH), 33.65

J_HH8.7, 2H, H₂), 7.27 (d, J_HH8.7, 2H, H₃), 7.00 (d, J_HH

3

ꢀ

8.3, 2H, H₃), 2.27 (t, J_HH7.4, 2H, CH₂CH₂CH₂CH₂SH),

3

1

3

ꢀ

2.11 (q, J_HH7.2, 2H, CH₂CH₂CH₂CH₂₃SH), 1.43–1.18

ꢀ

(m, 4H, CH₂CH₂CH₂CH₂SH), 1.06 (t, J_HH7.9, 1H,

ꢀ

(CH₂CH₂CH₂CH₂SH), 29.82 (CH₂CH₂CH₂CH₂SH), 24.35

(CH₂CH₂CH₂CH₂SH). δ_F(300 MHz, C₆D₆) –62.10. m/z (EI)

338 (76%, M⁺), 165 (89%, C₁₀H₁₃S⁺), 145 (96%, C₇H₅F⁺₃),

123 (100%), 91 (21%, C₇H⁺₇).

CH₂CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 151.83 (C₁), 151.45

ꢀ

(C₁), 146.34 (C₄), 132.54 (C₃), 129.37 (C₃), 125.37 (C₄),

124.63 (C₂), 123.53 (C₂), 35.36 (CH₂CH₂CH₂CH₂SH), 33.67

(CH₂CH₂CH₂CH₂SH), 29.84 (CH₂CH₂CH₂CH₂SH), 24.39

(CH₂CH₂CH₂CH₂SH). m/z (EI) 350 (100%, M⁺), 348 (96%,

M⁺), 165 (63%, C₁₀H₁₃S⁺), 155 (52%, C₆H₅Br), 123 (66%),

90 (21%, C₄H₁₀S).

ꢀ

4-[4-((4-Chlorophenyl)diazenyl)phenyl]butanethiol 30a

The residue was purified by chromatography on silica gel using

dichloromethane/light petroleum 1:4 → 7:3, followed by only

dichloromethane as eluent.

Yield: 0.7 g (2.4 mmol, 72%), orange solid. Mp 74–

76^◦C (Found: C 62.86, H 5.85, N 9.14, S 10.78. Calc.

for C₁₆H₁₇ClN₂S: C 63.04, H 5.62, N 9.19, S 10.52%.)

ν_max(KBr)/cm⁻¹3023 (ν_C–Har), 2929 (ν_–CH3, ν_–CH2), 2852

(ν_–CH2), 1574 (ν_C–Car), 1480, 1452 (δ_–CH2, δ_–CH3), 1413,

1150, 1098, 1083, 842 (δ_C–Har). δ_H(300 MHz, C₆D₆)

Deprotection of Azobenzenealkanethioate using

MeOH/K₂CO₃; 3-[4-(p-Tolyldiazenyl)phenyl]

propanethiol 25b; Typical Procedure

To

a

solution of 3-[4-(p-tolyldiazenyl)phenyl]propyl

ethanethioate 16b (0.9 g, 2.9 mmol) in dry methanol (80 mL)

was added degassed K₂CO₃(3.4 g, 25 mmol). The mixture

was stirred for 1.5 h until degassed hydrochloric acid (25%,

7 mL) was added and the solvent removed under vacuum. The

residue was dissolved in dichloromethane, washed with water

and dried under vacuum. The product was purified by chro-

matography on silica gel using dichloromethane/light petroleum

(1/9 → 1/4) and diethyl ether (1%) as eluent to yield 3-(4-(p-

tolyldiazenyl)phenyl)propanethiol 25b.

3

7.99 (d, J_HH8.4, 2H, H₂), 7.75 (d, J_HH8.8, 2H,

3

ꢀ

H₂), 7.10 (d, J_HH8.8, 2H, H₃), 7.00 (d, J_HH8.5,

3

2H, H₃), 2.27 (t, J_HH6.9, 2H, CH₂CH₂CH₂CH₂SH),

3

2.10 (q, J_HH7.2, 2H, CH₂CH₂CH₂CH₂₃SH), 1.44–1.18

(m, 4H, CH₂CH₂CH₂CH₂SH), 1.05 (t, J_HH7.9, 1H,

ꢀ

CH₂CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 151.51 (C₁), 151.45

Yield: 0.7 g (2.4 mmol, 84%), orange solid. Mp 57–59^◦C

(Found: C 71.09, H 6.84, N 10.31, S 11.84. Calc. for C₁₆H₁₈N₂S:

C 71.07, H 6.71, N 10.36, S 11.86%.) ν_max(KBr)/cm⁻¹3023

(ν_C–Har), 2923 (ν_–CH3, ν_–CH2), 2854 (ν_–CH2), 1599 (ν_C–Car),

1579 (ν_C–Car), 1496, 1437, 1415, 1153, 823 (δ_C–Har). δ_H

(400 MHz, C₆D₆) 8.03 (d, J_HH8.0, 4H, H_2,2), 7.01 (d,

ꢀ

(C₁), 146.30 (C₄), 136.87 (C₄), 129.55 (C₃), 129.38 (C₃),

ꢀ

124.42 (C₂), 123.52 (C₂) 35.35 (CH₂CH₂CH₂CH₂SH), 33.66

(CH₂CH₂CH₂CH₂SH), 29.86 (CH₂CH₂CH₂CH₂SH), 24.37

(CH₂CH₂CH₂CH₂SH). m/z (EI) 304 (84%, M⁺), 165 (86%,

C₁₀H₁₃S⁺), 139 (29%, C₆H₄ClN⁺₂), 123 (100%), 107 (100%,

C₇H₉N⁺), 90 (28%, C₄H₁₀S).

3

ꢀ

3

ꢀ

J_HH8.3, 2H, H₃), 6.98 (d, J_HH8.4, 2H, H₃), 2.35 (t,

³J_HH7.6, 2H, CH₂CH₂CH₂SH), 2.08 (q, J_HH7.4, 2H,

3

3-[4-((4-Chlorophenyl)diazenyl)phenyl]propanethiol 30b

CH₂CH₂CH₂SH), 2.04 (s, 3H, CH₃ar), 1.59–1.43 (m, 2H,

CH₂CH₂CH₂SH), 1.05 (t, J_HH7.9, 1H, CH₂CH₂CH₂SH).

We obtained a mixture of thiol and disulfide. The purification is

similar to compound 30a.

3

ꢀ

δ_C(100 MHz, C₆D₆) 151.79 (C₁), 151.49 (C₁), 144.79 (C₄),

Yield of disulfide: 0.4 g (0.7 mmol, 31%), orange solid. Mp

123–126^◦C

ꢀ

141.39 (C₄), 130.09 (C₃), 129.39 (C₃), 123.42 (C₂), 123.34

(C₂), 35.39 (CH₂CH₂CH₂SH), 34.28 (CH₂CH₂CH₂SH), 23.95

(CH₂CH₂CH₂SH), 21.28 (CH₃ar). m/z (EI) 270 (81%, M⁺), 151

(50%, C₉H₁₁S⁺), 119 (28%, C₇H₇N⁺₂), 107 (31%, C₇H₉N⁺),

91 (100%, C₇H⁺₇).

Yield of thiol: 0.3 g (1.0 mmol, 46%), orange solid. Mp 74–

76^◦C (Found for thiol: C 62.05, H 5.42, N 9.57, S 10.91.

Calc. for C₁₅H₁₅ClN₂S: C 61.95, H 5.20, N 9.63, S 11.03%.)

ν_max(KBr)/cm⁻¹3025 (ν_C–Har), 2931 (ν_–CH3, ν_–CH2), 2855

(ν_–CH2), 1574 (ν_C–Car), 1479, 1455 (δ_–CH2, δ_–CH3), 1413, 1296,

1217, 1149, 1103, 1083, 840 (δ_C–Har). δ_H(300 MHz, C₆D₆)

3-[4-((4-Triﬂuoromethoxyphenyl)diazenyl)phenyl]

propanethiol 26b

3

ꢀ

7.96 (d, J_HH8.4, 2H, H₂), 7.75 (d, J_HH8.8, 2H, H₂),

3

ꢀ

Yield: 0.7 g (2.1 mmol, 81%), orange solid. Mp 44–46^◦C (Found

C 56.41, H 4.78, N 8.06, S 9.43. Calc. for C₁₆H₁₅F₃N₂OS:

C 56.46, H 4.44, N 8.23, S 9.42%.) ν_max(KBr)/cm⁻¹3025

(ν_C–Har), 2935 (ν_–CH3, ν_–CH2), 2860 (ν_–CH2), 1603 (ν_C–Car),

1593 (ν_C–Car), 1494, 1458 (δ_–CH2, δ_–CH3), 1417, 1245, 1201,

7.10 (d, J_HH8.8, 2H, H₃), 6.97 (d, J_HH8.4, 2H, H₃), 2.35

3

(t, J_HH7.6, 2H, CH₂CH₂CH₂SH), 2.07 (q, J_HH7.4, 2H,

CH₂CH₂CH₂SH), 1.59–1.44 (m, 2H, CH₂CH₂CH₂SH), 1.03 (t,

³J_HH7.9, 1H, CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 151.56

ꢀ

(C₁), 151.53 (C₁), 145.50 (C₄), 136.92 (C₄), 129.56 (C₃),

ꢀ

3

129.46 (C₃), 124.42 (C₂), 123.55 (C₂) 35.30 (CH₂CH₂CH₂SH),

1167, 1100, 837 (δ_C–Har). δ_H(500 MHz, C₆D₆) 7.96 (d, J_HH

3

34.30 (CH₂CH₂CH₂SH), 23.91 (CH₂CH₂CH₂SH). m/z (EI) 290

(78%, M⁺), 151 (50%, C₉H₁₁S⁺), 139 (15%, C₆H₄ClN⁺₂), 123

(15%), 111 (57%), 91 (16%, C₆H₄Cl⁺).

ꢀ

8.3, 2H, H₂), 7.77 (d, J_HH8.9, 2H, H₂), 6.97 (d, J_HH8.4,

3

ꢀ

2H, H₃), 6.90 (d, J_HH8.2, 2H, H₃), 2.35 (t, J_HH7.6, 2H,

CH₂CH₂CH₂SH), 2.07 (q, J_HH7.4, 2H, CH₂CH₂CH₂SH),

1.57–1.48 (m, 2H, CH₂CH₂CH₂SH), 1.04 (t, J_HH7.9, 1H,

3

4-[4-((4-Bromophenyl)diazenyl)phenyl]butanethiol 31a

CH₂CH₂CH₂SH). δ_C(125 MHz, C₆D₆) 151.48 (C₁), 151.27

3

ꢀ

Purification is the same as for compound 30a.

(C₁), 150.88 (d, J_CF1.5, F–C₄), 145.69 (C₄), 129.49 (C₃),

1

Yield: 0.6 g (1.7 mmol, 56%), orange solid. Mp 86–88^◦C

(Found: C 55.04, H 5.19, N 8.01, S 8.85. Calc. for C₁₆H₁₇BrN₂S:

124.61 (C₂), 123.62 (C₂), 121.52 (C₃), 121.05 (q, J_CF

257.7, CF₃), 35.32 (CH₂CH₂CH₂SH), 34.28 (CH₂CH₂CH₂SH),

ꢀ

Self-Assembled Monolayers with Photoswitchable Properties

313

23.91 (CH₂CH₂CH₂SH). δ_F(300 MHz, C₆D₆) −57.49. m/z

(EI) 340 (100%, M⁺), 189 (18%, C₆H₄F₃N₂O⁺), 161 (77%,

C₇H₄F₃O⁺), 151 (98%, M⁺− C₆H₄F₃N₂O⁺), 123 (24%,), 117

(35%,), 91 (21%, C₇H⁺₇).

C₉H₁₃NS), 155 (29%, C₆H₅Br), 151 (100%, C₉H₁₁S⁺), 123

(18%), 106 (75%, C₆H₆N₂or C₇H₈N⁺), 91 (18%, C₇H₇⁺).

Methyl 4-[4-(3-Mercaptopropyl)phenyl]diazenyl Benzoate

32b; Separated while Purifying Compound 23b

3-[4-((4-Triﬂuoromethylphenyl)diazenyl)phenyl]

propanethiol 27b

Yield: 0.2 g (1.0 mmol), orange solid. Mp 87–89^◦C (Found: C

64.99, H 5.93, N 8.75, S 10.04. Calc. for C₁₇H₁₈N₂O₂S: C

Yield: 0.7 g (2.2 mmol, 81%), orange solid. Mp 50–52^◦C (Found:

C 59.41, H 4.90, N 8.58, S 9.94. Calc. for C₁₆H₁₅F₃N₂S:

C 59.25, H 4.66, N 8.64, S 9.89%.) ν_max(KBr)/cm⁻¹3055

(ν_C–Har), 2936 (ν_–CH3, ν_–CH2), 2855 (ν_–CH2), 1602 (ν_C–Car),

1503, 1455 (δ_–CH2, δ_–CH3), 1409, 1315, 1160, 1120, 1100, 849

64.94, H 5.77, N 8.91, S 10.20%.) ν_max(KBr)/cm⁻¹2934 (ν_–CH3

,

ν_–CH2), 2859 (ν_–CH2), 1719 (ν_C=O,COOCH3), 1601 (ν_C–Car),

1497, 1436, 1407, 1279 (ν_C–O,COOCH3), 1193, 1145, 1109,

3

865 (δ_C–Har). δ_H(300 MHz, C₆D₆) 8.16 (d, J_HH8.7, 2H,

3

ꢀ

H₃), 7.97 (d, J_HH8.4, 2H, H₂), 7.92 (d, J_HH8.7, 2H, H₂),

(δ_C–₃_Har). δ_H(400 MHz, C₆D₆) 7.93 (d, ³J_HH8.3, 2H, H₂), 7.77

3

ꢀ

6.97 (d, J_HH8.4, 2H, H₃), 3.48 (s, 3H, COOCH₃), 2.35

3

ꢀ

(d, J_HH8.2, 2H, H₂), 7.37 (d, J_HH8.4, 2H, H₃), 6.98 (d,

(t, J_HH7.6, 2H, CH₂CH₂CH₂SH), 2.08 (q, J_HH7.4, 2H,

CH₂CH₂CH₂SH), 1.59–1.43 (m, 2H, CH₂CH₂CH₂SH), 1.05 (t,

³J_HH7.9, 1H, CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 166.06

3

³J_HH8.2, 2H, H₃), 2.37 (t, J_HH7.6, 2H, CH₂CH₂CH₂SH),

3

2.09 (q, J_HH7.3, 2H, CH₂CH₂CH₂SH), 1.59–1.49 (m, 2H,

3

CH₂CH₂CH₂SH), 1.06 (t, J_HH7.9, 1H, CH₂CH₂CH₂SH).

ꢀ

(COOCH3), 155.59 (C₁), 151.65 (C₁), 145.95 (C₄), 132.36

ꢀ

δ_C(100 MHz, C₆D₆) 154.82 (C₁), 151.43 (C₁), 146.20 (C₄),

ꢀ

(C₄), 130.94(C₃), 129.47(C₃), 123.75(C₂), 122.98(C₂), 51.72

(COOCH₃), 35.27 (CH₂CH₂CH₂SH), 34.32 (CH₂CH₂CH₂SH),

23.92 (CH₂CH₂CH₂SH). m/z (EI) 314 (74%, M⁺), 179 (10%,

C₉H₁₁N₂S⁺), 151(100%, C₈H₉NO₂), 135(50%, C₈H₇O⁺₂), 123

(15%), 91 (13%, C₇H⁺₇).

2

3

ꢀ

132.04 (q, J_CF32.3, F–C₄), 129.49 (C₃), 126.46 (q, J_CF

1

ꢀ

3.7, C₃), 124.62 (q, J_CF272.3, CF₃), 123.75 (C₂), 123.26

(C₂), 35.27 (CH₂CH₂CH₂SH), 34.31 (CH₂CH₂CH₂SH), 23.92

(CH₂CH₂CH₂SH). δ_F(300 MHz, C₆D₆) −62.12. m/z (EI) 324

(77%, M⁺), 151 (100%, C₉H₁₁S⁺), 145 (59%, C₇H₅F⁺₃), 123

(20%), 91 (23%, C₇H⁺₇).

Accessory Publication

The synthesis and characterization of the compounds 7–15,

16–24a, b, and 34 are available on the Journal’s website.

3-[4-(Phenyldiazenyl)phenyl]propanethiol 28b

Yield: 0.6 g (2.3 mmol, 69%), orange liquid (Found: C 69.89,

H 6.34, N 10.83, S 12.38. Calc. for C₁₅H₁₆N₂S: C 70.27,

H 6.29, N 10.93, S 12.51%.) ν_max(KBr)/cm⁻¹3064 (ν_C–Har),

2928 (ν_–CH3, ν_–CH2), 2857 (ν_–CH2), 2570 (ν_S–H), 2543 (ν_S–H),

1599 (ν_C–Car), 1497, 1455 (δ_–CH2, δ_–CH3), 1441 (δ_–CH2, δ_–CH3),

1294, 1221, 1151, 1102, 849 (δ_C–Har). δ_H(400 MHz, C₆D₆)

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8.05 (d, J_HH7.5, 2H, H₂), 8.00 (d, J_HH8.3, 2H, H₂), 7.19

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(t, J_HH7.6, 2H, H₃), 7.09 (t, J_HH7.3, 1H, H₄), 6.97 (d,

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δ_C(100 MHz, C₆D₆) 153.31 (C₁), 151.73 (C₁), 145.10 (C₄),

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130.96 (C₄), 129.39 (C₃), 129.29 (C₃), 123.51 (C₂), 123.25

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3-[4-((4-Bromophenyl)diazenyl)phenyl]propanethiol 31b

Yield: 0.7 g (2.1 mmol, 78%), orange solid. Mp 89–91^◦C (Found:

C 53.71, H 4.69, N 8.38, S 9.52. Calc. for C₁₅H₁₅BrN₂S:

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(ν_C–Har), 2932 (ν_–CH3, ν_–CH2), 2856 (ν_–CH2), 1570 (ν_C–Car),

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3

1064, 1002, 837 (δ_C–Har). δ_H(300 MHz, C₆D₆) 7.95 (d, J_HH

3

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8.4, 2H, H₂), 7.67 (d, J_HH8.8, 2H, H₂), 7.27 (d, J_HH8.8,

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2H, H₃), 6.96 (d, J_HH8.5, 2H, H₃), 2.34 (t, J_HH7.6, 2H,

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3

ꢀ

CH₂CH₂CH₂SH). δ_C(75 MHz, C₆D₆) 151.85 (C₁), 151.54

ꢀ

(C₁), 145.54 (C₄), 132.56 (C₃), 129.45 (C₃), 125.42 (C₄),

ꢀ

124.62 (C₂), 123.56 (C₂) 35.28 (CH₂CH₂CH₂SH), 34.30

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Article Doi

Preparation of azobenzenealkanethiols for self-assembled monolayers with photoswitchable properties

DOI: 10.1071/CH09308

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Article abstract of DOI:10.1071/CH09308

Full text of DOI:10.1071/CH09308

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