Substituent effects at the benzyl position and aromatic ring of silane-coupling agents containing 2-nitrobenzyl esters on photosensitivity and hydrophobic surface of a self-assembled monolayer (SAM)

Article abstract of DOI:10.1246/bcsj.20150316

Silane-coupling agents with 2-nitrobenzyl esters containing alkyl substituents at the benzyl position and alkoxy and/or fluoroalkoxy groups of the aromatic ring were synthesized to prepare a self-assembled monolayer (SAM) on quartz glass, silicon wafer and thermally oxidized silicon wafer. The resulting photosensitive SAMs before and after photoirradiation were characterized by contact angle measurement, UV spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray reflectivity (XRR). Photosensitivity of the SAM was influenced by substituents at the benzyl position and aromatic ring as well as the irradiation conditions in air or solution and substrates employed. Silane-coupling agents with bulky substituent at the benzyl position and double fluoroalkoxy chains are preferable in terms of the photosensitivity and hydrophobic surface.

Full text of DOI:10.1246/bcsj.20150316

Substituent Effects at the Benzyl Position and Aromatic Ring of
Silane-Coupling Agents Containing 2-Nitrobenzyl Esters on
Photosensitivity and Hydrophobic Surface of
a Self-Assembled Monolayer (SAM)
Tsubasa Konishi,1 Teppei Hashimoto,1 Naoya Sato,1 Kazuki Nakajima,1 and Kazuo Yamaguchi*1,2
1Department of Chemistry, Kanagawa University, Tsuchiya, Hiratsuka, Kanagawa 259-1293
2Research Institute for Photofunctionalized Materials, Kanagawa University, Tsuchiya, Hiratsuka, Kanagawa 259-1293
E-mail: kazu@kanagawa-u.ac.jp
Received: September 14, 2015; Accepted: October 21, 2015; Web Released: January 15, 2016
Kazuo Yamaguchi
Kazuo Yamaguchi received his Master’s degree in Department of Chemistry from Tokyo Institute of
Technology (TIT), Japan in 1976. He became a Research Associate at Department of Polymer Chemistry of
TIT in 1978 before he received a Ph.D. degree in Department of Chemistry from TIT in 1982. He worked as a
postdoctoral fellow with Professor Regen at Marquette University, USA during 1982–1984. He moved to
Kanagawa University as an Assistant Professor in 1989 and has been a Professor since 1987. His current
research interests include the synthesis of photosensitive molecules and polymers, and application for
materials of electronics and biological sciences.
Abstract
coupling agent containing 2-nitrobenzyl ester as a photo-
degradable protecting group of carboxylic acid.5 The 2-nitro-
benzyl group was developed by Patchornik et al.6 and can be
cleaved by UV light under neutral condition as a protecting
group. Different types of photodegradable protecting groups
such as nitrophenethyl, coumarinylmethyl, and quinolinyl-
methyl groups were reported in the past.7 Among many
photodegradable groups studied, 2-nitrobenzyl derivatives have
gained a great deal of attention in the field of biologically
active compounds and those applications.8 We have used
silane-coupling agents containing 2-nitrobenzyl ester as de-
scribed above to apply for patterning of cells.9 These substrates
are improved and employed for further applications.10 Another
representative molecule to form SAM is thiol to bind noble
metals such as Au through sulfide bonds. Various functional
groups at the other terminal of thiol compounds are known to
be used for the introduction of photocleavable protecting
groups.11 Many examples of photosensitive SAMs from thiols
(Thiol-SAM) on Au substrate are reported, especially in the
application of biotechnology as well as photosensitive SAMs
based on silane coupling agents (Si-SAM).12 Thiol-SAM is
thermally rather unstable and therefore thermally stable Si-
SAM should be much more preferable for application to
electronics.13 In recent years, Si-SAMs have attracted much
attention due to application to electronics fields such as photo-
lithography14 and organic thin film transistors (OTFTs).15,16
Photosensitive SAM from compounds bearing a chlorosilyl
group and long alkyl or fluoroalkyl chain connected with 2-
nitrobenzyl ester have been used in attempt to pattern micro-
Silane-coupling agents with 2-nitrobenzyl esters containing
alkyl substituents at the benzyl position and alkoxy and/or
fluoroalkoxy groups of the aromatic ring were synthesized to
prepare a self-assembled monolayer (SAM) on quartz glass,
silicon wafer and thermally oxidized silicon wafer. The result-
ing photosensitive SAMs before and after photoirradiation
were characterized by contact angle measurement, UV spec-
troscopy, X-ray photoelectron spectroscopy (XPS), and X-ray
reflectivity (XRR). Photosensitivity of the SAM was influenced
by substituents at the benzyl position and aromatic ring as
well as the irradiation conditions in air or solution and sub-
strates employed. Silane-coupling agents with bulky substitu-
ent at the benzyl position and double fluoroalkoxy chains are
preferable in terms of the photosensitivity and hydrophobic
surface.
Silane-coupling agents, organosilicon compounds with alkyl
and hydrolysable chlorosilyl or alkoxysilyl groups are em-
ployed for modification of inorganic surfaces such as Si wafer,
indium tin oxide (ITO), titanium dioxide (TiO2) and zinc oxide
(ZnO).1-4 Silane-coupling agents containing several functional
groups such as amino, mercapto, cyano, and azido groups are
commercially available. However, silane-coupling agents con-
taining carboxy and sulfo groups are not known and few
hydroxy groups are found because these functional groups are
reactive and therefore incompatible with hydrolyzable group at
the other terminal of the coupling agent. We reported a silane-
Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan | 125

fluidic devices, resulting in lowering photosensitivity.17,18 We
have also employed a silane coupling agent bearing 2-nitro-
benzyl sulfonate with a long fluoroalkyl chain for fabrication of
an electrode for organic thin-film transistors on flexible plas-
tic substrate.19 A large hydrophobic-hydrophilic difference
between 4-fluoroalkoxy-2-nitrobenzyl sulfonate and the photo-
generated sulfonic acid was obtained, but photosensitivity
of the sulfonate was pretty low. Si-SAM is preferable for
electronics application as described above, however the photo-
sensitivity might not be enough for electronics applications
compared to conventional photolithography with resist materi-
als. In this paper, silane-coupling agents 1a-1n containing 2-
nitrobenzyl ester with alkyl groups at the benzyl position and
alkoxy and/or fluoroalkoxy groups at 4- and 5-positions of
the aromatic ring were synthesized to form and characterize
the photosensitive SAMs to improve the photosensitivity with
the large hydrophobic-hydrophilic deference before and after
photoirradiation as shown in Figure 1.
Synthesis of 1a-1n. Silane-coupling agents 1a-1n were
synthesized according to Schemes 1-4.
1-[2-Nitro-4,5-di(1H,1H,2H,2H,3H,3H-perfluoroheptyl-
oxy)phenyl]ethyl 5-(Trimethoxysilyl)pentanoate (1g):
A
solution of 1-[2-nitro-4,5-di(1H,1H,2H,2H,3H,3H-perfluoro-
heptyloxy)phenyl]ethyl 4-pentenoate (2g) (3.00 g, 3.74 mmol)
in dry THF (2 mL) was added to trimethoxysilane (4.57 g, 37.4
OR2
R1
CH
(CH3O)3Si (CH2)4
C
O
O
OR3
NO2
R2 = CH3
R2 = CH3
R2 = CH3
R2 = CH3
R2 = (CH2)3(CF2)7CF3
R2 = (CH2)17CH3
R2 = (CH2)3(CF2)3CF3
R2 = (CH2)9CH3
R2 = CH3
R2 = CH3
R2 = CH3
R2 = CH3
R2 = (CH2)3(CF2)3CF3
R2 = (CH2)3(CF2)3CF3
R1 = CH3
R1 = CH3
R1 = CH3
R1 = CH3
R1 = CH3
R3 = CH3
1a
1b
1c
1d
1e
R3 = (CH2)9CH3
R3 = (CH2)3(CF2)3CF3
R3 = (CH2)3(CF2)7CF3
R3 = CH3
1f R1 = CH3
R3 = CH3
R1 = CH3
R1 = CH3
R3 = (CH2)3(CF2)3CF3
R3 = (CH2)9CH3
R3 = CH3
R3 = CH3
R3 = CH3
R3 = CH3
1g
Experimental
1h
1i R1 = CH2CH3
Reagents and Materials. Most of the reagents and solvents
described herein were purchased either from Wako (Osaka,
Japan), TCI (Tokyo, Japan) or Sigma-Aldrich (St. Louis, MO).
Quartz glasses were purchased from Kogakugiken (Kanagawa,
Japan). Silicon wafers were provided by Enatek (Tokyo,
Japan). Silicon wafers with a thermally-oxidized film (thick-
ness of 150 nm) were purchased from Yamanaka semiconduc-
tor (Kyoto, Japan).
R1 = (CH2)2CH3
R1 = CH(CH3)2
1j
1k
1l R1 = C(CH3)3
R1 = CH(CH3)2
R1 = C(CH3)3
R3 = (CH2)3(CF2)3CF3
R3 = (CH2)3(CF2)3CF3
1m
1n
Figure 1. Synthesized
agents 1a-1n.
photosensitive
silane-coupling
O
O
OCH3
OCH3
OCH3
OCH3
R
O
I2
R
R
O
R
O
70 % HNO3
OCH3
OCH3
NO2
5a R = Me
5i R = Et
82%
55%
56%
4a R = Me
4i R = Et
R = n-Pr 57%
4k R = i-Pr
5j
R = n-Pr 71%
5k
5l
R = i-Pr 40%
R = t-Bu
4j
33%
44%
4l R = t-Bu 71%
OCH3
OCH3
OCH3
R
R
NaBH4
MeOH / THF
4-pentenoic acid
HO CH
CH2 CH (CH2)2 C O CH
O
OCH3
EDC HCl
DMAP / THF
NO2
3a R = Me 99%
NO2
2a
2i
2j
R = Me 85%
R = Et
R = n-Pr 87%
88%
3i R = Et
3j
3k
98%
99%
R = n-Pr
2k R = i-Pr 80%
2l
R = i-Pr 99%
R = t-Bu 97%
3l R = t-Bu
99%
OCH3
OCH3
(H3CO)3SiH
Karstedt's catalyst
R
(H3CO)3Si
(CH2)4
C O CH
O
NO2
1a R = Me 65%
1i
R = Et 76%
1j R = n-Pr 22%
R = i-Pr 74%
1k
1l R = t-Bu 76%
Scheme 1. Synthesis of photosensitive silane-coupling agents 1a, 1i, 1j, 1k, and 1l.
126 | Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan

Br-CH2Ph
K2CO3
OCH3
OH
OCH3
OCH2Ph
OCH3
OCH2Ph
68%
CH3
O
CH3
O
fuming HNO3
CH3COOH
CH3
O
dry-DMF
90%
NO2
OCH3
OH
OCH3
OR
CH3
CH3
O
I-R
NaBH4
CF3COOH
K2CO3 / dry DMF
O
MeOH / THF
NO2
69%
NO2
4b R = (CH2)9CH3
4c R = (CH2)3(CF2)3CF3 69%
4d R = (CH2)3(CF2)7CF3 84%
75%
OCH3
OR
OCH3
OR
CH3
CH3
4-pentenoic acid
HO CH
CH2 CH (CH2)2 C O CH
O
EDC HCl, DMAP / THF
NO2
3b R = (CH2)9CH3
3c R = (CH2)3(CF2)3CF3 98%
3d R = (CH2)3(CF2)7CF3 93%
NO2
2b R = (CH2)9CH3
79%
92%
2c R = (CH2)3(CF2)3CF3 77%
2d R = (CH2)3(CF2)7CF3 95%
OCH3
OR
CH3
(CH3O)3SiH
(CH3O)3Si
(CH2)4 C O CH
O
Karstedt's catalyst
NO2
55%
1b R = (CH2)9CH3
1c R = (CH2)3(CF2)3CF3 59%
1d R = (CH2)3(CF2)7CF3 52%
Scheme 2. Synthesis of photosensitive silane-coupling agents 1b, 1c, and 1d.
mmol) in the presence of Karstedt’s catalyst (10 drops). The for C32H39F18NO9Si: C, 40.38; H, 4.13; N, 1.47%. Found: C,
solution was stirred at room temperature for 4 h under a
nitrogen atmosphere and concentrated using a rotary evapo-
rator. The crude product was purified by silica gel column
chromatography (hexane/ethyl acetate/tetramethoxysilane,
6:1:0.07) to yield 2.25 g (2.43 mmol, 65%) of 1g as a yellowish
solid. 1H NMR (400 MHz, CDCl3): ¤ 7.56 (s, 1H), 6.99 (s, 1H),
6.45 (q, J = 6.5 Hz, 1H), 4.20-4.10 (m, 4H), 3.57 (s, 9H),
2.42-2.26 (m, 6H), 2.22-2.12 (m, 4H), 1.65 (q, J = 7.7 Hz,
2H), 1.60 (d, J = 6.5 Hz, 3H), 1.47-1.39 (m, 2H), 0.660-0.620
(m, 2H). Anal. Calculated for C30H35F18NO9Si: C, 39.01; H,
3.82; N, 1.52%. Found: C, 38.98; H, 3.37; N, 1.53%. 1b-1f and
1h-1l were synthesized in a similar way to synthesis of 1g.
40.45; H, 3.86; N, 1.50%.
1-[2-Nitro-4,5-di(1H,1H,2H,2H,3H,3H-perfluoroheptyl-
oxy)phenyl]-2,2-dimethylpropyl 5-(Trimethoxysilyl)pente-
noate (1n):
Yield: 67%, 1H NMR (400 MHz, CDCl3): ¤
7.54 (s, 1H), 6.90 (s, 1H), 6.63 (s, 1H), 4.13-4.10 (m, 4H), 3.55
(s, 9H), 2.41-2.23 (m, 6H), 2.21-2.14 (m, 4H), 1.68 (q,
J = 7.6 Hz, 2H), 1.49-1.42 (m, 2H), 0.96 (s, 9H), 0.66-0.62
(m, 2H). Anal. Calculated for C33H41F18NO9Si: C, 41.04; H,
4.28; N, 1.45%. Found: C, 40.74; H, 4.07; N, 1.40%.
1-[2-Nitro-4,5-di(1H,1H,2H,2H,3H,3H-perfluoroheptyl-
oxy)phenyl]ethyl 4-Pentenoate (2g): To a solution of 1-[2-
nitro-4,5-di(1H,1H,2H,2H,3H,3H-perfluoroheptyloxy)phenyl]-
ethan-1-ol (1.31 g, 2.21 mmol), 4-pentenoic acid (0.37 g, 3.70
mmol), 4-dimethylaminopyridine (0.27 g, 2.21 mmol) in dry
THF (6 mL) at 0 °C under a nitrogen atmosphere was added
dropwise a solution of 1-ethyl-3-(3-dimethylaminopropyl)-
carbodiimide hydrochloride (0.803 g, 4.19 mmol) in dry THF
(3 mL). The solution was stirred at room temperature overnight.
After concentrating the solution using a rotary evaporator, H2O
(40 mL) and 2 M HCl (10 mL) were added, and the solution
was extracted with ethyl acetate (40 mL © 2). The organic layer
was washed with 5% NaHCO3 (50 mL © 3) and dried over
MgSO4. The solvent was removed under reduced pressure to
yield 1.28 g (1.60 mmol, 88%) of 2g as a yellowish solid.
1H NMR (400 MHz, CDCl3): ¤ 7.58 (s, 1H), 6.99 (s, 1H), 6.45
(q, J = 6.4 Hz, 1H), 5.83-5.76 (m, 4H), 5.07-4.98 (m, 2H),
1-(4,5-Dimethoxy-2-nitrophenyl)ethyl
silyl)pentanoate (1a):
5-(Trimethoxy-
Yield: 65%, 1H NMR (400 MHz,
CDCl3): ¤ 7.58 (s, 1H), 7.01 (s, 1H), 6.47 (q, J = 6.4 Hz, 1H),
3.98 (s, 3H), 3.94 (s, 3H), 3.55 (s, 9H), 2.39-2.32 (m, 2H),
1.70-1.60 (m, 5H), 1.48-1.40 (m, 2H), 0.66-0.62 (m, 2H).
Anal. Calculated for C30H35F18NO9Si: C, 50.10; H, 6.77; N,
3.25%. Found: C, 49.98; H, 6.77; N, 3.27%.
1-[2-Nitro-4,5-di(1H,1H,2H,2H,3H,3H-perfluoroheptyl-
oxy)phenyl]-2-methylpropyl 5-(Trimethoxysilyl)pentenoate
1
(1m): Yield: 67%, H NMR (400 MHz, CDCl3): ¤ 7.57 (s,
1H), 6.87 (s, 1H), 6.30 (q, J = 5.8 Hz, 1H), 4.17-4.08 (m, 4H),
3.55 (s, 9H), 2.39-2.26 (m, 6H), 2.21-2.12 (m, 5H), 1.66 (q,
J = 7.6 Hz, 2H), 1.47-1.39 (m, 2H), 0.99 (d, J = 6.8 Hz, 3H),
0.97 (d, J = 6.8 Hz, 3H) 0.67-0.61 (m, 2H). Anal. Calculated
Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan | 127

Br-CH2Ph
K2CO3
OH
OCH2Ph
OCH3
OCH2Ph
OCH3
CH3
O
CH3
O
HNO3
CH3
O
OCH3
CH3COOH
dry-DMF
OH
NO2
60%
81%
OR
CH3
O
CH3
I-R
K2CO3 / dry DMF
NaBH4
MeOH / THF
OCH3
OCH3
CF3COOH
O
NO2
5e 81%
NO2
4e R = (CH2)3(CF2)7CF3 70%
4f R = (CH2)17CH3
91%
OR
OR
CH3
CH3
4-pentenoic acid
EDC HCl, DMAP / THF
HO CH
OCH3
CH2 CH (CH2)2 C O CH
O
OCH3
NO2
NO2
2e R = (CH2)3(CF2)7CF3 81%
3e R = (CH2)3(CF2)7CF3 99%
2f R = (CH2)17CH3
76%
3f R = (CH2)17CH3
99%
OR
CH3
(CH3O)3SiH
C O CH
O
OCH3
(CH3O)3Si
(CH2)4
Karstedt's catalyst
NO2
1e R = (CH2)3(CF2)7CF3 38 %
1f R = (CH2)17CH3
10%
Scheme 3. Synthesis of photosensitive silane-coupling agents 1e and 1f.
4.20-4.10 (m, 4H), 2.51-2.28 (m, 8H), 2.22-2.13 (m, 4H), 1.60
(d, J = 6.5 Hz, 3H). 2a-2f and 2h-2n were synthesized in a
similar way to synthesis of 2g.
purified by recrystallization with ethanol to yield 1.38 g (1.92
mmol, 60%) of 4g as yellow needle crystals. H NMR (400
MHz, CDCl3): ¤ 7.60 (s, 1H), 6.75 (s, 1H), 4.14 (m, 2H), 4.13
(m, 2H), 2.50 (s, 3H), 2.33-2.27 (m, 4H), 2.22-2.17 (m, 4H).
4h was synthesized in a similar way to that of 4g.
1
1-[2-Nitro-4,5-di(1H,1H,2H,2H,3H,3H-perfluoroheptyl-
oxy)phenyl]ethan-1-ol (3g):
Sodium tetrahydroborate
(0.14 g, 3.70 mmol) was added to a solution of 2-nitro-
4,5-di(1H,1H,2H,2H,3H,3H-perfluoroheptyloxy)acetophenone
(1.37 g, 1.91 mmol) in THF (6 mL) and methanol (2 mL) at
0 °C. The solution was stirred at 0 °C for 20 min and then at
room temperature for 3.5 h. After concentrating the solution
using a rotary evaporator, H2O (40 mL) and 2 M HCl (10 mL)
were added, and the solution was extracted with chloroform
(40 mL © 2). The organic layer was dried over MgSO4, and the
solvent was removed under a reduced pressure to yield 1.31 g
(1.82 mmol, 95%) of 3g as a yellow solid. 1H NMR (400 MHz,
CDCl3): ¤ 7.57 (s, 1H), 7.30 (s, 1H), 55.7 (q, J = 6.2 Hz, 1H),
4.24-4.08 (m, 4H), 2.39-2.29 (m, 4H), 2.23-2.12 (m, 5H), 1.55
(d, J = 6.2 Hz, 3H). 3a-3f and 3h-3n were synthesized in a
similar way to synthesis of 3g.
3,4-Di(1H,1H,2H,2H,3H,3H-perfluoroheptyloxy)aceto-
phenone (5g): Potassium carbonate (1.08 g, 7.81 mmol) was
added to a solution of 3,4-dihydroxyacetophenone (0.59 g,
3.88 mmol) in N,N-dimethylformamide (3 mL). The solution
was stirred at room temperature for 5 h. A solution of 1-iodo-
1H,1H,2H,2H,3H,3H-perfluoroheptane (3.10 g, 7.76 mmol) in
DMF (5 mL) was added dropwise to the solution. The solution
was refluxed at 60 °C overnight. After the solvent was removed
under reduced pressure, water (60 mL) and 2 M HCl (10 mL)
were added, and the solution was extracted with chloroform
(40 mL © 3). The organic layer was washed with saturated
NaCl (100 mL © 2) and dried over MgSO4. The resulting
material was finally concentrated under reduced pressure to
yield 2.14 g (3.18 mmol, 82%) of 5g as a white solid. 1H NMR
(400 MHz, CDCl3): ¤ 7.58 (dd, J = 2.0, 8.4 Hz, 1H), 7.52
(d, J = 2.0 Hz, 1H), 6.88 (d, J = 8.5 Hz, 1H), 4.14 (m, 2H),
4.13 (m, 2H), 2.56 (s, 3H), 2.34-2.32 (m, 4H), 2.19-2.15 (m,
4H). 4b-4f and 5h, 5m, 5n were synthesized in a similar way
to that of 5g.
2-Nitro-4,5-di(1H,1H,2H,2H,3H,3H-perfluoroheptyl-
oxy)acetophenone (4g):
To a solution of 3,4-
di(1H,1H,2H,2H,3H,3H-perfluoroheptyloxy)acetophenone
(2.14 g, 3.18 mmol) in diethyl ether (10 mL), HNO3 (15 mL)
was carefully added dropwise at 0 °C. The solution was sub-
sequently stirred at 0 °C for 5 h. The solution was added to ice
water (100 mL) and the solution was extracted with ethyl
acetate (40 mL © 2). The organic layer was washed with 5%
NaHCO3 (50 mL © 3) and dried over MgSO4. After concen-
trating the solution using a rotary evaporator, the residue was
5-Hydroxy-4-methoxy-2-nitroacetophenone (5e): 5-Ben-
zyloxy-4-methoxy-2-nitroacetophenone 1.23 g (4.09 mmol)
was added to trifluoroacetic acid (12 mL). The solution was
stirred at room temperature for 21 h. After concentrating the
solution using a rotary evaporator, 1 M NaOH (21 mL) and 1 M
128 | Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan

O
O
OCH3
OCH3
OCH3
OCH3
OH
R1
R1
O
R
O
I2
R
LiCl
OH
O
dry-DMF
6g
6h
6m
R = Me
R = Me
R = i-Pr
29%
7m R = i-Pr
7n R = t-Bu 24%
63%
6n R = t-Bu 81%
OR2
OR2
I-R2
R1
70 % HNO3
ether
K2CO3 / dry DMF
O
R2 = (CH2)3(CF2)3CF3
or R2 = (CH2)9CH3
R1 = Me R2 = (CH2)3(CF2)3CF3 75%
5h R1 = Me R2 = (CH2)9CH3
87%
5g
1
R = i-Pr R2 = (CH2)3(CF2)3CF3 91%
5m
5n R1 = t-Bu R2 = (CH2)3(CF2)3CF3 78%
OR2
OR2
OR2
OR2
R1
O
R1
4-pentenoic acid
NaBH4
C
HO CH
EDC HCl
DMAP / THF
MeOH / THF
NO2
NO2
R1 = Me R2 = (CH2)3(CF2)3CF3 89%
R1 = Me R2 = (CH2)3(CF2)3CF3 52%
3g
4g
3h R1 = Me R2 = (CH2)9CH3
87%
4h R1 = Me R2 = (CH2)9CH3
65%
1
R = i-Pr R2 = (CH2)3(CF2)3CF3 76%
1
R = i-Pr R2 = (CH2)3(CF2)3CF3 without isolation
3m
4m
3n R1 = t-Bu R2 = (CH2)3(CF2)3CF3 35%
4n R1 = t-Bu R2 = (CH2)3(CF2)3CF3 without isolation
OR2
OR2
OR2
OR2
R1
R1
(CH3O)3SiH
Karstedt's catalyst
CH2 CH (CH2)2 C O CH
O
(CH3O)3Si (CH2)4 C O CH
O
NO2
NO2
R1 = Me R2 = (CH2)3(CF2)3CF3 84%
2g
R1 = Me R2 = (CH2)3(CF2)3CF3 65%
1g
2h R1 = Me R2 = (CH2)9CH3
88%
1h R1 = Me R2 = (CH2)9CH3
64%
R = i-Pr R2 = (CH2)3(CF2)3CF3 67%
1n R1 = t-Bu R2 = (CH2)3(CF2)3CF3 69%
1
R = i-Pr R2 = (CH2)3(CF2)3CF3 92%
1
2m
1m
2n R1 = t-Bu R2 = (CH2)3(CF2)3CF3 92%
Scheme 4. Synthesis of photosensitive silane-coupling agents 1g, 1h, 1m, and 1n.
HCl (3 mL) were added, and the solution was extracted with
100 °C for 3 h. The modified substrates were rinsed with
methanol, sonicated in methanol for 10 min and then in chloro-
form for 10 min, and finally dried with nitrogen. Character-
ization was performed by contact angle measurements, UV,
XRR, and XPS. The modified substrates were irradiated with
an ultrahigh pressure mercury lamp (USH-500SH, Ushio,
Japan) through PYREX glass (- > 300 nm) and water (for
cutting off IR) or copper sulfate solution (- > 320 nm). The
light intensity was 50 mW cm¹2, as determined with a UIT-201
power meter equipped with a UVD-365PD (Ushio, Japan).
All irradiated SAMs were rinsed with chloroform and then
sonicated in chloroform for 10 min, and finally dried with
nitrogen.
chloroform (40 mL © 4). The organic layer was dried over
MgSO4. After concentrating the solution using a rotary evapo-
rator, the residue was purified by recrystallization with ethyl
acetate. The solvent was removed under reduced pressure to
yield 0.70 g (3.31 mmol, 81%) of 5e as a dark yellow solid.
1H NMR (400 MHz, CDCl3): ¤ 7.65 (s, 1H), 6.86 (s, 1H), 6.28
(s, 1H), 4.03 (s, 3H), 2.50 (s, 3H).
The purity of all compounds were comparable from 1H NMR
spectra in Supporting Information.
Compounds of 2a, 3a, 3i, 3j, 3k, 3l, 4a, 4i, 4j, 4k, 4l, 5j, 5k,
5l, 5h, 7m, and 7n were synthesized according to known
methods.
Preparation of SAMs and Photodeprotection.
The
Characterization. Water contact angle measurements were
conducted at room temperature using a DropMaster 700 contact
angle meter (Kyowa Interface Science, Japan). The pure water
was placed onto the surface and monitored with a camera. The
captured images were analyzed using FAMAS software (Kyowa
Interface Science) to determine the contact angle. The contact
formation and photodeprotection of SAM were carried out
according to Figure 2. Silicon wafers and quartz glasses were
cleaned and hydroxy terminated with a UV-ozone cleaner
(UV253, Filgen, Japan). The substrates were soaked in dry
toluene containing silane coupling agents 1a-1n (1 mM) at
Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan | 129

OR2
OR3
OR2
OR3
R1
OH
R1
(CH3O)3Si (CH2)4 C O CH
O
C O CH
O
O
Si (CH2)4
OH
OH
NO2
NO2
OR2
OR3
substrate
R1
hv
C
+
C OH
O
O
Si (CH2)4
O
NO
Figure 2. The formation of SAM on substrate using silane-coupling agent containing 2-nitrobenzyl ester, and photodeprotection of
SAM using UV irradiation to generate carboxy-functionalized SAMs.
angles reported in this study are the average of more than three
values taken at different points on the surface. UV-vis spectra of
the substrates were measured with a V-570 (JASCO, Japan).
Quartz glass plates were used for this experiment. The surface
density of the SAM, Γ (molecules cm¹2), can be estimated from
5j, 5k, and 5l were nitrated by 70% HNO3 to afford nitro
compounds 4a, 4i, 4j, 4k, and 4l which were reduced by
NaBH4 to afford alcohols 3a, 3i, 3j, 3k, and 3l. The resulting
alcohols were condensed with 4-pentenoic acid in the presence
of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/hydrochlo-
ride and 4-dimethylaminopyridine to get esters 2a, 2i, 2j, 2k,
and 2l. Finally the precursors were hydrosilylated with tri-
methoxysilane with Karstedt’s catalyst to obtain silane cou-
pling agents 1a, 1i, 1j, 1k, and 1l. Synthetic routes for 1b, 1c,
and 1d are shown in Scheme 2. 4-Hydroxy-3-methoxyaceto-
phenone was benzylated with benzyl bromide in the presence
of K2CO3, and nitrated with fuming HNO3 in acetic acid, and
debenzylated with trifluoroacetic acid, to nitro ketone. The
ketone reacted with the corresponding iodides in the presence
of K2CO3 in DMF to get ethers which were reduced with
NaBH4 to alcohols 4b, 4c, and 4d. The esterification and
hydrosilylation were carried out similar to Scheme 1 to get
final products 1b, 1c, and 1d. Synthetic routes for 1e and 1f are
shown in Scheme 3. Instead of 4-hydroxy-3-methoxyaceto-
phenone in Scheme 2, 3-hydroxy-4-methoxyacetophenone was
employed as a starting material using similar procedures to
get alcohols 4e and 4f. The esterification and hydrosilylation
were carried out similar to Scheme 1 to get final products 1e
and 1f. Synthetic routes for 1g, 1h, 1m, and 1n are shown
in Scheme 4. Acylation of 1,2-dimethoxybenzene with the
corresponding acid anhydrides was carried out followed by
demethylation with LiCl in DMF to obtain 4-acyl-1,2-di-
hydroxybenzenes. Dihydroxy compounds were etherified with
the corresponding iodides, nitrated with 70% HNO3, and
reduced with NaBH4 to the corresponding alcohols 4g, 4h,
4m, and 4n. The esterification and hydrosilylation were carried
out similar to Scheme 1 to get final products 1g, 1h, 1m, and
1n. The yields of ether synthesis using K2CO3 were 69-91%.
Diethyl ether was used for nitration of fluoroalkoxy compounds
as solvent. Yields of nitration were around 50% probably
because of a side reaction such as deacylation. Reduction of
ketones with NaBH4 proceeded in high yields. Condensation of
alcohols with 4-pentenoic acid gave the desired esters in high
yields. Yields of hydrosilylation were 22-76%. Hydrogenation
of the starting material as a side reaction resulted in low yields.
In addition, to prevent the trimethoxysilyl group of the desired
product from reacting and immobilizing to silica gel for
column chromatography, a small amount of tetramethoxysilane
was added to an eluent of column chromatography, however
the UV absorbance using Γ = 1/2[A-¾ ¹1NA] © 10¹3, where
-
A- is the absorbance of the surface layer at a given wavelength,
¾
-
is the molar extinction coefficient of the precursor in 0.1
mM ethanol solution (M¹1 cm¹1) at -, and NA is Avogadro’s
number.20 The thickness has been investigated by XRR
(UltimaIV, Rigaku, Japan) with monochromatized Cu Kα
radiation at 40 kV and 40 mA. The measurement profile was
analyzed using GlobalFit software (Rigaku) with multilayer
model of organic layer/oxidized silicon layer/silicon substrate.
XPS spectra were obtained using a X-ray photoelectron scope
(JPS-9010MC, JEOL, Japan) with a monochromated Mg Kα
source (10 kV, 10 mA).
Acid-Base Responsiveness. The modified silicon wafer
with 1m was irradiated, and alternately dipped in 5% NaHCO3
aqueous solution and 2 M HCl aqueous solution. Change of
wettability was estimated by contact angle measurement.
Photodegradation in Acidic Solution.
The modified
silicon wafer with 1m was irradiated in 0.1 M HCl 2-propanol.
Characterization was performed by contact angle measurements
and XPS.
SAMs on Different Substrates. SAMs were prepared on
quartz glass, silicon wafer and silicon wafers with a thermally-
oxidized film (thickness of 150 nm). They were characterized
by contact angle measurement and compared to one another.
Patterning of SAM. Photoirradiation (light intensity 50
mW cm¹2, exposure time 120 s, exposure dose 6 J) of SAM of
1a was carried out with a photomask composed of Cr patterns
on quartz glass in air. The patterned substrate was immersed in
5% NaHCO3 aqueous solution for 1 h. And then the substrate
was stained with amine-modified fluorescent microspheres
(Thermo Fisher Scientific, USA) aqueous solution for 1 h. The
patterned surface was observed by fluorescence microscope
(BX-FLA, OLYMPUS, Japan).
Results and Discussion
Synthesis. Synthetic routes for 1a, 1i, 1j, 1k, and 1l are
shown in Scheme 1. 1,2-Dimethoxybenzene was acylated by
the corresponding acid anhydrides with iodine to obtain 5i, 5j,
5k, and 5l. Commercially available 5a and the synthesized 5i,
130 | Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan

it was very difficult for the trimethoxysilyl group to avoid
hydrolysis and/or reaction with silica gel completely, resulting
in low yields.21
found from the results described above that fluoroalkoxy chain
and double substituents at 4- and 5-positions of the 2-
nitrobenzyl group are preferable to alkoxy chain and a single
substituent at 4- or 5-position for the hydrophobicity of
photosensitive SAM and that short-chain substituents at the 4-
and 5-positions of the aromatic ring and a bulky substituent are
desirable for the photosensitivity.
Characterization. Results of contact angle measurement of
photosensitive SAMs on silicon wafer prepared from 1a-1n
before and after photoirradiation as well as exposure dose
required for constant contact angles lowered are shown in
Table 1. Contact angles of SAMs from 1a-1n are 67-108°,
different from one another depending on the substituents of
1a-1n. The contact angle after complete photoreaction should
be the same value if the carboxylic acid was generated quan-
titatively. However, the contact angles were almost 50-60°,
suggesting that photoreaction was incomplete, side reaction
occurred, and/or decomposed products stayed on the surface.
With increase in length of alkoxy and fluoroalkoxy chains at
the 4-position of the aromatic ring, the contact angle of water
on the photosensitive SAM of 1a-1n increased, but the
exposure dose required for a constant contact angle decreased
by photoirradiation increase, that is, the photosensitivity was
lowered. Introduction of alkoxy and fluoroalkoxy chains at
the 5-position of the 2-nitrobenzyl group (1e and 1f) improved
the photosensitivity. From the contact angle values, the hydro-
phobicity of SAM from 1d with long fluoroalkoxy chain is
higher than that of 1b and 1f bearing alkoxy chain. Compounds
1g and 1h bearing double fluoroalkoxy and alkoxy chains at
4- and 5-positions retained a comparable hydrophobicity and
improved the photosensitivity. It was also proved that the sub-
stituent at benzyl position affected photosensitivity of SAM.
Ethyl-substituted compound 1i with two methoxy groups at the
aromatic ring was necessary for exposure dose of the cleavage
of benzyl ester on the SAM larger than that for SAM from 1a.
SAM of propyl-substituted 1j had a photosensitivity higher
than of 1a. Isopropyl-substituted 1k offered a SAM with higher
sensitivity, while SAM of t-butyl-substituted 1l was compara-
ble to that of 1a. Silane coupling agents 1m and 1n bearing
double fluoroalkoxy chains substituted with isopropyl and
t-butyl groups at the benzyl position gave hydrophobic SAM
(contact angle around 100°) which displayed a photosensitivity
four times that of methyl-substituted compound 1g. It was
Concerning 1a, 1g, and 1k-1n, thickness of the photo-
sensitive SAM on Si wafer before and after photoirradiation
and surface density of the SAM on quartz glass were mea-
sured by XRR and UV spectroscopy as shown in Table 2.
Film thickness of SAMs prepared from 1a, 1k, and 1l was
1.2 nm comparable with the calculated values of 1.5 nm from
ChemBioDraw Ultra 12.0. On the other hand, the measured
film thickness of SAMs with double fluoroalkoxy chains from
1g, 1m, and 1n was comparable with those of SAMs from 1a,
1k, and 1l and almost one half as much as the calculated values.
It can be seen that the SAMs from 1a, 1k, and 1l are formed
with nearly perpendicular and relatively dense orientation,
while SAMs from 1g, 1m, and 1n are poorly oriented and much
less dense leading to thickness much smaller than the calcu-
lated one. This is also supported from the fact that the densities
of 1a, 1k, and 1l of SAM on quartz glass were calculated from
the UV absorbance based on the 2-nitrobenzyl moiety to be
about 3 © 1014 molecules cm¹2 nearly one and half fold greater
than those of 1g, 1m, and 1n. Elemental ratio of C1s, N1s, and
F1s normalized with Si2p3/2 based on Si-Si at 99 eV was
determined from XPS measurement of Si wafer modified with
1g, 1m, and 1n before and after photoirradiation, shown in
Table 3. Peaks of N1s assigned to nitro group and F1s were
detected to confirm the substrates were modified with 1g, 1m,
and 1n. After irradiation, the peak of N1s of nitro group
disappeared and the peak of F1s decreased to less than 10%
indicating that photoreaction proceeded to cleave nitrobenzyl
ester and form carboxylic acid. Remaining peaks of F1s and
N1s other than nitro group were probably due to reduction as a
side reaction of nitro to amino group without scission of the
ester bond22 or due to damages of X-ray in XPS measure-
ment.23 Figure 3 shows C1s XPS spectra of the SAM (1m)
before (a) and after (b) photoirradiation. The peaks of fluoro-
alkyl, ether, carbonyl and neutral carbons were characterized
and confirmed reduction of the fluoroalkyl peaks after the UV
irradiation.
Table 1. Contact angle of water on SAMs with 1a-1n
before and after photoirradiation, and the UV dose for
completing photolysis of SAMs
Contact angle/degree
Acid-base response of carboxylic acid formed on the surface
of SAM by photoirradiation was investigated by measurement
of contact angle on the surface shown in Figure 4. The contact
Exposure dose
Compound
¹2
/J cm
Modified
Irradiated
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
67
93
85
108
89
81
108
97
66
75
73
51
61
73
61
55
56
57
58
50
53
54
51
52
52
12
540
180
360
24
12
60
36
16
9
7.5
12
15
15
Table 2. Results of XRR measurement and surface density
of SAMs
Thickness/nm
Surface density
Compound
Modified
Irradiated
¹2
/molecules cm
Found Calcd
Found Calcd
1a
1k
1l
1g
1m
1n
1.2
1.2
1.2
1.1
1.1
1.3
1.5
1.5
1.5
2.1
2.1
2.1
1.1
1.1
0.83
0.83
0.91
0.92
0.8
0.8
0.8
0.8
0.8
0.8
2.9 © 1014
2.7 © 1014
3.0 © 1014
1.9 © 1014
1.9 © 1014
1.7 © 1014
71
98
100
Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan | 131

Table 3. Normalized XPS peak area of the C1s, N1s, and F1s spectra to the Si2p (Si-Si) peak, of SAMs
before and after UV irradiation
C1s
Mod.
N1s (NO2)
F1s
Si2p (Si-Si)
Compound
Irr.
Mod.
Irr.
Mod.
Irr.
Mod.
Irr.
1g
1m
1n
0.50
0.58
0.75
0.39
0.44
0.73
0.018 (0.0077)
0.016 (0.0066)
0.021 (0.0090)
0.0084 (0.0)
0.0087 (0.0)
0.0075 (0.0)
0.47
0.54
0.66
0.037
0.043
0.016
1
1
1
1
1
1
10000
(b)
10000
(a)
8000
6000
4000
2000
8000
6000
4000
CH2/CH2 arom
CH2/CH2 arom
C-O
C-O
CF2
C=O
CF3
C=O
2000
0
0
296
292
288
284
280
296
292
288
284
280
Binding energy/eV
Binding energy/eV
Figure 3. C1s XPS spectra of the SAM (1m) before (a) and after (b) photoirradiation.
Table 4. Change of contact angle of water on SAMs (1m)
by irradiation in air and HCl 0.1 M 2-propanol solution
Contact angle/degree
Exposure dose
¹2
/J cm
Modified
Irradiated
In air
In solution
98
101
51
48
18
9
Table 5. Normalized XPS peak area of the C1s, N1s, and
F1s spectra to the Si peak, of SAMs (1m) before and after
UV irradiation in air or HCl 0.1 M 2-propanol solution
Figure 4. Change of contact angle of water on SAMs (1m)
by acid-base response.
Si2p
C1s
N1s
F1s
Si-O Si-Si
Before irradiation
Irradiation in air
Irradiation in solution 0.46 0.0059 0.014 0.42
0.58 0.016
0.44 0.0087 0.043 0.39
0.54
0.38
1
1
1
angle of 51° on the substrate after photoirradiation was lowered
to 21° by immersion of the substrate into 5% NaHCO3, which
was recovered to 39° by immersion in 2 M HCl. This response
was repeatedly observed confirming that the carboxylic acid
was generated by photoirradiation of SAM from 1m. The large
difference of contact angle of about 80° was obtained by basic
solution treatment of generated carboxylic acid surface between
the ester and sodium salt.
Photoirradiation of SAM from 1m in air and in acidic
solution was carried out as shown in Table 4. Exposure dose
in acidic solution required for getting a constant contact angle
was decreased to half as much as that in air. Photoreaction was
extremely improved in acidic solution. This is also supported
from elemental ratios determined by XPS spectra of N1s and
F1s on the substrate of SAM from 1m normalized with Si2p3/2
(Si-Si) shown in Table 5. Elemental ratio of N1s and F1s after
irradiation in acidic solution decreased clearly as well as those
irradiated in air. This is consistent with the literature22 which
indicates side reaction of reduction of nitro to amino was
inhibited.
Contact angles of SAMs from 1m on different substrates,
naturally and thermally oxidized Si wafers and quartz glass
were measured before and after photoirradiation shown in
Table 6. It was found that SAMs from 1m on thermally
oxidized Si wafer and quartz glass were photolyzed much faster
than that on naturally oxidized Si wafers (as shown in
Figure 5). The mechanism for this is not understood, but
significant difference was obtained between different types of
substrates.
Photoirradiation of SAM of 1a with a photomask was
carried out to fabricate the pattern of carboxylic acid generated
132 | Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan

on the substrate surface. The patterned surface was stained with
amine-modified fluorescent microspheres as shown in Figure 6.
Immobilization of amine-modified fluorescent microspheres on
the acid generated on the irradiated part with line width of
20 ¯m was observed by fluorescence microscope and scanning
electron microscope (Figures 6c and 6d).
Conclusion
Silane coupling agents 1a-1n with 2-nitrobenzyl esters
containing alkyl substituents at benzyl position and alkoxy
and/or fluoroalkoxy groups at 4- and 5-positions of the
aromatic ring were synthesized. The photosensitivity of SAMs
from the silane-coupling agents was affected by the substitu-
ents at the benzyl position and aromatic ring, density of SAMs,
environments and substrates. The highest sensitivity was given
by 1k with methoxy groups at the aromatic ring and isopropyl
group at the benzyl position. Fluoroalkoxy chains were better
than alkoxy ones and double chains better than single chain for
hydrophobicity of SAM. The significant change of contact
angle from 101 to 21° was obtained by basic solution treatment
of generated carboxylic acid surface. It was suggested by XPS
measurement that side reaction was highly depressed during
photolysis of the SAM in an acidic solution, leading to the rate
of photolysis was about twice as much as that in air. SAMs
formed on quartz glass and thermally oxidized Si exhibited to
highly improve the photosensitivity compared to that on natu-
rally oxidized Si. Finally, we demonstrate selective deposition
of amine-modified fluorescent particles to generated carboxylic
acid surface by UV irradiation.
Table 6. Contact angle measurement for SAMs (1m) on
different substrate
Contact angle/degree
Modified Irradiated
Exposure dose
Substrate
¹2
/J cm
Naturally oxidized Si
Thermally oxidized Si
Quartz glass
98
98
100
51
56
53
15.0
1.5
2.5
/J cm–2
Figure 5. Change of contact angle of water on irradiated
SAM (1m) on natural oxidation silicon, thermal oxidation
silicon and quartz glass.
This work was financially supported by MEXT (No.
S1311032)-Supported Program for the Strategic Research
Figure 6. (a) The procedures of photopatterning of SAM; (b) photomask; (c) fluorescence microscope image of patterned SAM with
amine-modified fluorescent microspheres; (d) SEM image of patterned SAM with amine-modified fluorescent microspheres.
Bull. Chem. Soc. Jpn. 2016, 89, 125–134 | doi:10.1246/bcsj.20150316
© 2016 The Chemical Society of Japan | 133

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Foundation at Private Universities on “Creation of new fusion
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JSPS KAKENHI Grant Number 22550114.
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© 2016 The Chemical Society of Japan