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stirred for 8 h. Finally, L was produced. The product was purified
by column chromatography (SiO2, ethyl acetate/petroleum ether 2/
1
10) to give L as a white powder in 87% yield. H NMR (600 MHz,
CD3OD): d=7.00 (s, 2H, ArH), 6.93 (s, 2H, ArH), 6.88 (s, 2H, ArH),
6.81 (s, 2H, ArH), 6.59 (s, 1H, ArH), 4.64 (s, 2H, OCH2), 4.59–4.57 (m,
4H, ArCH2Ar), 4.29–4.27 (d, J=12.5 Hz, 4H, ArCH2Ar), 3.45 (s, 6H,
NCH2), 2.79 (s, 1H, CꢁCH), 2.29 (s, 6H, NCH3), 2.17 (s, 12H, NCH3).
13C NMR (100 MHz, DMSO) d: 155.47, 154.57, 153.47, 134.06,
132.75, 130.10, 129.57, 128.59, 127.74, 126.41, 123.53, 122.40,
80.50, 77.60, 62.28, 61.35, 59.78, 45.41, 44.08, 43.77, 42.43, 32.36,
30.97; MS (EI+): m/z=633.8 [M]+ (80%); elemental analysis (%)
calcd for C40H47N3O4: C 75.80, H 7.47, N 6.63; found: C 75.70, H
7.41, N 6.53.
Fabrication of L-modified silicon surface
Fabrication of the micro/nanostructured Si surface: A silicon
wafer was used as the smooth substrate. The structured silicon
substrate was fabricated by using a combination of photolithogra-
phy and the inductively coupled plasma deep-etching technique
to obtain a patterned silicon micropillar structure on the silicon
wafer. The rough surface showed a geometrical pattern of square
pillars 20 mm high, 9 mm long and with an interpillar spacing of
12 mm on a flat silicon wafer.[19]
Figure 4. Cycling between CAs before and after irradiation with 365 nm UV
light on the L-modified silicon surface, showing six switching cycles between
hydrophobic and hydrophilic states.
1
which was verified by FL, UV, and H NMR spectroscopy, ESI-
MS, and TEM. This host–guest system was further coupled
onto a micro/nanostructured silicon surface through click
chemistry to act as a highly sensitive photoresponsive wetta-
bility switch triggered by UV/Vis irradiation. The fabricated
photoresponsive host–guest system is promising in potential
applications such as sensors and microfluidic devices.[18]
Preparation of the Si-N3-modified silicon substrates: The surface-
structured silicon substrates, cut into 1ꢁ1 cm square pieces, were
soaked in chromosulfuric acid solution for 30–60 min, rinsed with
double-distilled water, and dried under a stream of N2 gas. The
cleaned wafers were immersed in an aqueous solution of NaOH
(0.1 molLÀ1
) for 6 min and subsequently in aqueous HNO3
(0.1 molLÀ1) for 12 min to generate surface hydroxyl groups. The
silicon substrates were washed with an excess of water, dried
under a stream of N2, and immersed in a refluxing 5 wt% solution
of triethoxysilane azide (Si-N3) in dry toluene (10 mL) at 1108C for
6 h. Then the silicon wafer was washed with toluene and ethanol
to remove residual Si-N3 and dried under a stream of N2 gas.
Experimental Section
Materials and instrumentation
1H and 13C NMR spectra were recorded on Varian Mercury VX400
instrument at ambient temperature with TMS as internal standard.
ESI-MS was performed on a Finnigan LCQ-Advantage instrument.
The static CA of water was measured at 258C by means of an OCA
20 contact angle system (Dataphysics, Germany). FL spectra were
recorded on a Varain Cary Eclipse instrument. XPS was carried out
on a Kratos XSAM800 photoelectron spectrometer (FRR mode).
Click reaction between Si-N3 and L on the silicon surface: The sil-
icon surfaces modified with Si-N3 were immersed in a solution of L
in CH3OH (10À2 m), to which a mixture of copper sulfate (10À6 m)
and sodium ascorbate (10À7 m) was added. This solution was kept
at 758C for 8 h. Then the silicon wafers were washed with little
CH3OH and dried under a stream of N2 gas.
All chemicals were of A.R. grade and were purified by standard
procedures. Mill-Q water was used to prepare all solutions in this
study.
Wettability measurements on modified silicon surfaces: The
wettability of L-modified silicon surface was evaluated by CA mea-
surement with a 1.0 mL water droplet. Side-view photographs were
recorded after a contact time of 5 min. The L-modified silicon
wafer was incubated in a solution of the guest trans-O (0.1 mL,
1.0 mm) in CH3OH for 10 min to form the LꢀO complex on the sur-
face, and then washed with water and dried under a stream of N2
gas for CA evaluation. The above modified silicon surface was im-
mersed in CH3OH and irradiated by UV for 30 min, and then dried
under a stream of N2 gas for CA evaluation. Then, the modified sili-
con surface was also irradiated by visible light for 30 min and dried
under a stream of N2 gas for CA evaluation.
Synthesis of organic compounds
Propinyl calix[4]arene C4AM: C4DT (2.4 mmol) was dissolved in
acetonitrile (150 mL), sodium methylate (2.8 mmol) was added, and
the mixture stirred and heated to reflux for 0.5 h. Subsequently,
propargyl bromide (0.5 mL) was added, and then the mixture was
stirred for 8 h. The crude product was purified by column chroma-
tography (SiO2, petroleum ether/chloroform 3/1) to give C4AM in
1
85% yield. H NMR (400 MHz, CDCl3): d=9.67 (s, 1H, ArOH), 9.08 (s,
2H, ArOH), 7.09–6.98 (m, 9H, ArH), 6.69 (s, 3H, ArH), 4.95 (s, 2H,
ArOCH2), 4.49–4.46 (d, J=13.2 Hz, 2H, ArCH2Ar), 4.29–4.25 (d, J=
18.9 Hz, 2H, ArCH2Ar), 3.49–3.46 (d, J=13.8 Hz, 4H, ArCH2Ar), 2.75
(s, 1H, CꢁCH); elemental analysis (%) calcd for C31H26O4: C 80.50, H
5.67; found: C 80.42, H 5.52.[14]
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (21372092, 21102051), Natural
Science Foundation of Hubei Province (2013CFA112) and self-
determined research funds of CCNU from the colleges’ basic
research and operation of MOE (CCNU13F005).
Dimethylamino calix[4]arene L: C4AM (1.0 mmol) was dissolved in
THF (40 mL) and then acetic acid (5.0 mmol) was added. Subse-
quently, dimethylamine (5.0 m mol) was dripped into the system.
Later, formaldehyde (5.0 m mol) was added and the mixture was
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Chem. Eur. J. 2014, 20, 1 – 6
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