Synthesis and photochromic properties of thiolated N-salicylidene-anilines on silver nanoparticles

Article abstract of DOI:10.1016/j.molstruc.2016.08.043

Here, we synthesized the salicylidene-aniline (anil) photochromes with thiol group (thiolated Schiff base) to modify silver nanoparticles (AgNPs) surface and their photochromic properties were described. A photochromic response related to the light induced tautomerization of the anils functionality along with bathochromic shift in the absorption band is observed in AgNPs surfaces. We have also examined that enol→keto photoisomerization rate by UV light for functionalized AgNPs are clearly faster than free anils.

Full text of DOI:10.1016/j.molstruc.2016.08.043

Accepted Manuscript
Synthesis and photochromic properties of thiolated N-salicylidene-anilines on silver
nanoparticles
Nosrat O. Mahmoodi, Nafiseh Aghajani, Atefeh Ghavidast
PII:
S0022-2860(16)30873-0
10.1016/j.molstruc.2016.08.043
MOLSTR 22869
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 4 April 2016
Revised Date: 11 July 2016
Accepted Date: 15 August 2016
Please cite this article as: N.O. Mahmoodi, N. Aghajani, A. Ghavidast, Synthesis and photochromic
properties of thiolated N-salicylidene-anilines on silver nanoparticles, Journal of Molecular Structure
(2016), doi: 10.1016/j.molstruc.2016.08.043.
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Graphical Abstract
Synthesis and photochromic properties of thiolated N-salicylidene-anilines on silver
nanoparticles
Nosrat O. Mahmoodi*, Nafiseh Aghajani, Atefeh Ghavidast

ACCEPTED MANUSCRIPT
Synthesis and photochromic properties of thiolated N-salicylidene-anilines
on silver nanoparticles
Nosrat O. Mahmoodi , Nafiseh Aghajani, Atefeh Ghavidast
Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box 41335-1914, Rasht, Iran
Abstract
Here, we synthesized the salicylidene-aniline (anil) photochromes with thiol group (thiolated Schiff
base) to modify silver nanoparticles (AgNPs) surface and their photochromic properties were
described. A photochromic response related to the light induced tautomerization of the anils
functionality along with bathochromic shift in the absorption band is observed in AgNPs surfaces. We
have also examined that enol→keto photoisomerization rate by UV light for functionalized AgNPs
are clearly faster than free anils.
Keywords: Photochromism, N-salicylidene-anilines (anils), Self-assembled monolayers (SAMs),
Silver nanoparticles, Surface plasmon resonance absorption (SPRA).
1. Introduction
A great deal of attention has been focused on functionalized nanoparticles (NPs) due to the
broad range of applications for which they are potentially useful [1-10]. As such, the searches
for new functional and responsive conjugated NPs continue to be a subject of interest.
Specifically, optically responsive NPs exhibiting photochromism properties are particularly
sought after for use in such applications as display technology, data storage, molecular
recognition applications and photo-switchable surface wettability [11-17]. Recently,
azobenzenes, diarylethenes, and spiropyrans are representative classes of photochromes that
have been successfully incorporated into NPs surfaces [18-25]. In our research group, we
developed 1,3-diazabicyclo[3.1.0]hex-3-ene, as a class of photochromic compound that is
somewhat less well known, with thiol, disulfide and azobenzene-thiol groups on AgNPs
surfaces [26-28]. The modified AgNPs showed a pronounced bathochromic shift in the
Corresponding author. Tel./fax: +98 1313233262.
E-mail addresses: mahmoodi@guilan.ac.ir, nosmahmoodi@gmail.com (N. O. Mahmoodi).
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absorption band of the open ring photoisomers and in the surface plasmon resonance
absorption (SPRA) of AgNPs. Furthermore, we have also observed that trans/cis and cis/trans
photoisomerization rate by UV light and thermally induced condition for functionalized
azobenzene AgNPs are noticeably faster than free ligands.
Based on these developments, we have synthesized another interesting class of
photochromic compounds including N-salicylidene-anilines (anils, Schiff bases) with thiol
group that used to form self-assembled monolayers on AgNPs surface, as shown in Scheme
1.
Scheme 1 Photochromic behavior of Ag-TSB 1
Photochromic properties of N-salicylidene-anilines, including colorability and thermal
bleaching, are highly dependent on the molecular conformation and crystalline environment
around the molecule. Until now, different methods such as chemical modification [29-34],
mixing with polymers [35-37], zeolites [38-40], mesoporous silica [41-43], cyclodextrins
[44], cationic host matrix [45,46], clathrates [47,48] and bile acids [49], confining in a metal
organic frame work (MOF) [50,51] and co-crystal formation through acid-base interactions
[52,53] have been reported to modify the N-salicylidene-anilines with an aim to change
photochromic reactivity. Therefore, here, for the first time, the photochromic behaviors of
thiolated N-salicylidene-anilines on AgNPs surface were studied. Modifying the surroundings
of thiolated Schiff bases (TSB) is indeed expected to impact the optical properties of the
molecular switch. The photochromic property for TSB is based on a tautomerization reaction
between the enol-imine and keto-enamine forms upon UV light irradiation [54-56]. As a
result of this, the proton transfer tautomer possesses significant differences in structure and
electronic configuration from its related normal species. Many important applications of these
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phenomena such as probes for solvation dynamics and biological environments, the
development of laser dyes, ultraviolet stabilizers, metal ion sensors and scintillator counters
are attributed to this rare photophysical property [57]. The incorporation of TSB molecules
on the AgNPs surface (Ag-TSB), leads to photo-responsive systems, which their properties
can be manipulated by light and can be applied as materials for surface enhanced
spectroscopy [58], optical filters [59], plasmonic devices [60], and sensitive optical chemical
and biological nanosensors [61].
2. Experimental
2.1. Materials and apparatus
The following reagents were purchased from Merck and used without further
modification: AgNO3 (99.9%), polyvinylpyrrolidone (PVP, K30, MW 40000), 4-
aminothiophenol and NaBH4 (99%). The 1H NMR spectra were obtained on a Bruker Avance
400 MHz spectrometer using CDCl3 as a solvent and tetramethylsilane as an internal
standard. Chemical shifts (δ) are reported in ppm and the coupling constants (J) are given in
Hertz (Hz). The UV-Vis absorption spectra in the range of 200-500 nm (EtOH or CHCl3, c =
1.0×10-4 M) were measured with a Shimadzu UV-2100 spectrometer. The photoinduced
(trans-keto photoisomer) was formed upon UV irradiation (Hg lamp DRSh-260+UV-
transmitting glass filters). Spectral data were obtained using quartz cuvettes with 1 cm optical
path length before and after UV irradiation for various times. The FT-IR spectra for the
samples were obtained using Shimadzu FT-IR-8900 spectrophotometer by using KBr pellets.
The X-ray diffraction (XRD) patterns were recorded in air at ambient temperature by Phillips
(pw-1840) X-ray diffractometer with Cu-Kα radiation source (λ = 1.54056 Å) at 40 KV
voltage and 25 mA current in a wide angle range (2θ = 10-70). The morphology and particle
sizes of synthesized powder were characterized by transmission electron microscope (TEM)
images. The TEM samples were prepared by suspending the nanoparticles in EtOH followed
by sonication for several minutes. One drop of the dilute nanoparticles/EtOH suspension was
placed on a carbon-coated holey TEM copper grid and was dried in air. The dried grid was
then loaded into a double tilt sample holder. The sample was then examined with a Philips
CM-20 STEM equipped with a Gatan UltraScan 1000 CCD camera and an energy dispersive
X-ray spectrometer: INCA Energy TEM 200. TEM images were taken at 200 KV.
2.2. General procedure for synthesis of thiolated Schiff bases (TSB 1-4)
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4-Aminothiophenol (0.29 g, 1 mmol) and 2-hydroxybenzaldehyde (0.11 mL, 1 mmol)
o
were added to absolute EtOH (3 mL) and the mixture was refluxed at 80 C for 3-6 h. The
precipitate obtained was filtered, washed with cool water and recrystallized in EtOH to afford
pure desired product.
2.3. 2-(((4-Mercaptophenyl)imino)methyl)phenol (TSB 1)
Yield (92%), M.P. 138-139 ˚C, red solid; IR (KBr, υ/cm-1): 3400 (O-H stretch), 1617
(imine C=N stretch), 2689 (S-H stretch), 1560 (aromatic C=C stretch), 1258 (C-O stretch),
1
838, 757 (aromatic out of plane bend). H NMR (400 MHz, CDCl3, ppm): δ 13.50 (s, 1H,
OH), 8.63 (s, 1H, CH=N), 7.37 (m, 2H, Ar-H), 7.25 (d, J = 8.8 Hz, 2H, Ar-H), 7.04 (d, J =
8.0 Hz, 1H, Ar-H), 6.98 (t, J = 8.8 Hz, 1H, Ar-H), 6.93 (d, J = 8.8 Hz, 2H, Ar-H), 5.18 (s,
1H, SH). UV-Vis (EtOH) λmax/nm: 275 (n→π*) and 348 (π→π*) nm before irradiation and
275 (n→π*), 348 (π→π*) and 425 (SPRAB) nm after irradiation. Anal. Calcd for
C13H11NOS: C, 68.09; H, 4.84; N, 6.11; Found: C, 68.41; H, 4.52; N, 6.16.
2.4. 2-(((2-Mercaptophenyl)imino)methyl)-6-methoxyphenol (TSB 2)
Yield 84%, M.P. 165-166 ˚C, yellow solid; IR (KBr, υ/cm-1): 3428 (O-H stretch), 2570 (S-
H stretch), 1609 (imine C=N stretch), 1564 (aromatic C=C stretch), 1247 (C-O stretch), 855,
1
727 (aromatic out of plane bend). H NMR (400 MHz, CDCl3, ppm): δ 10.35 (s, 1H, OH),
8.62 (s, 1H, CH=N), 7.44 (t, J = 8.0 Hz, 1H, Ar-H), 7.39 (d, J = 8.4 Hz, 1H, Ar-H), 7.36 (t, J
= 8.0 Hz, 1H, Ar-H), 7.26 (d, J = 8.3 Hz, 1H, Ar-H), 7.08 (d, J = 8.6 Hz, 1H, Ar-H), 7.03 (d,
J = 8.8 Hz, 1H, Ar-H), 6.99 (t, J = 8.4 Hz, 1H, Ar-H), 5.71 (s, 1H, SH), 3.94 (s, 3H, OCH3).
UV-Vis (EtOH) λmax/nm: 268 (n→π*) and 346 (π→π*) nm before irradiation and 268
(n→π*), 360 (π→π*) and 400 (SPRAB) nm after irradiation. Anal. Calcd for C14H13BrNO2S:
C, 64.84; H, 5.05; N, 5.40; Found: C, 64.41; H, 5.27; N, 5.44.
2.5. 2-(((4-Mercaptophenyl)imino)methyl)-6-methoxyphenol (TSB 3)
Yield 86%, M.P. 135-136˚C, red solid; IR (KBr, υ/cm-1): 3420 (O-H stretch), 2588 (S-H
stretch), 1615 (imine C=N stretch), 1506 (aromatic C=C stretch), 1258 (C-O stretch), 836,
1
729 (aromatic out of plane bend). H NMR (400 MHz, CDCl3, ppm): δ 13.91 (s, 1H, OH),
11.16 (s, 1H, SH), 8.64 (s, 1H, CH=N), 7.27 (m, 3H, Ar-H), 7.06 (m, 2H, Ar-H), 6.93 (d, J =
8.4 Hz, 2H, Ar-H), 3.96 (s, 3H, OCH3). UV-Vis (EtOH) λmax/nm: 275 (n→π*) and 362
(π→π*) nm before irradiation and 275 (n→π*), 362 (π→π*) and 425 (SPRAB) nm after
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irradiation. Anal. Calcd for C14H13BrNO2S: C, 64.84; H, 5.05; N, 5.40; Found: C, 64.53; H,
5.14; N, 5.32.
2.6. 2-(((2-Mercaptophenyl)imino)methyl)phenol (TSB 4)
Yield 85%, M.P. 173-174˚C, red solid; IR (KBr, υ/cm-1): 3425 (O-H stretch), 2357 (S-H
stretch), 1611 (imine C=N stretch), 1560 (aromatic C=C stretch), 1275 (C-O stretch), 845,
1
748 (aromatic out of plane bend). H NMR (400 MHz, CDCl3, ppm): δ 10.30 (s, 1H, OH),
8.53 (s, 1H, CH=N), 7.48 (t, J = 8.1 Hz, 1H, Ar-H), 7.42 (d, J = 8.4 Hz, 1H, Ar-H), 7.37-7.40
(m, J = 8.4 Hz, 3H, Ar-H), 7.05-7.07 (m, 2H, Ar-H), 6.92 (t, J = 8.3 Hz, 1H, Ar-H), 3.61 (s,
1H, SH). UV-Vis (EtOH) λmax/nm: 278 (n→π*) and 370 (π→π*) nm before irradiation and
278 (n→π*), 374 (π→π*) and 400 (SPRAB) nm after irradiation. Anal. Calcd for
C13H11NOS: C, 68.09; H, 4.84; N, 6.11; Found: C, 68.33; H, 4.64; N, 6.20.
2.7. Synthesis of Ag-TSB 1 and Ag-TSB 3
A solution of AgNO3 (0.082 g, 0.48 mmol) in ultrapure H2O (10 mL) was prepared. To
this solution were added 0.051 g PVP in 5.0 mL ultrapure H2O and then the mixture was
stirred heavily for 30 min in an ice bath under N2 gas. A solution of TSB 1 or TSB 3 (0.48
mmol) in EtOH (10 mL) was added to the reaction vessel, and then the mixture was stirred
for further 30 min. Subsequently, a solution of NaBH4 (0.018 g, 0.48 mmol) in ultrapure H2O
(6 mL) was added dropwise to the aqueous solution, the color of solution suddenly turned
brown, attributed to the formation of AgNPs. The color of the solution became dark brown
and then turned to black. On complete addition of NaBH4, the resulting mixture was further
stirred for 2 h at r.t under N2 gas. The suspension obtained was then centrifuged at 18,000
rpm for 15 min and the precipitate washed three times with double distilled H2O and EtOH to
remove any water soluble impurity and excess organic ligands. The UV-Vis test of the upper
layer solution after centrifuge of the functionalized NPs was applied to make sure all the free
compounds were washed away. The precipitate was then dried in oven at 60 °C for 4 h and
the gray powder was obtained.
2.8. Synthesis of Ag-TSB 2 and Ag-TSB 4
An aqueous solution of AgNO3 (0.082 g, 0.48 mmol) in ultrapure H2O (10 mL) was mixed
with 0.051g PVP in 5.0 mL ultrapure H2O. The mixture was stirred heavily for 30 min in an
ice bath under N2 gas. A solution of TSB 2 or TSB 4 (0.48 mmol) in CHCl3 (10 mL) was
added to the reaction vessel. The two-phase mixture was vigorously stirred for further 30
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min. A solution of NaBH4 (0.018 g, 0.48 mmol) in ultrapure H2O (6 mL) was added dropwise
to the below solution, the color of the aqueous phase suddenly turned bright yellow,
attributed to the formation of AgNPs. Then, the color of the aqueous phase turned to red. On
complete addition of NaBH4, the resulting mixture was further stirred for 4 h at r.t under N2
gas. In this period of time, all of the TSB ligands were transferred into the aqueous phase,
which became deep red and then turned to black color while the organic phase became
colorless. The organic layer was evaporated. The residue was poured into EtOH (50 mL) and
was kept in a refrigerator overnight. The obtained suspension was then centrifuged at 18,000
rpm for 15 min and the precipitate washed three times with double distilled H2O to remove
any water soluble impurity. After that, the precipitate formed was washed 2-3 times by
dispersion and centrifugation using CHCl3 to remove excess organic ligands. The precipitate
was then dried in oven at 60 °C for 8 h and the gray powder Ag-TSB 2 and Ag-TSB 4 was
obtained.
3. Results and discussion
In continuation to our prior works [26-28], herein, the thiolated Schiff base derivatives
(TSB) were synthesized and used to form self-assembled monolayers (SAMs) on AgNPs
surface via strong covalent S-Ag bond as shown in Scheme 2. In this effort, thiolated Schiff
base TSB 1-4 was prepared by the reaction of between salicylaldehyde 1-2 and
aminothiophenol 3-4 in EtOH (1:1 mmole/mmole) under reflux conditions for 3-6 h (Scheme
1). Subsequently, 1.0 equivalent solution of TSB 1 or TSB 3 in EtOH was added to 1
equivalent solution of AgNO3 in ultrapure H2O and PVP as a capping agent stirring under
stream of nitrogen gas. Subsequently, a modified Brust reaction [62] was carried out through
the addition of excess amount of NaBH4 as a reducing agent that led to the formation of the
self-assembled monolayer on the AgNPs. In order to reduce all of the Ag+ ions to metallic
silver the molar ratio of metal to the reducing agent was selected as 0.5:1. Thiolated Schiff
base TSB 2 and TSB 4 were insoluble in EtOH solution. To overcome agglomeration and
deposit issues, colloidal processing is done using solvent composition of CHCl3/H2O. The
prepared Ag-TSB nanostructures exhibit photoisomerization conversion in the EtOH
solution.
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R3
OH
R1
CHO
R2
NH2 dry EtOH
N
TSB 1: R1 = H, R2 = H, R3 = SH
+
1
2
3
TSB 2
TSB 3
TSB 4
: R = OMe, R = SH, R = H
R2
reflux
R1
1
2
3
HO
: R = OMe, R = H, R = SH
1: R1 = H
2: R1 = OMe
3: R1 = H, R2 = SH
4: R1 = SH, R2 = H
R1
1
2
3
: R = H, R = SH, R = H
TSB 1-4
AgNO3 / H2O
PVP / NaBH4
enol form
keto form
=
=
EtOH or CHCl3
UV
heat
AgNPs
AgNPs
Ag-TSB
Ag-TSB
(enol-imine form)
(keto-enamin form)
Scheme 2. Preparation of AgNPs capped with TSB derivatives and their photochromic performance.
3.1. FT-IR spectra
In Fig. 1 the FT-IR spectra of TSB 2 and Ag-TSB 2 were compared. In both spectra, the
similar signals in the CH- (aromatic) and CH2 (aliphatic) stretch regions at 3050 and 2932-
2836 cm-1 were observed. The signals at 1455, 1564, 3428 and 1609 cm-1 are attributed to the
asymmetric and symmetric stretch of C=C (aromatic), OH and C=N vibration, respectively.
The S-H stretching band of neat ligand TSB 2 was observed at 2570 cm-1. These data and the
absence of the S-H stretching mode in the FT-IR spectrum of Ag-TSB 2, indicate the
existence of TSB 2 on AgNPs surface [63]. Similar results were observed for FT-IR spectra
of other derivatives.
Fig. 1. FT-IR spectra of TSB 2 (balck line) and Ag-TSB 2 (red line).
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3.2. TEM imaging and XRD
The morphology of the Ag-TSB 1 was considered by TEM (Fig. 2a). The TEM image
shows that the particles are fairly uniform in diameter and spherical in shape and the
approximate size of the AgNPs was found to be in the range of < 40 nm, however, the NPs
tended to aggregate to large particle. The phase of the Ag-TSB 1 was also investigated by X-
ray diffraction technique. As shown in Fig. 2b; the resultant product has shown all the major
peaks of metallic silver with fcc structure. The mean crystallite diameter using Scherrer’s
formula was calculated to be 18.60 nm. This value is in good agreement with the TEM
image. The intensity of peaks reflected the high degree of crystallinity of the AgNPs.
Fig. 2. (a) The TEM image and (b) the XRD pattern of Ag-TSB 1.
3.3. UV-Vis absorption spectra
The irradiation time-dependent absorption spectra of compounds TSB 1-4 at 254 nm are
shown in Fig. 3. For the absorbance spectra of all synthesized compounds in either EtOH or
CHCl3, before light irradiation, the maximum absorption bond in the region of 268 nm ~ 278
nm and 346 nm ~ 370 nm was observed due to the n→π* and π→π* transitions of enol-imine
photoisomer, respectively. After the solutions were irradiated under UV light at 254 nm the
absorption intensities gradually were increased with the irradiation time and reached the
maximum values within 10-20 min due to the formation of the cis-keto photoisomer and
increase in their population growth. After more irradiation time for 20-50 min, the intensity
of absorption band at 346 nm ~ 370 nm significantly reduced and a peak at about 400 nm ~
430 nm (visible region) appeared. This implies that the trans-keto photoisomer has been
formed.
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Fig. 3. The UV-Vis spectra of (a) TSB 1 (in EtOH), (b) TSB 2 (in CHCl3), (c) TSB 3 (in EtOH) and
(d) TSB 4 (in CHCl3) before and after UV irradiation for various times (c = 1.0 × 10-4 M, 293 K).
Subsequently, the absorption spectra of functionalized AgNPs Ag-TSB 1, Ag-TSB 2, Ag-
TSB 3 and AgTSB 4 were recorded using EtOH at room temperature and are given in Fig. 4.
Before irradiation, the pale yellow solution of Ag-TSB, with a characteristic strong surface
plasmon resonance absorption band (SPRAB) for AgNPs at around of 360-387 nm and
electronic transitions of the enol-imine photoisomer at 272 nm ~ 285 nm and around of the of
SPRAB at 360 nm ~ 387 nm due to n→π* and π→π*, respectively, showed a red-shifted
compared to the absorption band of enol-imine photoisomer of free TSB. This shift attributed
to the chemical bonding of TSB on the AgNP surface and overlap between absorption bands
of enol-imine photoisomer with SPRAB. After irradiation for 30-40 min, similar to TSB
derivatives increase of absorption intensity was detected and on 40-50 min irradiation,
absorption band at 360 nm ~ 387 nm decreases and absorption band at 450-460 nm was
appeared.
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Fig. 4. The UV-Vis spectra of (a) Ag-TSB 1, (b) Ag-TSB 2, (c) Ag-TSB 3 and (d) Ag-TSB 4
before and after UV light irradiation for various times in EtOH (c = 1.0 × 10-4 M, 293 K).
Fig. 5 shows the kinetics of the photoisomerization of TSB 1 at 348 nm (Fig. 5a), TSB 2
at 346 nm (Fig. 5b), TSB 3 at 362 nm (Fig. 5c) and TSB 4 at 370 nm (Fig. 5d) via the
corresponding Ln[A]versus time plots and the rate constants were calculated to be 0.005
(min-1) for TSB 1, 0.004 (min-1) for TSB 2, 0.003 (min-1) for TSB 3 and 0.001 (min-1) for
TSB 4.
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Fig. 5. The growth of the cis-keto photoisomer of (a) TSB 1 at 348 nm, (b) TSB 2 at 346 nm, (c) TSB
3 at 362 nm and (d) TSB 4 at 370 nm.
Also, the kinetics of the photoisomerization of Ag-TSB 1 at 360 nm, Ag-TSB 2 at 387
nm, Ag-TSB 3 at 366 nm and Ag-TSB 4 at 386 nm via the corresponding Ln[A] versus time
plots were obtained and the rate constants were calculated to be 0.014 (min-1) for Ag-TSB 1,
0.013 (min-1) for Ag-TSB 2, 0.012 (min-1) for Ag-TSB 3 and 0.010 (min-1) for Ag-TSB 4 as
shown in Fig. 6. It is clear that a notably increasing at a constant rate of 3-10 times for AgNPs
functionalized in range of Ag-TSB 4 (10 times) > Ag-TSB 3 (4 times) > Ag-TSB 2 (3.25
times) > Ag-TSB 1 (2.8 times) was detected. The same phenomena previously were reported
in cis→trans photoisomerization in anchored azobenzenes [28,64].
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Fig. 6. The growth of the cis-keto photoisomer of (a) Ag-TSB 1 at 360 nm, (b) Ag-TSB 2 at 387 nm,
(c) Ag-TSB 3 at 366 nm and (d) Ag-TSB 4 at 386 nm.
We have also studied the thermally induced isomerization of photochromic materials. The
change in absorption over time for all compounds in EtOH or CHCl3 solution that had been
isomerized by remaining in the oven at 55 oC are shown in Fig.7 and Fig. 8. The intensity of
absorption band at about 400 nm ~ 430 nm (visible region) for TSB 1-4 and at 450-460 nm
for Ag-TSB 1-4 significantly reduced by heating at 55 °C for 20 and 30 min, respectively.
This implies that the enol-imine photoisomer has been formed. According to Fig. 8, a
comparative decrease in rate of thermal bleaching observed in Ag-TSB nanostructures,
probably due to a steric hindrance in the keto-enol tautomerization of the TSB undergoing
thermal isomerization. A more available volume space around the switching unit is a major
reason that causes relative acceleration rate of the thermally bleaching to free TSB ligands
[65].
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Fig. 7. The thermal bleaching of (a) TSB 1 (in EtOH), (b) TSB 2 (in CHCl3), (c) TSB 3 (in EtOH)
and (d) TSB 4 (in CHCl3) before and after heating in oven for 20 min (c = 1.0 × 10-4 M).
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Fig. 8. The thermal bleaching of (a) Ag-TSB 1 (in EtOH), (b) Ag-TSB 2 (in CHCl3), (c) Ag-TSB 3
(in EtOH) and (d) Ag-TSB 4 (in CHCl3) before and after heating in oven for 30 min (c = 1.0 × 10-4
M).
4. Conclusion
Here, thiolated Schiff base derivatives (TSB) were successfully applied as a functional
agent on AgNPs surfaces and photochromic properties of Ag-TSB NPs have been
considered. The UV-Vis experiments demonstrated that enol→keto photoisomerization rate
with 265 nm light for Ag-TSB nanostructures are noticeably faster than free ligand TSB. The
electronic transitions of Ag-TSB were also shifted as a result of chemical bonding and
overlap between absorption bands of TSB with SPRAB of AgNPs. Therefore, incorporation
of Schiff base derivatives with NPs is very useful to control the photochromic property, and
can lead to the development of new functional tunable materials. This persuades us to
investigate the optical properties of this molecular switch on the other NPs surface for future
works.
Acknowledgments
This study was supported in part by the Research Committee of University of Guilan &
Iranian Nanotechnology Initiative Council (INIC).
Supporting information
The 1H NMR of TSB 1 and TSB 3 are available in supporting information.
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Highlights:
•
•
•
Self-assembly of thiolated Schiff base on AgNPs.
Salicylidene-anilines joined with surface plasmon resonance absorption of AgNPs.
Bathochromic shift in the surface plasmon resonance absorption (SPRA) of AgNPs.