Photochromism of azobenzene-thiol-1,3-diazabicyclo-[3.1.0]hex-3-ene on silver nanoparticles

Article abstract of DOI:10.1016/j.dyepig.2015.03.014

Abstract The new azobenzene-thiol terminated photochromic derivatives is designed, synthesized and used to form self-assembled monolayers on silver nanoparticles. The photochromic behavior of 1,3-diazabicyclo-[3.1.0]hex-3-ene joined with surface plasmon r

Full text of DOI:10.1016/j.dyepig.2015.03.014

Dyes and Pigments 118 (2015) 110e117
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Photochromism of azobenzene-thiol-1,3-diazabicyclo-[3.1.0]hex-3-
ene on silver nanoparticles
Nosrat O. Mahmoodi*, Atefeh Ghavidast, Safoura Mirkhaef, Mohammad Ali Zanjanchi
Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box 41335-1914, Rasht, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The new azobenzene-thiol terminated photochromic derivatives is designed, synthesized and used to
form self-assembled monolayers on silver nanoparticles. The photochromic behavior of 1,3-diazabicyclo-
[3.1.0]hex-3-ene joined with surface plasmon resonance absorption band of silver nanoparticles and
photoisomerisable azobenzene is presented. The ultravioletevisible experiments demonstrated that
electronic transitions of functionalized silver nanoparticles were shifted as a result of chemical bonding
and overlap between absorption bands of photochromic ligands with surface plasmon resonance ab-
sorption band of silver nanoparticle. Furthermore, we have also observed that trans/cis and cis/trans
photoisomerization rate by ultraviolet light and thermally induced condition for functionalized silver
nanoparticles are noticeably faster than free ligands.
Received 6 October 2014
Received in revised form
4 March 2015
Accepted 11 March 2015
Available online 14 March 2015
Keywords:
Photochromism
Azobenzene-thiol
1,3-Diazabicyclo[3.1.0]hex-3-ene
Silver nanoparticles
Self-assembled monolayers
Photoisomerization rate
© 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Recently, our group reported photochromism of 1,3-
diazabicyclo[3.1.0]hex-3-ene with thiol and disulfide groups on
The self-assembly of photo-responsive molecules on metal
nanoparticles (MNPs) surface has received significant attention
in recent years because provides the opportunity of using
switching devices as photo-responsive components in optical
storage, molecular recognition applications and photo-
switchable surface wettability [1e10]. Among these molecules,
azobenzene derivatives are most studied due to their higher
quantum yields of the photoisomerization in solution, simple
molecular structures and relatively good stability of both iso-
mers. These molecules demonstrate a transition from trans
configuration to cis configuration upon exposure to UV light and
a reversible isomerization under Vis light [2,11]. There has been a
significant interest in the properties of azobenzene derivatives in
self-assembled monolayers on surfaces. The photochemical and
electrochemical reactivity of these systems also have been
studied [12e23].
AgNPs surfaces [24,25]. The modified AgNPs showed a pronounced
bathochromic shift either in the absorption band of the open ring
photoisomers as well in the surface plasmon resonance absorption
(SPRA) of AgNPs. Several studies on AgNPs capped with other
photochromic molecules were reported and the correlation be-
tween the SPRAB and the photochemical property of the photo-
chromic ligands were investigated [26e32]. Here, we are interested
to convert the whole nanoparticle as a switch via attaching an
interacting photochromic molecule to nanoparticles [14,16].
In this study, AgNPs were immobilized with premade photo-
chromic thiol-terminated 1,3-diazabicyclo[3.1.0]hex-3-ene con-
tained an azobenzene functional group Az-TTP and their
photochromic behavior was studied. The Az-TTP derivatives
designed with two different photochromic units in the molecule
can serve as multicolor photochromic materials [33]. Photo-
isomerization of these photochromic compounds is illustrated
in Fig. 1. In Az-TTP ligands a reversible switching reaction
occurred between the close-E-photoisomer into the open-E-
photoisomer and open-Z-photoisomer under UV irradiation. The
latter, upon remaining in the oven or storage in the dark, un-
dergoes the reverse rearrangement to the Az-TTP close-E starting
form.
* Corresponding author. Tel./fax: þ98 133 333 3262.
E-mail
addresses:
mahmoodi@guilan.ac.ir,
nosmahmoodi@gmail.com
(N.O. Mahmoodi).
http://dx.doi.org/10.1016/j.dyepig.2015.03.014
0143-7208/© 2015 Elsevier Ltd. All rights reserved.

N.O. Mahmoodi et al. / Dyes and Pigments 118 (2015) 110e117
111
O stretch), 1618, 1568 (aromatic C]C stretch), 1478 (N]N stretch),
1280 (CeO stretch). 1H NMR (400 MHz, CDCl3)
: 7.15 (d, 1H,
d
J ¼ 8.8 Hz), 7.48e7.57 (m, 3H), 7.93 (dd, 2H, J ¼ 8.4, 1.2 Hz), 8.21 (dd,
1H, J ¼ 8.8, 2.4 Hz), 8.23 (d,1H, J ¼ 2.4 Hz),10.06 (s,1H),11.35 (s,1H).
Anal. Calcd for C13H10N2O2: C, 69.02; H, 4.46; N, 12.38; Found: C,
69.41; H, 4.62; N, 12.76.
2.3. (E)-2-(4-Bromobutoxy)-5-(phenyldiazenyl)benzaldehyde (2)
(E)-2-hydroxy-5-(phenyldiazenyl)benzaldehyde
3
(2.26 g,
10 mmol), 1,4-dibromobutane (7.1 mL, 60 mmol) and KOH (1.12 g,
20 mmol) were added to absolute EtOH (150 mL) and the mixture
was refluxed at 90 ꢂC for 24 h under N2. The EtOH was removed
under reduced pressure. The resulting dark brown residue was
dissolved in 200 mL of n-hexane and precipitate was filtered off.
The excess amount of MeOH was added to orange filtrate solution
and cooled in deepfreeze overnight. The orange precipitate was
collected and recrystalized using toluene and MeOH to yield orange
solid 2 (1.52 g, 42%). M.p.: 145e147 ꢂC. 1H NMR (500 MHz, CDCl3):
Fig. 1. Photochromic performance of Az-TTP close-E to Az-TTP open-Z.
d
1.83e1.94 (m, 4H), 3.44 (t, 2H, J ¼ 5.9 Hz), 4.14 (t, 2H, J ¼ 6.7 Hz),
7.17 (d, 1H, J ¼ 8.2 Hz), 7.55 (t, 1H, J ¼ 7.5 Hz), 7.60 (t, 2H, J ¼ 6.9 Hz),
7.92 (d, 2H, J ¼ 7.6 Hz), 8.19 (s, 1H), 8.24 (d, 1H, J ¼ 7.9 Hz), 10.05 (s,
1H). Anal. Calcd for C17H17BrN2O2: C, 56.52; H, 4.74; N, 7.75; Found:
C, 56.31; H, 4.57; N, 7.44.
2. Experimental
2.1. Materials and apparatus
2.4. (E)-2-(4-Mercaptobutoxy)-5-(phenyldiazenyl)benzaldehyde
(1)
The following reagents were purchased from Merck and used
without further modification: AgNO3 (99.9%), H2NCSNH2 (99%),
polyvinylpyrrolidone (PVP, K30, MW 40,000) and NaBH4 (99%).
The 1H NMR spectra were obtained on a Bruker Avance 500 and
400 MHz spectrometer. The UVeVis absorption spectra in the
range of 200e800 nm (EtOH, C ¼ 1.0 ꢀ 10ꢁ4 M) were measured
A solution of (E)-2-(4-bromobutoxy)-5-(phenyldiazenyl)benz-
aldehyde 3 (0.21 g, 0.57 mmol) and thiourea (0.22 gg, 2.89 mmol) in
EtOH (10 mL) was heated under reflux for 12 h. After cooling down
to r.t, a solution of KOH (0.19 g, 3.47 mmol) in water (10 mL) was
then added into the reaction mixture and continued to reflux for
another 3 h. The reaction mixture acidified (pH ¼ 1) by addition of
diluted HCl (1 N) and then was extracted twice with Et2O. The
organic phase was combined, washed with brine, dried over MgSO4
and removed. The crude residue was chromatographed over silica
gel using a mixture of EtOAc/hexane (1:5) to give thiol 1 as a viscose
with
a Shimadzu UV-2100 spectrometer. The photoinduced
(open-Z-photoisomer) was formed upon UV irradiation (Hg
lamp DRSh-260þUV-transmitting glass filters). The FTeIR
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 a wide angle range
liquid (0.12 g, 65%). 1H NMR (500 MHz, CDCl3):
d 1.41 (t, 1H,
(2
Cu-K
q
¼ 10e70) by Phillips (pw-1840) X-ray diffractometer with
J ¼ 7.4 Hz), 1.65e1.84 (m, 4H), 2.55 (q, 2H, J ¼ 7.5 Hz), 4.12 (t, 2H,
J ¼ 7.6 Hz), 7.15 (d, 1H, J ¼ 8.1 Hz), 7.52 (t, 1H), 7.57 (t, 2H, J ¼ 7.2 Hz),
7.93 (d, 2H, J ¼ 7.9 Hz), 8.18 (s, 1H), 8.22 (d, 1H, J ¼ 7.9 Hz), 9.90 (s,
1H). Anal. Calcd for C17H18N2O2S: C, 64.94; H, 5.77; N, 8.91; Found:
C, 64.24; H, 5.37; N, 8.71.
a
radiation. The morphology and particle sizes of synthe-
sized powder were characterized by transmission electron mi-
croscope (TEM) images on a Phillips CM-10 instrument with an
accelerating voltage of 100 kV.
2.2. (E)-2-Hydroxy-5-(phenyldiazenyl)benzaldehyde (3)
2.5. (E)-4-(2-(6-(4-Nitrophenyl)-4-phenyl-1,3-diazabicyclo[3.1.0]
hex-3-en-2-yl)-4-(phenyldiazenyl)phenoxy)butane-1-thiol (Az-TTP
1)
Aniline (0.28 g, 3 mmol), water (1.5 mL) and HCl (2.5 mL, 37%)
were stirred for 5 min in an ice bath to give an amine salt. To this
mixture, sodium nitrite (0.21 g, 3 mmol) dissolved in water
(1.0 mL), after cooling to 0e5 ꢂC, was added dropwise over 15 min.
The mixture was stirred for 30 min in an ice bath to obtain colorless
diazonium salt solution. In a second flask, salicylaldehyde (0.32 mL,
3 mmol) was dissolved in water (15 mL) containing sodium hy-
droxide (0.12 g, 3.0 mmol) and sodium carbonate (2.2 g, 21 mmol)
and cooled to 0 ꢂC in an ice bath. The diazonium solution was
slowly added to the phenolate solution over 30 min. The solution
was stirred at 0 ꢂC for 1 h, during which a brown precipitate
formed, and then was stirred for 7 h at room temperature. The
precipitate was collected and was washed with water and then was
poured into water and acidified (pH ¼ 6e7) by addition of diluted
HCl. The precipitate obtained was filtered, washed with cool water
and recrystallized in EtOH to afford desired product as a brown
solid 3 (53 g, 78%). M.p.: 128e129 ꢂC. IR (KBr, cmꢁ1): 3200 (OeH
stretch), 3030 (aromatic CeH stretch), 1660 (aromatic aldehyde C]
3-(4-Nitrophenyl)aziridin-2-yl (phenyl)methanone
7
[34]
(0.26 g, 1 mmol), 2 (0.31 g, 1 mmol) and NH4OAc (0.4 g, 5 mmol)
were dissolved in 2 mL of DMF and stirred at r.t. The reaction was
completed after overnight. The reaction mixture was filtered,
washed with EtOH and dried in air to give orange solid 1 (0.43 g,
76%), M.p.: 168e170 ꢂC. IR (KBr, cmꢁ1): 3066 (aromatic CeH
stretch), 2946e2841 (aliphatic CeH stretch), 2558 (eSH stretch),
1598 (C]N stretch), 1510 (NO2 asymmetric stretch), 1500 (aromatic
C]C stretch), 1465 (N]N stretch), 1342 (NO2 symmetric stretch),
1286 and 1248 (CeO stretch), 739, 691 (aromatic out of plane
bend). 1H NMR (500 MHz, CDCl3):
d
1.63 (t, 1H, J ¼ 7.5 Hz), 1.78 (m,
2H), 1.94e1.97 (m, 2H), 2.61e2.68 (m, 2H), 2.74 (s, 1H), 3.98 (s, 1H),
4.12 (t, 2H, J ¼ 6.6 Hz), 6.84 (s,1H), 7.06 (d,1H, J ¼ 8.2 Hz), 7.43 (t,1H,
J ¼ 7.6 Hz), 7.48 (t, 2H, J ¼ 7.3 Hz), 7.55e7.61 (m, 3H), 7.63e7.67 (m,
2H), 7.75 (d, 2H, J ¼ 7.9 Hz), 7.87 (d, 2H, J ¼ 8.4 Hz), 7.98 (d, 2H,
J ¼ 8.8 Hz), 8.25 (d, 2H, J ¼ 8.8 Hz). UVeVis (EtOH) lmax/nm: 265,

112
N.O. Mahmoodi et al. / Dyes and Pigments 118 (2015) 110e117
Scheme 1. Preparation of AgNPs capped.
Fig. 2. (a,b) The TEM image of Ag-Az-TTP 1 and Ag-Az-TTP 2, respectively and (c,d) XRD patterns of Ag-Az-TTP 1 and Ag-Az-TTP 2, respectively.
387 nm before and after irradiation. Anal. Calcd for C32H29N5O3S: C,
68.19; H, 5.19; N, 12.42; Found: C, 68.11; H, 5.36; N, 12.91.
stretch), 2555 (-SH stretch), 1598 (C]N stretch), 1529 (NO2 asym-
metric stretch), 1480 (aromatic C]C stretch and N]N stretch),
1347 (NO2 symmetric stretch), 1251 (CeO stretch), 731, 688 (aro-
2.6. (E)-4-(2-(6-(3-Nitrophenyl)-4-phenyl-1,3-diazabicyclo[3.1.0]
matic out of plane bend). 1H NMR (500 MHz, CDCl3):
d 1.64 (t, 1H),
hex-3-en-2-yl)-4-(phenyldiazenyl)phenoxy)butane-1-thiol (Az-TTP
2)
1.78e1.84 (m, 2H), 1.97 (m, 2H), 2.51e2.55 (m, 2H), 2.70 (s, 1H), 3.97
(s, 1H), 4.13 (t, 2H, J ¼ 6.7 Hz), 6.84 (s, 1H), 7.07 (d, 1H, J ¼ 8.0 Hz),
7.43 (t,1H, J ¼ 7.8 Hz), 7.48 (t, 2H, J ¼ 7.8 Hz), 7.56e7.61 (m, 3H), 7.64
(t, 1H, J ¼ 7.7 Hz), 7.72 (d, 1H, J ¼ 7.7 Hz), 7.76 (d, 2H, J ¼ 7.7 Hz), 7.88
(t, 1H, J ¼ 7.3 Hz), 8.01 (d, 2H, J ¼ 7.8 Hz), 8.09 (s, 1H), 8.21 (d, 1H,
Yield: 72% (0.41 g), M.p.: 174e176 ꢂC, yellow solid. IR (KBr,
cmꢁ1): 3077 (aromatic CeH stretch), 2978e2838 (aliphatic CeH

N.O. Mahmoodi et al. / Dyes and Pigments 118 (2015) 110e117
113
3. Results and discussion
The new azobenzene-thiol-1,3-diazabicyclo-[3.1.0]hex-3-ene
derivatives (Az-TTP) were synthesized and used to form self-
assembled monolayers (SAMs) on AgNPs surface as shown in
Scheme 1. In this effort, aniline 4 was reacted with NaNO2 in
aqueous HCl to give diazonium salt followed by coupling with
salicylaldehyde to obtain azosalicylaldehyde 3. The azosalicy-
laldehyde 3 was alkylated with an excess of 1,4-dibromobutane to
obtain the brominated product 2. The brominated product 2 was
converted to thiol 1 by reacting with thiourea in basic media.
Reaction of thiol 1 with premade ketoaziridine 5 or 6 [34] in the
presence of excess NH4OAc and DMF afforded the desired Az-TTP
1 and Az-TTP 2, respectively. Then, 1.0 equivalent solution of Az-
TTP derivatives in toluene was added to 1 equitant solution of
AgNO3 in ultrapure H2O and PVP as a capping agent stirring under
stream of nitrogen gas. Subsequently, a modified Brust reaction
[35] 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
Agþ ions to metallic silver the molar ratio of metal to the reducing
agent was selected as 0.5:1. The prepared Ag-Az-TTP 1 and Ag-Az-
TTP 2 exhibit reversible photochromic conversion in the EtOH
solution.
Fig. 3. FTeIR spectra of Az-TTP 1 (black line) and Ag-Az-TTP 1 (red line). (For inter-
pretation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
J ¼ 7.6 Hz), 8.26 (s, 1H). UVeVis (EtOH) lmax/nm: 254, 373 nm
before and after irradiation. Anal. Calcd for C32H29N5O3S: C, 68.19;
H, 5.19; N, 12.42; Found: C, 68.45; H, 5.71; N, 12.23.
2.7. Synthesis of Ag-Az-TTP 1 and Ag-Az-TTP 2
An aqueous solution of AgNO3 (0.082 g, 0.48 mmol) in ultrapure
H2O (10 mL) was mixed with 0.051 g 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 Az-TTP 1 or Az-TTP 2 (0.27 g, 0.48 mmol) in
toluene (10 mL) was added to the reaction vessel. The two-phase
mixture was vigorously stirred for further 30 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
photochromic ligand was 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 centri-
fuged at 18,000 rpm for 15 min and the precipitate washed three
times with double distilled H2O to remove any water soluble im-
purity. After that, the precipitate formed was washed 2e3 times by
dispersion and centrifugation using toluene to remove excess
organic ligand. The precipitate was then dried in oven at 60 ꢂC for
8 h and the black powder Ag-Az-TTP 1 and Ag-Az-TTP 2 was
obtained.
3.1. TEM imaging and XRD
The morphology of the Ag-Az-TTP 1 and Ag-Az-TTP 2 were
investigated by TEM (Fig. 2a and b). 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. The phase of the Ag-Az-TTP 1 and Ag-Az-TTP 2 was
investigated by X-ray diffraction technique. As shown in Fig. 2c
and d; 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 24 and 26 nm,
respectively. This value is in good agreement with the TEM image.
The intensity of peaks reflected the high degree of crystallinity of
the AgNPs.
3.2. FT-IR spectra
In Fig. 3 the FTeIR spectra of Az-TTP 1 and Ag-Az-TTP 1 were
compared. In both spectra, the similar signals in the CHe (aromatic)
and CH2 (aliphatic) stretch regions at 3066 and 2946e2841 cmꢁ1 of
Az-TTP 1 and 3066 and 2946e2841 cmꢁ1 of Ag-Az-TTP 1 were
observed. The signals at 1510, 1342, 1465 and 1598 cmꢁ1 are
attributed to the asymmetric and symmetric stretch of NO2, N]N
Fig. 4. The UVeVis spectra of (a) Az-TTP 1 and (b) Az-TTP 2 before and after UV light irradiation for various times in EtOH (C ¼ 1.0 ꢀ 10ꢁ4 M, 293 K).

114
N.O. Mahmoodi et al. / Dyes and Pigments 118 (2015) 110e117
Table 1
photoisomer. After the Az-TTP 1 solution was irradiated under UV
light at 254 nm for 20 s (Fig. 4a), the absorption intensity at 265 and
387 nm increased. This attributed to the formation of the open-E-
photoisomer. The open photoisomer band of bicyclic aziridinesis
typically near 400 nm [37e40], that also corresponds to the n / p*
transition of the N]N bond in azobenzene. Following subsequent
irradiation under UV light for 80 s, the absorption peak intensity at
265 and 387 nm in the solution increased again (orange line (in web
version)) due to the increase of population of open-E-photoisomer
(Fig.1). After irradiation for 30 min, the absorption peak intensity at
387 nm increased again. Conversely, absorption peak intensity at
265 nm simultaneously decreased. This implies that the open-Z-
photoisomer has been formed. Further irradiation for 60 min, the
intensity of absorption band at 265 nm significantly reduced. When
comparing the spectra of Fig. 4a and b, similar behavior for Az-TTP
2 was observed. While, the azomethine ylide form of Az-TTP 1 is
more stabilized than that of Az-TTP 2 due to the p-NO2 conjugation
effect, which account for the longer wavelength of the visible range
absorption maximum (Table 1).
UVeVis absorption data for photochromic new
compounds.
Entry
lmax (nm)
Azo-TTP 1
Azo-TTP 2
Ag-Az-TTP 1
Ag-Az-TTP 2
265, 387
254, 373
262, 413
259, 402
and C]N vibration, respectively. The SeH stretching band of neat
ligand Az-TTP 1 was observed at 2558 cmꢁ1. These data and the
absence of the SeH stretching mode in the FT-IR spectrum of Ag-
Az-TTP 1, indicate the existence of Az-TTP 1 on AgNPs surface [36].
Similar results were observed for FTeIR spectra of Az-TTP 2 and Ag-
Az-TTP 2 (see supplementary data).
3.3. UVeVis absorption spectra
Fig. 4 shows the UVeVis spectra of Az-TTP 1 and Az-TTP 2
through irradiation with UV light at 254 nm for various times in
EtOH. Before light irradiation, the maximum absorption at 265 and
387 nm for Az-TTP 1 and 254 and 373 nm for Az-TTP 2 was
In Fig. 5 the absorption spectra for both of Ag-Az-TTP 1 and Ag-
Az-TTP 2 in EtOH are shown. Before irradiation, the yellow color
solution of Ag-Az-TTP 1, with a characteristic strong surface plas-
mon resonance absorption band (SPRAB) for AgNPs at 413 nm and
observed due to the
p /
p* and n / p* transitions of close-E-
Fig. 5. The UVeVis spectra of (a) Ag-Az-TTP 1 and (b) Ag-Az-TTP 2 before and after UV light irradiation for various times in EtOH (C ¼ 1.0 ꢀ 10ꢁ4 M, 293 K).
Fig. 6. The growth of the open-Z photoisomer of (a) AZ-TTP 1 at 387 nm, (b) Az-TTP 2 at 373 nm, (c) Ag-Az-TTP 1 at 413 nm and (d) Ag-Az-TTP 2 at 402 nm.

N.O. Mahmoodi et al. / Dyes and Pigments 118 (2015) 110e117
115
Fig. 7. The UVeVis absorption spectra of (a) Az-TTP 1, (b) Az-TTP 2, (c) Ag-Az-TTP 1 and (d) Ag-Az-TTP 2 before and after remaining in the oven at 60 ꢂC for various times in EtOH
(C ¼ 1.0 ꢀ 10ꢁ4 M).
Fig. 8. The growth of the close-E photoisomer of (a) AZ-TTP 1 at 387 nm, (b) Az-TTP 2 at 373 nm, (c) Ag-Az-TTP 1 at 413 nm and (d) Ag-Az-TTP 2 at 402 nm.
electronic transitions of the trans isomer at 262 nm and around of
the SPRAB due to * showed a red-shifted
p* and n /
compared to the absorption band of close-E-photoisomer of free
Az-TTP 1. This shift attributed to the chemical bonding of Az-TTP 1
on the AgNP surface and overlap between absorption bands of
close-E-photoisomer with SPRAB. After irradiation for 10 and 20 s,
similar to Az-TTP 1 increase of absorption intensity was detected
and on 30e50 s irradiation, absorption intensity band at 262 nm
decreases and absorption intensity band at 413 nm increases. These
results demonstrated that Ag-Az-TTP 1 carried out very fast
trans/cis photoisomerization with 265 nm light within 30e50 s.
The same phenomena previously were reported [15,41]. Similar
p
/
p

116
N.O. Mahmoodi et al. / Dyes and Pigments 118 (2015) 110e117
behavior for Ag-Az-TTP 2 was observed. The intensity of absorption
spectra in Ag-Az-TTP was small (Fig. 5 vs. Fig. 4). This suggests that
the formation of open-E-photoisomer and open-Z-photoisomer of
Az-TTP was heavily quenched by AgNPs due to the energy transfer
from the Az-TTP to the AgNPs and the overlap between absorption
of Az-TTP and SPRAB of AgNPs [28].
Fig. 6 shows the kinetics of the photoisomerization of AZ-TTP
1 at 387 nm (Fig. 6a), Az-TTP 2 at 373 nm (Fig. 6b), Ag-Az-TTP 1
at 413 nm (Fig. 6c) and Ag-Az-TTP 2 at 402 nm (Fig. 6d) via the
corresponding Ln[A] versus time plots and the rate constants
were calculated to be 0.008 (sꢁ1) for Az-TTP 1, 0.009 (sꢁ1) for Az-
TTP 2 and 0.012 and 0.011 (sꢁ1) for Ag-Az-TTP 1 and Ag-Az-TTP
2, respectively. It is clear that an increase in rate (1.5 times) oc-
curs when photochromic ligands are anchored on the AgNP
surface.
References
[1] Edel JB, Kornyshev AA, Urbakh M. Self-assembly of nanoparticle arrays for use
as mirrors, sensors, and antennas. ACS Nano 2013;7:9526e32.
[2] Ichimura K, Oh SK, Nakagawa N. Light-driven motion of liquids on a photo-
resistive surface. Science 2000;288:1624e6.
[3] Zhang X, Wen Y, Li Y, Li G, Du S, Guo H, et al. Molecularly controlled modu-
lation of conductance on azobenzene monolayer-modified silicon surfaces.
J Phys Chem C 2008;112:8288e93.
[4] Werts MHV, Allix F, Francais O, Frochot C, Griscom L, Le Pioufle B, et al.
Manipulation and optical detection of colloidal functional plasmonic nano-
structures in microfluidic systems. IEEE J Sel Top Quant Electron 2014;20:
6900613e24.
[5] Dietrich P, Michalik F, Schmidt R, Gahl C, Mao G, Breusing M, et al. An
anchoring strategy for photoswitchable biosensor technology: azobenzene-
modified SAMs on Si (111). Appl Phys A 2008;93:285e92.
[6] Kamenjicki M, Lednev IK, Asher SA. Photoresponsive azobenzene photonic
crystals. J Phys Chem B 2004;108:12637e9.
[7] Joshi GK, Blodgett KN, Muhoberac BB, Johnson MA, Smith KA, Sardar R. Ul-
trasensitive photoreversible molecular sensors of azobenzene-functionalized
plasmonic nanoantennas. Nano Lett 2014;14:532e40.
[8] Ferri V, Elbing M, Pace G, Dickey MD, Zharnikov M, Samori P, et al. Light-
powered electrical switch based on cargo-lifting azobenzene monolayers.
Angew Chem Int Ed 2008;47:3407e9.
[9] Delorme N, Bardeau JF, Bulou A, Poncin-Epaillard F. Azobenzene-con-
taining monolayer with photoswitchable wettability. Langmuir 2005;21:
12278e82.
[10] Wan P, Jiang Y, Wang Y, Wang Z, Zhang X. Tuning surface wettability through
photocontrolled reversible molecular shuttle. Chem Commun 2008;44:
5710e2.
[11] Motta SD, Avellini T, Silvi S, Venturi M, Ma X, Tian H, et al. Photophysical
properties and conformational effects on the circular dichroism of an
azobenzene-cyclodextrin [1] rotaxane and its molecular components. Chem
Eur J 2013;19:3131e8.
[12] Sidhaye DS, Kashyap S, Sastry M, Hotha S, Prasad BLV. Gold nanoparticle
networks with photo-responsive interparticle spacings. Langmuir 2005;21:
7979e84.
[13] Shankar BV, Patnaik A. Surface pressure driven supramolecular architectures
from mixed H-aggregates of dye-capped azobenzene derivative. Langmuir
2006;22:4758e65.
[14] Ahonen P, Schiffrin DJ, Paprotny J, Kontturi K. Optical switching of coupled
plasmons of Ag-nanoparticles by photoisomerisation of an azobenzene ligand.
Phys Chem Chem Phys 2007;9:651e8.
We have also studied the thermally induced isomerization of
photochromic materials. The change in absorption over time for all
compounds in EtOH solution that had been isomerized by
remaining in the oven at 60 ꢂC is shown in Fig. 7. The
p /
p* ab-
sorption band of the close-E photoisomer gains intensity, while the
n / p* band of the open-Z photoisomer loses intensity. The ki-
netics of the thermally isomerization of AZ-TTP 1 at 387 nm
(Fig. 8a), Az-TTP 2 at 373 nm (Fig. 8b), Ag-Az-TTP 1 at 413 nm
(Fig. 8c) and Ag-Az-TTP 2 at 402 nm (Fig. 8d) via the corresponding
Ln[A] versus time plots were obtained and the rate constants were
calculated to be 0.003 (minꢁ1) for Az-TTP 1 and Az-TTP 2 and 0.013
and 0.019 (minꢁ1) for Ag-Az-TTP 1 and Ag-Az-TTP 2, respectively. A
notably increase in constant rate (5e6 times) for AgNPs function-
alized was detected. Therefore, both of clos-E / open-Z photo-
isomerization rate and open-Z / close-E thermal isomerization
rate become accelerated when Az-TTP is anchored on the AgNPs
surface.
The maximum absorption wavelength of Az-TTP 1, Az-TTP 2,
Ag-Az-TTP 1 and Ag-Az-TTP 2 in EtOH are shown in Table 1.
[15] Shin Kh, Shin EJ. Photoresponsive azobenzene-modified gold nanoparticle.
Bull Korean Chem Soc 2008;29:1259e62.
[16] Ahonen P, Laaksonen T, Schiffrinc DJ, Kontturi K. Photoswitching electron
transport properties of an azobenzene containing Thiol-SAM. Phys Chem
Chem Phys 2007;9:4898e901.
[17] Manna A, Chen PL, Akiyama H, Wei TX, Tamada K, Knoll W. Optimized pho-
toisomerization on gold nanoparticles capped by unsymmetrical azobenzene
disulfides. Chem Mater 2003;15:20e8.
[18] El Khoury JM, Zhou X, Qu L, Dai L, Urbas A, Li Q. Organo-soluble photo-
responsive azo thiol monolayer-protected gold nanorods. Chem Commun
2009:2109e11.
[19] Suda M, Kameyama N, Ikegami A, Suzuki M, Kawamura N, Einaga Y. Size
reduction induced ferromagnetism and photo-magnetic effects in
azobenzene-thiol-passivated gold nanoparticles. Polyhedron 2009;28:
1868e74.
[20] Kumar AS, Ye T, Takami T, Yu BC, Flatt AK, Tour JM, et al. Reversible photo-
switching of single azobenzene molecules in controlled nanoscale environ-
ments. Nano Lett 2008;8:1644e8.
[21] Pace G, Ferri V, Grave C, Elbing M, von Hanisch C, Zharnikov M, et al.
Cooperative light-induced molecular movements of highly ordered azo-
benzene self-assembled monolayers. Proc Natl Acad Sci U S A 2007;104:
9937e42.
[22] Smaali K, Lenfant S, Karpe S, Ocafrain M, Blanchard P, Deresmes D, et al. High
on-off conductance switching ratio in optically-driven self-assembled conju-
gated molecular systems. ACS Nano 2010;4:2411e21.
4. Conclusion
Here, photochromic thiol-terminated bicyclic aziridine de-
rivatives with the azobenzene moiety which was applied as a
functional agent on AgNPs was successfully synthesized and
photochromic properties of AgNPs functionalized have been
considered. Absorbance bands of 1,3-diazabicyclo[3.1.0]hex-3-
ene, azobenzene and SPRAB of AgNPs are matching and
appeared typically near 400 nm. The UVeVis experiments
demonstrated that trans/cis photoisomerization rate with
265 nm light and cis/trans thermally isomerization for Ag-Az-
TTP 1 and Ag-Az-TTP 2 solutions is noticeably faster than free
ligand Az-TTP 1 and Az-TTP 2 solutions. The electronic transitions
of Ag-Az-TTP 1 and Ag-Az-TTP 2 were also shifted as a result of
chemical bonding and overlap between absorption bands of Az-
TTP with SPRA of AgNPs.
[23] Suda M, Kameyama N, Ikegami A, Einaga Y. Reversible photo-tuning of large
anisotropic magnetization at interface between self-assembled photochromic
monolayer and gold. J Am Chem Soc 2009;131:865e70.
[24] Ghavidast A, Mahmoodi NO, Zanjanchi MA. Synthesis and photochromic
properties of a novel thiol-terminated 1,3-diazabicyclo[3.1.0]hex-3-ene on
silver nanoparticles. J Mol Struct 2013;1048:166e71.
[25] Ghavidast A, Mahmoodi NO, Zanjanchi MA. Synthesis and photochromic
properties of disulfide-1,3-diazabicyclo[3.1.0]hex-3-ene functionalized silver
nanoparticles. J Mol Liq 2014;198:128e33.
Acknowledgments
This study was supported in part by the Research Committee of
University of Guilan & Iranian Nanotechnology Initiative Council
(INIC).
[26] Cao J, Wu S, Zhai B, Wang Q, Li J, Ma X. Photo-responsive spiropyran mono-
layer protected gold nanorod. Dyes Pigments 2014;103:89e94.
[27] Matsuda K, Ikeda M, Irie M. Photochromism of diarylethene-capped gold
nanoparticles. Chem Lett 2004;33:456e7.
Appendix A. Supplementary data
[28] Yamaguchi H, Matsuda K, Irie M. Excited-state behavior of a fluorescent and
photochromic diarylethene on silver nanoparticles. J Phys Chem C 2007;111:
3853e62.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2015.03.014.

N.O. Mahmoodi et al. / Dyes and Pigments 118 (2015) 110e117
117
[29] Matsuda K, Yamaguchi H, Sakano T, Ikeda M, Tanifuji N, Irie M. Conductance
photoswitching of diarylethene gold nanoparticle network induced by
photochromic reaction. J Phys Chem C 2008;112:17005e10.
[36] Gole A, Dash C, Ramakrishnan V, Rao M, Sastry M. Pepsin-gold colloid con-
jugates: preparation, characterization, and enzymatic activity. Langmuir
2001;17:1674.
[30] Nishi H, Asahi T, Kobatake S. Light-controllable surface plasmon resonance
absorption of gold nanoparticles covered with photochromic diarylethene
polymers. J Phys Chem C 2009;113:17359e66.
[37] Kiyani H, Mahmoodi NO, Tabatabaeian K, Zanjanchi MA. Photochromic
behavior of several new synthesized bis-1,3-diazabicyclo[3.1.0]hex-3-enes.
J Phys Org Chem 2009;22:559e67.
[31] Imao S, Nishi H, Kobatake S. Thermo- and photoresponsive reversible changes
in localized surface plasmon resonance of gold nanoparticles covered by
poly(N-isopropylacrylamide) with photochromic diarylethene end group.
J Photochem Photobiol A Chem 2013;252:37e45.
[32] Zhu L, Zhu MQ, Hurst JK, Li ADQ. Light-controlled molecular switches
modulate nanocrystal fluorescence. J Am Chem Soc 2005;127:8968e70.
[33] Irie M. Photochromism of diarylethene molecules and crystals. Proc Jpn Acad
Ser B 2010;86:472e83.
[38] Mahmoodi NO, Tabatabaeian K, Ghavidast A. Synthesis and photochromic
behavior of mono-, and biphotochromic system linked by p-phenylene bridge.
Chin Chem Lett 2010;21:1199e202.
[39] Mahmoodi NO, Ghavidast A. Synthesis of photochromic bis-1,3-diazabicyclo-
[3.1.0]hex-3-ene derivatives having a bisindole linkage. Chem Heterocycl
Compd 2014;49:1451e7.
[40] Mahmoodi NO, Tabatabaeian K, Kiyani H. Two 1,3-diazabicyclo[3.1.0]hex-3-
enes with a ‘tripod’ core. Helv Chim Acta 2012;95:536e42.
[41] Hallett-Tapley GL, D'alfonso C, Pacioni NL, McTiernan CD, Gonza'lez-Be'jar M,
Lanzalunga O, et al. Gold nanoparticle catalysis of the cis-trans isomerization
of azobenzene. Chem Commun 2013;49:10073e5.
[34] Mahmoodi NO, Yazdanbakhsh MR, Kiyani H, Sharifzadeh B. Synthesis and
photochromic properties of new heterocyclic derivatives of 1,3-diazabicyclo
[3.1.0]hex-3-ene. J Chin Chem Soc 2007;54:635e41.
[35] Brust M, Walker M, Bethell D, Schiffrin DJ, Whyman R. Synthesis of thiol-
derivatised gold nanoparticles in a two-phase liquid-liquid system. J Chem
Soc Chem Commun 1994;7:801e2.