New 1,3-diazabicyclo-[3.1.0]hex-3-ene photochromic azo dyes: Synthesis, characterization and spectroscopic studies

Article abstract of DOI:10.1016/j.molliq.2013.05.026

Ten new 1,3-diazabicyclo-[3.1.0]hex-3-ene-based azo dyes (3a-3k) were synthesized via three-component reaction between [3-(x-phenyl)aziridin-2-yl] (phenyl)methanone (x = 4-NO₂, 3-NO₂), NH₄OAc and azo-coupled o-vanillin or

Full text of DOI:10.1016/j.molliq.2013.05.026

Journal of Molecular Liquids 187 (2013) 43–48
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Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
New 1,3-diazabicyclo-[3.1.0]hex-3-ene photochromic azo dyes:
Synthesis, characterization and spectroscopic studies
Nosrat O. Mahmoodi ⁎, Meysam Pasandideh Nadamani, Tahereh Behzadi
University of Guilan, Department of Organic Chemistry, P.O. Box 1914, Rasht, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Ten new 1,3-diazabicyclo-[3.1.0]hex-3-ene-based azo dyes (3a–3k) were synthesized via three-component
Received 13 December 2012
Received in revised form 30 April 2013
Accepted 5 May 2013
2 2 4
reaction between [3-(x-phenyl)aziridin-2-yl](phenyl)methanone (x = 4-NO , 3-NO ), NH OAc and azo-
1
coupled o-vanillin or salicylaldehyde precursors (1a–1e) and characterized by UV–Vis, IR and H NMR spec-
troscopic techniques. The synthesized azo dyes undergo ring opening in EtOH by irradiation with 254 nm UV
light. The properties and photochromic structural behavior relationship (PSBR) of these dyes has been ana-
lyzed. The spectroscopic information show that the close-E photoisomer prevails in ordinary room light,
however by irradiation with UV light the open-Z photoisomer is prominent.
Available online 20 June 2013
Keywords:
Azo dye
1,3-Diazabicyclo-[3.1.0]hex-3-ene
© 2013 Elsevier B.V. All rights reserved.
Ketoaziridine
Photochromism
Photoisomerization
1
. Introduction
Photochromism is a vast field encompassing well known phenom-
representative family of photochromic molecules, is usually induced by
alternating irradiation with ultraviolet (UV) and blue lights, which con-
duct E to Z and vice versa isomerization through azo π–π* and azo n–π*
excitations, respectively [27,28]. Recently, several reports regarding syn-
thesis of azo dyes bearing heterocyclic moieties such as thiophene, pyr-
role and azoles have been published. These azo dyes were used for
multiple optical and electronic applications such as second harmonic
generation, optical switching, chemosensing, organic sensitized solar
cells and memories [29–33].
In consideration of these characteristics, it is of interest to examine
for the first time the coupling of the photoactive azo group and 1,3-
diazabicyclo-[3.1.0]hex-3-ene to give single azo-1,3-diazabicyclo-
[3.1.0]hex-3-ene dyes (3a–3k) and investigate their PSBR (Scheme 1).
ena associated with reversible transformations of photoisomers hav-
ing different absorptions upon irradiation with UV and visible light.
This phenomena is not limited to the color or absorption spectra, as
the changes are based on two different molecules with different
physical and chemical properties [1,2]. There has been significant
scientific interest in the photochromic compounds used in optical
memories, photo-switches, data-storage systems, full color displays,
molecular motors and mechanical machines, optoelectronic systems,
liquid-crystalline actuators and responsive photonic crystals [3–8].
1
,3-Diazabicyclo-[3.1.0]hex-3-ene derivatives possess exclusive pho-
tochromic properties and display good photochromic properties
both in the solid and solution states. 1,3-Diazabicyclo[3.1.0]hex-3-ene
photochromic compounds can undergo reversible photocyclization
between their closed-ring isomer and open-ring isomer under irradi-
ation using a light source of appropriate wavelength [9–15]. Recently,
we used a novel type of potentiometry with membrane sensors based
on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diazabicyclo[3.1.0]hex-2-ene
and 6-(4-nitrophenyl)-2-phenyl-4,4-dipropyl-3,5-diazabicyclo[3,1,0]
hex-2-ene for detection of Sn(II) and Sr(II) ions at trace levels in
real samples, respectively [16–18].
2. Experimental
2.1. Materials and apparatus
All reagents were purchased from Fluka, Merck and Aldrich and used
without further purification. [3-(4-Nitrophenyl)aziridin-2-yl](phenyl)
methanone (2a), and [3-(3-nitrophenyl) aziridin-2-yl](phenyl)
methanone (2b), were prepared as described previously [9]. Azo
dyes precursors, 1a–1e, were prepared according to the well
known literature procedure [34].
Azo dyes are an important class of organic colorants used in many
practical applications [19,20]. The photochromism and thermochromism
of aromatic azo dyes make them suitable as optical sensors and molecular
memory storage [21–26]. Reversible E/Z isomerization of azobenzenes, a
The absorption spectra of azo dyes were measured by Shimadzu
UV-2100 spectrophotometer in the range 200–800 nm (EtOH, c =
−
4
2 × 10
M, cell path length 1 cm). A light at 254 nm from a low-
pressure Hg lamp was used for the photoisomerization from the
close-E form to the open-Z. The structure of all synthesized com-
pounds was confirmed by 1H and C NMR spectra, recorded on
⁎
Corresponding author. Fax: +98 131 3233262.
E-mail address: mahmoodi@guilan.ac.ir (N.O. Mahmoodi).
13
0167-7322/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molliq.2013.05.026

44
N.O. Mahmoodi et al. / Journal of Molecular Liquids 187 (2013) 43–48
Scheme 1. Synthesis of azo-1,3-diazabicyclo-[3.1.0]hex-3-ene dyes.
Bruker Avance 500 and 400 MHz spectrometers. IR spectra were
recorded on a Shimadzu IR 470 spectrophotometer in the region of
124.82, 127.93, 129.24, 129.55, 130.10, 130.58, 133.26, 141.36,
144.76, 147.07, 148.05, 151.02, 158.52, 171.84. After irradiation
with UV light converted to the open form, 19%, 1H NMR (500 MHz,
−
1
4
00–4000 cm
in KBr pellets. Melting points of all prepared com-
pounds were determined on Mettler FP-5 melting point apparatus
and are uncorrected. C. H. N. analyses were performed on a Vario-EL
III elemental analyzer.
3
CDCl ) δ: 2.47 (s, 1H), 2.99 (s, 1H), 3.88 (s, 1H), 6.50 (s, 1H), 7.08
(d, 1H, J = 8.6 Hz), 7.34 (d, 2H, J = 8.1 Hz), 7.57–7.52 (m, 4H),
7.66–7.61 (m, 3H), 7.89 (dd, 1H, J =10.9, 2.27 Hz), 7.98 (d, 2H,
1
3
J = 8.4 Hz), 8.00 (s, 1H), 8.31 (d, 2H, J =8.6 Hz).
(500 MHz, CDCl ) δ: 21.86, 47.94, 57.15, 95.00, 118.27, 122.99,
23.46, 123.80, 124.39, 124.82, 127.76, 129.33, 129.51, 130.14,
130.58, 133.12, 141.36, 144.76, 146.91, 148.05, 151.02, 158.52,
C NMR
2
.2. General procedure for the synthesis of photochromic azo dyes 3a–3k
3
1
4
Ketoaziridine 2a or 2b (0.268 g, 1 mmol) and NH OAc (0.77 g,
−
1
1
0 mmol) were dissolved in absolute EtOH (10 ml) and the solution
171.84. IR (KBr, cm ): 1600, 1510, 1480, 1340, 1260. Anal. Calcd.
was stirred vigorously for 10 min at r.t. To this, an azo aldehyde 1a–1e
1 mmol) was added and the mixture stirred at r.t. The reaction was
for C29
14.42.
23 5 3
H N O : C 71.15, H 4.74, N 14.31, found C 71.03, H 4.73, N
(
monitored by TLC (EtOAc:petrol, 2:6). The reaction was completed
after 24 h and the product was collected by filtration, washed with
EtOH and recrystallized from EtOH or MeOH.
4-(4-Chlorophenylazo)-2-[6-(4-nitrophenyl)-4-phenyl-1,3-diazabicyclo
[3.1.0]hex-3-en-2-yl] phenol (Table 1, 3c): Yield 70%, M.p 170–172 °C,
1
Close form 81%, H NMR (400 MHz, CDCl
3
) δ: 2.64 (s, 1H), 3.96 (dd, 1H,
J = 0.8, 2 Hz), 6.80 (s, 1H), 7.04 (d, 1H, J = 8.8 Hz), 7.43 (d, 2H, J =
8.8 Hz), 7.57–7.48 (m, 4H), 7.69–7.60 (m, 3H), 7.85 (dd, 1H, J = 1.6,
2
.3. Spectral data for the synthesis of dye derivatives
5
.6 Hz), 7.97 (d, 2H, J = 8.4 Hz), 8.00 (s, 1H), 8.24 (d, 2H, J = 8.8 Hz),
13
2
-[6-(4-Nitrophenyl)-4-phenyl-1,3-diazabicyclo[3.1.0]hex-3-en-2-yl]-
3
9.90 (s, 1H). C NMR (100 MHz, CDCl ) δ: 43.38, 57.22, 94.54, 117.73,
1
4
(
-(phenylazo)phenol (Table 1, 3a): Yield 78%, M.p 135–137 °C, H NMR
500 MHz, CDCl ) δ: 2.68 (s, 1H), 3.98 (s, 1H), 6.84 (s, 1H), 7.06 (d, 1H,
J = 8.6 Hz), 7.43 (t, 1H, J = 7.18 Hz), 7.48 (t, 2H, J = 7.39 Hz), 7.56 (t,
3
Table 1
Properties of photochromic azo compounds 3a–3k.
4
8
H), 7.64 (t, 1H, J = 7.3 Hz), 7.75 (d, 2H, J = 8.1 Hz), 7.87 (dd, 1H, J =
.6, 2.4 Hz), 7.99 (dd, 2H, J = 8.4, 1.03 Hz), 8.06 (s, 1H), 8.25 (d, 2H,
Entry
λ
max(nm)(EtoH)
m.p.(°C)
Color
Purification
Yield%
1
3
J = 8.7 Hz). C NMR (500 MHz, CDCl
3
) δ: 43.81, 57.61, 95.00, 118.05,
22.89, 123.77, 123.82, 124.31, 124.88, 127.91, 129.25, 129.44, 129.57,
30.54, 130.86, 133.29, 144.72, 147.01, 148.08, 152.94, 158.79, 171.90.
1a[35]
3a
233, 335
250, 347
250, 350
238, 340
250, 355
250, 350
237, 346
250, 360
250, 355
249, 386
255, 368
251, 368
240, 272, 379
257, 368
251, 368
128–129
135–137
140–141
150–152
181–183
159–160
213–215
170–172
163–165
172–173
149–151
174–176
102–104
156–158
147–149
Brown
EtOH/H O
EtOH
EtOH
78
78
68
87
84
79
90
70
63
78
86
81
73
83
80
2
1
1
Orange-green
Yellow
Brown
Orange
Yellow
Yellow
Orange
Orange
Brown
Yellow
Pea green
Brown
Yellow
Yellow
3f
−
1
1b[35]
EtOH/H
MeOH
MeOH
EtOH
2
O
IR (KBr, cm ): 1595, 1500, 1440, 1340, 1280. Anal. Calcd. for
: C 70.73, H 4.45, N 14.73, found C 70.65, H 4.57, N 14.79.
-[6-(4-Nitrophenyl)-4-phenyl-1,3-diazabicyclo[3.1.0]hex-3-en-2-
yl]-4-(p-tolylazo)phenol (Table 1, 3b): Yield 84%, M.p 181–183 °C,
3
3
b
g
28 21 5 3
C H N O
2
1c[36]
3c
MeOH
EtOH
EtOH/CHCI
EtOH
1
3h
Close form, 81%, H NMR (500 MHz, CDCl
H), 3.97 (s, 1H), 6.83 (s, 1H), 7.05 (d, 1H, J = 8.7 Hz), 7.28 (d, 2H,
J =8.15 Hz), 7.57–7.52 (m, 4H), 7.66–7.61(t, 3H, J =8.1 Hz), 7.85
dd, 1H, J = 10.4, 2.04 Hz), 7.99 (d, 2H, J = 7.5 Hz), 8.00 (s, 1H),
3
) δ: 2.43 (s, 3H), 2.67 (s,
1
3
d
d
3
1
3i
1e
3e
EtOH
(
8
2
EtOH/H
EtOH
2
O
.25 (d, 2H, J = 8.6 Hz), 9.80 (s, 1H). 1 C NMR (500 MHz, CDCl
3
3
) δ:
1.86, 43.80, 57.59, 95.04, 118.00, 122.89, 123.46, 123.80, 124.29,
3k
EtOH

N.O. Mahmoodi et al. / Journal of Molecular Liquids 187 (2013) 43–48
45
123.47, 123.57, 123.73, 123.89, 124.47, 127.47, 128.82, 129.16, 129.26,
3
(500 MHz, CDCl ) δ: 2.43 (s, 3H), 2.69 (s, 1H), 3.98 (s, 1H), 6.83
1
30.08, 132.91, 136.24, 144.26, 146.40, 147.66, 150.86, 158.63, 171.52.
(s, 1H), 7.06 (d, 1H, J = 8.7 Hz), 7.28 (d, 2H, J = 8.1 Hz), 7.57–7.54
(t, 3H), 7.64 (t, 1H, J = 6.7 Hz), 7.66 (d, 2H, J = 8.1 Hz), 7.72 (d, 1H,
J = 7.67 Hz), 7.85 (dd, 1H, J = 8.6, 2.19 Hz), 8.01 (d, 2H, J = 7.3 Hz),
1
After irradiation with UV light converted to the open form, 19%,
NMR (400 MHz, CDCl
H
3
) δ: 2.98 (d, 1H, J = 2 Hz), 3.88 (dd, 1H, J =
0
8
5
.4,2.4 Hz), 6.50 (s, 1H), 7.07 (d, 2H, J = 8.8 Hz), 7.43 (d, 2H, J =
.8 Hz), 7.57–7.48 (m, 4H), 7.69–7.60 (m, 3H), 7.85 (dd, 1H, J = 1.6,
.6 Hz), 7.95 (d, 2H, J = 7.6 Hz), 8.00 (s, 1H), 8.32 (d, 2H, J = 8.8 Hz).
8.07 (s, 1H), 8.22 (d, 1H, J = 8.1 Hz), 8.26 (s, 1H), 9.92 (s, H). 13
C
3
NMR (500 MHz, CDCl ) δ: 21.85, 43.60, 57.34, 95.03, 118.00, 121.90,
122.89, 123.30, 123.52, 123.84, 124.83, 129.24, 129.54, 130.00, 130.06,
130.61, 133.23, 133.39, 139.70, 141.00, 147.00, 149.00, 151.00, 158.54,
1
3
3
C NMR (100 MHz, CDCl ) δ: 48.20, 56.00, 96.47, 117.96, 123.47,
−
1
1
1
23.57, 123.73, 123.84, 124.47, 127.32, 128.88, 129.11, 129.26, 130.08,
32.73, 136.24, 144.26, 146.40, 147.66, 150.80, 158.60, 171.50. IR (KBr,
171.89. IR (KBr, cm ): 1600, 1580, 1520, 1480, 1340, 1260. Anal.
23 5 3
Calcd. for C29H N O : C 71.15, H 4.74, N 14.31, found C 71.08, H 4.81,
−
1
20 5 3
cm ): 1600, 1520, 1480, 1340, 1280. Anal. Calcd. for C28H N O Cl: C
N 14.22.
6
5.95, H 3.95, N 13.73, found C 65.87, H 3.87, N 13.74.
-Methoxy-4-(4-methoxyphenylazo)-6-[6-(4-nitrophenyl)-4-phenyl-
,3-diazabicyclo[3.1.0]hex-3-en-2-yl]phenol (Table 1, 3d): Yield 86%, M.p
4-(4-Chlorophenylazo)-2-[6-(3-nitrophenyl)-4-phenyl-1,3-diazabicyclo
2
[3.1.0]hex-3-en-2-yl] phenol (Table 1, 3h): Yield 63%, M.p 164 °C, Close
1
1
1
3
7
form, 72%, H NMR (400 MHz, CDCl
3
) δ: 2.66 (s, 1H), 3.97 (s, 1H), 6.80
1
3
49–151 °C, Close form, 70%, H NMR (400 MHz, CDCl ) δ: 2.69 (s, 1H),
(s, 1H), 7.04 (d, 1H, J = 8.8 Hz), 7.42 (d, 2H, J = 8.8 Hz), 7.49 (d, 1H,
J = 8.4 Hz), 7.58–7.52 (m, 2H), 7.63–7.61 (m, 1H), 7.68 (d, 2H, J =
8.4 Hz), 7.85 (dd, 1H, J = 8.8, 2.4 Hz), 7.88 (d, 1H, J = 8.8 Hz), 7.98 (d,
2H, J = 7.2 Hz), 8.00 (s, 1H), 8.20 (d, 1H, J = 8 Hz), 8.24 (s, 1H), 10.00
.89 (s, 3H), 3.91 (s, 1H), 4 (s, 3H), 6.90 (s, 1H), 7 (d, 2H, J =9.2 Hz),
.47 (d, 1H, J = 2 Hz), 7.50–7.63 (m, 6H), 7.80 (d, 2H, J =9.2 Hz), 8
(
(
d, 2H, J = 7.2 Hz), 8.21 (d, 2H, J = 8.8 Hz), 9.29 (br, 1H). 13C NMR
100 MHz, CDCl
3
) δ: 42.83, 55.58, 56.14, 57.19, 93.81, 102.1, 114.21,
18.85, 123.14, 123.82, 124.33, 127.5, 128.76, 129.09, 130.4, 132.67,
44.65, 146.18, 146.83, 147.42, 147.53, 148.74, 161.66, 171.50. After ir-
(s, 1H). 13C NMR (100 MHz, CDCl
3
) δ: 43.19, 56.94, 94.51, 117.72,
1
1
121.49, 122.92, 123.51, 123.71, 123.75, 124.60, 128.84, 129.15, 129.22,
129.60, 130.00, 132.88, 132.89, 136.15, 139.22, 146.37, 148.57, 150.90,
1
radiation with UV light converted to the open form, 30%, H NMR
400 MHz, CDCl ) δ: 2.94 (s, 1H), 3.89 (s, 1H), 3.91 (s, 3H), 4.03 (s,
H), 6.62 (d, 1H, J = 2.8 Hz), 7.03 (d, 2H, J = 8.8 Hz), 7.50–7.63 (m,
H), 7.91 (d, 2H, J = 9.2 Hz), 8 (d, 2H, J = 7.2 Hz), 8.27 (d, 2H, J =
.4 Hz), 8.6 (br, 1H). 13C NMR (100 MHz, CDCl
) δ: 47.82, 55.58,
158.67, 171.58. After irradiation with UV light converted to the open
1
(
3
form, 28%, H NMR (400 MHz, CDCl
3
) δ: 2.90 (s, 1H), 3.89 (s, 1H), 6.40
3
7
8
5
1
1
1
(s, 1H), 7.07 (d, 1H, J = 8.8 Hz), 7.42 (d, 2H, J = 8.8 Hz), 7.49 (d, 1H,
J = 8.4 Hz), 7.58–7.52 (m, 2H), 7.63–7.61 (m, 1H), 7.70 (d, 2H, J =
6.4 Hz), 7.82 (d, 1H, J = 8.8 Hz), 7.88 (d, 1H, J = 8.8 Hz), 7.96 (d, 2H,
3
6.24, 56.99, 93.84, 101.21, 114.21, 119.33,123.86, 124.38, 125.54,
27.38, 128.85, 128.97, 130.79, 132.28, 144.48, 146.13, 146.48, 147.01,
47.61, 148.45, 161.61, 170.2. IR (KBr, cm−1): 1595, 1510, 1500, 1465,
J = 8 Hz), 8.25 (s, 1H), 8.34 (s, 1H), 8.52 (s, 1H), 10.26 (s, 1H). 13
C
3
NMR (100 MHz, CDCl ) δ: 47.39, 56.43, 95.14, 117.90, 121.64, 123.11,
123.54, 123.83, 123.89, 125.59, 128.90, 129.00, 129.27, 129.80, 130.20,
132.42, 132.70, 136.00, 139.28, 146.24, 148.57, 151.14, 158.20, 170.26.
25 5 5
340, 1285. Anal. Calcd. for C30H N O : C 67.28, H 4.71, N 13.08,
−
1
found C 67.18, H 4.86, N 13.07.
-Methoxy-4-(2-methylphenylazo)-6-[6-(4-nitrophenyl)-4-phenyl-1,
-diazabicyclo[3.1.0] hex-3-en-2-yl]phenol (Table 1, 3e): Yield: 83%, M.p
IR (KBr, cm ): 1600, 1580, 1520, 1480, 1340, 1260. Anal. Calcd. for
Cl: C 65.95, H 3.95, N 13.73, found C 65.88, H 3.98, N 13.65.
2-Methoxy-4-(4-methoxyphenylazo)-6-[6-(3-nitrophenyl)-4-phenyl-
1,3-diazabicyclo [3.1.0]hex-3-en-2-yl]phenol (Table 1, 3i): Yield 81%, M.p
2
28 20 5 3
C H N O
3
1
2
1
1
1
3
56–158 °C, Close form, 72%, H NMR (400 MHz, CDCl ) δ: 2.49 (s, 3H),
1
.7 (s, 1H), 3.91 (t, 1H, J = 1.6 Hz), 4.01 (s, 3H), 6.90 (s, 1H), 7.23 (td,
H, J = 8, 1.6 Hz), 7.27–7.36 (m, 2H), 7.50–7.65 (m, 7H), 7.68 (dd,
H, J = 2, 0.8 Hz), 7.98–8.02 (m, 2H), 8.22 (d, 2H, J = 8.8 Hz), 9.65
3
174–176 °C, Close form, 65%, H NMR (400 MHz, CDCl ) δ: 2.71 (s, 1H),
2.89 (s, 3H), 3.92 (s, 1H), 4 (s, 3H), 6.91 (s, 1H), 6.98 (d, 2H, J = 8.8 Hz),
7.47–7.64 (m, 5H), 7.67 (m, 2H), 7.78–7.81 (m, 2H), 8 (d, 2H, J =
1
3
13
(
br, 1H). C NMR (100 MHz, CDCl
3
) δ: 17.22, 43, 56.12, 57.36, 93.98,
7.2 Hz), 8.1 (d, 1H, J = 8 Hz), 8.22 (s, 1H), 9.35 (br, 1H).
C
1
1
1
04.6, 115.34, 116.91, 123.23, 123.86, 126.42, 127.42, 128.78, 129.12,
30.24, 130.41, 131.16, 132.77, 137.41, 144.59, 146.54, 147.58, 147.93,
NMR(100 MHz, CDCl ) δ: 42.63, 55.57, 56.14, 56.94, 93.8, 102.12,
3
114.18, 118.93, 121.56, 122.76, 123.2, 124.34, 128.77, 129.08, 129.52,
130.43, 132.64, 132.91, 139.55, 146.15, 146.87, 147.46, 148.52, 148.76,
161.61, 171.55. After irradiation with UV light converted to the open
48.76, 150.55, 171.44. After irradiation with UV light converted to
1
the open form, 28%, H NMR (400 MHz, CDCl
3
) δ: 2.73 (s, 3H), 2.96
(
d, 1H, J = 1.6 Hz), 3.89 (t, 1H, J = 2.4 Hz), 4.03 (s, 3H), 6.63 (d, 1H,
form, 35%, 1H NMR (400 MHz, CDCl
3
) δ: 2.95 (s, 1H), 3.74 (quar, 1H,
J = 2.8 Hz), 7.27–7.36 (m, 3H), 7.50–7.65 (m, 8H), 7.98–8.02 (m, 2H),
J = 6.8 Hz), 3.9 (s, 3H), 4.02 (s, 3H), 6.62 (d, 1H, J = 2.4 Hz), 7.02
(d, 2H, J = 8.8 Hz), 7.47–7.64 (m, 5H), 7.78–7.81 (m, 1H), 7.91–7.93
(m, 3H), 8 (d, 2H, J = 7.2 Hz), 8.21 (m, 1H), 8.3 (s, 1H), 8.61 (br, 1H).
8
1
1
1
.27 (d, 2H, J = 8.8 Hz), 8.66 (br, 1H). 13C NMR (100 MHz, CDCl
) δ:
3
7.52, 47.82, 56.19, 56.95, 93.73, 101.88, 115.52, 119.51, 132.86,
25.53, 126.49, 127.36, 128.91, 129.01, 130.31, 130.63, 131.16, 132.41,
37.32, 144.75, 146.54, 146.9, 147.64, 148.45, 150.84, 170.3. IR (KBr,
13
3
C NMR (100 MHz, CDCl ) δ: 47.71, 55.57, 56.22, 56.62, 93.8, 101.26,
114.2, 119.3, 121.69, 122.87, 124.4, 125.63, 128.89, 128.97, 129.63,
130.8, 132.28, 132.57, 139.78, 146.11, 146.48, 147.01, 148.44, 148.48,
−
1
25 5 4
cm ): 1600, 1510, 1450, 1340, 1260. Anal. Calcd. for C30H N O : C
−
1
6
9.35, H 4.85, N 13.48, found C 69.52, H 4.89, N 13.37.
-[6-(3-Nitrophenyl)-4-phenyl-1,3-diazabicyclo[3.1.0]hex-3-en-2-yl]-
-(phenylazo)phenol (Table 1, 3f): A similar procedure as applied for 3a
161.58, 170.26. IR (KBr, cm ): 1600, 1575, 1525, 1470, 1345, 1280.
2
25 5 5
Anal. Calcd. for C30H N O : C 67.28, H 4.71, N 13.08, found C 67.34, H
4
4.76, N 13.01.
was practical but instead of 2a same amount of 2b was utilized. Yield
8%, M.p 140 °C. 1H NMR (500 MHz, CDCl
): δ 2.70 (s, 1H), 3.98
s, 1H), 6.84 (s, 1H), 7.07 (d, 1H, J = 8.7 Hz), 7.43 (t, 1H, J = 7.2 Hz),
.48 (t, 2H, J = 7.34 Hz), 7.56 (t, 3H), 7.64 (t, 1H, J = 7.4 Hz,), 7.72
d, 1H, J = 7.6 Hz,), 7.76 (d, 2H, J = 7.4 Hz), 7.88 (dd, 1H, J = 8.6,
.2 Hz), 8.01 (d, 2H, J = 7.3 Hz), 8.09 (s, 1H), 8.21 (dd, 1H, J = 1.22,
.39 Hz), 8.26 (s, 1H), 10 (s, 1H). 13C NMR (500 MHz, CDCl
) δ: 43.61,
7.36, 94.98, 118.06, 121.89, 122.91, 123.33, 123.79, 123.86, 124.94,
29.27, 129.41, 129.56, 130.00, 130.57, 130.79, 133.28, 133.36, 139.66,
46.99, 149.00, 152.99, 158.82, 171.96. IR (KBr, cm−1): 1600, 1560,
2-Methoxy-4-(2-methylphenylazo)-6-[6-(3-nitrophenyl)-4-phenyl-1,3-
6
(
7
(
2
9
5
1
1
1
3
diazabicyclo[3.1.0] hex-3-en-2-yl]phenol (Table 1, 3k): Yield 80%, M.p
1
147–149 °C, Close form, 54%, H NMR (400 MHz, CDCl
3
) δ: 2.5 (s, 3H),
2.72 (s, 1H), 3.89–3.91 (m, 1H), 4.01 (s, 3H), 6.91 (s, 1H), 7.24 (td, 1H,
J = 7.4, 2 Hz), 7.27–7.32 (m, 1H), 7.35 (d, 1H, J = 4 Hz), 7.5–7.63
(m, 5H), 7.68–7.71 (m, 2H), 7.8 (d, 1H, J = 7.6 Hz), 7.99–8.02 (m, 2H),
13
3
8.18 (dd, 1H, J = 8.4, 1 Hz), 8.24 (s, 1H), 9.68 (br, 1H). C NMR
3
(100 MHz, CDCl ) δ: 17.24, 42.79, 56.12, 57.15, 93.98, 104.55, 115.37,
117.06, 121.48, 122.79, 123.31, 126.41, 128.78, 129.1, 129.58, 130.28,
131.11, 132.73, 132.77, 137.4, 139.54, 149.53, 147.97, 148.43, 148.78,
21 5 3
540, 1470, 1340, 1270. Anal. Calcd. for C28H N O : C 70.73, H 4.45,
150.58, 171.47. After irradiation with UV light converted to the open
1
N 14.73, found C 70.76, H 4.57, N 14.81.
-[6-(3-Nitrophenyl)-4-phenyl-1,3-diazabicyclo[3.1.0]hex-3-en-2-yl]-
form, 46%, H NMR (400 MHz, CDCl
3
) δ: 2.74 (s, 3H), 2.96 (d, 1H, J =
2
1.6 Hz), 3.89–3.91 (m, 1H), 4.02 (s, 3H), 6.63 (d, 1H, J = 2.4 Hz), 7.27–
7.32 (m, 2H), 7.35 (d, 1H, J = 4 Hz), 7.5–7.63 (m, 7H), 7.99–8.02
1
4
-(p-tolylazo)phenol (Table 1, 3g): Yield 79%, M.p 160 °C, H NMR

46
N.O. Mahmoodi et al. / Journal of Molecular Liquids 187 (2013) 43–48
Scheme 2. Photoisomerization of photochromic dyes via imine ylide upon the UV–light irradiation.
(
m, 3H), 8.21 (dd, 1H, J = 8.4, 1.2 Hz), 8.31 (s, 1H), 8.70 (br, 1H). 13C
NMR (100 MHz, CDCl ) δ: 17.52, 47.68, 56.17, 56.62, 93.8, 102.18,
15.54, 119.14, 121.64, 122.88, 125.72, 126.46, 128.87, 128.98, 129.63,
30.35, 130.77, 131.16, 132.3, 132.54, 137.4, 139.77, 146.53, 146.88,
absorption related to the azo precursors 1a–1e and the N\H stretching
related to the ketoaziridines 2a–2b in addition to the appearance of a
new C_N absorption band in the range of 1597–1605 cm indicated
3
−
1
1
1
1
1
6
that 1,3-diazabicyclo[3.1.0]hex-3-en moiety was formed.
−
1
48.51, 148.57, 150.84, 170.34. IR (KBr, cm ): 1605, 1575, 1525, 1475,
3
The NMR spectra of dyes were recorded in CDCl at 25 °C. All of
25 5 4
345. Anal. Calcd. for C30H N O : C 69.35, H 4.85, N 13.48, found C
the synthesized azo dyes except for 3a, 3f and 3g showed a new set
1
13
9.28, H 4.91, N 13.52.
of signals in H and C NMR in addition to the original ones because
of Photoisomerization between their closed-ring A photoisomer and
open-ring B photoisomer via conrotatory (σ2s + n2s) heterolytic
cleavage of the three-member ring under irradiation with light source
of appropriate wavelength (254 nm) [9–11]. Photoisomerization of
these photochromic azo dyes via proposed zwitter ionic double-
3
. Result and discussion
In our approach, o-vanillin or salicylaldehyde in the first step was
coupled with the diazonium chloride obtained from aniline deriva-
tives to give 1a–1e. In the next efforts, the photochromic azo dyes
charged imine ylides were depicted in Scheme 2.
1
3
a–3k were synthesized via three-component reactions between
The H NMR spectra of compound 3c in CDCl
3
indicate mixture of
ketoaziridine 2a or 2b, NH
Scheme 1 and Table 1.
4
OAc and azo dye precursor, as shown in
two photoisomers with ratio of 78:22 (3c:3c′) closed to open forms
upon exposure to UV light. The ratios of close to open photoisomers
were measured from integral ratio of certain peaks in 1H NMR spec-
The characteristic IR absorption bands of compounds were deter-
mined in KBr disk. In the IR spectra of 3a–3k, absence of a C_O
tra. The characteristic shifts of their H
a
, H
b
, H
c
were observed in the
a
b
a
b
a
c
b
a
b
c
d
d
Fig. 1. 1HNMR of 3c indicates mixture of two photoisomers with ratio of 78:22 for close and open forms.

N.O. Mahmoodi et al. / Journal of Molecular Liquids 187 (2013) 43–48
47
Table 2
ratio between close and open photoisomers. The spectroscopy data
showed that the close photoisomers prevail in ordinary room light;
however by irradiation with UV light the open photoisomers are
prominent.
1
H NMR chemical shifts of close and open-ring isomers for 3a–3k.
Entry δb,b′
δa,a′
δc,c′
δOH,OH′
Close/open form ratio (%)
3
3
3
3
3
3
3
3
3
3
a
b
c
d
e
f
g
h
i
2.67, –
3.97, –
6.83, –
–
100/0
81/19
78/22
70/30
72/28
100/0
100/0
68/32
65/35
54/46
2.67, 2.99 3.97, 3.88 6.83,6.50 9.8, –
2.64, 2.98 3.96, 3.88 6.80, 6.50 9.90, –
2.69, 2.94 3.91, 3.89 6.90, 6.62 9.29, 8.60
2.70, 2.96 3.91, 3.89 6.90, 6.63 9.65, 8.66
Acknowledgments
We thank the Research Committee of the University of Guilan for
partial support given to this study.
2,70, –
2.69, –
3.98, –
3.98, –
6.84, –
6.83, –
10, –
9.92, –
2.66, 2.90 3.97, 3.89 6.80, 6.40 10, –
2.71, 2.95 3.92, 3.74 6.91, 6.62 9.35, 8.61
2.72, 2.96 3.90, 3.90 6.91, 6.63 9.68, 8.70
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