Diarylethene-based imines and amines: Synthesis, photochromic properties and effects of substitution

Article abstract of DOI:10.1016/j.jphotochem.2010.12.017

Condensation of dialdehyde 1 with different aromatic amines gave a series of symmetrical diarylethenes containing Schiff-base moieties, which were reduced with NaBH₄ to give the corresponding diarylethene amines. The structures of all new compo

Full text of DOI:10.1016/j.jphotochem.2010.12.017

Journal of Photochemistry and Photobiology A: Chemistry 218 (2011) 192–198
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Diarylethene-based imines and amines: Synthesis, photochromic properties and
effects of substitution
Ziyong Li, Jun Yin∗, Xianghua Wu, Yan Lin, Qingbin Zeng, Fangying Fan, Sheng Hua Liu∗
Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, 152 Luoyu Road, Wuhan 430079, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Condensation of dialdehyde 1 with different aromatic amines gave a series of symmetrical diarylethenes
containing Schiff-base moieties, which were reduced with NaBH4 to give the corresponding diarylethene
amines. The structures of all new compounds were confirmed by NMR spectroscopy, mass spectrom-
etry, X-ray diffraction and elemental analysis. Their photochromic properties were also investigated,
revealing that diarylethene imines displayed better photochromic properties in solution than their amine
analogues. Furthermore, we found that by varying the aromatic amine precursor, diarylethenes with dif-
ferent polychromic behavior could be obtained. A number of different aromatic amines were investigated,
including different carbon skeletons and substitution with different halogens in various positions, to tune
the polychromic behavior.
Received 9 October 2010
Received in revised form
13 December 2010
Accepted 27 December 2010
Available online 31 December 2010
Keywords:
Diarylethene
Imine
© 2010 Elsevier B.V. All rights reserved.
Amine
Photochromism
Substituent effects
1. Introduction
at the 2- and 2ꢀ-positions of the thiophene rings can strongly sup-
press cycloreversion quantum yields. Recently, Yamaguchi and Irie
Photochromism is the reversible transformation between two
isomers with different absorption spectra caused by alternating
irradiation with UV and visible light. The design and synthesis
of novel photochromic molecules has attracted significant inter-
est due to their potential application in photonic devices such as
memory media and optical switching [1,2]. Recently, photochromic
compounds such as spiropyrans [3], azobenzene [4], fulgides [5]
and diarylethenes [6–8] have been extensively investigated. Among
these compounds, diarylethenes with heterocyclic aryl groups,
especially those bearing two thiophene or benzothiophene rings,
are considered the most promising candidates for technological
applications because of their excellent thermal stability, remark-
able fatigue resistance, and high sensitivity [9–24]. Photochromic
diarylethenes have therefore attracted much attention, and pre-
vious studies have shown that their properties can be tuned by
variation of the size and nature of substituent groups. For exam-
ple, Irie et al. [25] and Uchida et al. [26], Pu et al. [27–30] and Fan
et al. [31,32] reported that variation of the terminal substituted
phenyl groups affected the photochromic properties and the pho-
tochemical reactivity of diarylethenes. Morimitsu et al. [33], and
Takami and Irie [34] demonstrated that bulky alkoxy substituents
[35,36] reported that bulky alkyl chains at the 2-positions of ben-
zothiophene and benzofuran rings can increase the cyclization
quantum yields.
Imines act as an excellent ligand and are widely used in coor-
dination chemistry [37–42], macrocyclic chemistry [43–47] and
biochemistry [48,49]. When part of a conjugated ␲-system, imines
have also been used in optoelectronic materials. Therefore it
was anticipated that the incorporation of an imine into a pho-
tochromic diarylethene system would impart novel photochemical
properties on the system. Herein, we report the synthesis of a
series of diarylethene imines and amines bearing different sub-
stituents. Their structures were confirmed by NMR spectroscopy,
mass spectrometry, X-ray diffraction and elemental analysis. The
photochromic properties of these compounds were studied, and
we discuss here the effects of different substituents, substitution
sites and the size of the substituted groups on the photochromic
properties of the compounds.
2. Results and discussion
2.1. Synthesis, structure and characterization
The target diarylethene imines 2a–h were obtained by
condensation of different substituted aromatic amines with 1,2-
bis(5-formyl-2-methylthien-3-yl)cyclopentene 1 in the presence
of excess anhydrous magnesium sulfate in yields of 21–89%. The
∗
Corresponding authors. Tel.: +86 27 67867725.
E-mail addresses: yinj@mail.ccnu.edu.cn (J. Yin), chshliu@mail.ccnu.edu.cn
(S.H. Liu).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.12.017

Z. Li et al. / Journal of Photochemistry and Photobiology A: Chemistry 218 (2011) 192–198
193
Scheme 1. Synthesis of diarylethene imines 2a–h and amines 3a–h.
imines 2a–h were reduced using sodium borohydride (NaBH4) in
a solution of MeOH and THF to give the corresponding amines in
67–91% yields (Scheme 1). All of the target compounds were fully
characterized by standard spectroscopic techniques such as NMR,
X-ray, MS and elemental analysis. For example, in the 1H NMR spec-
tra, the resonance of the imine protons in 2a–h (CH N) appeared
as a singlet at 8.24–8.51 ppm, and after reduction, the resonance
of amine protons (NH) in diarylethenes 3a–h were observed at
4.01–4.67 ppm.
had been reduced to an amine. The crystal structures also revealed
that the intramolecular distance between the two reactive carbons
˚
˚
(C5–C5a and C7–C7a) were 3.555 A and 3.572 A, respectively. This
distance is considered sufficiently small to allow cyclization to take
˚
place (less than 4.2 A [51,52]). However the color changes were not
obvious when the crystal were irradiated with UV light.
Table 1
Crystal data and structure refinement parameters for 2d and 3g.
2d
3g
2.2. Single X-crystal diffraction
Formula
C29H24Br2N2S2
624.44
292 (2)
0.71073
Monoclinic
C2/c
15.2572 (19)
20.257 (2)
9.2415 (11)
109.438 (2)
2693.4 (6)
4
C29H28Br2N2S2
628.47
298 (2)
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
Single crystals of 2d and 3g were obtained from a mixed
dichloromethane and hexane solution. The molecular structures of
2d and 3g were determined by X-ray crystallography. Fig. 1 shows
ORTEP drawings of the ring-opened isomers 2d and 3g and crys-
tallographic details are listed in Table 1. The diarylethenes 2d and
3g crystallized with an approximate C2 symmetry with the pho-
toactive antiparallel conformation in the crystalline phase, which
can undergo photocyclization [50]. The molecules feature three
types of planar ring system, and two dihedral angles between
each of the adjacent planar rings. The dihedral angles between
the cyclopentene ring and the thiophene ring were found to be
54.64◦ for diarylethene 2d and 47.23◦ for diarylethene 3g, and those
between the thiophene ring and the benzene ring (attached via
carbon–nitrogen double or single bonds) were 61.03◦ and 84.78◦,
respectively. For diarylethene 2d, the C9–N1 bond distance was
0.71073
Monoclinic
C2
20.506 (3)
8.0332 (11)
8.6121 (12)
96.690 (2)
1409.0 (3)
2
b (Å)
c (Å)
ˇ (◦)
Volume (Å−3
)
Z
Dcal (Mg/m3)
1.540
1256
1.481
636
F (0 0 0)
Crystal size (mm3)
Goodness-of-fit on F2
0.40 × 0.20 × 0.10
0.20 × 0.19 × 0.18
1.073
1.060
Final R indices [I > 2ꢀ(I)]
R1
wR2
0.0512
0.1274
0.0485
0.1354
˚
R indices (all data)
R1
wR2
1.268 A, indicating that this bond was a double bond, being signifi-
0.0928
0.1417
0.0607
0.1419
˚
cantly shorter than the carbon–nitrogen single bond (1.399 A). The
C9–N1 bond distance was longer in 3g (1.459 A), where the imine
˚

194
Z. Li et al. / Journal of Photochemistry and Photobiology A: Chemistry 218 (2011) 192–198
Table 2
Absorption characteristics and photochromic quantum yields of 2a–h in CH2Cl2
(3.0 × 10−5 mol/L).
Compound ꢁmaxAbs/nma
(ε × 104)
ꢁmaxAbs/nmb
(ε × 104)
˚
c
(Open)
(PSS)
ϕo-c (ꢁ/nm) ϕc-o (ꢁ/nm)
2a
2b
2c
2d
2e
2f
348 (2.36)
282 (2.52)
350 (2.97)
282 (3.37)
348 (2.28)
282 (3.03)
348 (2.38)
282 (3.25)
352 (2.37)
288 (3.27)
350 (3.64)
282 (3.53)
352 (2.99)
282 (3.07)
368 (3.79)
284 (3.38)
598 (0.68)
0.218 (598) 0.0070 (348)
600 (0.86)
594 (0.44)
606 (0.63)
588 (0.27)
608 (1.33)
602 (0.57)
610 (0.18)
0.027 (600) 0.0006 (350)
0.080 (594) 0.0090 (348)
0.050 (606) 0.0080 (348)
0.016 (588) 0.0003 (352)
0.023 (608) 0.0013 (350)
0.062 (602) 0.0040 (352)
0.237 (610) 0.0059 (368)
2g
2h
a
Absorption maxima of open-ring isomers.
Absorption maxima of closed-ring isomers.
Quantum yields of open-ring (ϕc-o) and closed-ring isomers (ϕo-c), respectively.
b
c
(Fig. 2). For example, Fig. 3A shows the changes observed in 2f,
where upon irradiation with UV light (ꢁ = 302 nm) the appearance
of a new absorption band at 608 nm was observed, along with a
decrease in the absorption band in the UV region. Furthermore,
the pale yellow dichloromethane solution was observed to turn
pale blue immediately upon irradiation (Fig. 4). In addition, a well-
defined isosbestic point was observed at 368 nm, which clearly
indicated that the diarylethene imine 2f was converted to a pho-
tocyclized isomer. Moreover, upon irradiation with visible light
(ꢁ > 402 nm), the pale blue solution reverted to pale yellow. The
other diarylethene imines with halogen substituted benzene rings
also exhibited similar photochromic behaviors. From these data,
shown in Table 2, it was found that the effects of different sub-
stituents and substitution sites on the absorption maxima of the
closed-ring isomers of diarylethene imines 2a–h were not signifi-
cant. However, compared with the starting material diarylethene
dialdehyde 1, these imines displayed 8–30 nm red-shifts due to
more extended ␲-conjugation systems. [53]
While the effects of substitution were not obvious from the
absorption wavelength, the effect of substitution on the quantum
yields and the molar absorption coefficients was striking. Among
the diarylethene imines containing halogen substituted benzene
rings, 2b–g, the cyclization quantum yield of ortho-chloro sub-
stituted 2c was the largest (ϕo-c = 0.08), while that of ortho-iodo
substituted 2e was the smallest (ϕo-c = 0.016). In dichloromethane
solution, the molar absorption coefficients of both the open-ring
isomer and the closed-ring isomer of meta-bromo substituted
2f were the largest, while the open-ring isomer of ortho-chloro
substituted 2c and the closed-ring isomer of ortho-iodo substi-
tuted 2e were the smallest. As the cyclization quantum yields
showed, the ortho-chloro substituted 2c and the ortho-iodo sub-
stituted 2e exhibited the largest and the smallest cycloreversion
quantum yields, respectively. In addition, compared with the
Fig. 1. ORTEP drawing of molecular structures of open-ring isomers 2d (A) and 3g
(B).
2.3. Photochromic properties
The UV/Vis absorption spectra of the diarylethenes were mea-
sured in dichloromethane solution. Table 2 shows the absorption
spectra of diarylethene imines 2a–h. The results indicated that
the substituted groups and substitution positions on the benzene
rings did not significantly change the UV/Vis absorption spectra in
imines 2a–g. However, compared with 2a–g, the maximum absorp-
tion wavelength of imine 2h, which has a fluorene moiety rather
than a benzene, showed a 15 nm red shift. The similar absorption
spectra for 2a–g and different spectrum for 2h indicates that the
UV/Vis absorption is more significantly affected by the extent of the
conjugated system than the substituents attached.
The photochromic behaviors of the diarylethene imines 2a–h
were measured using photo irradiation in dichloromethane solu-
tion at room temperature. Upon irradiation with UV light, a new
absorption band at 588–610 nm appeared for all compounds, as
shown in Table 2, due to the formation of the ring-closed isomer
UV
Vis
N
N
N
N
R
R
R
R
S
S
S
S
Fig. 2. Photochromism of diarylethenes imines.

Z. Li et al. / Journal of Photochemistry and Photobiology A: Chemistry 218 (2011) 192–198
195
1.2
1.0
0.8
0.6
0.4
0.2
0.0
A
Vis
UV
1.0
0.8
0.6
3a
3b
3f
3g
3h
Vis
UV
0.4
0.2
0.0
300
400
500
600
700
800
250
300
350
400
450
Wavelength / nm
Wavelength / nm
1.2
1.0
0.8
0.6
0.4
0.2
0.0
B
Fig. 5. The UV/Vis absorption spectra of diarylethene amines 3a and b, f–h in CH2Cl2
(3.0 × 10−5 mol/L) at room temperature.
UV
Vis
amine 3d, a new absorption band due to the formation of the closed-
ring isomer was observed in the region of 315–540 nm along with
a decrease in the absorption band at 250 nm (Fig. 3B) and the col-
orless solution became pale yellow (Fig. 4). Upon irradiation with
visible light (ꢁ > 402 nm), the pale yellow solution reverted to color-
less. Similar results were obtained for the photochromic reaction of
all other diarylethene amines (3a–c and 3e–h) in dichloromethane.
UV
Vis
3. Conclusion
A
series
of
symmetrical
diarylethenes
containing
300
400
500
600
700
800
carbon–nitrogen double and single bonds have been synthe-
sized and their photochromic properties in solution investigated.
The results indicated that substitution (F, Cl, Br, I) and the sub-
stituent position of the precursor amine can affect the cyclization
and cycloreversion quantum yields of the diarylethene imines and
amines produced, however, they do not affect the UV/Vis absorp-
tion spectra observed upon irradiation with UV or visible light.
Compared with the diarylethene amines, the diarylethene imines
displayed better photoswitching properties in solution. Further
research efforts will focus on utilizing the excellent coordinative
ability of the Schiff base to investigate the effect of metal ions on
the photochromic properties of these ligands.
Wavelength / nm
Fig. 3. Absorption spectral changes of diarylethene imine 2f (A) and amine 3d (B)
by photoirradiation in CH2Cl2 (3.0 × 10−5 mol/L) at room temperature.
chloro-, bromo- and iodo-substituted diarylethene imines, we
found that the introduction of strongly electron-deficient fluorine
atoms did not significantly affect photochromic behavior. While
the more extended conjugated system of the fluorene containing
diarylethene imine 2h did not enhance this compound’s pho-
tochromic behavior, the cyclization quantum yield of 2h was larger
than that of the halogen substituted diarylethene imines. Accord-
ing to the Table 2, such low quantum yields may attribute to the
heavy atom effect of dichloromethane as solvent.
After reduction using NaBH4, the UV/Vis absorption spectra of
diarylethene amines, 3a–h, exhibited significant blue-shifts when
compared with their imine analogues, due to a decrease in the
length of the conjugated system (Fig. 5). Their photochromic prop-
erties were investigated under the same conditions as above for
2a–h. For example, upon irradiation with UV light (ꢁ = 302 nm) of
4. Experimental
4.1. General
All manipulations were carried out under an argon atmo-
sphere by using standard Schlenk techniques, unless other-
wise stated. THF was distilled under nitrogen from sodium-
benzophenone. EtOH and MeOH were distilled under drying
pipe from magnesium–iodine. 1, 2-Bis(5-formyl-2-methylthien-3-
yl)cyclopentene (1) was prepared by the previous literature [53].
Amines and other starting materials were obtained commercially
as analytical-grade and used without further purification. The rel-
ative quantum yields were determined by comparing the reaction
yield with the known yield of the compound 1,2-bis(2-methyl-5-
phenyl-3-thienyl)perfluorocyclopentene [54]. Elemental analyses
(C, H, N) were performed by the Microanalytical Services, College of
Chemistry, CCNU. 1H and 13C NMR spectra were collected on Amer-
ican Varian Mercury Plus 400 spectrometer (400 MHz) or 600 MHz.
The chemical shifts are relative to TMS. UV–Vis absorption spectra
were recorded on U-3310 UV Spectrophotometer.
Fig. 4. Photograph of the color change of compounds 2f and 3d.

196
Z. Li et al. / Journal of Photochemistry and Photobiology A: Chemistry 218 (2011) 192–198
4.2. General synthetic procedure of 2a–h
136.56, 138.44, 141.38, 150.32 (s, Ar, ethene, thiophene), 153.07 (s,
CH N). MS (m/z): 624 [M]+. Anal. Calcd for C29H24Br2N2S2: C, 55.78;
H, 3.87; N, 4.49. Found: C, 55.53; H, 3.59; N, 4.68.
Synthesis of 2: To a solution of 1 (1.0 mmol) in anhydrous EtOH
(80 mL) was added amines (2.0 mmol) with anhydrous magnesium
sulfate acting as drying agent under argon atmosphere. The mixture
was refluxed for 24 h. After removing the solvent, the compound
was recrystallized from the mixture solution of dichloromethane
and hexane to give diarylethene imines in 21–89% yields.
Compound 2h: Yield, 87%. 1H NMR (400 MHz, CDCl3): ı 2.09 (s,
6H, CH3), 2.04–2.11 (m, 2H, CH2), 2.84 (t, J = 7.2 Hz, 4H, CH2), 3.90
(s, 4H, CH2), 7.17 (s, 2H, thiophene-H), 7.23–7.39 (m, 8H, fluorene),
7.52 (d, J = 7.6 Hz, 2H, fluorene), 7.75 (d, J = 8.0 Hz, 4H, fluorene), 8.49
(s, 2H, CH N). 13C NMR (100 MHz, CDCl3): ı 15.12 (s, CH3), 22.96 (s,
CH2), 36.92 (s, CH2), 38.36 (s, CH2), 117.66, 119.68, 120.28, 124.97,
126.42, 126.80, 133.31, 134.72, 136.53, 138.98, 139.78, 140.85,
141.40, 143.33, 144.37, 150.34 (s, fluorene, ethene, thiophene). MS
(m/z): 642 [M]+. Anal. Calcd for C43H34N2S2: C, 80.34; H, 5.33; N,
4.36. Found: C, 80.50; H, 5.15; N, 4.52.
Compound 2a: Yield, 83%. 1H NMR (400 MHz, CDCl3): ı 2.06 (s,
6H, CH3), 1.98–2.09 (m, 2H, CH2), 2.83 (t, J = 7.2 Hz, 4H, CH2), 7.15
(s, 2H, thiophene-H), 7.17–7.37 (m, 10H, Ar), 8.28 (s, 2H, CH N),
13C NMR (100 MHz, CDCl3): ı 15.10 (s, CH3), 22.89 (s, CH2), 38.33
(s, CH2), 120.99, 125.81, 129.05, 133.51, 134.63, 136.45, 138.70,
140.89, 151.44 (s, Ar, ethene, thiophene), 154.87 (s, CH N). MS
(m/z): 466 [M]+. Anal. Calcd for C29H26N2S2: C, 74.64; H, 5.62; N,
6.00. Found: C, 74.46; H, 5.80; N, 5.87.
4.3. General synthetic procedure of 3a–h
Compound 2b: Yield, 58%. 1H NMR (400 MHz, CDCl3): ı 2.07 (s,
6H, CH3), 2.16–2.18 (m, 2H, CH2), 2.83 (t, J = 7.2 Hz, 4H, CH2), 7.18
(s, 2H, thiophene-H), 7.10–7.13 (m, 8H, Ar), 8.46 (s, 2H, CH N),
13C NMR (100 MHz, CDCl3): ı 15.12 (s, CH3), 22.85 (s, CH2), 38.30
(s, CH2), 116.13,(d, Ar), 122.31, 1124.36, 126.44, 134.02, 134.59,
136.49, 138.50, 139.34, 141.63, 153.99, 155.30, (s, Ar, ethene, thio-
phene), 156.47 (s, CH N). MS (m/z): 502 [M]+. Anal. Calcd for
Synthesis of 3: To a solution of 2 (1.0 mmol) in anhydrous MeOH
(8 mL) and THF (10 mL) was added sodium borohydride (10 mmol)
under a argon atmosphere. The mixture was reacted under dark
conditions for 12 h at room temperature. The product was extracted
with absolute ethyl ether, then dried over sodium sulfate, upon
removed of solvent under reduced pressure and purified on a silica
gel column using petroleum ether/ethyl acetate (9:1) as the eluent
to give diarylethene amines in 67–91% yields.
C
29H24F2N2S2: C, 69.30; H, 4.81; N, 5.57. Found: C, 69.47; H, 4.52;
N, 5.78.
Compound 2c: Yield, 47%. 1H NMR (400 MHz, CDCl3): ı 2.07 (s,
Compound 3a: Yield, 85%. 1H NMR (400 MHz, CDCl3): ı 1.87
(s, 6H, CH3), 1.98–2.02 (m, 2H, CH2), 2.73 (t, J = 7.6 Hz, 4H, CH2),
4.02 (s, 2H, N–H), 4.34 (s, 4H, N–CH2), 6.60 (s, 4H, Ar), 6.62 (s, 2H,
thiophene-H), 6.71 (t, J = 7.6 Hz, 2H, Ar), 7.15 (t, J = 8.4 Hz, 4H, Ar).
13C NMR (100 MHz, CDCl3): ı 14.19 (s, CH3), 29.66 (s, CH2), 38.24
(s, CH2), 43.53 (s, N–CH2) 113.12, 117.88, 126.09, 129.15, 133.70,
134.47, 135.21, 138.26, 147.57 (s, Ar, ethene, thiophene). MS (m/z):
470 [M]+. Anal. Calcd for C29H30N2S2: C, 74.00; H, 6.42; N, 5.95.
Found: C, 74.30; H, 6.24; N, 5.64.
6H, CH3), 2.04–2.09 (m, 2H, CH2), 2.83 (t, J = 7.6 Hz, 4H, CH2), 7.01 (d,
J = 7.6 Hz, 2H, Ar), 7.07–7.25 (m, 4H, Ar), 7.18 (s, 2H, thiophene-H),
7.40 (d, J = 8.0 Hz, 2H, Ar), 8.32 (s, 2H, CH N), 13C NMR (100 MHz,
CDCl3): ı 15.14 (s, CH3), 22.84 (s, CH2), 38.31 (s, CH2), 120.07,
126.20, 127.45, 128.03, 129.82, 134.10, 134.58, 136.49, 138.30,
141.80, 148.84, (s, Ar, ethene, thiophene), 154.32 (s, CH N). MS
(m/z): 534 [M]+.Anal. Calcd for C29H24Cl2N2S2: C, 65.04; H, 4.52; N,
5.23. Found: C, 65.21; H, 4.26; N, 5.08.
Compound 3b: Yield, 80%. 1H NMR (600 MHz, CDCl3): ı 1.87 (s,
6H, CH3), 2.00–2.02 (m, 2H, CH2), 2.74 (t, J = 7.2 Hz, 4H, CH2), 4.22
(s, 2H, N–H), 4.37 (s, 4H, N–CH2), 6.63 (s, 2H, thiophene-H), 6.65
(s, 2H, Ar), 6.70 (t, J = 7.8 Hz, 2H, Ar), 6.96 (t, J = 9.0 Hz, 4H, Ar). 13C
NMR (150 MHz, CDCl3): ı 14.19 (s, CH3), 22.93 (s, CH2), 38.24 (s,
CH2), 43.12 (s, N–CH2), 112.58 (s), 114.42 (d), 117.19 (d), 124.46 (s),
126.21 (s), 133.90 (s), 134.48 (s), 135.24 (s), 135.99 (s), 137.80 (s),
150.77 (s), 152.36 (s), (Ar, ethene, thiophene). MS (m/z): 506 [M]+.
Anal. Calcd for C29H28F2N2S2: C, 68.74; H, 5.57; N, 5.53. Found: C,
69.02; H, 5.34; N, 5.29.
Compound 2d: Yield, 64%. 1H NMR (400 MHz, CDCl3): ı 2.09
(s, 6H, CH3), 2.08–2.11 (m, 2H, CH2), 2.83 (t, J = 7.2 Hz, 4H, CH2),
6.99–7.05 (m, 4H, Ar), 7.18 (s, 2H, thiophene-H), 7.25–7.58 (m,
2H, Ar), 7.59 (d, J = 8.0 Hz, 2H, Ar), 8.28 (s, 2H, CH N), 13C NMR
(100 MHz, CDCl3): ı 15.40 (s, CH3), 22.92 (s, CH2), 38.37 (s, CH2),
118.43, 119.82, 126.50, 128.20, 132.96, 134.01, 134.70, 136.59,
138.40, 141.88, 150.21 (s, Ar, ethene, thiophene), 154.02 (s, CH N).
MS (m/z): 624 [M]+.Anal. Calcd for C29H24Br2N2S2: C, 55.78; H, 3.87;
N, 4.49. Found: C, 55.59; H, 4.15; N, 4.50.
Compound 2e: Yield, 71%. 1H NMR (400 MHz, CDCl3): ı 2.10 (s,
6H, CH3), 2.08–2.12 (m, 2H, CH2), 2.83 (t, J = 7.2 Hz, 4H, CH2), 7.88 (t,
J = 7.6 Hz, 2H, Ar), 6.98 (d, J = 7.6 Hz, 2H, Ar), 7.19 (s, 2H, thiophene-
H), 7.31 (t, J = 7.2 Hz, 2H, Ar), 7.85 (d, J = 7.6 Hz, 2H, Ar), 8.24 (s, 2H,
CH N), 13C NMR (100 MHz, CDCl3): ı 15.18 (s, CH3), 22.86 (s, CH2),
38.31 (s, CH2), 95.34, 118.34, 126.87, 129.18, 133.89, 134.58, 136.57,
138.31, 138.93, 141.83, 152.34 (s, Ar, ethene, thiophene), 153.25 (s,
CH N). MS (m/z): 718 [M]+. Anal. Calcd for C29H24I2N2S2: C, 48.48;
H, 3.37; N, 3.90. Found: C, 48.19; H, 3.55; N, 3.66.
Compound 3c: Yield, 67%. 1H NMR (600 MHz, CDCl3): ı 1.87 (s,
6H, CH3), 1.93–2.02 (m, 2H, CH2), 2.73 (t, J = 6.6 Hz, 4H, CH2), 4.38
(s, 4H, N–CH2), 4.65 (s, 2H, N–H), 6.62 (s, 2H, thiophene-H), 6.65
(d, J = 8.4 Hz, 4H, Ar), 7.08 (t, J = 7.2 Hz, 2H, Ar), 7.23 (d, J = 7.8 Hz,
2H, Ar). 13C NMR (150 MHz, CDCl3): ı 14.16 (s, CH3), 22.90 (s, CH2),
38.20 (s, CH2), 43.12 (s, N–CH2), 111.63, 117.68, 119.25, 126.13,
127.62, 129.03, 133.84, 134.47, 135.22, 137.60, 143.33 (s, Ar, ethene,
thiophene). MS (m/z): 538 [M]+. Anal. Calcd for C29H28Cl2N2S2: C,
64.55; H, 5.23; N, 5.19. Found: C, 64.81; H, 5.01; N, 4.99.
Compound 2f: Yield, 73%. 1H NMR (400 MHz, CDCl3): ı 2.06 (s,
6H, CH3), 2.06–2.10 (m, 2H, CH2), 2.82 (t, J = 7.2 Hz, 4H, CH2), 7.11
(d, J = 7.2 Hz, 2H, Ar), 7.17 (s, 2H, thiophene-H), 7.21 (t, J = 7.2 Hz,
2H, Ar), 7.31 (d, J = 6.4 Hz, 4H, Ar), 8.35 (s, 2H, CH N), 13C NMR
(100 MHz, CDCl3): ı 15.12 (s, CH3), 22.88 (s, CH2), 38.30 (s, CH2),
120.16, 122.67, 123.73, 128.58, 130.34, 134.16, 134.68, 136.58,
138.29, 141.64, 152.81 (s, Ar, ethene, thiophene), 153.65 (s, CH N).
MS (m/z): 624 [M]+. Anal. Calcd for C29H24Br2N2S2: C, 55.78; H,
3.87; N, 4.49. Found: C, 55.91; H, 4.07; N, 4.53.
Compound 3d: Yield, 85%. 1H NMR (600 MHz, CDCl3): ı 1.87 (s,
6H, CH3), 1.93–2.02 (m, 2H, CH2), 2.74 (t, J = 6.6 Hz, 4H, CH2), 4.38 (s,
4H, N–CH2), 4.67 (s, 2H, N–H), 6.57 (d, J = 7.2 Hz, 4H, Ar), 6.63 (s, 2H,
thiophene-H), 7.13 (d, J = 7.2 Hz, 2H, Ar), 7.40 (d, J = 6.6 Hz, 2H, Ar).
13C NMR (150 MHz, CDCl3): ı 14.21 (s, CH3), 22.93 (s, CH2), 38.21
(s, CH2), 43.32 (s, N–CH2), 109.86, 111.75, 118.25, 126.16, 128.34,
132.34, 133.87, 134.50, 135.25, 137.55, 144.31 (s, Ar, ethene, thio-
phene). MS (m/z): 626 [M]+. Anal. Calcd for C29H28Br2N2S2: C,
55.42; H, 4.49; N, 4.46. Found: C, 55.43; H, 4.26; N, 4.17.
Compound 2g: Yield, 21%. 1H NMR (400 MHz, CDCl3): ı 2.06 (s,
6H, CH3), 2.02–2.11 (m, 2H, CH2), 2.82 (t, J = 7.6 Hz, 4H, CH2), 7.05 (d,
J = 8.4 Hz, 4H, Ar), 7.16 (s, 2H, thiophene-H), 7.45 (d, J = 8.4 Hz, 4H,
Ar), 8.35 (s, 2H, CH N), 13C NMR (100 MHz, CDCl3): ı 15.08 (s, CH3),
22.87 (s, CH2), 38.30 (s, CH2), 119.12, 122.66, 132.07, 133.88, 134.66,
Compound 3e: Yield, 90%. 1H NMR (600 MHz, CDCl3): ı 1.88 (s,
6H, CH3), 1.94–2.02 (m, 2H, CH2), 2.75 (t, J = 6.6 Hz, 4H, CH2), 4.38
(s, 4H, N–CH2), 4.53 (s, 2H, N–H), 6.45–6.58 (m, 4H, Ar), 6.63 (s, 2H,
thiophene-H), 7.17 (d, J = 6.6 Hz, 2H, Ar), 7.65 (d, J = 7.2 Hz, 2H, Ar).
13C NMR (150 MHz, CDCl3): ı 14.24 (s, CH3), 22.94 (s, CH2), 38.21

Z. Li et al. / Journal of Photochemistry and Photobiology A: Chemistry 218 (2011) 192–198
197
(s, CH2), 43.70 (s, N–CH2), 85.58, 111.09, 119.12, 126.21, 129.29,
133.89, 134.52, 135.27, 137.46, 138.96, 146.61 (s, Ar, ethene, thio-
phene). MS (m/z): 722 [M]+.Anal. Calcd for C29H28I2N2S2: C, 48.21;
H, 3.91; N, 3.88. Found: C, 48.91; H, 3.65; N, 3.69.
[13] B.Z. Chen, M.Z. Wang, Q.F. Luo, H. Tian, Novel bisthienylethene-based pho-
tochromic materials with photoregulating fluorescence, Synth. Met. 137 (2003)
985–987.
[14] Q.F. Luo, H. Tian, B.Z. Chen, W. Huang, Effective non-destructive readout of pho-
tochromic bisthienylethene–phthalocyanine hybrid, Dyes Pigments 73 (2007)
118–120.
[15] W.J. Tan, Q. Zhang, J.J. Zhang, H. Tian, Near-infrared photochromic diarylethene
iridium (III) complex, Org. Lett. 11 (2009) 161–164.
[16] M. Irie, O. Miyatake, K. Uchida, Blocked photochromism of diarylethenes, J. Am.
Chem. Soc. 114 (1992) 8715–8716.
[17] M. Irie, O. Miyatake, K. Uchida, T. Eriguchi, Photochromic diarylethenes with
intralocking arms, J. Am. Chem. Soc. 116 (1994) 9894–9900.
[18] O. Miyatake, T. Fukaminato, M. Irie, Chemical control of the photochromic
reactivity of diarylethene derivatives, Chem. Commun. (2005) 3921–3923.
[19] Z.G. Zhou, S.Z. Xiao, J. Xu, Z.Q. Liu, M. Shi, F.Y. Li, T. Yi, C.H. Huang, Modulation of
the photochromic property in an organoboron-based diarylethene by a fluoride
ion, Org. Lett. 8 (2006) 3911–3914.
[20] Z.G. Zhou, H. Yang, M. Shi, S.Z. Xiao, F.Y. Li, T. Yi, C.H. Huang, Photochromic
organoboron-based dithienylcyclopentene modulated by fluoride and mer-
curic(II) ions, ChemPhysChem 8 (2007) 1289–1292.
[21] T. Yamaguchi, Y. Fujita, H. Nakazumi, S. Kobatake, M. Irie, Photochromic proper-
ties of diarylethene derivatives having chryso[b]thiophene rings, Tetrahedron
60 (2004) 9863–9869.
[22] M. Morimoto, M. Irie, Photochromism of diarylethene single crystals: crys-
tal structures and photochromic performance, Chem. Commun. (2005)
3895–3905.
Compound 3f: Yield, 82%. 1H NMR (400 MHz, CDCl3): ı 1.87 (s,
6H, CH3), 1.97–2.05 (m, 2H, CH2), 2.73 (t, J = 7.2 Hz, 4H, CH2), 4.04
(s, 2H, N–H), 4.29 (s, 4H, N–CH2), 6.49–7.00 (m, 8H, Ar), 6.49–6.51
(m, 2H, Ar), 6.61 (s, 2H, thiophene-H), 6.73 (t, J = 1.6 Hz, 2H, Ar), 6.81
(d, J = 8.0 Hz, 2H, Ar), 6.98 (t, J = 8.0 Hz, 2H, Ar). 13C NMR (100 MHz,
CDCl3): ı 14.23 (s, CH3), 22.91 (s, CH2), 38.23 (s, CH2), 43.23 (s,
N–CH2), 111.79, 115.62, 120.57, 123.13, 123.20, 130.38, 133.91,
134.45, 135.25, 137.51, 144.74 (s, Ar, ethene, thiophene). MS (m/z):
626 [M]+.Anal. Calcd for C29H28Br2N2S2: C, 55.42; H, 4.49; N, 4.46.
Found: C, 55.60; H, 4.19; N, 4.51.
Compound 3g: Yield, 91%. 1H NMR (400 MHz, CDCl3): ı 1.87
(s, 6H, CH3), 1.99–2.03 (m, 2H, CH2), 2.73 (t, J = 7.6 Hz, 4H, CH2),
4.01 (s, 2H, N–H), 4.29 (s, 4H, N–CH2), 6.46–6.48 (m, 4H, Ar), 6.58
(s, 2H, thiophene-H), 7.20–7.24 (m, 4H, Ar). 13C NMR (100 MHz,
CDCl3): ı 14.20 (s, CH3), 22.91 (s, CH2), 38.17 (s, CH2), 43.41 (s,
N–CH2), 109.47, 114.67, 126.20, 131.80, 133.81, 134.48, 135.22,
137.73, 146.45 (s, Ar, ethene, thiophene). MS (m/z): 626 [M]+. Anal.
Calcd for C29H28Br2N2S2: C, 55.42; H, 4.49; N, 4.46. Found: C, 55.13;
H, 4.21; N, 4.57.
[23] T. Yamada, S. Kobatake, M. Irie, Single-crystalline photochromism of
diarylethene mixture, Bull. Chem. Soc. Jpn. 75 (2002) 167–173.
[24] H. Tian, S. Wang, Photochromic bisthienylethene as multi-function switches,
Chem. Commun. (2007) 781–792.
Compound 3h: Yield, 84%. 1H NMR (600 MHz, CDCl3): ı 1.88 (s,
6H, CH3), 1.99–2.03 (m, 2H, CH2), 2.73 (t, J = 6.6 Hz, 4H, CH2), 3.75 (s,
4H, CH2), 4.01 (s, 2H, N–H), 4.34 (s, 4H, N–CH2), 6.59–6.63 (m, 4H,
fluorene), 6.76 (s, 2H, thiophene-H), 7.15 (t, 2H, J = 7.2 Hz, fluorene),
7.27 (t, 2H, J = 7.2 Hz, fluorene), 7.42 (d, 2H, J = 7.2 Hz, fluorene), 7.53
(d, 2H, J = 7.8 Hz, fluorene), 7.58 (d, 2H, J = 7.8 Hz, fluorene), 13C NMR
(150 MHz, CDCl3): ı 14.23 (s, CH3), 22.91 (s, CH2), 36.88 (s, CH2),
38.21 (s, CH2), 43.73 (s, N–CH2), 109.54, 112.18, 118.43, 120.52,
124.64, 124.83, 126.05, 126.54, 132.29, 133.67, 134.47, 135.22,
138.27, 142.14, 144.99, 147.03 (s, fluorene, ethene, thiophene). MS
(m/z): 646 [M]+. Anal. Calcd for C43H38N2S2: C, 49.84; H, 5.92; N,
4.33. Found: C, 49.65; H, 5.80; N, 4.60.
[25] M. Irie, K. Sakemura, M. Okinaka, K. Uchida, Photochromism of dithienylethenes
with electron-donating substituents, J. Org. Chem. 60 (1995) 8305–8309.
[26] K. Uchida, T. Matsuoka, S. Kobatake, T. Yamaguchi, M. Irie, Substituent effect on
the photochromic reactivity of bis(2-thienyl)perfluorocyclopentenes, Tetrahe-
dron 57 (2001) 4559–4565.
[27] S.Z. Pu, T.S. Yang, J.K. Xu, L. Shen, G.Z. Li, Q. Xiao, B. Chen, Syntheses and opto-
electronic properties of four photochromic dithienylethenes, Tetrahedron 61
(2005) 6623–6629.
[28] S.Z. Pu, T.S. Yang, G.Z. Li, J.K. Xu, Substituent position effect on the optoelec-
tronic properties of photochromic diarylethenes, Tetrahedron Lett. 47 (2006)
3167–3171.
[29] S.Z. Pu, T.S. Yang, J.K. Xu, B. Chen, Syntheses and properties of new pho-
tochromic diarylethene derivatives having a pyrazole unit, Tetrahedron Lett.
47 (2006) 6473–6477.
[30] S.Z. Pu, L.S. Yan, Z.D. Wen, G. Liu, L. Shen, Synthesis and chlorine atom posi-
tion effect on the properties of unsymmetrical photochromic diarylethene, J.
Photochem. Photobiol. A: Chem. 196 (2008) 84–93.
[31] C.B. Fan, S.Z. Pu, G. Liu, T.S. Yang, Substituent position effect on the properties
of isomeric photochromic diarylethenes bearing chlorine atoms, J. Photochem.
Photobiol. A: Chem. 194 (2008) 333–343.
Acknowledgements
[32] C.B. Fan, S.Z. Pu, G. Liu, T.S. Yang, Substituent position effect on the proper-
ties of new unsymmetrical isomeric diarylethenes having a chlorine atom, J.
Photochem. Photobiol. A: Chem. 197 (2008) 415–425.
[33] K. Morimitsu, K. Shibata, S. Kobatake, M. Irie, Dithienylethenes with a novel
photochromic performance, J. Org. Chem. 67 (2002) 4574–4578.
[34] S. Takami, M. Irie, Synthesis and photochromic properties of novel yellow
developing photochromic compounds, Tetrahedron 60 (2004) 6155–6161.
[35] T. Yamaguchi, M. Irie, Photochromism of bis(2-alkyl-1-benzothiophen-3-yl)
perfluorocyclopentene derivatives, J. Photochem. Photobiol. A: Chem. 178
(2006) 162–169.
[36] T. Yamaguchi, M. Irie, Photochromism of diarylethene derivatives having n-
alkylbenzothiophene and n-alkylbenzofuran units, Bull. Chem. Soc. Jpn. 7
(2006) 1100–1105.
[37] T. Akitsu, Y. Einaga, Syntheses, crystal structures and electronic properties of a
series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands
and their solutions, Polyhedron 24 (2005) 2933–2943.
[38] T Akitsu, Y. Einaga, Synthesis, crystal structures and electronic properties of
Schiff base nickel (II) complexes: towards solvatochromism induced by a pho-
tochromic solute, Polyhedron 24 (2005) 1869–1877.
[39] J.M. Veauthier, W.S. Cho, V.M. Lynch, J.L. Sessler, Calix[4]pyrrole Schiff base
macrocycles: novel binucleating ligands for í-oxo iron complexes, Inorg. Chem.
43 (2004) 1220–1228.
[40] J.M. Veauthier, E. Tomat, V.M. Lynch, J.L. Sessler, U. Mirsaidov, J.T. Markert,
Calix[4]pyrrole Schiff base macrocycles: novel binucleating ligands for Cu(I)
and Cu(II), Inorg. Chem. 44 (2005) 6736–6743.
[41] A.J. Gallant, J.H. Chong, M.J. MacLachlan, Heptametallic bowl-shaped complexes
derived from conjugated Schiff-base macrocycles: synthesis, characterization,
and X-ray crystal structures, Inorg. Chem. 45 (2006) 5248–5250.
[42] P.D. Frischmann, A.J. Gallant, J.H. Chong, M.J. MacLachlan, Zinc carboxylate
cluster formation in conjugated metallomacrocycles: evidence for templation,
Inorg. Chem. 47 (2008) 101–112.
The authors acknowledge financial support from National Nat-
ural Science Foundation of China (Nos. 2072039, 20931006, and
21072070) and Program for Changjiang Scholars and Innovative
Research Team in University (No. IRT0953).
References
[1] G.H. Brown, Photochromism, Wiley, New York, 1971.
[2] H. Durr, H. Bouas-Laurent, Photochromism, Molecules and Systems, Elsevier,
Amsterdam, 1990.
[3] K. Fukushima, A.J. Vandenbos, T. Fujiwara, Spiropyran dimer toward photo-
switchable molecular machine, Chem. Mater. 19 (2007) 644–646.
[4] X.Y. Zhao, M.Z. Wang, Synthesis and photoresponsive behavior of azobenzene-
functionalized polythiophene films, Eur. Polym. J. 42 (2006) 247–253.
[5] Y. Yokoyama, Fulgides for memories and switches, Chem. Rev. 100 (2000)
1717–1740.
[6] M. Irie, Diarylethenes for memories and switches, Chem. Rev. 100 (2000)
1685–1716.
[7] S. Kawata, Y. Kawata, Three-dimensional optical data storage using pho-
tochromic materials, Chem. Rev. 100 (2000) 1777–1788.
[8] H. Tian, S. Yang, Recent progresses on diarylethene based photochromic
switches, J. Chem. Soc. Rev. 33 (2004) 85–97.
[9] T. Tsujioka, M. Kume, M. Irie, Optical density dependence of write/read charac-
teristics in photon-mode photochromic memory, Jpn. J. Appl. Phys. 35 (1996)
4353–4360.
[10] B.Z. Chen, M.Z. Wang, Y.Q. Wu, H. Tian, Reversible near-infrared fluorescence
switch by novel photochromic unsymmetrical-phthalocyanine hybrids based
on bisthienylethene, Chem. Commun. (2002) 1060–1061.
[11] B. Qin, R.X. Yao, X.L. Zhao, H. Tian, Enhanced photochromism of 1,2-
dithienylcyclopentene complexes with metal ion, Org. Biomol. Chem. 1 (2003)
2187–2191.
[43] N.E. Borisova, M.D. Reshetova, Y.A. Ustynyuk, Metal-free methods in
the synthesis of macrocyclic Schiff bases, Chem. Rev. 107 (2007) 46–
79.
[44] P.A. Vigato, S. Tamburini, The challenge of cyclic and acyclic Schiff bases and
related derivatives, Coord. Chem. Rev. 248 (2004) 1717–2128.
[12] H. Tian, B. Qin, R.X. Yao, X.L. Zhao, S.J. Yang, A single photochromic molecular
switch with four optical outputs probing four inputs, Adv. Mater. 15 (2003)
2104–2107.

198
Z. Li et al. / Journal of Photochemistry and Photobiology A: Chemistry 218 (2011) 192–198
[45] K. Tanaka, R. Shimoura, M.R. Caira, Synthesis, crystal structures and pho-
tochromic properties of novel chiral Schiff base macrocycles, Tetrahedron Lett.
51 (2010) 449–452.
[46] A.J Gallant, J.H. Chong, M.J. MacLachlan, Heptametallic bowl-shaped complexes
derived from conjugated Schiff-base macrocycles, Inorg. Chem. 45 (2006)
5248–5250.
[47] B.N. Boden, J.K.H. Hui, M.J.J. MacLachlan, Social and antisocial [3 + 3] Schiff base
macrocycles with isomeric backbones, J. Org. Chem. 73 (2008) 8069–8072.
[48] C.P. Jaroniec, J.C. Lansing, B.A. Tounge, M. Belenky, J. Herzfeld, R.G. Griffin,
Measurement of dipolar couplings in a uniformly 13C, 15N-labeled membrane
protein: distances between the Schiff base and aspartic acids in the active site
of bacteriorhodopsin, J. Am. Chem. Soc. 123 (2001) 12929–12930.
[49] M.M. Greenberg, C.R. Kreller, S.E. Young, J. Kim, Reactivity of the C2ꢀ-oxidized
abasic lesion and its relevance to interactions with type I base excision repair
enzymes, Chem. Res. Toxicol. 19 (2006) 463–468.
[50] M. Morimoto, H. Miyasaka, M. Yamashita, M. Irie, Coordination assemblies of
[Mn4] single-molecule magnets linked by photochromic ligands: photochemi-
cal control of the magnetic properties, J. Am. Chem. Soc. 131 (2009) 9823–9835.
[51] V. Ramamurthy, K. Venkatesan, Photochemical reactions of organic crystals,
Chem. Rev. 87 (1987) 433–481.
[52] S. Kobatake, K. Uchida, E. Tsuchida, M. Irie, Single-crystalline photochromism
of diarylethenes: reactivity–structure relationship, Chem. Commun. (2002)
2804–2805.
[53] L.N. Lucas, J.J.D. de Jong, J.H. van Esch, R.M. Kellogg, B.L. Feringa, Syntheses of
dithienylcyclopentene optical molecular switches, Eur. J. Org. Chem. (2003)
155–166.
[54] M. Irie, T. Lifka, S. Kobatake, N. Kato, Photochromism of 1,2-bis(2-methyl-5-
phenyl-3-thienyl)perfluorocyclopentene in a single-crystalline phase, J. Am.
Chem. Soc. 122 (2000) 4871–4876.