Crystal structures and photoisomerization behaviors of five novel pyrazolone derivatives containing furoyl group

Article abstract of DOI:10.1016/j.jphotochem.2010.09.027

Five novel pyrazolone derivatives containing a furoyl group, 1-phenyl-3-furoyl-4-(4-chlorobenzal)-5-pyrazolone thiosemicarbazone (PF4ClBP-TSC) (1)/methylthiosemicarbazone (PF4ClBP-MTSC) (2)/ ethylthiosemicarbazone (PF4ClBP-ETSC) (3), 1-phenyl-3-furoyl-4-(

Full text of DOI:10.1016/j.jphotochem.2010.09.027

Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 117–124
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Crystal structures and photoisomerization behaviors of five novel pyrazolone
derivatives containing furoyl group
Jianping Hu, Lang Liu, Dianzeng Jia∗, Jixi Guo, Xiangyun Xie, Dongling Wu, Rui Sheng
Institute of Applied Chemistry, Xinjiang University, Urumqi 830046, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 April 2010
Received in revised form 7 September 2010
Accepted 29 September 2010
Available online 7 October 2010
Five novel pyrazolone derivatives containing a furoyl group, 1-phenyl-3-furoyl-4-(4-chlorobenzal)-
5-pyrazolone thiosemicarbazone (PF4ClBP-TSC) (1)/methylthiosemicarbazone (PF4ClBP-MTSC) (2)/
ethylthiosemicarbazone (PF4ClBP-ETSC) (3), 1-phenyl-3-furoyl-4-(2-chlorobenzal)/(3-chlorobenzal)-5-
pyrazolone methylthiosemicarbazone (PF2ClBP-MTSC) (4)/(PF3ClBP-MTSC) (5), have been synthesized
and characterized by elemental analysis, IR, 1H NMR spectra, and the molecular structures of 2 and 5
were determined by X-ray single crystal diffraction. Photoisomerization properties have been studied
by UV–vis and fluorescence spectra. Based on theoretical calculation and crystal structural analysis, the
compounds undergo photoisomerization from the enol form to the keto form through an intermolecu-
lar proton transfer upon UV light irradiation. Moreover, the photoisomerization rate decreases with the
increase of volume of substituent groups on 4-position of thiosemicarbazide and the steric hindrance of
Cl atom on benzal of 4-positon on the pyrazolone ring.
Keywords:
Photoisomerization
Crystal structure
Pyrazolone
Intermolecular proton transfer
Thiosemicarbazide
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
groups on the 3- or 4-position on the pyrazolone ring and using
other thiosemicarbazide derivatives. Previous works are focused
Organic photochromic compounds have attracted considerable
interest due to their promising applications in many fields, such
as high-density optical storage media [1–3], molecular switches
[4–8], information processors [9,10] and molecular sensors [11,12].
Considerable work on spiropyrans [13,14], spiroxazine [15–18],
dithienylethenes [19,20], fulgides [21], and Schiff bases [22–25]
have been extensively reported, but little work have been done
on photochromism in solid state [26–28]. Most of organic pho-
tochromic compounds can only show photochromic properties in
solution, however, these limit their application in solid state, such
as ophthalmic plastic lenses, optical disks and digital versatile
disks [29–31]. Recently, pyrazolones and their derivatives play
important roles in many fields, especially biology, catalysis, cor-
rosion inhibitors and medicine etc. [32–36]. Furthermore, 4-acyl
pyrazolone derivatives have a potential to form tautomeric effect
between the enol form and the keto form. So the molecular design
and synthesis of novel pyrazolone derivatives is still an active
research area. Many thiosemicarbazones derived from 4-acyl
pyrazolones with photoisomerization properties have been sys-
temically studied in our laboratory [37–41], but the majority show
irreversible photoisomerization behaviors, thus many efforts have
been dedicated to design the structures by changing the substitute
on 1-phenyl-3-methyl or 1,3-diphenyl-4-acyl-5-pyrazolone
thiosemicarbazone derivatives. For example, 1,3-diphenyl-4-
(2-chlorobenzal)-5-hydroxypyrazole
methylthiosemicarbazone
[40], 1-phenyl-3-methyl-4-(2-fluorobenzal)-5-hydroxypyrazole
methylthiosemicarbazone/ethylthiosemicarbazone [41], show a
reversible photoisomerization. But these compounds display slow
response to UV and visible light or incomplete reversibility. So
their derivatives need to be further developed by the structural
modification in order to improve the photochromic properties and
establish the relation between structures and properties.
In this paper, five novel compounds, 1-phenyl-3-furoyl-4-(4-
chlorobenzal)-5-pyrazolone thiosemicarbazone (1)/methylth-
iosemicarbazone (2)/ethylthiosemicarbazone (3), 1-phenyl-
3-furoyl-4-(2-chlorobenzal)/(3-chlorobenzal)-5-pyrazolone met-
hylthiosemicarbazone (4)/(5), are synthesized by the incorporation
of the furoyl group on 3-position of pyrazolone. They are charac-
terized by elemental analysis, IR, 1H NMR spectra. With the aim of
gaining a deeper insight into the photoisomerization mechanism,
crystallographic structure analysis and theoretical calculation of
the compounds have been carried out. The results show that the
five compounds undergo photoisomerization from the enol form to
the keto form through an intermolecular proton transfer upon UV
light irradiation. In addition, the effects of volume of substituent
groups on 4-position of thiosemicarbazide and the position of Cl
atom on benzal on 4-position of pyrazolone ring on structures
and photoisomerization properties of compounds were discussed
∗
Corresponding author. Fax: +86 991 8588883.
E-mail addresses: jdz0991@gmail.com, llyhs1973@sina.com (D. Jia).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.09.027

118
J. Hu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 117–124
in detail. These results will increase the knowledge to design
and synthesize novel pyrazolone derivatives with photochromic
properties in solid state.
purchased from commercial suppliers, and used without further
purification.
2.3. Synthesis of compound 1
2. Experimental
1-Phenyl-3-furoyl-4-(4-chlorobenzal)-5-pyrazolone thiosemi-
carbazone was synthesized by refluxing of PF4ClBP (5 mmol) and
thiosemicarbazide (5 mmol) in 15 ml of ethanol in the presence of
glacial acetic acid (1 ml) at 80 ◦C for 4 h under magnetic stirring.
Then the resulting mixture was cooled to room temperature in the
dark and filtered, white powders 1 were obtained. Yield: 65.5%,
m.p. 199.4–200.7 ◦C. Elemental analysis results for C21H16N5SO2Cl:
found (%) C, 57.10; H, 3.67; N, 15.81; calcd. (%) C, 57.60; H, 3.68;
N, 15.99. IR (ꢀ cm−1): (white) 3429 ꢁ(NH), 3332, 3281 ꢁ(NH),
3122 ꢁ(furoyl), 3064–2000 ꢁ(OH), 1612 ꢁ(C N), 1581–1501 ꢁ(Ph-
ring), 1413, 1374 ꢁ(Pz-ring), 1302 ꢁ(C S). 1H NMR (DMSO-d6) (ı):
9.728 (1H, NH), 8.301 (1H, NH), 8.479 (1H, NH), 6.321–7.876 (12H,
phenyl + furoyl), 3.453(1H, CH).
2.1. Measurements
Melting point was measured with a TECH X-6 melting point
apparatus without correction. The C, H, and N elemental analysis
was determined on a FLASHEA 1112 elemental analyzer. The FT-
IR spectra were recorded on a BRUKER EQUINOX-55 Spectrometer
as KBr disk. 1H NMR spectra were carried at ambient tempera-
ture on an INOVA-400 NMR Spectrometer in DMSO-d6. The UV–vis
spectra of powders were measured using a Hitachi U-3010 spec-
trophotometer equipped with an integrating sphere accessory [36].
365 nm excitation light (1579 mW/cm2 on the sample) were down
with a ZF-8 Ultraviolet Analysis Instrument, the reflective filter size
is 200 × 80 mm, the distance between the sample and light source
was 15 cm. Fluorescence spectra of powders were measured on a
Hitachi F-4500 spectrophotometer with a front face experiment,
and the breadths of excitation and emission slits were both 2.5 nm.
2.4. Synthesis of compounds 2–5
According to the synthetic method of 1, compounds 2–5 were
prepared. The synthesis routine and the photoisomerization pro-
cess of five compounds are presented in Scheme 1. For yellowish
powders 2, yield: 84.5%, m.p. 227.3–229.1 ◦C. Elemental analysis
results for C22H18N5SO2Cl: found (%) C, 57.94; H, 3.98; N, 15.52;
calcd. (%) C, 58.47; H, 4.01; N, 15.50. IR (ꢀ cm−1): 3361, 3344 ꢁ(NH),
3114 ꢁ(furoyl), 3051–2215 ꢁ(OH), 1622 ꢁ(C N), 1589–1501 ꢁ(Ph-
ring), 1417, 1375 ꢁ(Pz-ring), 1305 ꢁ(C S). 1H NMR (DMSO-d6) (ı):
9.756 (1H, NH), 8.795 (1H, NH), 6.328–7.873 (12H, phenyl + furoyl),
3.380 (1H, CH), 3.058–3.069 (3H, CH3).
2.2. Materials
4-Methylthiosemicarbazide and 4-ethylthiosemicarbazide
were purchased from the Aldrich Company, USA. 1-Phenyl-3-
furoyl-5-pyrazolone (PFP) [42], 1-phenyl-3-furoyl-4-(4-chloro-
benzal)-5-pyrazolone (PF4ClBP), 1-phenyl-3-furoyl-4-(2-chloro-
benzal)-5-pyrazolone (PF2ClBP), and 1-phenyl-3-furoyl-4-(3-
chlorobenzal)-5-pyrazolone (PF3ClBP) [43] were synthesized
according to the literature. All other reagents were AR grade and
Scheme 1. Synthetic route and photoisomerization process of compounds.

J. Hu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 117–124
119
For compound 3, yield: 81.0%, m.p. 214.8–215.3 ◦C. Elemental
2.5. X-ray crystallography
analysis results for C23H20N5SO2Cl: found (%) C, 58.84; H, 4.30; N,
15.03; calcd. (%) C, 59.29; H, 4.33; N, 15.03. IR (ꢀ cm−1): 3331,
3311 ꢁ(NH), 3121 ꢁ(furoyl), 3069–2000 ꢁ(OH), 1619 ꢁ(C N),
1579–1500 ꢁ(Ph-ring), 1400, 1373 ꢁ(Pz-ring), 1308 ꢁ(C S). 1H
NMR (DMSO-d6) (ı): 9.652 (1H, NH), 8.845 (1H, NH), 6.334–7.874
(12H, phenyl + furoyl), 3.618–3.650 (3H, CH2 + CH), 1.159–1.195
(3H, CH3).
The X-ray diffraction data of compounds 2 and 5 were collected
by the ␻-scan mode using a graphite monochromatized MoKa
radiation(ꢂ = 0.71073 A) on an imaging plate system (Rigaku R-AXIS
SPIDER) at 296 K. Crystal structures were solved by direct methods
and refined on F2 using the full-matrix least-squares method. All
non-H atoms were refined anisotropically. H atoms on nitrogen
atoms are located from Fourier maps, and all of the other H atoms
were placed in geometrically idealized position. All calculations and
drawings were carried out using the SHELXTL-97 crystallographic
software package [44].
˚
For compound 4, yield: 64.1%, m.p. 195.2–196.4 ◦C. Elemental
analysis results for C22H18N5SO2Cl: found (%) C, 58.28; H, 4.12; N,
15.46; calcd. (%) C, 58.47; H, 4.01; N, 15.50. IR (ꢀ cm−1): 3351 ꢁ(NH),
3116 ꢁ(furoyl), 3054–2347 ꢁ(OH), 1644 ꢁ(C N), 1594–1495 ꢁ(Ph-
ring), 1432, 1397 ꢁ(Pz-ring), 1306 ꢁ(C S). 1H NMR (DMSO-d6) (ı):
9.746 (1H, NH), 8.402 (1H, NH), 6.130–7.942 (12H, phenyl + furoyl),
2.921–3.038 (4H, CH + CH3).
3. Results and discussion
For compound 5, yield: 76.8%, m.p. 214.8–216.4 ◦C. Elemental
analysis results for C22H18N5SO2Cl: found (%) C, 58.27; H, 3.81; N,
15.31; calcd. (%) C, 58.47; H, 4.01; N, 15.50. IR (ꢀ cm−1): 3351,
3331 ꢁ(NH), 3123 ꢁ(furoyl), 3072–2000 ꢁ(OH), 1520 ꢁ(C N),
1537–1480 ꢁ(Ph-ring), 1416, 1373 ꢁ(Pz-ring), 1307 ꢁ(C S). 1H
NMR (DMSO-d6) (ı): 9.849 (1H, NH), 8.813 (1H, NH), 6.324–8.015
(12H, phenyl + furoyl), 3.070–3.082 (4H, CH + CH3).
3.1. Photoisomerization properties in solid state and kinetics of
the reaction
The UV spectra of five compounds in solid state at room tem-
perature for different irradiation time intervals are recorded and
shown in Fig. 1. It can be observed that new bands appear between
370 and 480 nm for 1, 390 and 460 nm for 2, 390 and 460 nm for 3,
Fig. 1. UV spectra of five powders in the solid state with increasing irradiation times at room temperature. (1) Each irradiation time (min) for 1 is 0, 5, 15, 20, 25, 35, 45, 75,
105, 165. (2) Each irradiation time (min) for 2 is 0, 10, 20, 30, 50, 70, 110, 160, 200, 260, 330. (3) Each irradiation time (min) for 3 is 0, 30, 90, 150, 210, 290, 370, 450, 515,
650. (4) Each irradiation time (min) for 4 is 0, 10, 30, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, 280, 370, 500. (5) Each irradiation time (min) for 5 is 0, 30, 60, 100, 160,
220, 280, 330, 390, 420, 500.

120
J. Hu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 117–124
410 and 480 nm for 4, and 390 and 460 nm for 5 upon the irradia-
tion of 365 nm light, and their intensities the increase of irradiation
time. Subsequently, the white powders (I) changed to yellow (III)
(Scheme 1). The results indicate that the photoisomerization from
the enol form to the keto form occurs in solid state during the irra-
diation. No mater they are heated or irradiated by visible light or
placed in the dark, the photogenerated yellow forms cannot return
to the original forms, which indicate that the colored forms are
very stable and the photoisomerization of five compounds is irre-
versible.
According to the literature [45], the kinetic rate constant can be
determined from the plot of ln[(A∞ − A0)/(A∞ − At)] against time (t).
From Fig. 2, it can be observed that the enol-to-keto isomerization
reaction of five compounds follow the pseudo-first-order kinetics
and the rate constants were obtained from the slope. Obviously,
the order of the photoisomerization rate of compounds 1, 2 and
3 is k1 > k2 > k3, which indicates that the photoisomerization rate
decreases with the increase of volume of substituent groups on 4-
position of thiosemicarbazide due to the larger steric hindrance.
Compared with the photoisomerization rate constants of 4 and 5,
the photoisomerization rate of compound 2 is much faster than that
of compounds 4 and 5, which is due to the steric hindrance of Cl
Fig. 2. First-order kinetic plot of photoisomerization reaction.
atom on the 4-position of the benzal is smaller than that of Cl on
the 3-, 2-position of the phenyl group.
For the analogue compound 1,3-diphenyl-4-(2-chlorobenzal)-
5-hydroxypyrazole 4-methylthiosemicarbazone, the kinetic con-
Fig. 3. Fluorescent emission spectra of five compounds under the irradiation of 365 nm UV light at room temperature (excited at 300 nm). (1) Each irradiation time (min)
for 1 is 0, 0.5, 1, 3, 6, 12, 24, 51. (2) Each irradiation time (min) for 2 is 0, 2, 6, 12, 21, 30, 39, 48. (3) Each irradiation time (min) for 3 is 0, 1, 6, 12, 18, 27, 36, 42. (4) Each
irradiation time (min) for 4 is 0, 0.5, 1, 2, 5, 11, 21, 31, 41, 56, 76, 96. (5) Each irradiation time (min) for 5 is 0, 3, 9, 15, 21, 27, 36, 45, 51.

J. Hu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 117–124
121
Table 1
Absorption bands, kinetics constants and fluorescence maximum spectra of compounds.
Compounds
Absorption bands (nm)
Kinetics constants
Fluorescence maximum spectra
1
2
3
4
5
370–480
390–460
390–460
410–480
390–460
3.69 × 10−4 s−1
1.28 × 10−4 s−1
4.1 × 10−5 s−1
8.02 × 10−5 s−1
9.17 × 10−5 s−1
415 nm, 474 nm
425 nm, 474 nm
427 nm, 474 nm
448 nm
417 nm, 516 nm
stant of the photoisomerization is 1.72 × 10−5 s−1, which is smaller
than that of the compound 4. The result shows that the photoiso-
merization rate of the compound 4 increases due to the electron
withdrawing property of the O atom, when the furoyl group on
3-position of pyrazolone instead of the phenyl group.
somerization behaviors. However, UV light stationary irradiation
has no influence on the absorption and fluorescence spectra of the
different compounds in solution.
3.2. Crystal structure, stability and photoisomerization
mechanism
The fluorescent emission spectra of five compounds irradiated
by 365 nm UV light at different times at room temperature are
shown in Fig. 3. It can be seen that there are two bands in the flu-
orescent emission spectra of 1, 2 and 3, which appear at 415 nm
and 474 nm for 1, 425 nm and 474 nm for 2, 427 nm and 474 nm
for 3, respectively (Table 1), their intensity gradually decreased
with the irradiation of 365 nm light. Furthermore, the second bands
of three compounds lie in the same position, but the first bands
have the red-shift phenomenon with the increase of volume of
substituent groups on 4-position of thiosemicarbazide, which are
consistent with those of their UV absorption spectra. Compared
with the second band of 2, the fluorescent emission spectra of 4
blue shifts to 448 nm and that of 5 red shifts to 516 nm after being
excited at 300 nm, which is due to the steric hindrance of Cl atom
on the 4-position of benzal. Obviously, their intensity gradually
decreased with the irradiation of 365 nm light, and the emission
band at 415 nm (1), 427 nm (3) and 417 nm (5) finally disappeared.
Subsequently, the white enol form (I) gradually changed to the yel-
low keto form (III), the dramatic color changes can be explained
by the photoinduced proton transfer from one moiety to another,
the proton transfer and configuration rearrangement of the ␲ elec-
trons lead to fluorescent emission spectra changes in the solid
state, which further indicate that five compounds have photoi-
Single crystals of compounds 2 and 5 were obtained by the slow
evaporation of their methanol at room temperature with avoid-
ing sunlight. The crystal data and structure refinement details of
compounds 2 and 5 are given in Table 2. Selected bond lengths
and bond angles are listed in Table 3. The dihedral angles (◦) of
two compounds are listed in Table 4. The molecular structures of
compounds 2 and 5 are shown in Fig. 4.
From Table 2, it can be seen that compounds 2 and 5 have the
same composition, but they have the different crystal system, space
group and unit cell parameter. From Table 3, it can be found that
the two compounds have similar bond length and bond angles,
leading to similar structures as shown in Fig. 4. But obvious dif-
ference is the relative orientation of two groups (chlorophenyl and
methylthiosemicarbazide) on the 4-position of the pyrazolone ring.
From Table 4, it can be found that the dihedral angle of the pyra-
zole ring (I) and the furoyl ring(III) on 3-position is almost 1.4◦
for 2, which indicates that the two planes are coplanar. In addition,
the dihedral angles between the chlorophenyl(IV) and the plane(V)
defined by N3, N4, N5, C21 atoms are 3.4◦ for 2 and 4.5◦ for 5, respec-
tively, which show that the side-chain groups for 2 and 5 are almost
coplanar.
Table 2
Crystal data and structure refinement for compounds 2 and 5.
Compounds
2
5
Empirical formula
Formula weight
Temperature
C22H18ClN5O2S
451.92
C22H18ClN5O2S
451.92
153(2) K
153(2) K
˚
˚
Wavelength
0.71073 A
0.71073 A
Crystal system
Space group
Orthorhombic
Monoclinic
Pna2(1)
a = 11.771(2) A, ˛ = 90
P2(1)/c
◦
◦
◦
◦
˚
a = 13.0250(8) A, ˛ = 90
˚
◦
˚
b = 14.4207(8) A, ˇ = 104.490
˚
Unit cell dimensions
b = 11.916(2) A, ˇ = 90
◦
˚
˚
c = 14.556(3) A, ꢃ = 90
c = 11.6216(6) A, ꢃ = 90
3
3
˚
˚
Volume
2041.9(7) A
2113.4(2) A
Z
4
4
Calculated density
Absorption coefficient
F(0 0 0)
1.470 g/cm3
0.321 mm−1
936
1.420 g/cm3
0.310 mm−1
936
Crystal size
Theta range for data collection
Limiting indices
0.50 × 0.35 × 0.23 mm
0.35 × 0.14 × 0.11 mm
3.42–27.48◦
3.06–27.48◦
−15 ≤ h≤ 15, −15 ≤ k≤ 15, −18 ≤ l ≤ 18
18605/2430 [R(int) = 0.0237]
0.9310 and 0.8556
−16 ≤ h ≤ 16, −18 ≤ k ≤ 18, −15 ≤ l ≤ 15
20103/4843 [R(int) = 0.0434]
0.9667 and 0.8993
Reflections collected/unique
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2ꢄ (I)]
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
Full-matrix least-squares on F2
2430/4/292
Full-matrix least-squares on F2
4843/3/293
1.080
1.087
R1 = 0.0266, wR2 = 0.0686
R1 = 0.0270, wR2 = 0.0689
0.0059(8)
R1 = 0.0434, wR2 = 0.1204
R1 = 0.0514, wR2 = 0.1280
0.0063(12)
−3
−3
˚
˚
0.240 and −0.297 eA
0.366 and −0.422 eA

122
J. Hu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 117–124
Table 3
Table 5
Selected bond lengths (Å) and angles (◦) for compounds 2 and 5.
Calculated electronic energies E (in a.u.), relative electronic energies ꢅE (in
kcal mol−1), and dipole moment ꢆ (in Debye) of compounds 2 and 5 in the gas
2
5
phase and methanol solution.
Bond lengths
S–C(21)
N(1)–N(2)
N(1)–C(7)
C(8)–C(9)
N(1)–C(6)
N(2)–C(9)
N(3)–C(14)
N(3)–N(4)
2
5
1.683(2)
1.389(2)
1.378(2)
1.389(2)
1.432(2)
1.356(2)
1.286(3)
1.359(2)
1.365(3)
1.324(3)
1.253(2)
S–C(21)
1.6811(2)
1.3756(2)
1.3845(2)
1.391(2)
1.427(2)
1.345(2)
1.290(2)
1.3559(2)
1.372(2)
1.323(2)
1.2548(2)
N(1)–N(2)
N(1)–C(7)
C(8)–C(9)
N(1)–C(6)
N(2)–C(9)
N(3)–C(14)
N(3)–N(4)
N(4)–C(21)
N(5)–C(21)
O(1)–C(7)
Egas
Egas
(a.u.)
(a.u.)
−2131.715360
−2131.714540
0.52
3.6912
5.4892
−2131.744713
−2131.752006
−4.58
−2131.711851
−2131.714047
−1.38
enol
keto
ꢅEgas
keto
ꢆgas
ꢆgas
4.3981
4.4993
enol
keto
Esol
(a.u.)
(a.u.)
−2131.744199
−2131.751616
−4.66
enol
Esol
keto
N(4)–C(21)
N(5)–C(21)
O(1)–C(7)
ꢅEsol
enol
Bond angles
N(2)–N(1)–C(6)
C(9)–N(2)–N(1)
C(7)–N(1)–N(2)
N(3)–C(14)–C(8)
N(1)–C(7)–C(8)
N(2)–C(9)–C(8)
N(5)–C(21)–N(4)
N(5)–C(21)–S
N(4)–C(21)–S
However, the chlorophenyl and methylthiosemicarbazide will
rotate around the C8–C14 bond when the position of Cl atom
changes. As shown in Scheme 2, it is very clear that the relative
orientation of chlorophenyl and methylthiosemicarbazide with the
pyrazole ring are different due to the steric hindrance of Cl atom,
leading to the dihedral angle between the pyrazole ring(I) and the
phenyl ring(II) on 1-position is also different.
120.37(15)
107.71(14)
109.80(16)
125.65(17)
105.91(15)
109.78(16)
116.42(18)
124.99(16)
118.59(15)
N(2)–N(1)–C(6)
C(9)–N(2)–N(1)
C(7)–N(1)–N(2)
N(3)–C(14)–C(8)
N(1)–C(7)–C(8)
N(2)–C(9)–C(8)
N(5)–C(21)–N(4)
N(5)–C(21)–S
121.64(12)
108.94(11)
108.80(12)
124.39(14)
106.34(13)
109.14(14)
115.62(15)
126.59(14)
117.79(12)
˚
˚
The C7–O1 bond distances are 1.253(2) A for 2 and 1.2548(2) A
for 5, respectively, which is consistent with the length of the C
N(4)–C(21)–S
O
double bond. It can be deduced that their structures belong to the
keto (III) form in Scheme 1, which is in agreement with the com-
pounds reported previously [40,41]. Actually, we only obtained the
keto form crystals from their solution. In order to further analyze
the stability of the keto and enol forms, theoretical calculations
are performed with the GAUSSIAN 03W program package [46].
The geometric parameters of the keto form are taken from the
X-ray diffraction crystal data. The calculated electronic energies
E, relative electronic energies ꢅE, and dipole moment ꢆ of com-
pounds 2 and 5 in the gas phase and methanol solution are shown
in Table 5. Although the enol form of 2 is more stable than the
keto form in the gas phase, the keto form of 2 is the favored form
in methanol solution, as the larger dipole moment ꢆ of keto form
(5.4892 Debye for keto, 3.6912 Debye for enol) [47,48] and a small
energy gap of 0.52 kcal mol−1 between the two forms. On the con-
Table 4
The dihedral angles (◦) of two compounds.
The mean plane deviation
Dihedral angles
2
I (N1, N2, C7, C8, C9)
II (C1–C6)
III (C10–C13, O2)
IV (C15–C20)
0.0139
0.0146
0.0036
0.01
47.1
1.4, 46.9
65.6, 34.8, 66.3
67.0, 33.5, 36.7, 3.4
V (N3, N4, N5, C21)
0.0123
5
I (N1, N2, C7, C8, C9)
II (C1–C6)
III (C10–C13, O2)
IV (C15–C20)
0.0091
0.0110
0.0009
0.0059
0.0391
32.2
8.5, 27.2
76.2, 83.4, 73.7
70.6, 79.6, 67.3, 7.8
V (N3, N4, N5, C21)
Fig. 4. Molecular structures of compound 2 (A) and 5 (B).

J. Hu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 117–124
123
Scheme 2. Rotation of the chlorophenyl and methylthiosemicarbazide around the C8–C14
.
Fig. 5. Hydrogen bond connection diagrams of compounds 2 (A) and 5 (B).
trary, the keto form of 5 is predicted as the more stable form in the
gas phase, and the order of stability is preserved in methanol solu-
tion because of the small difference of ꢆ (ꢆgasenol = 4.3981 Debye,
ꢆgasketo = 4.4993 Debye). The calculated results suggest that the
keto form of 2 and 5 is the most stable isomer in methanol solu-
tion, which is in good agreement with the experimental fact that the
single crystal structures of the compounds obtained from methanol
are the keto forms [41].
chlorobenzal)-5-hydroxypyrazole methylthiosemicarbazone [37],
but is different from that of the analogous compound 1,3-diphenyl-
4-(2-chlorobenzal)-5-hydroxypyrazole methylthiosemicarbazone,
which is not only an intramolecular proton transfer from the O atom
of the hydroxyl group to the N(4) atom of the same molecule, but
also an intermolecular proton transfer from the S atom to the N(2)
atom on pyrazole ring of the adjoining molecule [40]. These results
indicate that substituent groups on 3-, 4-position have important
effect on the structures and photochromic properties.
From the hydrogen bond connection diagrams (Fig. 5), it can
be seen that there is a similar hydrogen bonding configuration
in the two crystals, and they are stabilized by the intermolec-
4. Conclusion
˚
˚
ular hydrogen bond (N2–H· · ·O1, 2.784 A or 2.642 A). Based on
the above analysis, a reasonable photoisomerization mechanism
is proposed. Under UV light irradiation, the intermolecular pro-
ton transfers from the O atom to the N2 atom by the channel of
N2–H· · ·O1, forming an intermolecular hydrogen bond N2–H· · ·O1.
Thus, it results in the enol–keto photoisomerization through the
intermolecular hydrogen bond via the intermediated state (II) as
shown in Scheme 1. The photoisomerization mechanism of the
title compounds is consistent with that of 1-phenyl-3-methyl-4-(3-
Five novel pyrazolone derivates containing a furoyl ring have
been synthesized. Crystal structure analysis and theoretical calcu-
lation suggest the photoisomerization is the result of isomerization
from the enol-form to the keto-form by the intermolecular proton
transfer via hydrogen bond. After the furoyl group on 3-position
of pyrazolone ring instead of the phenyl group, the photoisomer-
ization rate decreases with the increase of volume of substituent
groups on 4-position of thiosemicarbazide and the steric hindrance

124
J. Hu et al. / Journal of Photochemistry and Photobiology A: Chemistry 217 (2011) 117–124
of Cl atom on benzal of 4-positon of the pyrazolone ring. These
results are useful for the design and synthesis of novel pyrazolone
derivatives with photochromic properties in solid state.
[21] Y. Ishibashi, M. Murakami, H. Miyasaka, S. Kobatake, M. Irie, Y. Yokoyama,
Laser multiphoton- gated photochromic reaction of a fulgide derivative, J. Phys.
Chem. C 111 (2007) 2730–2737.
[22] M. Ziólek, J. Kubicki, A. Maciejewski, R. Naskrecki, A. Grabowska, Enol-keto
tautomerism of aromatic photochromic Schiff base N,Nꢀ-bis(salicylidene)-p-
phenylenediamine: ground state equilibrium and excited state deactivation
studied by solvatochromic measurements on ultrafast time scale, J. Chem. Phys.
124 (2006), 124518-1–124518-10.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 20762010), Program for New Century
Excellent Talents in Universities of China (NCET-09-0904), The Key
Project of Ministry of Education, China (209138), and the Nat-
ural Science Foundation of Xinjiang Uygur Autonomous Region
(2009211B02).
[23] Z. Liang, Z.L. Liu, Y.H. Gao, Synthesis, characterization and photochromic stud-
ies of three novel calyx[4]arene-Schiff base, Spectrochim. Acta A 68 (2007)
1231–1235.
[24] M. Sliwa, N. Mouton, C. Ruckebush, S. Aloïse, O. Poizat, G. Buntinx, R. Métivier,
K. Nakatani, H. Masuhara, T. Asahi, Comparative investigation of ultrafast pho-
toinduced processed in salicylidene-aminopyridine in solution and solid state,
J. Phys. Chem. C 113 (2009) 11959–11968.
[25] M. Sliwa, A. Spangenberg, I. Malfant, P.G. Lacroix, R. Métivier, R.B. Pansu,
K. Nakatani, Structural, optical, and theoretical studies of a thermochromic
organic crystal with reversibly variable second harmonic generation, Chem.
Mater. 20 (2008) 4062–4068.
Appendix A. Supplementary data
[26] F. Robert, A.D. Naik, B. Tinant, R. Robiette, Y. Garcia, Insights into the origin of
solid-state photochromism and thermochromism of n-salicylideneanils: the
intriguing case of aminopyridines, Chem. Eur. J. 15 (2009) 4327–4342.
[27] N.S.S. Kumar, S. Varghese, C.H. Suresh, N.P. Rath, S. Das, Correlation between
solid-state photophysical properties and molecular packing in a series of
indane-1,3-dione containing butadiene derivatives, J. Phys. Chem. C 113 (2009)
11927–11935.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotochem.2010.09.027.
References
[28] L. Liu, X.Y. Xie, D.Z. Jia, J.X. Guo, X.L. Xie, Synthesis and properties of a novel
photochromic compound with modulated fluorescence in the solid state, J. Org.
Chem. 75 (2010) 4742–4747.
[29] J.C. Crano, R.J. Guglielmetti, Organic Photochromic and Thermochromic Com-
pounds, Plenum Press, New York, 1999.
[30] 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.
[31] V.A. Barachevsky, Photonics of organic photochromic systems: modern trends,
J. Photochem. Photobiol. A: Chem. 196 (2008) 180–189.
[32] T. Yoshikuni, Cerium complexes with phthaloylbis(pyrazolone) ligands as an
efficient catalysts for cresols dioxygenation, J. Mol. Catal. A: Chem. 148 (1999)
285–288.
[33] A. Kimata, H. Nakagawa, R. Ohyama, T. Fukuuchi, S. Ohta, T. Suzuki, N. Miyata,
New series of antiprion compounds: pyrazolone derivatives have the potent
activity of inhibiting protease-resistant prion protein accumulation, J. Med.
Chem. 50 (2007) 5053–5056.
[34] M.F. Bran˜a, A. Gradillas, A.G. Ovalles, B. López, N. Acero, F. Llinares, D.M. Min-
garro, Synthesis and biological activity of N,N-dialkylaminoalkyl-substituted
bisindolyl and diphenyl pyrazolone derivatives, Bioorg. Med. Chem. 14 (2006)
9–16.
[35] D. Costa, A.P. Marques, R.L. Reis, J.L.F.C. Lima, E. Femandes, Inhibition of human
neutrophil oxidative burst by pyrazolone derivatives, Free Radic. Biol. Med. 40
(2006) 632–640.
[1] G.Y. Jiang, S. Wang, W.F. Yuan, Z. Zhao, A.J. Duan, C.M. Xu, L. Jiang, Y.L. Song,
D.B. Zhu, Photo- and proton-dual-responsive fluorescence switch based on a
bisthienylethene-bridged naphthalimide dimer and its application in security
data storage, Eur. J. Org. Chem. (2007) 2064–2067.
[2] S.Z. Xiao, Y. Zou, M.X. Yu, T. Yi, Y.F. Zhou, F.Y. Li, C.H. Huang, A photochromic
fluorescent switch in an organogel system with non-destructive readout ability,
Chem. Commun. (2007) 4758–4760.
[3] G.Y. Jiang, S. Wang, W.F. Yuan, L. Jiang, Y.L. Song, H. Tian, D.B. Zhu, Highly
fluorescent contrast for rewritable optical storage based on photochromic
bisthienylethene-bridged naphthalimide dimer, Chem. Mater. 18 (2006)
235–237.
[4] F.L.E. Jakobsson, P. Msrsal, S. Braun, M. Fahlman, M. Berggren, J. Cornil, X.
Crispin, Tuning the energy levels of photochromic diarylethene compounds
for opto-electronic switch devices, J. Phys. Chem. C 113 (2009) 18396–18405.
[5] C.W. Lee, Y.H. Song, Y. Lee, K.S. Ryu, K.W. Chi, Reversible photochromic switch
ensemble and its photoimaging using H+ transfer between spiropyran and flu-
orescein in a polymer matrix, Chem. Commun. (2009) 6282–6284.
[6] Z.X. Li, L.Y. Liao, W. Sun, C.H. Xu, C. Zhang, C.J. Fang, C.H. Yan, Reconfigurable
cascade circuit in a photo- and chemical-switchable fluorescent diarylethene
derivative, J. Phys. Chem. C 112 (2008) 5190–5196.
[7] M. Tomasulo, S. Sortino, F. Raymo, Bichromophoric photochromes based on the
opening and closing of a single oxazine ring, J. Org. Chem. 73 (2008) 118–126.
[8] N.V. Mockus, D. Rabinovich, J.L. Petersen, J.J. Rack (Eds.), Femtosecond iso-
merization in a photochromic molecular switch, Angew. Chem. Int. 47 (2008)
1458–1461.
[9] J. Andrasson, S.D. Straight, S. Bandyopadhyay, R.H. Mitchell, T.A. Moore, A.L.
Moore, D. Gust, A molecule-based 1:2 digital demultiplexer, J. Phys. Chem. C
111 (2007) 14274–14278.
[10] J. Andre#asson, S.K. Straight, T.A. Moore, A.L. Moore, D. Gust, Molecular all-
photonic encoderdecoder, J. Am. Chem. Soc. 130 (2008) 11122–11128.
[11] V.A. Krongauz, C.P. Bosnjak, A. Chudnovsky, Use of photochromic spiropyran
as a molecular probe of large strain in polycarbonate, High Energy Chem. 43
(2009) 454–460.
[36] A.S. Fouda, A.A. Al-Sarawy, E.E. El-Katori, Pyrazolone derivatives as corrosion
inhibitors for C-steel in hydrochloric acid solution, Desalination 201 (2006)
1–13.
[37] J.X. Guo, L. Liu, D.Z. Jia, J.H. Wang, X.L. Xie, Solid-state photochromic properties
and mechanism of 1-phenyl-3-methyl-4-(3-chlorobenzal)-5-hydroxypyrazole
4-methylthiosemicarbazone, J. Phys. Chem. A 113 (2009) 1255–1258.
[38] L. Liu, D.Z. Jia, Y.L. Ji, K.B. Yu, Synthesis, structure and photochromic properties
of 4-acyl pyrazolone derivants, J. Photochem. Photobiol. A: Chem. 154 (2003)
117–122.
[39] T. Zhang, G.F. Liu, L. Liu, D.Z. Jia, L. Zhang, Solid-state proton transfer studies on
phototautomerization of 1-phenyl-3-methyl-4-furoyl-5-pyrazolone 4-methyl
thiosemicarbazone, Chem. Phys. Lett. 427 (2006) 443–448.
[12] V. Lemieux, N.R. Branda, Reactivity-gated photochromism of 1,2-
dithienylethenes for potential use in dosimetry applications, Org. Lett.
(2005) 2969–2972.
7
[40] J.X. Guo, L. Liu, G.F. Liu, D.Z. Jia, Synthesis and solid-state pho-
[13] J.R. Chen, D.Y. Yang, Design and synthesis of an o-hydroxyphenyl-containing
spiropyran thermochromic colorant, Org. Lett. 11 (2009) 1769–1772.
[14] X.F. Guo, D.Q. Zhang, G.X. Zhang, D.B. Zhu, Molecular logic: “Half-Adder” based
on multistate/multifunctional photochromic spiropyrans, J. Phys. Chem. B 108
(2004) 11942–11945.
[15] Z.B. Zhang, C.R. Zhang, M.G. Fan, W.P. Yan, Synthesis and complexation mecha-
nism of europium ion (Eu3+) with spiro[indoline-phenanthrolineoxazine], Dyes
Pigments 77 (2008) 469–473.
[16] M.R. di Nunzio, P.L. Gentili, A. Romani, G. Favaro, Photochromic, ther-
mochromic, and fluorescent spirooxazines and naphthopyrans: a spectroki-
netic and thermodynamic study, ChemPhysChem 9 (2008) 768–775.
[17] M Suzuki, T. Asahi, H. Masuhara, Temperature dependence of ultrafast
photoinduced ring-opening and -closure reactions of spironaphthoox-
azine in crystalline phase, J. Photochem. Photobiol. A: Chem. 178 (2006)
170–176.
[18] M. Suzuki, T. Asahi, K. Takahashi, H. Masuhara, Ultrafast dynamics of photoin-
duced ring-opening and the subsequent ring-closure reactions of spirooxazines
in crystalline state, Chem. Phys. Lett. 368 (2003) 384–392.
tochromism
of
1,
3-diphenyl-4-(2-chlorobenzal)-5-hydroxypyrazole
4-methylthiosemicarbazone, Org. Lett. 9 (2007) 3989–3992.
[41] X.Y. Xie, L. Liu, D.Z. Jia, J.X. Guo, D.L. Wu, X.L. Xie, Photo-switch and INHIBIT logic
gate based on two pyrazolone thiosemicarbazone derivatives, New J. Chem. 33
(2009) 2232–2240.
[42] H. Chui, G.F. Liu, L. Liu, D.Z. Jia, Z.P. Guo, J.P. Lang, Crystal structure and
spectroscopic study on photochromism of 1,3-diphenyl-4-(4ꢀ-fluoro)benzal-
5-pyrazolone N(4)-phenyl semicarba-zone, J. Mol. Struct. 752 (2005) 124–129.
[43] B.S. Jensen, The synthesis of 1-phenyl-3-methtyl-4-acylpyrazolone-5, Acta
Chem. Scand. 13 (1959) 1668–1670.
[44] G.M. Sheldrick, SHELXS-97 Program for the Solution of Crystal Structures, Uni-
versity of Göttingen, Göttingen, Germany, 1997.
[45] T. Kawato, H. Koyama, H. Kanatomi, M. Isshiki, Photoisomerization and
thermoisomerization I: Unusual photochromism of N-(3,5-di-tert-butyl-
salicylidene) amines, J. Photochem. 28 (1985) 103–110.
[46] M.J. Frisch, et al., GAUSSIAN 03, Revision B. 04, Gaussian, Inc., Pittsburgh, PA,
2003.
[47] V. Sathyabama, K. Anandan, R. Kanagaraju, Quantum chemical studies of sol-
vent effects on cytosine tautomers, J. Mol. Struct. Theochem. 897 (2009)
106–110.
[48] I. Alkorta, J. Elguero, Influence of intermolecular hydrogen bonds on the tau-
tomerism of pyridine derivatives, J. Org. Chem. 67 (2002) 1515–1519.
[19] M. Akazawa, K. Uchida, J.J.D. de Jong, J. Areephong, M. Stuart, G. Caroli, W.R.
Browne, B.L. Feringa, Photoresponsive dithienylethene-urea-based organogels
with “reversed” behavior, Org. Biomol. Chem. 6 (2008) 1544–1547.
[20] R.H. Mitchell, S. Bandyopadhyay, Linked photoswitches where both pho-
tochromes open and close, Org. Lett. 6 (2004) 1729–1732.