Photo-switch and INHIBIT logic gate based on two pyrazolone thiosemicarbazone derivatives

Article abstract of DOI:10.1039/b908326j

Two novel compounds containing a pyrazolone-ring unit, i.e. 1-phenyl-3-methyl-4-(2-fluorobenzal)-5-hydroxypyrazole 4-methylthiosemicarbazone and 1-phenyl-3-methyl-4-(2-fluorobenzal)-5-hydroxypyrazole 4- ethylthiosemicarbazone, have been synthesized and ch

Full text of DOI:10.1039/b908326j

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Photo-switch and INHIBIT logic gate based on two pyrazolone
thiosemicarbazone derivativesw
Xiangyun Xie,a Lang Liu,a Dianzeng Jia,*a Jixi Guo,a Dongling Wua and
Xiaolin Xieb
Received (in Victoria, Australia) 27th April 2009, Accepted 3rd September 2009
First published as an Advance Article on the web 30th September 2009
DOI: 10.1039/b908326j
Two novel compounds containing a pyrazolone-ring unit, i.e. 1-phenyl-3-methyl-4-
(2-fluorobenzal)-5-hydroxypyrazole 4-methylthiosemicarbazone and 1-phenyl-3-methyl-4-
(2-fluorobenzal)-5-hydroxypyrazole 4-ethylthiosemicarbazone, have been synthesized and
1
characterized by MS, IR, H NMR spectra and X-ray single crystal diffraction. In solid state,
they exhibit reversible photochromic properties under UV light irradiation and heating. Based on
the crystal structure, solid IR spectra and theoretical calculation, the photochromic mechanism of
the intra- and intermolecular double-proton transfer from the enol form to the keto form is
proposed. In solution, stimulated by three chemical inputs (H+, OHꢀ and Zn2+), they undergo
the deprotonation–protonation and complexation reactions. Based on an absorption band at
355 nm as the output signal, an INHIBIT logic gate combining a NOT and an AND gate has
been obtained.
as light, pH variation, and metal ions. For example, Zhu4 et al.
1. Introduction
reported spiropyran molecules have the function of AND,
INHIBIT, NAND, XOR logic gates and a half-adder in
response to UV light, Fe3+, Zn2+ and H+, or a unimolecular
half-adder based upon the facile reversible coordination
Organic photochromic compounds have attracted considerable
interest because of their potential applications in the fields of
high-density data storage, molecular sensors, switches, and
information processors et al.1 Lots of work on spiropyrans,
spiroxazine, dithienylethenes, fulgides, and Schiff bases have
been extensively reported.2 However, most of them show the
reversible photochromic behavior only in the solution state.
To develop new compounds with reversible photochromic
behavior in the solid state is very important for their applications.
Since the first molecular AND logic gate was reported by de
Silva and co-workers,3 molecular systems with photochromic
units have been demonstrated to mimic the functions of
molecular switches, elementary logic gates and integrated logic
gates. New properties can be achieved through the use of a
simple molecule upon inputs of different external stimuli, such
between small molecules and the metal ions Cd2+ and Zn2+
.
Li5 et al. designed an INHIBIT logic gate based on a
spiropyran sensitized semiconductor electrode with the variation
of photocurrent upon the input signals of 365 nm UV light and
4450 nm. Yan6 et al. reported an unsymmetric diarylethene
derivative with multiswitched behavior through protonation,
coordination and photochemical reactions, and mimic logic
functions from an INHIBIT logic gate to a half-subtractor.
Jiang7 et al. reported a Schiff base, N-3,5-dichloro-salicylidene-
(S)-R-phenyl ethylamine, undergoing reactions of photochemistry,
deprotonation, and complexation upon UV stimulation, OHꢀ
and Zn2+. One mono-molecular circuit was obtained, which
integrates one OR, two NOT, and four AND gates. So the
development of novel mono-molecule system with photo- and
chemical switches is becoming an interesting area.
a Prof. D.Z. Jia, Institute of Applied Chemistry, Xinjiang University,
Urumqi 830046, P. R. China. E-mail: jdz@xju.edu.cn;
Fax: +86–991–8588883
b Prof. Dr X. L. Xie, Department of Chemistry and Chemical
Engineering, Huazhong University of Science and Technology,
National Anti-counterfeit Engineering Research Center, Wuhan
430074, China
Many thiosemicarbazones derived from 4-acyl pyrazolones
with photoisomerization properties have been systemically
studied in our laboratory.8 Although they can offer an
enormous structural diversity and tunable photoisomerization
properties, they also suffer from a lack of photochromic
reversibility in the solid state. In order to overcome the
disadvantage, many efforts have been dedicated to design the
structure. Finally, the photochromic compound with good
reversibility, 1,3-diphenyl-4-(2-chlorobenzal)-5-hydroxypyrazole
4-methylthiosemicarbazone was obtained by the incorporation
of 2-ClPh at the 4-position and Ph at the 3-position of
pyrazolone.8e On the one hand, its derivatives need to be
further developed by the structural modification in order to
improve the photochromic properties. On the other hand, we
w Electronic supplementary information (ESI) available: Synthetic
procedure for 2, 1H NMR data of 1–2, mass spectra of 1–2, first-
order kinetic plots of the photoisomerization reaction of 1 and 2
induced by 365 nm light at room temperature, molecular structure of
II with atom numberings of 1 and 2, the crystal data and structure
refinement details for 1 and 2, selected bond lengths (A) and angles (1),
intra- and intermolecular hydrogen bonding geometry in keto form
crystal for 1 and 2, crystal packing in unit cell along the c axis for 1 and
2 and the absorption spectra changes under OHꢀ action; Zn2+ action;
H
+ action; OHꢀ and Zn2+ actions; OHꢀ and H+ actions; Zn2+ and
H+ actions; OHꢀ, Zn2+, and H+ actions in solution, theoretical
calculated details are given. CCDC reference numbers 708004, 708005.
For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/b908326j
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previously studied the photochromic properties of pyrazolone
thiosemicarbazones in solid state, but rarely paid attention to
the effect of pH on their spectral properties in solution.
In this paper, we introduced the halogen F atom in the
4-position of 1-phenyl-3-methyl-4-benzal-5-hydroxypyrazole
4-methylthiosemicarbazone (PMBP-MTSC)8b in order to
improve the reversible photochromic ability and the photo-
chromic speed, synthesized two new compounds namely
1-phenyl-3-methyl-4-(2-fluorobenzal)-5-hydroxypyrazole 4-methyl-
thiosemicarbazone (1) and 1-phenyl-3-methyl-4-(2-fluorobenzal)-
5-hydroxypyrazole 4-ethylthiosemicarbazone (2), which exhibit
reversible photochromism in the solid state. By analyses of
crystal structure and solid IR spectra, we put forward a
photochromic mechanism of the title compounds which is
different from the photochromic processes of PMBP-MTSC.
At the same time, the molecular logic function of the title
compounds in solution was studied by using OHꢀ, Zn2+ and
H+ as inputs and the absorbance value as an output.
2. Results and discussion
2.1 UV absorption and fluorescence spectra in the solid state
Scheme 1 illustrates the synthetic route of the title compounds
and their photoisomerization from the white enol form (I) to
the yellow keto form (II). As shown in Fig. 1, it can be
observed that new bands appear at 420 nm for 1 and
430 nm for 2 in the UV-Vis absorption spectra of 1 and 2
powders (enol form) irradiated by 365 nm UV light at room
temperature, and their intensities increase with irradiation
time. Additionally, no change is observed in their UV spectra
and decomposition does not occur when these yellow
compounds were kept in a dark box for half a year, which
indicates that the yellow forms are very stable and retain its
coloration memory for a long time. However, the yellow forms
(II) quickly reverted to the pale yellow (I) for 1 at 180 1C and
Fig. 1 UV spectra of 1 and 2 powders in the solid state at room
temperature. (A) From a to i, each irradiation time (min) for 1 is 0, 4,
8, 12, 20, 30, 48, 72, 150. (B) From a to i, each irradiation time (min)
for 2 is 0, 12, 24, 36, 48, 60, 72, 84, 160. Inset: thermobleaching spectra
by heating.
the cream for 2 at 195 1C, and the intensity of peaks at 420 and
430 nm gradually decreased. Based on their absorption values,
the degree of thermobleaching is ca. 79% of 1 and 98% of 2.
Under UV irradiation, the decolored powders return to yellow
again. These results suggest that photochromism is reversible.
According to the literature,9 kinetic rate constants can be
determined from the plot of ln[(AN ꢀ A0)/(AN ꢀ At)] against
the time (t) (Fig. S4, ESIw). The enol-to-keto isomerization
reaction follows well the pseudo-first-order kinetics and the
rate constant was obtained from the slope as k1 = 3.56 ꢂ 10ꢀ3 sꢀ1
and k2 = 2.17 ꢂ 10ꢀ4
s
ꢀ1, respectively. Obviously, the
photochromic rate of compound 1 is faster than that of
compound 2 due to the smaller steric hindrance of the methyl
group than the ethyl group. For the analogue compound
1-phenyl-3-methyl-4-benzal-5-hydroxypyrazole 4-methylthio-
semicarbazone,8b the kinetic constant of the photoisomerization
is 3.91 ꢂ 10ꢀ4
s
ꢀ1, which indicates its photoisomerization
reaction is slower than that of the compound 1. The result
Scheme
1
Synthetic route and photoisomerization of the title
compounds.
shows that the electron withdrawing property of the F atom of
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evaporating the solution of methanol at room temperature
without avoiding sunlight. The molecular structures of 1 and
2, crystal packing for 1 and 2, the crystal data and structure
refinement details for 1 and 2, selected bond lengths (A) and
angles (1) and intra- and intermolecular hydrogen bonding
geometry in keto form crystals are shown in Fig. S5–S7 and
Table S1–S3 (see ESIw). The structures of the two compounds
have similar bond length, same space group and unit-cell
dimensions. The C7–O1 bond distance is 1.251 or 1.250 A,
which is consistent with the length of the CQO and that of the
previously reported analogue compound.8e The bond lengths
of C–S (1.697 A for 1 and 1.704 A for 2) are also close to the
CQS double bond length. It can be deduced that their
structures belong to the keto (II) form. In solution, we only
obtained the keto form crystals. In order to further analyze the
stability of the keto and enol forms, theoretical calculations
are performed with the GAUSSIAN 03W program package.
Taking the total energy of the most stable configuration as a
reference, the energy differences (DE) of the other isomers
obtained in gas phase and in methanol solution are presented
in Table S4 (see ESIw). In the gas phase, the calculated DE is
0.34 kcal molꢀ1 for 1 (0.27 kcal molꢀ1 for 2), which indicates
the enol form is more stable than the keto one. But the relative
energies between the enol and the keto isomers are so small
that the interconversion among these isomers easily occurs. In
addition, the dipole moment of the keto form (9.28 Debye or
9.22 Debye) is greater than that of the enol form (5.23 Debye
or 5.13 Debye). According to the reaction field approach, the
polarity increase of the medium should favor a tautomer with
greater dipole moment.10 So in polar media, the energy
difference between isomers would be smaller or even that the
keto form would become the most stable.11 The following
energy calculation results in methanol solution suggest that the
keto form is the most stable isomer, which is in agreement with
the experimental fact that the single crystal structures of the
title compounds which obtained from the methanol solution
are the keto forms.
Fig. 2 Fluorescent emission spectra of powders 1 (A) and 2 (B) under
365 nm UV light irradiation at room temperature.
benzyl groups on the 4-position of pyrazole rings increases the
photochromic speed.
Hydrogen bond connection diagrams of 1 and 2 are shown
in Fig. 3. It can be seen that there is a similar hydrogen
bonding configuration in the two crystals, and they are
stabilized by intermolecular hydrogen bonds (N20–H2N0ꢃ ꢃ ꢃS,
3.261 A or 3.206 A; N500–H5N00ꢃ ꢃ ꢃO0, 2.966 A or 3.011 A, the
single and double quotation marks represent different molecules)
and intramolecular hydrogen bonds (N40–H4N0ꢃ ꢃ ꢃO0, 2.704 A
or 2.712 A). It is remarkable that the O atom is not only
involved in an intermolecular hydrogen bond (N500–H5N00ꢃꢃꢃO0),
but also takes part in an intramolecular hydrogen bond
(N40–H4N0ꢃ ꢃ ꢃO0). Moreover, the length of the intramolecular
hydrogen bond is obviously shorter than that of the inter-
molecular one. At the same time, Etter12 stated that
six-membered-ring intramolecular hydrogen bonds take
precedence of intermolecular hydrogen bonds. So the proton
transfer by the intramolecular hydrogen bond (N40–H4N0ꢃꢃꢃO0)
is much easier than that by the intermolecular hydrogen bond
(N500–H5N00ꢃꢃ ꢃO0).
Fig. 2 is the fluorescent emission spectra of powders 1 and 2
irradiated by 365 nm UV light at different times at room
temperature. It can be seen that the emission bands of the
white enol form (I) for 1 appear at 410 nm and 470 nm after
being excited at 310 nm, their intensity gradually decreased
with irradiation time, and the emission band at 410 nm finally
disappeared. Subsequently, the white enol form (I) gradually
changes to the yellow keto form (II). After heating at 180 1C,
the yellow returned to the pale yellow, the emission band at
410 nm appears again, which further indicates that compound
1 has a reversible photochromic property. Similar phenomena
are observed in the fluorescent emission spectra of 2 (shown in
Fig. 2B). The intensity of the emission bands decreases
significantly upon irradiation of 365 nm UV-light due to the
formation of the yellow keto form.
2.2 Crystal structure, stability and photochromic mechanism
Methanol molecules are present in the crystal structure of 1,
which interact with the S atom of the methylthiosemicarbazone
moiety, leading to the weak hydrogen bond of O2–H2Aꢃ ꢃ ꢃS
(3.524 A, 1471). In the packing arrangement of 1 and 2, both
In order to ascertain the photochromic mechanism, the single
crystal structures have been determined. The pale yellow
transparent single crystals of 1 and 2 were obtained by slowly
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compounds is different from that of the analogous compound
1-phenyl-3-methyl-4-benzal-5-hydroxypyrazole 4-methylthio-
semicarbazone, which is only an intermolecular proton trans-
fer from the O atom of the hydroxyl group to the nitrogen
atom on pyrazole ring of the adjoining molecule.8b
Numerous attempts have been made to obtain the structures
of the colorless single crystals, but we failed because the
calculated results indicate the keto form is more stable in
polar solution. Solid IR spectroscopy was employed to
investigate the configurational changes during the photo-
isomerization transition. Fig. 4 shows IR spectra of 1 and 2
before and after UV light irradiation at room temperature.
Obviously, broad middle vibration bands in the range of
2500–3100 cmꢀ1 are observed, characteristic of Schiff bases
with a medium strength intramolecular hydrogen bond.13 This
phenomenon is similar to the light-induced hydroxypyrazole
derivants8a,e and other systems.14
However, upon irradiation with UV light, new sharp bands
appear at 1671 cmꢀ1 for 1 and 1664 cmꢀ1 for 2, respectively,
which are attributed to CQO stretching vibrations. It is
Fig.
3 Hydrogen bond connection diagrams in the molecular
structures of 1 (A) and 2 (B) (hydrogen atoms of carbon atoms are
omitted, and a prime (0) character in the atom labels are at the
equivalent position (1 ꢀ x,1 ꢀ y,1 ꢀ z).)
donor and acceptor in these hydrogen bonds are involved in a
neighboring molecule, leading the two dimensional network
configuration by an antisymmetric way along the c axis.
Based on the analysis above, a reasonable photochromic
mechanism is proposed. Under UV light irradiation, the
intramolecular proton transfers from the O atom to the N4
atom by the channel of N4ꢃ ꢃ ꢃH–O. At the same time, the
intermolecular proton transfers from the S0 atom to the N2
atom by the channel of N2ꢃ ꢃ ꢃH–S0, forming an intermolecular
hydrogen bond N2–Hꢃ ꢃ ꢃS0. These processes lead to the
enol–keto photoisomerization through the intra- and inter-
molecular double-proton transfer via the intermediated (I0) as
shown in Scheme 1. The photochromic mechanism of the title
Fig. 4 IR spectra of 1 and 2 before (a) and after (b) 365 nm UV light
irradiation.
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similar to the analogous compound reported previously,8e The
results indicate that configurational transformation between
the enol form and the keto form is in agreement with the
analysis of the crystal structure above.
2.3 Absorption spectral changes stimulated by three inputs
in solution
We previously focused on the photochromic properties and
complexation behaviours of pyrazolone thiosemicarbazones,
but rarely paid attention to the effect of pH on the spectral
properties of these kind of compounds in solution. Actually,
the compounds 1 and 2 are quite sensitive to acid and base.
When aqueous NaOH (0.1 M) is added into the system,
a deprotonation reaction takes place immediately. So we
selected OHꢀ as the first input signal. As shown in Fig. 5,
the absorption bands at 320 nm gradually decrease and red
shift as the pH value increase. At the same time, the new
absorption bands attributed to the deprotonated products
(III in Scheme 2) appear at 344 nm for 1 and 261, 345 nm
for 2, respectively. But the changes are not obvious when the
Scheme
2
Transitions among deprotonation, protonation and
coordination reactions.
pH value is above 7.04 for 1 (7.94 for 2). Moreover, there are
isosbestic points at 336 nm for 1 and 289, 338 nm for 2,
respectively.
Pyrazolones are an important class of ligands in coordination
chemistry and have been extensively studied for selectivity and
sensitivity towards various metal ions.15 Zinc complexes often
Fig. 5 Absorption spectra of compounds 1 (A) and 2 (B) in methanol
solution (2 ꢂ 10ꢀ5 mol Lꢀ1) before (dashed line) and after (solid line)
titration with the 0.1 M NaOH aqueous. (A) pH values are 4.74, 5.14,
5.62, 6.93, 7.04, respectively. (B) pH values are 4.56, 5.04, 5.47, 6.95,
7.41, 7.94, respectively.
Fig. 6 UV-vis absorption spectra of 1 (A) and 2 (B) in methanol
solution (2 ꢂ 10ꢀ5 mol Lꢀ1) with continuous titration by the ZnCl2
solution (0.1 M).
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display strong spectral changes, which can be used as a
detectable output signal for molecular devices. So we introduced
the Zn2+ ion as the second input signal. The coordination
reaction takes place as soon as the ZnCl2 solution (0.1 M) is
added into the methanol solution of 1 or 2, leading to obvious
changes in the absorption spectra, as shown in Fig. 6. For
compound 1, it can be seen that the intensity of the original
peak around 320 nm (dashed line) gradually decreases with
Zn2+ titration, but the new peak at the 355 nm appears due
to the formation of the Zn-complex. Similar phenomena
were also observed from the UV-vis absorption spectra of
compound 2. However, there are some differences on spectra
changes in the range of 235–275 nm. It may be due to the
substituent effect of methyl group or ethyl group on the
side-chain of thiosemicarbazone. Compared with the absorption
spectra of the ligands, that of the complexes take on the red-shift
phenomenon due to metal perturbed intra-ligand p - p*
transition.
and 345 nm red shifted to 355 nm (curves b to c), which is
attributed to the bands of the zinc complexes mentioned
above. So we can also obtain the zinc complex after the
two-step process.
Finally, we choose H+ as the third input signal. First, by
titrating 1 and 2 with aqueous NaOH, we get the deprotonated
product (III). Then titrating deprotonated products continuously
with hydrochloric acid (0.1 M) produces spectral changes
(Fig. 8). In the case of compound 1, the absorption band at
344 nm decreases, while the new band at 320 nm appears with
the addition of hydrochloric acid, finally recovering the original
spectral shape, as depicted in Fig. 8A. Similar phenomona also
are observed for compound 2 in Fig. 8B. When the protonated
form (I) in acidic methanol solution is continuously added the
base solution, it returns to the deprotonated form. This circle
can be repeated for many times, which shows that the
deprotonated-protonated process of compounds 1 and 2 is
reversible. Under the alternating action of base and acid, it
can perform the reversible process as a pH switch through
Then the cooperated actions of two inputs are studied. As
shown in Fig. 7 (curves a to b), the typical absorption bands at
344 nm and 345 nm appear after the methanol solutions of 1
and 2 were titrated with the NaOH aqueous, which indicates
that the ligands 1 and 2 are deprotonated, and transformed to
(III) in Scheme 2. Then by titrating the deprotonated form
(III) with the ZnCl2 solution, the absorption bands at 344 nm
Fig. 8 (A) Absorption spectra of 1-(III) (dashed line, deprotonated
form) and after continuous titration with H+ (solid line, protonated
form), pH values are 7.04, 6.28, 5.88, 4.97, 3.98, respectively; (B)
Absorption spectra of 2-(III) (dashed line, deprotonated form) and
after continuous titration with H+ (solid line, protonated form).
pH values are 7.94, 6.28, 5.07, 4.42, 3.80, respectively.
Fig. 7 Absorption spectra of compounds 1(A) and 2(B) titrated by
the NaOH (0.1 M) and the ZnCl2 solution (0.1 M).
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isosbestic point, which indicates that the acid–base equilibrium
occurs between the deprotonated and protonated species
of 1 and 2, respectively.
actions, OHꢀ, Zn2+, and H+ actions, are illustrated in the
ESI (Fig. S8–S11w), respectively. Among all of the stimulations,
only the Zn2+ action and the OHꢀ plus Zn2+ actions can
induce a strong absorption at 355 nm due to the formation of
the zinc complexes. Fig. 10 presents the final absorbance
intensity at 355 nm of title compounds at all possible actions
relating to the three inputs. In summary, under the individual
actions of the OHꢀ, Zn2+, and H+ as well as the combination
of these, 1 and 2 can accomplish the reactions of deprotonation,
complexation, and protonation producing obvious optical
outputs: a UV-vis absorption band at 355 nm.
No color change could be detected by the naked eye on
addition of the acid or the base. However, a blue shift can be
observed with dropwise addition of hydrochloric acid to the
basic methanol solution of 1 and 2 from Fig. 8. With the pH
value decreasing from 7.04 to 3.98 for compound 1 and from
7.94 to 3.80 for 2, the maximum absorption band moves
hypsochromically by 344 nm to 320 nm and 345 nm to
320 nm, respectively.
As mentioned above, when compounds 1 and 2 are titrated
with the ZnCl2 solution, the complexes are formed. Then we
utilize hydrochloric acid to titrate these complexes. As shown
in Fig. 9, the intensity of the absorption bands at 355 nm
decreases gradually and blue shifts to 334 nm when titrating
with excessive hydrochloric acid, which indicates that the zinc
complexes can decompose under acidic conditions.
2.4 INHIBIT logic function
The communication between the input signals, OHꢀ (IN1),
Zn2+ (IN2), and H+ (IN3) and the output signals, the
absorbance value at 355 nm (OUT), can be described with
the binary logic. The absence of inputs (OHꢀ, Zn2+, and H+)
or output values (absorption) below a predefined threshold
Subsequently, we introduce the three inputs to 1 and 2 one
by one. For the title compounds, the absorption spectra
changes under OHꢀ action, Zn2+ action, H+ action, OHꢀ
and Zn2+ actions, OHꢀ and H+ actions, Zn2+ and H+
Fig. 10 Under the stimulation of OHꢀ (0.1 M, IN1), Zn2+ (IN2), and
H+ (0.1 M, IN3) (IN1, IN2, IN3 in the string of a: 0 0 0; b: 0 0 1; c:
0 1 0; d: 0 1 1; e: 1 0 0; f: 1 0 1; g: 1 1 0; h: 1 1 1), (A) the changes of
absorbance intensity at 355 nm of 1; (B) the changes of absorbance
intensity at 355 nm of 2. (& represents inputs that are 0, ’ represents
inputs that are 1).
Fig. 9 Absorption spectra of the zinc-complex corresponding to 1 (A)
and 2 (B) (dashed line) and after titrating with excessive hydrochloric
acid (0.1 M) (curves e to f).
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Table 1 Truth table for the INH logic gate
stimulated inputs and one optical output can be exploited to
implement logic operation at the molecular level. Indeed, the
logic function executed by this particular molecular switch is
equivalent to an INHIBIT logic circuit incorporating a NOT
and an AND gate. This contribution not only develops a
multi-switch single molecular logic circuit but also presents a
potential candidate for future high-density optical storage
devices.
Input
OHꢀ
Output (at 355 nm)
Zn2+
H+
1
2
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
0
1
0
0
0
1
0
0
0
1
0
0
0
1
0
4. Experimental section
4.1 Instrumentation
Melting point was measured with a TECH X-6 melting point
apparatus and was uncorrected. The IR spectra were recorded
1
on a BRUKER EQUINOX-55 Spectrometer, and H NMR
experiments were carried on an INOVA-400 1H NMR Spectro-
meter in DMSO-d6. Mass spectra were determined with
HP1100 LC-MS. The absorption spectra were measured using
Hitachi U-3010 spectrophotometer. A 15 W lamp in ZF-8
Ultraviolet Analysis Instrument was used as the light source
for photocoloration and the distance between the sample and
light source was 15 cm. Solutions for UV-vis absorption
spectra were titrated directly in 1 cm absorption cells by
successive additions of corresponding chemical reagent using
a microlitre syringe. All of the spectral analyses were accomplished
in methanol. The solution concentrations of 1 and 2 for
spectral analysis was 2.0 ꢂ 10ꢀ5 M. Fluorescence spectra were
measured with a Hitachi F-4500 spectrophotometer (A 100 W
Xenon lamp as light source), and the breadths of excitation
and emission slits were both 5.0 nm. All measurements were
performed at ambient temperature.
Fig. 11 INHIBIT Logic circuit of compound 1 and 2 with inputs.
level (absorbance value of 0.3) are translated into binary ‘‘0’’,
while the presence of an input or outputs above the threshold
corresponds to binary ‘‘1’’, in accordance with the positive
logic convention. For example, the input string 0 0 0 indicates
that the three stimulation inputs are off. Under these conditions,
the absorbance at 355 nm is low. The output string is 0.
Instead, the input string 1 1 0 indicates that the OHꢀ and
Zn2+ are on. Under these conditions, the zinc complex is the
dominant product. The output string is 1. Following similar
consideration, the eight output strings corresponding to the
eight possible combinations of input strings can be determined.
From the spectral investigations illustrated above, the absorption
band at 355 nm (OUT) can be achieved in two situations: one
is by directly titrating with the ZnCl2 solution, the other one is
by titrating the deprotonated form with Zn2+. In other words,
only when IN1 = 0, IN2 = 1, and IN3 = 0 or IN1 = 1,
IN2 = 1, and IN3 = 0, the output signal (OUT) is 1.
4.2 Materials
4-Ethyl-3-thiosemicarbazide and 4-methyl-3-thiosemicarbazide
were purchased from the Aldrich Company, USA. 1-Phenyl-
3-methyl-4-(2-fluorobenzal)-5-hydroxypyrazole (PM2FHP)
was synthesized according to the literature with a minor
modification.16 (Yield: 88.76%; m.p. 118.6–120.1 1C). All
other reagents were AR. grade and purchased from commercial
suppliers, and used without further purification.
According to the two histograms (Fig. 10), the truth table
(Table 1) can be obtained. From which, we can see that this
chemical system responds to an input string of three binary
digits (IN1, IN2, IN3) producing an output string of one
binary digits (OUT). Consequently, the logic behavior of the
molecular switch corresponds to an INHIBIT logic gate by
combining a NOT and an AND gate (Fig. 11).
4.3 Synthesis of compound 1
1-Phenyl-3-methyl-4-(2-fluorobenzal)-5-hydroxypyrazole 4-
methylthiosemicarbazone was prepared by mixing PM2FHP
(5 mmol) and 4-methyl-3-thiosemicarbazide (5 mmol) in 30 ml
of methanol in the presence of glacial acetic acid (1 ml) at
70 1C for ca. 4 h under magnetic stirring. After cooling down
to room temperature in the dark, white powders were obtained
in a 73.49% yield. m.p. 219.7–220.9 1C. The spectroscopic
data are as follows. IR (v cmꢀ1): (a) the white powder before
irradiation: 3298 v(N–H), 3066–2596 v(O–H), 1630 v(CQN),
1561, 1496 v(phenyl), 1408, 1374 v(pyrazolone-ring), 1303
v(CQS). (b) the yellow powder after irradiation: 3298
v(N–H), 3066–2596 v(O–H), 1671 v(CQO), 1630 v(CQN),
1561, 1496 v(phenyl), 1408, 1374 v(pyrazolone–ring), 1303
v(CQS). MS: [M + 1] = 384.1 (C19H18N5OSF formula
weight: 383.44). 1H NMR (DMSO-d6) (d, ppm): 1.651 (3H,
N5–CH3), 3.013–3.002 (3H, Pz–CH3), 7.454–7.174 (5H, Ph),
3. Conclusion
Two novel pyrazolone thiosemicabazone derivatives which
exhibit reversible photochromic properties in the solid state
are synthesized. The analyses of crystal structures and IR
spectra suggest that the photochromic mechanism is the intra-
and intermolecular double-proton transfer via hydrogen
bonds, accompanied by the isomerization between the enol
form (I) and the keto form (II). This is further confirmed by
theoretical calculations. In solution, the interplay of the three
ꢁc
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7.778–7.507 (5H, C6H4F + N4–H), 7.912 (1H, N5–H), 8.233
(1H, Pz–NH).
4 (a) X. Guo, D. Zhang and D. Zhu, Adv. Mater., 2004, 16, 125–130;
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Compound
2 was prepared in a very similar way.
Experimental details and spectroscopic information can be
found in the ESI.w The synthesis routine of 1 and 2 is
presented in Scheme 1.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Nos. 20762010 and 20866009),
Scientific Research Program of the Higher Education Institution
of XinJiang (XJEDU2006I04 and XJEDU2008S08), the Key
Project of Ministry of Education (209138) and the Project of
‘‘Western light’’ of Chinese Academy of Science.
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