Design, synthesis, photochromism and electrochemistry of a novel material with pendant photochromic units

Article abstract of DOI:10.1016/j.tet.2014.06.005

In the present work, the synthesis, photochromism and electrochemistry of a novel material 1, 1-(4-[3,4-bis(2,5-dimethyl-3-thienyl)cyclopent-3-en-1-yl] phenyl)-2,5-di-2-thienyl-1H-pyrrole, with pendant dithienylethene (DTE) photochromic units are described. It should be noted that the system 1 can be reversibly and efficiently switched between open (1o) and closed (1c) states by light in both solution and in the solid poly(methyl methacrylate) matrix. It is also noteworthy that the two isomers (1o and 1c) of this novel system 1 can be smoothly polymerized on ITO by electrochemical means. Surprisingly, the DTE unit in 1 does not retain its photochemical switching properties after immobilization onto ITO. The morphology of the polymer film was investigated by AFM analysis. Furthermore, it was found that the polymer exhibited remarkable electrochromic features that can be switched from green in the neutral state to violet state under applied external potentials without disturbing the photochromic units.

Full text of DOI:10.1016/j.tet.2014.06.005

Accepted Manuscript
Design, synthesis, photochromism and electrochemistry of a novel material with
pendant photochromic units
Melek Pamuk Algi , Atilla Cihaner , Fatih Algi
PII:
S0040-4020(14)00851-5
10.1016/j.tet.2014.06.005
TET 25670
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 25 March 2014
Revised Date: 19 May 2014
Accepted Date: 2 June 2014
Please cite this article as: Algi MP, Cihaner A, Algi F, Design, synthesis, photochromism and
electrochemistry of a novel material with pendant photochromic units, Tetrahedron (2014), doi: 10.1016/
j.tet.2014.06.005.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Design, synthesis, photochromism and electrochemistry of a novel material with
pendant photochromic units
Melek Pamuk Algi, Atilla Cihaner, Fatih Algi
N
N
S
S
S
S
n
S
S
S
S

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Design, synthesis, photochromism and electrochemistry of a novel material with
pendant photochromic units
Melek Pamuk Algi†,, Atilla Cihaner‡,*, Fatih Algi╘,Ⱡ*
† Health Services Vocational School, Aksaray University, TR-68100 Aksaray, Turkey.
‡ Atilim Optoelectronic Materials and Solar Energy Laboratory (ATOMSEL), Department of
Chemical Engineering and Applied Chemistry, Atilim University, TR-06836 Ankara, Turkey.
╘
Laboratory of Organic Materials (LOM), Canakkale Onsekiz Mart University, TR-17100
Canakkale, Turkey.
Ⱡ
Department of Biotechnology and Molecular Biology, ASU BioNanoTech Lab., Aksaray
University, TR-68100 Aksaray, Turkey.
Abstract
In the present work, the synthesis, photochromism and electrochemistry of a novel material
1, 1-(4-[3,4-bis(2,5-dimethyl-3-thienyl)cyclopent-3-en-1-yl]phenyl)-2,5-di-2-thienyl-1H-pyrrole,
with pendant dithienylethene (DTE) photochromic units are described. It should be noted that
the system 1 can be reversibly and efficiently switched between open (1o) and closed (1c)
states by light in both solution and in the solid poly(methyl methacrylate) matrix. It is also
noteworthy that the two isomers (1o and 1c) of this novel system 1 can be smoothly
polymerized on ITO by electrochemical means. Surprisingly, the DTE unit in 1 does not
retain its photochemical switching properties after immobilization onto ITO. The morphology
of the polymer film was investigated by AFM analysis. Furthermore, it was found that the
polymer exhibited remarkable electrochromic features that can be switched from green in the
neutral state to violet state under applied external potentials without disturbing the
photochromic units.
Keywords: Dithienylethene, dithienylpyrrole, photochromic, electrochromic, thiophene.

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*Corresponding authors. Tel.: +903125868304-8817; Fax: +903125868091; E-mail:
cihaner@atilim.edu.tr (A. Cihaner) and Tel.:+902862180018-2415; Fax: +902862180533; E-
mail: falgi@comu.edu.tr (F. Algi).
1. Introduction
The design and synthesis of novel functional organic compounds has attracted considerable
attention since they lead to a variety of advanced technological applications in the field of
molecular electronics and photonics, sensors, machines and devices, light emitting diodes,
photovoltaics, transistors, electrochromics, data processing and storage media.1
Photochromic dithienylethene (DTE) derivatives are highly valuable materials due to their
unique properties such as thermal stability and high fatigue resistance which are
indispensable for optoelectronic applications.2,3 However, some other properties of DTEs
such as fast switching, high quantum yield and large differences between the absorption
wavelengths of two isomers have also contributed to the ever increasing popularity of these
compounds, which have found diverse applications as smart materials (e.g. molecular
switches, optical data processing and storage devices, molecular probes, machines and
imaging agents) in both bio- and nano-technological sciences as well as in materials
science.4-10 Thus, excellent molecular DTE systems, which hold great promise for
applications in the field of molecular electronics and optics, have been created thus far.11-21
Unfortunately, however, only a few photochromic conducting polymers22-23 based on DTE
systems have been reported to date.24-27 In this context, it is a challenging task to attain novel
DTE based conducting polymers.
2,5-Dithienylpyrrole (SNS) is one of the most useful core units in order to obtain materials
with distinct properties.28-34 For instance, the flavin functionalized polydithienylpyrrole (PSNS)
fabricated by electrochemical methods could be used for the detection of 2,6-
diamidopyridine, which is a biologically important redox-active molecule.35 It was recently

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shown that a chemiluminescent PSNS functionalized with luminol appendages could be used
for the detection of reactive oxygen species and blood (in forensic science).36 Furthermore, it
is noteworthy that SNS based materials can be amplified to create viable materials as
molecular sensors and/or probes for the detection of metal ions.37-39 In addition, by the help
of fluorescent substituents, PSNS based polymers could exhibit both fluorescent and
electrochromic properties.40-44 It was also shown that the intrinsic properties could easily be
controlled through rational design of the backbone structures.44 Nonetheless, examples of
electrochromic polymeric materials based on SNS with pendant DTE photochromic units
have not been reported so far. Therefore, novel SNS based conducting polymers with
pendant photochromic DTE units are welcome.
Considering the fact that both DTE and SNS units are synthetically versatile, we have
designed a new molecular architecture merging these two systems; SNS with pendant DTE
units (1, Scheme 1). Herein we wish to report the design, synthesis, photochromic features
and electrochemistry of this novel molecular system. This novel photochrome 1 can be
reversibly and efficiently switched between open (1o) and closed (1c) states by light in both
solution and in the solid PMMA matrix. It is noteworthy that two isomers (open (1o) and
closed (1c) forms) of this novel system 1 can be polymerized electrochemically. Furthermore,
it was found that the polymer exhibited remarkable electrochromic features that can be
switched from green color in the neutral state to violet under applied external potentials
without disturbing the photochromic units.
N
N
S
S
S
S
S
S
S
S
1o
1c

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Scheme 1. The structures of target compounds 1o and 1c.
2. Results and Discussion
The synthesis of the target compound 1 was started with a Knoevenagel type condensation
reaction.45,46 4-Nitrobenzaldehyde (2) was treated with ethyl acetoacetate (3) in the presence
of piperidine to give bisacetoacetate 4 in 75% yield (Scheme 2). Hydrolysis of 4 was carried
out with NaOH to get β-arylglutaric acid 5 in a yield of 60%. β-Arylglutaric acid 5 was
1
characterized on the basis of H, 13C NMR, and FTIR spectroscopy and elemental analysis,
1
which firmly established the structure (see Supporting Information for H and 13C NMR
spectra, Fig. S1-S2).
1. NaOH
NO2
COCH3
CO2Et
NH
O
O
H2O, 100 oC
COOH
COOH
O2N
O2N
OEt
C2H5OH
CO2Et
COCH3
2. HCl
CHO
5
4
2
3
SOCl2
CH2Cl2
NO2
NH2
S
O
O
O
O
SnCl2, HCl
7
COCl
COCl
O2N
C2H5OH
80 oC
AlCl3
CH2Cl2
S
S
S
S
8
9
6
Scheme 2. Synthesis of compounds 4-9.
In the next step, diacid 5 was converted to diacid chloride 6 with SOCl2, which was directly
used in the next step without purification (Scheme 2). At this stage, Friedel-Crafts reaction of
diacid chloride 6 with 2,5-dimethylthiophene (7) provided 8 in a yield of 50% (see SI for
spectroscopic data, Fig. S3-S5). The treatment of compound 8 with SnCl2 in the presence of

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HCl in refluxing ethanol resulted in the formation of the corresponding amine 9 in 90% yield
(see SI for spectroscopic data).
Finally, Paal-Knorr reaction of compounds 9 and 1041 afforded 11, which was followed by
McMurry coupling with TiCl3(THF)3 in the presence of zinc to give the target compound 1
(Scheme 3). Initial characterization of 11 and 1 was based on NMR and FTIR spectroscopic
data along with the elemental and MALDI TOF mass analysis (see Supporting Information,
Fig. S9-S14), which confirmed the structures.
NH2
N
N
S
S
S
S
O
PTSA
TiCl3(THF)3
+
S
O
O
C6H5CH3
110 oC
Zn, THF
40 oC
S
O
O
O
10
S
S
S
S
9
11
S
S
1
Scheme 3. Synthesis of compounds 11 and 1.
The absorption profile of compound 1 was examined in CH2Cl2 solution. The UV-Vis
spectrum of 1 was characterized by broad bands between 250-400 nm (λmax= 335 nm) with
molar extinction coefficient (εm) of 18733 M-1cm-1. On the other hand, it was noted that 1
induced blue emission with a λmax of 413 nm when excited at 335 nm light.
When the photochemical switching behavior of compound 1 was investigated in solution, it
was found that 1 underwent efficient photochemical ring closing and opening upon irradiation
with UV (365 nm) and visible (>400 nm) light, respectively (Scheme 4 and Figure 1a). The
absorption changes could also be detected by the naked eye. By irradiating the colorless
open isomer (1o) with UV light, the deep brown closed isomer (1c) is formed by conrotatory
6π6 electrocyclization (Figure 2a).

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N
N
S
S
S
S
UV
Vis
S
S
S
S
1o
1c
Scheme 4. Photochemical switching of 1o/1c in CH2Cl2 with UV (365 nm) and visible light
(>400 nm).
Figure 1. (a) UV/vis absorption spectra of 1 (33 µM in CH2Cl2) in the open (1o) and closed
(1c) state upon irradiation with UV (365 nm) and visible (>400 nm) light. (b) Emission
spectral changes of 1 (3.3 µM) during irradiation in CH2Cl2, (λexc= 335 nm).

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Figure 2. Compound 1 in CH2Cl2 before (1o) and after (1c) irradiation under (a) day light and
(b) UV light (365 nm).
Figure 3a illustrates the photochromic film which was prepared by the introduction of this
novel photochromic system 1o in polymethylmetacrylate (PMMA) matrix as dopant. After the
preparation of the film, it was homogeneously irradiated with UV light through a patterned
mask. The color change was quite prominent on the regions that were exposed to UV light
(Figure 3b). It should be noted that the system 1 can be reversibly and efficiently switched by
light in both solution and in the solid poly(methyl methacrylate) (PMMA) film state (Figure 3).
Figure 3. Images of 1 (0.25 wt.-%) in Propylene carbonate/ PMMA (2 wt.-%) matrix (a)
before and (b) after irradiation.
It was also noted that compound 1 exhibited obviously different fluorescence in open and
closed states under alternating irradiation of UV and visible light (Figure 2b). This is probably

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due to a non-radiative fluorescence-resonance energy transfer process between SNS and
the closed form of the pendant DTE units, which could also be switched on and off upon
irradiation (Figure 1b).
To reveal the electrochemical properties of 1o, the redox behavior was investigated in
different electrolyte solutions by cyclic voltammetry between 0.0 and 2.0 V (vs. Ag/AgCl). It
was found that 1o (3.0 x 10-3 M) induced multiple oxidation peaks at 0.77, 1.30, 1.56, 1.72
and 1.96 V in an electrolyte solution consisting of 0.1 M TBAPF6 dissolved in a mixture of
CH3CN and CH2Cl2 (95:5, v/v) at a scan rate of 100 mV/s (vs. Ag/AgCl) (Figure 4a). The first
peak at 0.77 V was attributed to the oxidation of SNS unit and others were probably due to
the overoxidation of oligomeric species formed at 0.77 V or oxidation of DTE unit. At this
stage the electropolymerization of 1o was explored. Unfortunately, all attempts to obtain an
electroactive polymer film via potentiodynamic methods were unsuccessful. Although the
cyclic voltammogram in Figure 4b was promising as a characteristic signature of the
formation of an electroactive polymer film on electrode surface, it was found that the product
remained in the solution as a dark yellow color when the electrode was removed from the
bulk solution. This was mainly attributed to the solubility and/or mechanical instability of the
product under the given conditions.

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Figure 4. Cyclic voltammogram of (a) 1o (3.0 x 10-3 M) and (b) electropolymerization in an
electrolyte solution consisting of 0.1 M TBAPF6 dissolved in a mixture of CH3CN and CH2Cl2
solution (95:5, v/v) at a scan rate of 100 mV/s.
In order to overcome this problem, electropolymerization of 1o was carried out in a C2H5OH-
CH2Cl2 mixture (95:5, v/v) containing 0.1 M LiClO4 electrolyte. During the first anodic scan,
an irreversible oxidation peak at 0.72 V was observed (Figure 5a). After repetitive cycles
between 0.0 V and 0.9 V, a new redox couple began to appear and its intensity was
increased after each successive cycle. To our delight, a dark yellowish polymer film (P1o)
was successfully obtained on the electrode surface when C2H5OH and CH2Cl2 mixture was
used instead of CH3CN and CH2Cl2 mixture (Scheme 5).
Figure 5. (a) Electropolymerization of 1o (3.0 x 10-3 M) by potential scanning to give polymer
P1o in an electrolyte solution consisting of 0.1 M LiClO4 dissolved in C2H5OH and CH2Cl2
mixture (95:5, v/v) at a scan rate of 100 mV/s. (b) Repetitive cyclic voltammograms of P1o
film on Pt electrode to break-in polymer film in an electrolyte solution consisting of 0.1 M
TBAPF6 dissolved in CH3CN at a scan rate of 100 mV/s (vs. Ag/AgCl).

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N
N
S
S
S
S
n
Electropolymerization
LiClO4 / C2H5OH / CH2Cl2
S
S
S
S
P1o
1o
Vis
UV
N
N
S
S
S
S
n
Electropolymerization
LiClO4 / C2H5OH / CH2Cl2
S
S
S
S
1c
P1c
Scheme 5. Photochemical switching and electrochemical polymerization of 1o and 1c states.
We were unable to determine the exact molecular weight of the polymer by gel permeation
chromatography since it was insoluble in common organic solvents (CH2Cl2, CHCl3, THF
etc.). The redox properties of the polymer film P1o was investigated in a monomer free
electrolyte solution consisting of 0.1 M TBAPF6 in CH3CN. The polymer film was cycled
several times between its redox states in order to get reproducible results (see Figure 5b).
After a certain number of cycles, the polymer exhibited a stable and reversible redox couple
with a half wave potential of 0.69 V. Also, the peak current intensity of the redox couple
increased with increasing scan rate and a linear increase in the peak currents as a function
of the scan rates confirmed that the polymer P1o was tightly bound to the electrode surface
and the redox process was non-diffusional (Figure 6).

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Figure 6. (a) Scan rate dependence of P1o on a Pt disk electrode in 0.1 M TBAH in CH3CN
at different scan rates (mVs-1): a= 20; b= 40; c= 60; d= 80; e= 100; f= 120; g= 140 and h=
160. (b) Relationship of anodic (ia) and cathodic (ic) current peaks as a function of scan rate
between neutral and oxidized states of P1o in 0.1 M TBAPF6 in CH3CN.
In order to elucidate the electropolymerizability of the two-isomers of compound 1 without
distruption of the DTE units, electrochemical studies on the open (1o) and the closed (1c)
states were extended. As expected, the formation of the polymer film P1c also proceeded
smoothly when the closed isomer (1c) was subjected to polymerization (Scheme 5, Figure
7). Since peak currents of the redox couple of polymer film increased linearly as a function of
scan rates, it was assumed that the corresponding polymer film P1c was tightly bonded to
the electrode surface. These results clearly suggested that the electropolymerization of both
the open (1o) and the closed (1c) states of this novel photochrome 1 can be achieved
successfully without disturbing the pendant DTE units.

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Figure 7. (a) Electropolymerization of 1c (3.0 x 10-3 M) by potential scanning to give polymer
P1c in an electrolyte solution consisting of 0.1 M LiClO4 dissolved in C2H5OH and CH2Cl2
mixture (95:5, v/v) at a scan rate of 100 mV/s. The scan shown in red line is the first scan.
(b) Scan rate dependence of P1c on a Pt disk electrode in 0.1 M TBAH in CH3CN at different
scan rates (mVs-1): a= 20; b= 40; c= 60; d= 80; e= 100; f= 120 and g= 140.
It was reported that immobilization of molecules that function as switches (e.g. DTEs) might
provide smart surfaces which could be controlled electrochemically or photochemically.47-51
Indeed, it should be noted that immobilization and/or processability of the material is sine qua
non in the context of practical and/or industrial applications, which are not accessible in
solution state. Note that solution state does not always allow such applications. Keeping
these facts in mind, it was envisaged that this novel photochrome 1 could also be used as an
electrochromic switch due to the presence of SNS unit in the structure. In order to
demonstrate the applicability of this novel photochrome 1 as electrochromicly switchable
material, immobilization of 1 on ITO surface was investigated through electrochemical
polymerization. Figure 8 depicts the cyclic voltammogram of 1o during the polymerization

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process while the inset in Figure 8 depicts the modified P1o-ITO electrode, which was
obtained by electropolymerization of 1o as a mechanically stable and insoluble (CH2Cl2,
toluene, CH3CN) green film.
Figure 8. Electropolymerization of 1o (1 x 10-5 M) by potential scanning to in an electrolyte
solution consisting of 0.1 M LiClO4 dissolved in C2H5OH-CH2Cl2 mixture (95:5, v/v) at a scan
rate of 100 mV/s (vs. Ag/AgCl). Inset: photograph of P1o coated ITO electrode.
Surprisingly, DTE unit in 1 could not retain its photochemical switching properties after
immobilization onto ITO. It was likely that the polymer structure was inflexible to
accommodate the conformational requirements of the photoisomerization reaction. It should
be noted that this was especially important in the case of DTEs since the ring-closing
reaction could occur only from the anti-parallel conformation of the ring-open isomer.1, 52 The
morphology of the polymer film deposited on ITO was analyzed by AFM. Figure 9
demonstrates the AFM image of the P1o on ITO. The image unambiguously showed that the
surface of the polymer film was rough.

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Figure 9. AFM image of P1o on ITO.
In view of the above facts, it was also reasonable to assume that the interconversion
between parallel and antiparallel forms was not feasible within a densely-packed polymer film
of 1. Therefore, the polymer was found to be highly ordered and inflexible disallowing for
conformational interconversion.
The modified ITO electrode exhibited a reversible redox couple at 0.65 V, when it was
anodically scanned in a monomer-free electrolyte solution of 0.1 M TBAPF6 in CH3CN (Figure
10-inset). After constructing a simple device, the electrochromic features of the modified ITO

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electrode was examined by recording spectroelectrochemical behavior of the electrode under
a variety of voltage pulses between 0.0 V and 0.9 V. During p-doping, the higher energy
absorbance at a wavelength shorter than 500 nm (π-π* transition at 435 nm) started to
decrease with an apparent new absorption band at around 650 nm, which was attributed to
the formation of polaron charge (Figure 10). Upon further oxidation, the polaron charge
carriers turned into the bipolaron charge carriers above 800 nm. The band gap (Eg) of the
modified electrode was calculated from the onset of π-π* transition at 435 nm, and it was
found to be 2.29 eV. In this process, it was assumed that charge carriers (polarons and
bipolarons) were probably delocalized as the conformation of the polymer backbone on ITO
was forced to be planarized to some extent. More importantly, as a result of these variations
in the conformation of the polymer backbone and the absorption spectrum of the modified
electrode, the color changed from green in the neutral state to violet upon doping (Figure 10).
The reversibility of this process through redox cycling with full recovery of the initial state at
0.0 V unambigiously confirmed that the electrocyclic ring closure did not take place in the
redox cycling of the polymer modified electrode. These results clearly indicated that the
material exhibited remarkable electrochromic features that can be switched from green in the
neutral state to violet state upon application of voltage pulses.
Figure 10. Electronic absorption spectra and colors of modified ITO electrode in 0.1 M
TBAH-CH3CN at various applied potentials between 0.0 V and 0.9 V. Inset: Cyclic

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voltammogram of modified ITO electrode in an electrolyte solution consisting of 0.1 M
TBAPF6 dissolved in CH3CN at a scan rate of 20 mV/s.
Switching time is the necessary time to change the color of the electrochromic polymer
with 95 % of the full contrast (after which point the naked eyes could not sense the
changes in the color) between various redox states. For this aim, a square-wave potential
method was applied between 0.0 V and 0.9 V with 10 s time intervals. As depicted in
Figure 11, the polymer film could be successfully switched between redox states bearing
different colors in a response time of about 6.0 s for 95% of full optical switch.
Figure 11. Chronoabsorptometry experiments for P1o on ITO in 0.1 M TBAH/ACN while the
polymer was switched between 0.0 V and 0.9 V.
3. Conclusion
In conclusion, the synthesis, photochromism and electrochemistry of a novel material 1 with
pendant DTE photochromic units are described. It should be noted that the system 1 can be
reversibly and efficiently switched between open (1o) and closed (1c) states by light in both
solution and in the solid PMMA matrix. It is also noteworthy that the two isomers (1o and 1c)

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of this novel system 1 can be smoothly polymerized on ITO by electrochemical means.
Surprisingly, the DTE unit in 1 does not retain its photochemical switching properties after
immobilization onto ITO. On the other hand, it was found that the polymer exhibited
remarkable electrochromic features that can be switched from green in the neutral state to
violet state under applied external potentials without disturbing the photochromic units.
Further work on the development of novel systems is currently underway in our laboratories.
4. Experimental
General Methods. All chemicals were purchased from Sigma Aldrich or Merck and used as
received unless otherwise noted. FTIR spectra were recorded on a Perkin Elmer Spectrum
1
100 model FTIR with an attenuated total reflectance (ATR). H (400 or 300 MHz) and 13C
(100 or 75 MHz) NMR spectra were recorded on a Bruker DPX-400 or Ultrashield 300 NMR
Spectrometers. Combustion analyses were carried out by using a LECO CHNS-932
analyzer. Mass spectra were recorded on Waters SYNAPT MS system (TOF MS ESI+) or
Bruker Daltonics model MALDI TOF MS analyzer. UV-Vis and fluorescence measurements
were recorded on Varian Cary 50 and Varian Cary Eclipse spectrophotometers, respectively.
AFM images were collected using an atomic microscope (WITEC TS 150) in ac mode (42
N/m, 285 kHz). Data visualization was achieved using Witec Project Plus software.
0.1 M Tetrabutylammonium hexafluorophosphate (TBAH) dissolved in acetonitrile was used
as electrolyte solution. A platinum button (0.02 cm2) and a platinum wire were used as
working and counter electrodes, respectively, as well as a Ag/AgCl reference electrode
(calibrated externally using 10 mM solution of ferrocene/ferrocenium couple which is an
internal standard calibrated to be 0.44 V in acetonitrile solution vs. Ag/AgCl). Melting points
were determined on a Schorrp MPM-H2 model apparatus and are uncorrected. Column
chromatography was performed on silica gel (60-200 mesh) from Merck Company. TLC was
carried out on Merck 0.2 mm silica gel 60 F254 analytical aluminum plates. The synthesis of
compound 1041 was carried out according to a previously published procedure.

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Diethyl 2,4-diacetyl-3-(4-nitrophenyl)pentanedioate (4)
Compound 4 was synthesized according to literature method with little modification.45-46
A
mixture of 4-nitrobenzaldehyde (2, 0.06 mol), ethyl acetoacetate (3, 0.12 mol), and piperidine
(2.4 mL) in 95% ethanol (60 mL) was placed in a one-neck flask and allowed to stand while
stirring at room temperature until the mixture became solid (ca. 8 h). The solid was filtered,
washed with 95% ethanol, and recrystallized twice from 95% ethanol to give a white powder
17.7 g (75% yield), m.p. 160-161 oC (lit. m.p. 158-160 oC)
3-(4-Nitrophenyl)pentanedioic acid (5)
4 (45 mmol) was dissolved in a mixture of distilled water (67.5 mL) and sodium hydroxide
(67.5 g). The resulting mixture was refluxed vigorously for 3 h, and then cooled to room
temperature and poured into water (340 mL). The resulting mixture was extracted with ether
(2x100 mL). The water phase was acidified with concentrated hydrochloric acid (190 mL).
The precipitated glutaric acid was removed by filtration and washed with cold water to
remove sodium chloride. The acid was recrystallized from water and dried in vacuum to give
o
1
a pale brown solid (6.84 g), 60% yield, m.p. 236-237 C. H NMR (400 MHz, CDCl3) δ/ppm:
12.20 (s, 2H), 8.15 (d, J = 6.9 Hz, 2H), 7.57 (d, J = 6.9 Hz, 2H), 3.60-3.50 (m, 1H), 2.73 (dd,
J = 8.1-8.1 Hz, 2H), 2.60 (dd, J = 8.1-8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ/ppm: 172.9,
152.1, 146.6, 129.4, 123.7, 39.9, 38.3; FTIR (cm-1): 3209, 2983, 2933, 2907, 1696, 1607,
1515, 1402, 1347, 1311, 1286, 1250, 1220, 1186, 1162, 1118, 884, 862, 849, 753, 698. Anal.
Calcd for C11H11NO6: C, 52.18; H, 4.38; N, 5.53. Found: C, 52.16; H, 4.40; N, 5.57.
3-(4-Nitrophenyl)pentanedioyl dichloride (6)
SOCl2 (0.45 mL, 6 mmol) was added to a suspension of diacid 5 (0.506 g, 2 mmol) in dry
CH2Cl2 (20 mL) while stirring at room temperature. After 2 h, the mixture was heated under
reflux overnight. The solvent was removed under reduced pressure and the diacid chloride 6
was directly used in the next step without further purification.

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1,5-Bis(2,5-dimethylthiophen-3-yl)-3-(4-nitrophenyl)pentane-1,5-dione (8)
A solution of the diacid chloride 6 (0.58 g, 2 mmol) and 2,5-dimethylthiophene (7, 0.46 mL, 4
mmol) in dry CH2Cl2 (15 mL) was added dropwise to a suspension of AlCl3 (0.64 g, 4.8
mmol) in dry CH2Cl2 (5 mL) while stirring magnetically at room temperature. After addition,
the reaction mixture was allowed to stand at room temperature until all the starting materials
were consumed. Cold water (20 mL) was carefully added to the mixture and the organic
phase was washed with saturated NaHCO3 solution (100 mL), and water (100 mL), and
saturated NaCl solution (100 mL), dried with MgSO4, filtered, and the solvent evaporated in
vacuum to yield a brown solid. The solid was purified over silica gel column eluting with
o
1
CHCl3 to give 8 (0.45 g) as white solid in a yield of 50%. M.p. 176-179 C. H NMR (300
MHz, CDCl3) δ/ppm: 8.15 (d, J = 8 Hz, 2H), 7.47 (d, J = 8.3 Hz, 2H), 7.00 (s, 2H), 4.09 (p, J =
6.94, 1H), 3.29 (dd, J = 16.4-16.8 Hz, 2H, A- part of AB system), 3.18 (dd, J = 16.5-16.8 Hz,
2H, B- part of AB system), 2.60 (s, 6H), 2.40 (s, 6H); 13C NMR (75 MHz, CDCl3) δ/ppm:
193.4, 152.2, 148.0, 146.5, 135.4, 135.0, 128.5, 125.6, 123.7, 47.2, 36.5, 16.0, 14.9; FTIR
(cm-1): 2917, 2897, 2856, 1664, 1596, 1509, 1483, 1396, 1346, 1233, 1124, 1111, 1077, 973,
957, 871, 833, 822, 757, 725, 697, 683. Anal. Calcd for C23H23NO4S2: C, 62.56; H, 5.25; N,
3.17; S, 14.52. Found: C, 62.55; H, 5.27; N, 3.19; S, 14.56. MALDI TOF MS Calcd for
C23H23NO4S2: 441.56, found: 442.582 [M+H]+.
3-(4-Aminophenyl)-1,5-bis(2,5-dimethylthiophen-3-yl)pentane-1,5-dione (9)
A mixture of 8 (0.442 g, 1 mmol), SnCl2 (0.76 g, 4 mmol) and conc. HCl (7.5 mL) in ethanol
(30 mL) was heated under reflux until 8 was totally consumed. The yellow mixture was
allowed to cool to room temperature and most of the solvent was removed. The product was
extracted with CH2Cl2 (3x100 mL) after neutralization with saturated NaHCO3 solution (100
mL). Organic phases were washed with water (100 mL), and saturated NaCl solution (100
mL), dried with MgSO4, filtered, and the solvent was evaporated in vacuum to yield 9 (0.370
g) as yellow viscous oil in 90% yields. 1H NMR (300 MHz, CDCl3) δ/ppm: 7.03 (d, J = 9.1 Hz,
2H), 6.62 (d, J = 9.1 Hz, 2H), 7.00 (s, 2H), 3.83 (p, J = 7.0 Hz, 1H), 3.18 (dd, J = 12.1-16.1

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Hz, 2H, A- part of AB system), 3.05 (dd, J = 20.7-11.5 Hz, 2H, B- part of AB system), 2.58 (s,
6H), 2.40 (s, 6H); 13C NMR (75 MHz, CDCl3) δ/ppm: 195.5, 147.2, 144.7, 135.6, 134.9, 134.1,
128.2, 126.0, 115.9, 48.0, 36.3, 15.0, 14.1; FTIR (cm-1): 3458, 3368, 3225, 2919, 1662, 1623,
1548, 1517, 1477, 1439, 1411, 1365, 1322, 1236, 1252, 1221, 1181, 1126, 1034, 970, 951,
823, 776, 733, 701, 679. Anal. Calcd for C23H25NO2S2: C, 67.12; H, 6.12; N, 3.40; S, 15.58.
Found: C, 67.09; H, 6.15; N, 3.43; S, 15.60. MALDI TOF MS Calcd for C23H25NO2S2: 411.13,
found: 412.45 [M+H]+.
3-(4-(2,5-Di(thiophen-2-yl)-1H-pyrrol-1-yl)phenyl)-1,5-bis(2,5-dimethylthiophen-3-
yl)pentane-1,5-dione (11)
A solution of 9 (0.412 g, 1 mmol), 10 (0.25 g, 1 mmol) and p-toluenesulfonic acid (5 mg) in
dry toluene (75 mL) were heated under reflux in a Dean–Stark apparatus until all the starting
materials were consumed. The flask was cooled and the solvent was removed under
reduced pressure. The residue was filtered through a short pad of silica gel by eluting with
CH3OH/CH2Cl2 (1%, v/v) to give analytically pure 11 (0.313 g) as gray solid in 50% yield.
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1
M.p. 117-119 C. H NMR (400 MHz, CDCl3) δ/ppm: 7.30 (d, J = 9 Hz, 2H), 7.21 (d, J = 9
Hz, 2H), 7.04 (s, 2H), 6.96 (dd, J = 5-1 Hz, 2H), 6.74 (dd, J = 5-3 Hz, 2H), 6.51 (s, 2H), 6.45
(dd, J = 3-1 Hz, 2H), 4.04 (p, J = 8 Hz, 1H), 3.28 (dd, J = 16-7 Hz, 2H, A- part of AB system),
3.14 (dd, J = 16-7 Hz, 2H, B- part of AB system), 2.58 (s, 6H), 2.41 (s, 6H); 13C NMR (100
MHz, CDCl3) δ/ppm: 194.2, 147.4, 145.4, 136.7, 135.6, 135.2, 135.0, 130.1, 129.9, 128.5,
126.8, 125.9, 124.0, 123.7, 109.6, 47.9, 37.0, 15.9, 15.0; FTIR (cm-1): 3101, 3071, 3035,
2952, 2921, 2893, 2851, 1665, 1544, 1511, 1476, 1412, 1366, 1229, 1221, 1127, 846, 833,
824, 768, 742, 691. Anal. Calcd for C35H31NO2S4: C, 67.16; H, 4.99; N, 2.24; S, 20.49.
Found: C, 67.15; H, 4.97; N, 2.26; S, 20.53. MALDI TOF MS Calcd for C35H31NO2S4: 625,89,
found: 625,69 [M]+.
1-(4-[3,4-Bis(2,5-dimethyl-3-thienyl)cyclopent-3-en-1-yl]phenyl)-2,5-di-2-thienyl-1H-
pyrrole (1)

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A mixture of 11 (0.626 g, 1 mmol), TiCl3(THF)3 (0.742 g; 2 mmol) and Zn dust (0.163 g; 2.5
o
mmol) in dry THF (20 mL) was heated to 40 C under inert atmosphere (N2) for 1 h. The
mixture was allowed to cool to room temperature and the solvent was removed. The product
was isolated by filtering through a short pad of silica gel by eluting with n-hexane/CH2Cl2
(5%, v/v) as colorless liquid. Yield: 49%, 0.29 g. 1H NMR (400 MHz, CDCl3) δ/ppm: 7.29 (d, J
= 9 Hz, 2H), 7.16 (d, J = 9 Hz, 2H), 6.95 (dd, J = 5-1 Hz, 2H), 6.73 (dd, J = 5-4 Hz, 2H), 6.47-
6.46 (m, 4H), 6.36 (bs, 2H), 3.63 (p, J = 8 Hz, 1H), 3.18 (dd, J = 14-8 Hz, 2H, A- part of AB
system), 2.83 (dd, J = 14-8 Hz, 2H, B- part of AB system), 2.28 (s, 6H), 1.82 (s, 6H); 13C
NMR (100 MHz, CDCl3) δ/ppm: 148.4, 136.2, 135.3, 133.0, 132.6, 130.2, 129.9, 126.8,
125.9, 123.9, 109.6, 46.4, 42.1, 15.2, 14.0; FTIR (cm-1): 3103, 3069, 3040, 2915, 2852, 2734,
1721, 1673, 1563, 1511, 1430, 1413, 1378, 1350, 1323, 1299, 1264, 1223, 1198, 1140,
1105, 1072, 1044, 1015, 973, 910, 896, 843, 824, 763, 736, 689. Anal. Calcd for C35H31NS4:
C, 70.78; H, 5.26; N, 2.36; S, 21.60. Found: C, 70.75; H, 5.21; N, 2.32; S, 21.55. MALDI TOF
MS Calcd for C35H31NS4: 593,13, found: 593,117 [M]+.
Acknowledgements
F. A. is indebted to National Young Researchers Career Development Program (3501
CAREER 110T871) of the Scientific and Technological Research Council of Turkey
(TUBITAK) for financial support. Atilim University (ATU-ALP-1011-02) and Turkish Academy
of Sciences (TUBA) are also gratefully acknowledged. M. P. thanks TUBA for graduate
fellowship.
Supporting Information
Copies of 1H, 13C NMR and HRMS spectra for all new compounds. This material is available
free of charge via the Internet.
References

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Supporting Information
Design, synthesis, photochromism and electrochemistry of a novel material with
pendant photochromic units
Melek Pamuk Algi†,, Atilla Cihaner‡,*, Fatih Algi╘,Ⱡ*
† Health Services Vocational School, Aksaray University, TR-68100 Aksaray, Turkey.
‡ Atilim Optoelectronic Materials and Solar Energy Laboratory (ATOMSEL), Department of
Chemical Engineering and Applied Chemistry, Atilim University, TR-06836 Ankara, Turkey.
╘
Laboratory of Organic Materials (LOM), Canakkale Onsekiz Mart University, TR-17100
Canakkale, Turkey.
Ⱡ
Department of Biotechnology and Molecular Biology, ASU BioNanoTech Lab., Aksaray
University, TR-68100 Aksaray, Turkey.
*Corresponding authors. Tel.: +903125868304-8817; Fax: +903125868091; E-mail:
cihaner@atilim.edu.tr (A. Cihaner) and Tel.:+902862180018-2415; Fax: +902862180533; E-
mail: falgi@comu.edu.tr (F. Algi).
1

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Table of Contents
1H NMR spectrum of 5 (300 MHz, DMSO-d6).
3
13C NMR spectrum of 5 (75 MHz, DMSO-d6).
1H NMR spectrum of 8 (300 MHz, CDCl3).
13C NMR spectrum of 8 (75 MHz, CDCl3).
MALDI TOF Mass spectrum of 8.
4
5
6
7
1H NMR spectrum of 9 (300 MHz, CDCl3).
13C NMR spectrum of 9 (75 MHz, CDCl3).
MALDI TOF Mass spectrum of 9.
7
8
9
1H NMR spectrum of 11 (400 MHz, CDCl3).
13C NMR spectrum of 11 (100 MHz, CDCl3).
MALDI TOF Mass spectrum of 11.
9
10
10
11
11
12
1H NMR spectrum of 1 (400 MHz, CDCl3).
13C NMR spectrum of 1 (100 MHz, CDCl3).
MALDI TOF Mass spectrum of 1.
2

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Fig. S1. 1H NMR spectrum of 5 (300 MHz, DMSO-d6).
3

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Fig. S2. 13C NMR spectrum of 5 (75 MHz, DMSO-d6).
4