Design and synthesis of polydiacetylenes, and their low temperature irreversible thermochromic properties

Article abstract of DOI:10.1016/j.dyepig.2020.108839

A thermochromic material that show irreversible color change at or below freezing temperatures has potential utility as a temperature indicator for frozen food and meat products, therefore, the goods transporters and customers would easily recognize when the goods exposed to high temperatures during their storage and delivery. In this study, we have successfully synthesized and used polydiacetylenes functionalized with glycol ester groups as a thermochromic dye, which show irreversible thermochromic behavior at below freezing temperatures. The photochromic and thermochromic properties of diacetylenes were investigated in the solid state, and color-transition temperatures for poly(DCDA-EGME), poly(DCDA-DGME) and poly(DCDA-TGME) were found to be 2, ?10 and ?16 °C, respectively. Moreover, we prepared a paper test strip and used as a warning indicator for deep freeze products.

Full text of DOI:10.1016/j.dyepig.2020.108839

Dyes and Pigments 184 (2021) 108839
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Design and synthesis of polydiacetylenes, and their low temperature
irreversible thermochromic properties
*
Naveen Mergu, Young-A. Son
Department of Advanced Organic Materials Engineering, Chungnam National University, 220 Gung-dong, Yuseong-gu, Daejeon, 305-764, South Korea
A R T I C L E I N F O
A B S T R A C T
Keywords:
A thermochromic material that show irreversible color change at or below freezing temperatures has potential
utility as a temperature indicator for frozen food and meat products, therefore, the goods transporters and
customers would easily recognize when the goods exposed to high temperatures during their storage and de-
livery. In this study, we have successfully synthesized and used polydiacetylenes functionalized with glycol ester
groups as a thermochromic dye, which show irreversible thermochromic behavior at below freezing tempera-
tures. The photochromic and thermochromic properties of diacetylenes were investigated in the solid state, and
color-transition temperatures for poly(DCDA-EGME), poly(DCDA-DGME) and poly(DCDA-TGME) were found
to be 2, ꢀ 10 and ꢀ 16 ◦C, respectively. Moreover, we prepared a paper test strip and used as a warning indicator
for deep freeze products.
Polydiacetylene
Irreversible thermochromism
Photo-polymerization
Non-planar ene-yne backbone
1
. Introduction
Thermochromic materials have gained much attention due to their
alternating ene-yne conjugated backbone. Typically, PDAs are blue in
color and non-fluorescent, and have absorption at 640 nm, which un-
dergo a color transition from blue-to-red along with a change from
non-fluorescent to red-fluorescent, and the absorption maximum shifts
to shorter wavelength (550 nm) upon environmental stimulation such as
pH, heat, stress, solvent, and metal ion [23–36]. These stimuli-induced
optical changes are mainly due to the reduction of the effective conju-
gate chain length in the PDA system, which could be caused by twisting
of longer alkyl chains attached to the PDA backbone [26,37–40].
However, the development of PDA-based materials that show chromatic
response to temperature has received great attention. The majority of
thermochromic PDAs reported to date exhibit color transitions above
importance as temperature sensors in life sciences, as well as in indus-
trial and engineering fields [1–8]. Various organic and inorganic com-
pounds [9,10] polymers [11,12], and sol-gels [13,14] based
thermochromic materials have been reported till date. The most
well-known thermochromic compounds are spiropyrans and poly-
diacetylenes [15,16]. A thermochromic material that show color change
◦
at or below freezing (0 C) temperatures has potential utility as a tem-
perature indicator for goods that require refrigeration or freezing.
Moreover, the materials which exhibit an irreversible color change are
more desirable for this type of applications, thus the customers and
freight transporters would easily recognize when the goods have been
exposed to an environmental temperature (above freezing) during their
storage and delivery. Therefore, the irreversible color change which
cannot be reversed upon cooling provides permanent records that can be
visualized offline.
◦
room temperature (typically >40 C) [25,26,37,41–44]. There are only
◦
a few reports describing low-temperature (up to 0 C) thermochromic
behavior [40,45,46]. To the best of our knowledge, only one example of
the irreversible thermochromic response at or below freezing tempera-
tures of PDA materials has been reported [47]. In addition, L.H. Nguyen
et al. reported a polydiacetylene-based sensor to detect ammonia gas
generated by the food spoilage process at temperatures ranging between
Over the last decade, a considerable research has focused on poly-
diacetylenes (PDAs), mainly due to their unique properties such as self-
photo-polymerization, and stimuli-responsive colorimetric and fluoro-
metric behavior [17–20]. PDAs can be produced with a high degree of
purity by irradiation of UV or γ-ray of diacetylene monomers without
requirement of initiators or catalysts [21,22]. The obtained PDAs have
◦
ꢀ 20 C and room temperature [48].
In the current study, we designed and synthesized a new series of
symmetrical polydiacetylenes consisting of methyl or glycol ester
groups. An attempt to tune down the irreversible color-transition tem-
perature was achieved by increasing ethyleneoxy units, this is mainly
*
Corresponding author.
E-mail address: yason@cnu.ac.kr (Y.-A. Son).
https://doi.org/10.1016/j.dyepig.2020.108839
Received 21 May 2020; Received in revised form 12 August 2020; Accepted 4 September 2020
Available online 8 September 2020
0
143-7208/© 2020 Elsevier Ltd. All rights reserved.

N. Mergu and Y.-A. Son
Dyes and Pigments 184 (2021) 108839
Scheme 1. Synthesis (a) and chemical structures (b) of diacetylene monomers.
due to the lack of adequate intermolecular hydrogen bonding interac-
tion between ester groups within the polymer. The synthesized PDAs
2.3. General procedure for synthesis of diacetylenes
exhibited irreversible thermochromism in temperature ranging between
To a stirred solution of DCDA (0.73 g, 2 mmol) in tetrahydrofuran
(THF) (20 mL), methanol/glycol methyl ethers (0.64 g, 20 mmol of
Methanol; 1.5 g, 20 mmol of Ethylene glycol monomethyl ether; 2.4 g,
20 mmol of Diethylene glycol monomethyl ether; 3.3 g of Triethylene
glycol monomethyl ether), 1-(3-dimethylaminopropyl)-3-ethyl-
carbodiimide hydrochloride (EDC, 1.15 g, 6 mmol) and 4-(dimethyla-
mino)pyridine (DMAP, 50 mg) were added at RT. The stirring was
continued for 18 h and the solution was evaporated to dryness, and the
residue was dissolved in ethyl acetate (30 mL). The residue was washed
◦
ꢀ
18 and + 2 C which has never been reported in any other PDA-based
material. Diacetylene monomers of these PDAs were found to be liquids
at RT (except methyl ester), and they begin to solidify at zero or below
zero degrees Celsius. The thermochromic response of PDAs is based on
the self-assembly of monomers and subsequent polymerization.
2
. Experimental section
2
.1. Materials and instruments
2 4
with saturated aqueous NaCl solution (brine), and dried over Na SO .
The ethyl acetate solvent was removed in vacuo, and the resulting crude
residue was purified via column chromatography using ethyl acetate
and hexane solvent system (1:10 (v/v) for DCDA-Me, 1:4 (v/v) for
DCDA-EGME, 1:1 (v/v) for DCDA-DGME, 4:1 v/v) for DCDA-TGME) to
give the pure diacetylene monomer.
Ethylene glycol monomethyl ether, diethylene glycol monomethyl
ether and triethylene glycol monomethyl ether were purchased from
TCI. 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride
(
EDC), 4-(dimethylamino)pyridine (DMAP) and Copper(I) chloride were
obtained from Alfa Aesar. 10-Undecynoic acid and polystyrene (PS)
Dimethyl Docosa-10,12-diynedioate (DCDA-Me): Yield: 0.72 g,
1
1
(
Avg. Mw = 192,000 g mol⁻ ) were purchased from Sigma Aldrich. All
92%; H NMR (CDCl
3
, 600 MHz), δ (ppm): 1.29 (s, 12H), 1.37 (m, 4H),
other solvents were purchased from commercial sources and used
without further purification. The proton and carbon-13 NMR spectra
were recorded at 600 and 150 MHz respectively on a Bruker AVANCE III
1.50 (qn, J = 7.8 Hz, 4H), 1.61 (qn, J = 7.2 Hz, 4H), 2.23 (t, J = 7.2 Hz,
13
4H), 2.29 (t, J = 7.2 Hz, 4H), 3.66 (s, 6H); C NMR (CDCl
3
, 150 MHz), δ
(ppm): 19.16, 24.89, 28.27, 28.72, 28.86, 29.05, 34.06, 51.42, 65.26,
+
spectrometer using CDCl
3
as a solvent. Mass spectra obtained on a
77.46, 174.26. HRMS m/z: C24
H
38
O
4
(M + H) : 391.2848, found:
Bruker micrOTOF-Q mass spectrometer. Differential scanning calorim-
etry (DSC) analysis was carried out on a Mettler-Toledo DSC 1 by
391.2850.
Bis(ethylene glycol methyl ether) docosa-10,12-diynedioate
(DCDA-EGME): Yield: 0.84 g, 88%; 1H NMR (CDCl
, 600 MHz), δ
◦
heating and cooling the samples from ꢀ 50 to 50 C at the scan rate of
3
◦
1
0 C/min. Absorption and Raman spectra were collected on a Shimadzu
(ppm): 1.24–1.31 (m, 12H), 1.33–1.38 (m, 4H), 1.49 (qn, J = 7.2 Hz,
4H), 1.61 (qn, J = 7.2 Hz, 4H), 2.22 (t, J = 7.2 Hz, 4H), 2.33 (t, J = 7.2
Hz, 4H), 3.38 (s, 6H), 3.58 (t, J = 4.8 Hz, 4H), 4.21 (t, J = 4.8 Hz, 4H);
UV-2600 spectrophotometer and Horiba Jobin Yovn LabRAM HR-800
Raman spectrometer with the 785 nm excitation laser, respectively.
Spin-coating was performed on a SF-100NA spin coater.
1
3
3
C NMR (CDCl , 150 MHz), δ (ppm): 19.14, 24.83, 28.26, 28.71, 28.85,
2
9.00, 29.03, 34.11, 58.94, 63.23, 65.24, 70.49, 77.43, 173.77. HRMS
+
2
.2. Synthesis of diacetylene
m/z: C28
H
46
O
6
(M + H) : 479.3373, found: 479.3384.
Bis(diethylene glycol methyl ether) docosa-10,12-diynedioate
(DCDA-DGME): Yield: 0.96 g, 85%; 1H NMR (CDCl
, 300 MHz), δ
Docosa-10,12-diynedioic acid (DCDA) was synthesized according to
3
the procedure described in the literature [49]. All final symmetrical
diacetylene monomers are prepared by a similar method [40] was
described in Scheme 1a.
(ppm): 1.28–1.37 (m, 16H), 1.44–1.53 (m, 4H), 1.59 (qn, J = 7.2 Hz,
4H), 2.22 (t, J = 6.9 Hz, 4H), 2.31 (t, J = 7.5 Hz, 4H), 3.37 (s, 6H),
3.52–3.56 (m, 4H), 3.60–3.64 (m, 4H), 3.68 (t, J = 4.8 Hz, 4H), 4.22 (t, J
=
4.8 Hz, 4H); 13C NMR (CDCl
, 150 MHz), δ (ppm): 19.10, 24.77,
3
2
8.21, 28.67, 28.81, 28.97, 28.99, 34.09, 58.98, 63.24, 65.21, 69.16,
2

N. Mergu and Y.-A. Son
Dyes and Pigments 184 (2021) 108839
Fig. 1. Photographic images of diacetylenes under continuous UV irradiation at various temperatures.
+
7
0.40, 71.82, 77.38, 173.69. HRMS m/z: C32
H
54
O
8
(M + H) : 567.3897,
fabricated and used. The liquid diacetylenes were dropped on the top of
the Peltier device, and visually characterized upon UV irradiation with
simultaneous cooling from 20 to ꢀ 20 ◦C. As shown in Fig. 1, even
though DCDA-Me exists as solid at room temperature, polymerization
did not take place due to week attractive forces between methyl ester
head groups, whereas others (DCDA-EGME, DCDA-DGME and DCDA-
TGME) exist as liquids at room temperature. In the liquid states, the
monomers are randomly distributed and are not aligned properly for
formation of PDAs upon UV irradiation. Solidified diacetylenes, DCDA-
EGME, DCDA-DGME and DCDA-TGME obtained by lowering the tem-
found: 567.3886.
Bis(triethylene glycol methyl ether) docosa-10,12-diynedioate
DCDA-TGME): Yield: 1.1 g, 84%; 1H NMR (CDCl
, 600 MHz), δ
(
3
(
(
ppm): 1.29 (s, 12H), 1.34–1.39 (m, 4H), 1.50 (qn, J = 7.2 Hz, 4H), 1.61
qn, J = 7.2 Hz, 4H), 2.23 (t, J = 7.2 Hz, 4H), 2.32 (t, J = 7.2 Hz, 4H),
3
4
1
6
.38 (s, 6H), 3.54–3.55 (m, 4H), 3.64–3.67 (m, 12H), 3.69 (t, J = 4.8 Hz,
13
H), 4.22 (t, J = 4.8 Hz, 4H); C NMR (CDCl
3
, 150 MHz), δ (ppm):
9.16, 24.83, 28.28, 28.74, 28.87, 29.06, 34.15, 59.02, 63.34, 65.24,
9.18, 70.57, 70.60, 71.92, 77.45, 173.76. HRMS m/z: C36
+
H
62
O
10 (M +
◦
H) : 655.4421, found: 655.4438.
perature to 0, ꢀ 12 and ꢀ 18 C, respectively underwent polymerization
upon UV irradiation, and transformed to red (for DCDA-EGME) and
purple (for DCDA-DGME and DCDA-TGME), indicating the formation of
polydiacetylenes. The variation in color of PDAs is mainly due to the
presence of different length of carbon chain of glycolic ester.
2
.4. Fabrication of spin-coated polymer thin films
A mixture of DA monomer (200 mg) and polystyrene (2:1, w/w) in
chloroform (2 mL) was sonicated for 5–10 min to obtain a homogeneous
and transparent solution. The DA samples were then deposited on glass
substrate and spin coated (2000 rpm) for 2 min at RT. The polymer thin
3
.2. Thermochromism of polydiacetylenes in solid state
films approximately 2
surface in air.
μ
m thick were obtained after 30 min of drying the
The polymerized diacetylenes were further monitored their low-
temperature thermochromic behavior in the range of temperatures be-
◦
◦
tween ꢀ 20 C and 4 C. As shown in Fig. 2, the red color of the poly
3
. Results and discussion
The diacetylene monomers, DCDA-Me, DCDA-EGME, DCDA-DGME
◦
(
DCDA-EGME) in the solid state turned yellow-orange at 2 C, whereas,
the purple-colored PDAs (poly(DCDA-DGME) and poly(DCDA-TGME))
underwent color transitions to orange phase at ꢀ 10 ◦C and ꢀ 16 C,
respectively. All three PDAs show a sharp color change at their color-
transition temperatures and those exist as liquids at these tempera-
tures, and the observed final colors (orange) do not return to the original
color as the temperature decreases below the freezing point. Thus, PDAs
exhibits irreversible color transition at lower temperatures. The color-
transition temperatures of thermochromic PDAs are closely related to
the melting point of the corresponding diacetylene monomer.
◦
and DCDA-TGME (Scheme 1b) were prepared using two-step synthetic
procedure starting from 10-Undecynoic acid involving formation of
diacetylene (PCDA) from acetylene followed by conversion of carboxylic
acid to methyl or glycol ester, and confirmed by 1H a nd C NMR
spectroscopies and Mass spectrometry. The DA monomers are liquids
13
(
except methyl ester, DCDA-Me) at room temperature, and solidification
occurs at zero or below zero degrees Celsius. The polymerization and
thermochromism of synthesized diacetylenes are discussed in detail in
this section.
According to the general rule, the thermochromic transition tem-
perature of a polydiacetylene is close to the melting point of the corre-
sponding diacetylene monomer. As shown in Figs. 1 and 2, it is observed
that the melting points of DA monomers are matched to the thermo-
chromic transition temperature of their corresponding PDAs. Differen-
tial scanning calorimetry (DSC) thermograms provided the information
of thermal properties of the diacetylene monomers (Fig. 3). Thermo-
grams of the heating run show an endothermic peak corresponding to
the melting transition of DA monomer. The melting temperatures are
3
.1. Polymerization of diacetylenes in solid state
Photo-induced solid state polymerization of synthesized diacetylenes
is checked at various temperatures by irradiate with a hand-held labo-
ratory UV lamp (254 nm). To control the surface temperature, a small-
scale Peltier device connected with
a digital thermometer was
Fig. 2. Photographic images of (a) poly(DCDA-EGME), (b) poly(DCDA-DGME) and (c) poly(DCDA-TGME) at different temperatures.
3

N. Mergu and Y.-A. Son
Dyes and Pigments 184 (2021) 108839
◦
Fig. 3. DSC heating and cooling thermograms of diacetylene monomers at the scan rate of 10 C/min.
Fig. 4. The simultaneous UV spectral and color changes of DA-embedded thin films upon UV irradiation at 254 nm. (For interpretation of the references to color in
this figure legend, the reader is referred to the Web version of this article.)
found to be 41.5, 0.7, ꢀ 10.8 and ꢀ 16.3 ◦C for DCDA-EGME, DCDA-
DGME and DCDA-TGME, respectively. The results obtained suggest that
an increase in the number of ethylene glycol units in the terminal esters
of DA monomers causes a decrease in melting point. From the cooling
thermograms, it can be seen that the crystallization temperature of the
corresponding diacetylene monomer, it was also found to decrease as
the number of ethylene glycol units increases.
4

N. Mergu and Y.-A. Son
Dyes and Pigments 184 (2021) 108839
Fig. 5. Absorption spectra of the different phases PDA thin films, and their corresponding color changes. (For interpretation of the references to color in this figure
legend, the reader is referred to the Web version of this article.)
3
.3. Polymerization of DA-embedded thin films
The spin-coated thin film containing DA monomers were allowed to
investigate their spectral properties along with naked-eye color change
upon irradiation with 254 nm ultraviolet lamp which induces the top-
ochemical polymerization within the diacetylene monomer units. The
polymerization test was conducted at below the solidification temper-
atures of the corresponding DA monomers using dry ice. As shown in
Fig. 4, the diacetylene monomer present in the colorless thin film did not
exhibit any absorption peaks in the visible region. Upon irradiation with
UV light for 10 min at frozen temperature, the color change (from
colorless to orange for DCDA-EGME, and colorless to purple for DCDA-
DGME and DCDA-TGME) was observed simultaneously with the poly-
merization of thin films which were further analysed by absorption
spectroscopy. As can be seen in the figure, a new broad dual absorption
peak appeared in the wavelength range between 400 and 700 nm for the
colored thin films, whereas no significant spectral and color changes are
noticed for DCDA-Me-embedded thin film. The generation of unusual
absorption bands centered at 526, 561 and 568 nm corresponding to
poly(DCDA-EGME), poly(DCDA-DGME) and poly(DCDA-TGME),
respectively support the development of a novel colored-PDAs (orange
and purple).
Fig. 6. Raman spectra of two different phases of (a) poly(DCDA-EGME), (b)
poly(DCDA-DGME) and (c) poly(DCDA-TGME).
3
.4. Thermochromism of DA-embedded thin films
for poly(DCDA-EGME), from 561 to 518 nm for poly(DCDA-DGME)
and from 568 to 527 for poly(DCDA-TGME)) as the surface temperature
increases above the melting point of their corresponding DA monomers.
The observed spectral and color transitions at higher temperatures do
not return to the original color as the temperature decreases below the
freezing point. Thus, the permanent spectral and color changes proved
its low temperature irreversible thermochromic performance of these
PDAs.
The low-temperature, thermochromic property of polymerized DA-
embedded thin films was further inspected by UV–vis absorption spec-
troscopy. Due to the difficulty in maintaining the lower temperatures of
glass surface, we examined only two different phases (initial-red/purple
and final-yellow/orange) of PDAs. The initial red and purple-colored
films consisting of poly(DCDA-EGME) and poly(DCDA-DGME) or
poly(DCDA-TGME), respectively were immediately turned yellow and
orange when the surface temperature rise to the melting points of their
corresponding DA monomers (Fig. 5). The absorption maxima of orig-
inal PDAs are shifted towards shorter wavelength (from 526 to 505 nm
The conformational structural adjustments occurring in PDA supra-
molecular assemblies upon thermochromism were also examined by
Raman spectroscopy using spin-coated polymer thin films. As shown in
5

N. Mergu and Y.-A. Son
Dyes and Pigments 184 (2021) 108839
Fig. 7. Schematic illustrations of the hypothetical conformations of (a) common diacetylene, (b) DCDA-EGME and (c) DCDA-DGME/DCDA-TGME monomers upon
UV and heat treatments.
Fig. 6, the initial color phases of photo-polymerized PDA thin films
band centered at 520 and 600 nm for DCDA-EGME and DCDA-DG-
ME/DCDA-TGME respectively is assigned to the formation of red and
purple-colored poly(DCDA-EGME) and poly(DCDA-DGME)/poly
(DCDA-TGME) respectively.
1
exhibit two Raman bands at 1515 and 2117 cm⁻ (for poly(DCDA-
1
EGME)), 1472 and 2090 cm⁻ (for poly(DCDA-DGME)), and 1466 and
2
087 cm⁻1 (for poly(DCDA-TGME)) attributed to C=C and C≡C
respectively, confirmed the formation of ene-yne backbone of PDAs. As
compared to usual PDAs (blue phase), the Raman bands associated to
C=C and C≡C in the initial color phases (red and purple) are red shifted
for the current PDAs suggested that the formation of a more twisted form
From the results obtained it can be concluded that the absorption
maxima (λmax) of PDA in different phases (from blue-to-purple-to-red-to-
orange phase) decreases with increasing degree of C–C single bond free
rotation in the conjugated ene-yne backbone, which mainly due to the
generation of the steric repulsions between the terminal ester groups
within the PDA macromolecule (Fig. 7b and c). The shorter ester groups
lead to a stronger repulsion at short distances [53,54], resulting in the
formation of red-colored PDAs upon UV irradiation, which further
transform to strongly repulsive orange-colored PDAs upon heat treat-
(
for poly(DCDA-EGME)) and a less twisted form (for poly(DCDA-
DGME)/poly(DCDA-TGME)) of the planar ene-yne backbone. The
polymerized red and purple colored thin films on the glass substrate
were further examined by Raman spectroscopy at ambient temperature.
The Raman bands associated with conjugated C–C double and triple
bonds in the initial red and purple phases were shifted to 1519 and 2124
cm⁻ (for poly(DCDA-EGME)), 1521 and 2121 cm⁻1 (for poly(DCDA-
DGME)), and 1520 and 2119 cm⁻1 (for poly(DCDA-TGME)), respec-
tively are corresponding to the final orange phase, which clearly sug-
gested that the non-planar configuration of the PDAs. Thus, the results of
ment. Thus, the attractive forces (i.e., hydrophobic and
π-
π
stacking in-
promotes
1
teractions) between diacetylene monomers
photo-polymerization leads to development of blue color that mainly
due to the generation of highly -conjugated ene-yne backbone, and the
π
steric repulsions between adjacent terminal groups in the PDA promotes
distortion of the conjugated p-orbital array that ultimately leads to color
deviations from its original blue color (i.e., purple, red, orange, etc.),
which mainly due to the twisting of the polymer backbone followed by
changing the amount of conjugation in the system. It is clear that the
attractive forces are weaker compared to repulsive forces in the poly-
merized form of diacetylenes used in the present study. In conclusion,
the generation of the higher steric repulsion aroused in red and orange
phases compared to blue and purple phases of PDAs leads to develop-
the Raman studies demonstrated that the planar
π
-conjugated PDA
backbone turn into the non-planar conformer upon heating, it may
consist of twisted backbone with rotated and/or distorted long alkyl side
chains.
3
.5. Structural features of polydiacetylenes
For a better insight into the structural evolution of diacetylenes
ment of non-planar
backbone.
π
-conjugated orbitals in the planar -conjugated
π
during photo-polymerization then heat treatment, a possible mechanism
is proposed (Fig. 7). Generally, the diacetylene monomers generate blue-
colored polydiacetylene upon UV irradiation, which transforms to red in
the presence of external stimuli (such as heat). The planar “blue” form
3.6. Practical application
has unbroken -electron overlap and a full conjugation length (Fig. 7a).
π
Upon heat treatment, the accumulated stress during the photo-
polymerization is released by partial disorder of long alkyl chains that
To investigate the practical application of low temperature irre-
versible thermochromism of PDAs synthesized, paper test strips were
prepared by simple dipping and drying method, and used as a warning
indicator. For this, a filter paper was immersed in a liquid DCDA-DGME,
and paper strip was attached to the frozen meat package stored at
eventually twist the
π
orbitals to the non-planar states, which reduces
the effective conjugation length and blue-shifts the absorption spectrum
to that of the red form [26,50–52]. The generation of a broad absorption
6

N. Mergu and Y.-A. Son
Dyes and Pigments 184 (2021) 108839
Fig. 8. Photographs of color change of a test strip immobilized with polymerized DCDA-DGME at <ꢀ 10 and >0 ◦C. (For interpretation of the references to color in
this figure legend, the reader is referred to the Web version of this article.)
◦
approx. ꢀ 15 C. Consecutively, the strip was exposed to UV light for 30
min, resulted in the development of a purple colored paper strip. The test
strips turned orange when the frozen meat exposed to high temperature
[5] Flam E. Method of monitoring the condition of the skin or wound. US Patent
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[
6] Cellini F, Peterson SD, Porfiri M. Flow velocity and temperature sensing using
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(
Fig. 8), as expected. Therefore, this experiment exhibits that the poly
DCDA-DGME) and poly(DCDA-TGME) are quite useful for the on-site
[
[
7] Pelvich CW, Foulk DL, Polec TW. Method of sensing high surface temperature in an
aircraft. Patent EP1959246 A2; 2008.
(
observation of frozen foods and meat products that stored under proper
temperature conditions.
8] Lataste E, Demourgues A, Salmi J, Naporea C, Gaudon M. Thermochromic
◦
◦
behaviour (400 < T C < 1200 C) of barium carbonate/binary metal oxide
mixtures. Dyes Pigments 2011;91:396–403.
[
9] Samat A, Lokshin V. Organic photochromic and thermochromic compounds. In:
Crano JC, Guglielmetti RJ, editors2. New York: Kluwer Academic; 1999. p. 415–66.
4
. Conclusion
[
[
10] Day JH. Thermochromism of inorganic compounds. Chem Rev 1968;68:649–57.
11] Chance RR. Chromism in polydiacetylene solutions and crystals. Macromolecules
In conclusion, we have successfully synthesized and described the
1
980;13:6–398.
thermochromic properties of novel PDAs consisting of glycol esters. We
have observed a strange color (purple) for polymerized DCDA-DGME
and DCDA-TGME at the deep freezing temperature in the solid state,
which further showed an irreversible color change from purple to orange
when exposed to higher temperatures. The spectral (absorption and
Raman) spectroscopic investigation of the photochromic and thermo-
chromic properties of DA monomers were carried out using spin-coated
thin films. In addition, a possible mechanism is proposed for structural
alternations of PDAs present in various color phases such as common
blue, purple, red and orange. Furthermore, low temperature thermo-
chromic paper test strip as a warning indicator was also prepared for
deep freeze products.
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CRediT authorship contribution statement
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8–1968.
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[
19] Sun X, Chen T, Huang S, Li L, Peng H. Chromatic polydiacetylene with novel
sensitivity. Chem Soc Rev 2010;39:4244–57.
Naveen Mergu: Conceptualization, Methodology, Investigation,
Formal analysis, Visualization, Writing - original draft. Young-A. Son:
Writing - review & editing, Supervision.
20] Lee S, Kim JY, Chen X, Yoon J. Recent progress in stimuli-induced polydiacetylenes
for sensing temperature, chemical and biological targets. Chem Commun 2016;52:
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21] Wegner G. Topochemical polymerization of monomers with conjugated triple
bonds. Makromol Chem 1972;154:35–48.
Declaration of competing interest
[22] Enkelmann V. Structural aspects of the topochemical polymerization of
diacetylenes. In: Cantow HJ, editor. Polydiacetylenes. vol. 63. Berlin, Heidelberg:
Springer; 1984. p. 91–136.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[
23] Cheng Q, Stevens RC. Charge-induced chromatic transition of amino acid-
derivatized polydiacetylene liposomes. Langmuir 1998;14:4–1976.
24] Yapor JP, Alharby A, Gentry-Weeks C, Reynolds MM, Alam AKMM, Li YV.
Polydiacetylene nanofiber composites as a colorimetric sensor responding to
Escherichia coli and pH. ACS Omega 2017;2:7334–42.
[
Appendix A. Supplementary data
[25] Mergu N, Kim H, Heo G, Son YA. Development of naphthalimide-functionalized
thermochromic conjugated polydiacetylenes and their reversible green-to-red
chromatic transition in the solid state. Dyes Pigments 2019;164:355–62.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2020.108839.
[
26] Chae S, Lee JP, Kim JM. Mechanically drawable thermochromic and
mechanothermochromic polydiacetylene sensors. Adv Funct Mater 2016;26:
1
769–76.
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27] Samyn P, Rühe J, Biesalski M. Polymerizable biomimetic vesicles with controlled
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