Tuning down of color transition temperature of thermochromically reversible bisdiynamide polydiacetylenes

Article abstract of DOI:10.1021/ma101264k

A series of bisdiynamide lipids containing various lengths of methylene spacer (m=2,3 and 4) between the diynes and the diamide headgroup and number of methylene units (n = 6 and 9) in their hydrophobic tails are synthesized. All six lipids synthesized can be dispersed in water and photopolymerized by UV irradiation to give the corresponding polydiacetylene (PDA) sols. The color transitions from blue to red during heating-cooling cycles of the PDA sols are photographically recorded and monitored byUV-vis absorption spectroscopy. The bisdiynamide PDAs exhibit excellent thermochromic reversibility and the color transition temperature can be tuned between ca. 25-55 °C by the variation of m and n values. Temperature indicators can be obtained by applying a screen printing ink formulated from the bisdiynamide monomer on plastic substrates followed byUVirradiation to generate desired patterns of thermochromically reversible PDAs.

Full text of DOI:10.1021/ma101264k

7540 Macromolecules 2010, 43, 7540–7548
DOI: 10.1021/ma101264k
Tuning Down of Color Transition Temperature of Thermochromically
Reversible Bisdiynamide Polydiacetylenes
Chaiwat Phollookin,† Sumrit Wacharasindhu,† Anawat Ajavakom,† Gamolwan Tumcharern,‡
Sasikarn Ampornpun,§ Thichamporn Eaidkong,§ and Mongkol Sukwattanasinitt*,†
†Organic Synthesis Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University
Bangkok, 10330, Thailand, ‡Thailand National Nanotechnology Center, National Science and Technology
§
Development Agency Patumthanee, 12120, Thailand, and Program of Petrochemistry and Polymer Science,
Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand
Received June 7, 2010; Revised Manuscript Received July 29, 2010
ABSTRACT: A series of bisdiynamide lipids containing various lengths of methylene spacer (m = 2, 3 and
4) between the diynes and the diamide headgroup and number of methylene units (n = 6 and 9) in their
hydrophobic tails are synthesized. All six lipids synthesized can be dispersed in water and photopolymerized
by UV irradiation to give the corresponding polydiacetylene (PDA) sols. The color transitions from blue to
red during heating-cooling cycles of the PDA sols are photographically recorded and monitored by UV-vis
absorption spectroscopy. The bisdiynamide PDAs exhibit excellent thermochromic reversibility and the
color transition temperature can be tuned between ca. 25-55 °C by the variation of m and n values.
Temperature indicators can be obtained by applying a screen printing ink formulated from the bisdiynamide
monomer on plastic substrates followed by UV irradiation to generate desired patterns of thermochromically
reversible PDAs.
Introduction
The reduction of the aliphatic chain length of the diacetylene
monomers has been reported to decrease the thermal stability of
Polydiacetylenes (PDAs) are ene-yne π-conjugated poly-
mers possessing unique chromic properties that can be deve-
loped into practical colorimetric transducers in biological1 and
chemical2 sensors. A PDA is generally obtained from a
topopolymerization of a diacetylene monomer under UV or
γ-ray irradiation. Various forms of PDAs such as bulk crystals,3
monolayer,4 multilayer films,5 and composites6 have been
prepared and studied. Most interestingly, their π-conjugated
backbone can be disturbed by various external stimuli to cause
changes in its electronic absorption and color. The colori-
metric transition caused by the external stimuli such as heat
(thermochromism),7 solvent (solvatochromism),8 mechanical
stress (mechanochromism)9 and ligand-receptor interaction,10
are often detectable by naked eye.
thermochromically irreversible PDAs attributed to the weaken-
ing of cohesive hydrophobic interaction.11c We figured that the
shortening of the aliphatic chain length may also be used as a strat-
egy for tuning down the color transition temperature of thermo-
chromically reversible PDAs. Report herein is the synthesis and
thermochromic properties of bisdiynamide monomers 1 with var-
ied length of the methylene spacer between the diyne and amide
headgroup (m) and the number of methylene groups within its tail
(n) which form thermochromically reversible PDAs with color
transition temperature near or below ambient temperature.
Thermochromism is probably one of the earliest known
properties of PDAs and most widely studied for its mechanism.
Thermochromic reversibility of PDAs have been achieved by
increasing the attractive intramolecular interaction among their
side-chains.7a-c,11 In our continuing attempt to develop PDA-
based sensors, we have recently found that thermochromically
reversible PDAs can be obtained from the diamide derivatives of
10,12-pentacosadiynoic acid (PCDA).7i These diamide PDAs
and all other thermochromically reversible PDAs reported to
date possess color transition temperature higher than that of
poly(PCDA) which is above 65 °C. Reducing the color transition
temperature of the PDAs without severe distress of their thermo-
chromic reversibility is mechanistically challenging. Further-
more, the thermochromically reversible materials with color
transition temperatures near or below ambient temperature are
of commercial interest as temperature indicators for various
consumer products such as foods and beverages.
Results and Discussion
1. Synthesis of Diacetylene Monomers. The synthesis of the
diamide diacetylene (1) began with the copper-catalyzed
cross coupling reaction (Scheme 1) between an iodoalkyne
(2 or 3) and an alkynoic acid (4-6) under a modified
Cadiot-Chodkiewicz condition12 to afford the diynoic acids
(7-12) in moderate to good yields (49-75%). The compe-
titive homocoupling of the iodoalkyne sometimes lessened
the diynoic acid yield. Subsequent treatment of the diynoic
acids with 0.5 equiv of ethylenediamine in the presence of N,
N0-dicyclohexylcarbodiimide (DCC) coupling reagent af-
forded the desired bisdiynamide monomers (1a-1f) as white
solids in good yields (68-78%). These bisdiynamides were
*Corresponding author. E-mail smongkol@chula.ac.th.
pubs.acs.org/Macromolecules
Published on Web 08/19/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 18, 2010 7541
readily isolated from dicyclohexyl urethane (DCU) bypro-
duct and the monoamide side-product by crystallization in
methanol.
2. Preparation of PDA Sols. The phospholipid-liked
monomers 1a-f, containing two hydrophobic tails, were
well dispersed in Milli-Q water under sonication at 80-85 °C
to form either transparent or semitransparent sols (see Sup-
porting Information S15, first row) suggesting a good for-
mation of lipid assembly. Notworthingly, the corresponding
fatty acid-liked monomers, containing only one hydropho-
bic tail, i.e. diynoic acids and monoamide diacetylenes with
m = 2, 3 and n = 6, 9, formed large aggregate and precipitate
under the same preparative condition. Upon UV-irradiation
(254 nm, 900 μw/cm2) in an ice bath, the diacetylene sols
rapidly turned intense blue or purple color within 5 min,
signifying an efficient topopolymerization of the monomer
assemblies to form the ene-yne conjugated PDAs. The blue
PDA sols showed a characteristic absorption band with two
maxima near 640 and 580 nm corresponding to the π-π*
electronic transition with double bond vibronic coupling. In
addition, the blue PDA sols of EB-4,6-17DA and EB-4,6-
14DA also showed an extra peak at unusually long wave-
length near 700 nm. The origin of this low energy absorption
remains mysterious to us.7i
Scheme 1. Synthesis of Diacetylene Lipid Monomers
After the temperature of the polymerized sols was allowed
to warm up to 20 °C, the appearance of the PDA sols were
photographically recorded (see Supporting Information
S15, second row). Notably, the PDA sols obtained from EB-
4,6-14DA, EB-4,6-17DA, EB-5,7-18DA and EB-6,8-19DA
(1a, 1d, 1e, and 1f) appeared as a blue color while the PDA
Figure 1. (a) Size distribution obtained from dynamic light scattering (b) AFM images of poly(bisdiynamide).

7542 Macromolecules, Vol. 43, No. 18, 2010
Phollookin et al.
Figure 2. Electronic absorption spectra of bisdiynamide PDA sols upon stepwise heating from 20 to 90 °C along with the color appearance of the sols
recorded by photography.
sols obtained from EB-5,7-15DA and EB-6,8-16DA (1b and
1c) appeared as a purple color at room temperature. The
results suggested that both the numbers of the m and n values
played subtle roles in governing the thermochromic sensiti-
vity of this PDA series which will be elaborated in the sub-
sequent section.
The sizes and shapes of the lipid assembled particles
within the PDA sols were characterized by dynamic light
scattering (DLS) technique and atomic force microscopy
(AFM). The DLS size distribution revealed the average
hydrodynamic diameter of the particles in the range of
75-195 nm (Figure 1a). The PDA sol obtained from EB-
6,8-19DA showed the smallest particle size of 75 nm while
the largest size of 195 nm was observed for the sol obtained
from EB-4,6-17DA indicating that the particle size tended
to increase with the decreasing m value. The AFM image
of the dry sample of poly(EB-4,6-17DA) sol showed
mainly spherical structures while those of poly(EB-5,7-
18DA) and poly(EB-6,8-19DA) sols illustrated mixtures of
spherical and rod-like structures (Figure 1b) that is in good
agreement with the decreasing packing parameter (F) of
the lipids.
3. Thermochromic Properties of PDA Sols. The thermo-
chromic transition of the successfully prepared PDA sols
was monitored from 20 to 90 °C using photography and
electronic absorption spectroscopy. From the results shown
in Figure 2, both the numbers of the m and n values in
the bisdiynamide lipid structures cast effects on the color
transition temperature. By fixing the m value, the reduction
of the n value decreased the color transition temperatures:

Article
Macromolecules, Vol. 43, No. 18, 2010 7543
Figure 3. Hypothetical packing of the diamide side-chains of the PDAs with m = 2, 3 and 4.
Figure 4. The colorimetric responses (% CR) of bisdiynamide PDA sols during two cycles of stepwise heating/cooling processes. The inset color
photographs show the appearance of the sols at initial temperature of 20 °C, after being heated to 90 °C, and after lowering the temperature back to
20 °C.
poly(EB-5,7-18DA) > poly(EB-5,7-15DA) and poly(EB-
6,8-19DA) > poly(EB-6,8-16DA). Considering PDAs with
the same n value, the effect of m value was more complicated.
For instance, poly(EB-4,6-17DA) and poly(EB-4,6-14DA)
which has m = 2 are unusually thermally stable and did not
turn red at 90 °C. In fact, in solid state these PDAs did not
turn red even at 150 °C (data is not shown). In contrast, the
PDAs with m = 3 such as poly(EB-5,7-18DA) and poly-
(EB-5,7-15DA) are rather thermally sensitive exhibiting blue-
red color transition temperature below the ambient temperature
and those of PDAs with m = 4 were slightly higher (10-
15 °C). The trend in thermal stability of the PDAs containing
m = 3 and 4 may be attributed to either the length11c or odd/
even effects.13 However, these effects cannot account for the
unexpectedly high thermal stability of poly(EB-4,6-17DA)
and poly(EB-4,6-14DA). We hypothesize that, with m = 2,
the diamide side-chains of the PDAs form extraordinary
strong hydrogen bonding accommodated by the well posi-
tioned ene-yne backbone (Figure 3), but a clearer explana-
tion on this issue will need further investigation.

7544 Macromolecules, Vol. 43, No. 18, 2010
Phollookin et al.
Figure 5. Normalized absorbance at the initial λmax (Aλ) of the PDA sols at 20 and 90 °C in the heating/cooling cycles. The degree of reversibility
(% DR) is the percentage ration of the average absorbance change in the second to tenth heating against the absobance change in the first heating.
From the results discussed above, the PDAs with color
transition temperature near or below ambient temperature
were successfully prepared and, to complete our research
goal, the thermochromic reversibility of these PDAs was
explored in the following section.
presence of extraordinary strong force prevailing over
the backbone strain in these PDAs. With m = 2, the side
chain geometry (Figure 3) ene-yne backbone and the
double hydrogen bonding of the diamide groups work
collaboratively.
4. Thermochromic Reversibility of PDA Sols. To our de-
light, all the bisdiynamide PDAs were thermochromically
reversible even the ones that showed relatively low color
transition temperature such as EB-5,7-15DA, EB-5,7-
18DA, EB-6,8-16DA and EB-6,8-19-DA (Figure 2, color
photographic insets). Notably, PDAs obtained from these
four monomers offer reversible thermochromic materials
with significantly lower color transition temperature
(25-55 °C) comparing to the bisdiynamide derivatives of
PCDA (70-80 °C).7i The colorimetric response (% CR, see
Experimental Section for calculation) of the PDA sols
obtained from the first two cycles of stepwise heating/
cooling processes, in the range of 20 to 90 °C, showed
nearly complete reversibility (Figure 4). Despite complete
reversibility after the first cycle, the % CR did not return to
the initial zero value at the starting point. The discrepancies
in % CR represent the degrees of unrecoverable backbone
strain present in the as prepared PDAs, upon thermal
annealing. Again, the fact that poly(EB-4,6-14DA) and
poly(EB-4,6-17DA) showed the least discrepancy in % CR
after the first heating/cooling cycle along with their barely
visible color transition has confirmed the hypothetical
Quantitative evaluation of the thermochromic reversibil-
ity was performed by monitoring the absorbance of the PDA
sols at their initial λmax for 10 heating/cooling cycles. The
plots in Figure 5 indicate that all bisdiynamide PDA sols
possess excellent thermochromic reversibility up to at least
10 cycles. The degree of reversibility (% DR),7i of these PDA
sols calculated (see Experimental Section for the calculation)
for the first 10 cycles were higher than 84% and increa-
sed with the lessening m values but with the levitat-
ing n values. It is also interesting to note that the wider
range of the absorbance change during the thermochromic
process of the PDAs prepared from the monomers contain-
ing higher n value denotes the greater contrast in color
change, desirable for practical application as a temperature
indicator.
The bisdiynamide PDA sols were incubated at 95 ( 2 °C in
an oil bath for evaluation of their long-term thermal stabi-
lity. The incubated sols were sampled out at each time
interval and allowed to cool to 20 °C. The electronic absorp-
tion spectra and photographs of the samples were recorded
and presented in Figure S16. The color of poly(EB-4,6-
17DA) remained blue but appeared much paler after 64 h

Article
Macromolecules, Vol. 43, No. 18, 2010 7545
Conclusion
Tuning of color transition temperature of thermochromically
reversible bisdiynamide series of polydiacetylenes (PDAs) can be
achieved by systematic variation of the length of methylene
spacer (m) between the diyne and the diamide headgroup as well
as the number of methylene units (n) in the hydrophobic tail.
While the decrease of n value enhances the thermal sensitivity
resulting in lower color transition temperature, the effect of m
value is not as straightforward. Not only the length and odd/even
effects but also a magic number of n = 2 play important role in
governing the thermal sensitivity of the PDAs. With appropriate
m and n values, thermochromically reversible PDAs with color
transition temperature near or below ambient temperature were
obtained from the bisdiynamide monomers. Screen printing pro-
cess can be conveniently used to fabricate the monomer into
thermochromic labels that suggests potential applications in the
field of smart labeling as a temperature indicator.
Figure 6. Preparation of thermochromic labels by screen printing
process of a bisdiynamide monomer: (a) screen printing ink containing
the bisdiynamide monomer, (b, c) screen printed transparency sheet
before (b) and after (c) UV irradiation (insets are microscopic images
under optical microscope), and (d) color transition of the thermochro-
mic labels sleeving around a stainless ring.
Experimental Section
Chemicals and Instruments. The starting acetylenic com-
pounds were purchased from GFS Chemicals (USA). N,N0-
dicyclohexylcarbodiimide (DCC), morpholine, pyrrolidine, io-
dine, ammonium chloride, sodium thiosulphate, sodium sulfate
anhydrous, sodium carbonate were purchased from Fluka
(Switzerland). Copper(I) iodide was purchased from Riedel-
of incubation due to serious precipitation. The intensity of
the absorption band significantly decreased after 32 h of
incubation (Figure S15 in Supporting Information). How-
ever, no significant change of the spectral shape was ob-
served throughout the incubation period. The descent in the
absorption is in association with the amount of precipitation
observed. These results indicated that poly(EB-4,6-17DA)
possesses exceptional chromic stability upon thermal stress
despite undergoing extensive aggregation. The color appear-
ance and the absorption spectra of poly(EB-5,7-18DA) and
poly(EB-6,8-19DA) displayed obvious shift of color from
blue to purple along with precipitation after 32 h of incuba-
tion. These bisdiynamide PDAs may be used as temperature
indicators under conditions where there is no prolonged
exposure to high temperature.
5. Fabrication of Thermochromic Labels. Although the
colloidal liquid sol of PDAs is good for spectroscopic study
due to its homogeneity and high polymerization yield,
this form of PDAs is not practical for many applications
requiring portability and long shelf life. Preparation of
PDA thin films is a sensible solution for these limitations.
A commercial transparent screen printing polymeric resin,
composed of PVC and poly(vinyl acetate) as a major com-
ponent was selected as a matrix for formulation of screen
printing ink. (Figure 6a). The ink containing diacetylene
monomer was applied on a transparency sheet by screen
printing process (Figure 6b). The screen printed monomeric
films was successfully polymerized by UV irradiation to
generate the desired blue PDA pattern on the substrate
(Figure 6c). The success of this method critically relies on
the molecular self-assembly of the diacetylene lipids in
the ink matrix that is necessary for topological polymeri-
zation of the diacetylene units. The microscopic images
of the UV-irradiated film showed blue and purple micro
dots corresponding to polydiacetylene aggregates dispersed
within the white matrix (inset of Figure 6c). The blue PDA
pattern was cut and used to form a sleeve aroud a stainless
ring. The thermochromic transition of this PDA sleeve
was photographically recorded in the temperature range
of 20-65 °C (Figure 6d) that showed a blue-red color
transtion temperature around 40-45 °C. The screen print-
ing technique is thus proved to be useful for fabrication
of a smart thermochromic label from our bisdiynamide
monomers.
€
deHaen (Germany). Ethylenediamine was perchased from
Aldrich (USA). Diethyl ether (reagent grade) was perchased
from AnalaR (U.K.). Toluene (AR grade) was purchased from
Fisher Scientific (U.K.). 1,1,1-Trichloromethane (AR grade)
was purchased from Labscan (Thailand). All reagent grade
compounds were used as purchased without further purification
unless stated otherwise. For extraction and chromatography,
solvents were commercial grade and they were distilled prior to
use. Column chromatography was performed using Merck silica
gel 60 (70-230 mesh). 1H spectra were recorded on Varian
Mercury 400 MHz NMR spectrometer (Varian, USA) using the
residual solvent proton resonance of CDCl3 at 7.26 ppm as the
reference. Electronic absorption spectra were recorded on a
temperature variable UV-visible spectrophotometer (Varian
Cary 100 Bio). AFM images were taken on a SPA 400 atomic
forced microscope (Seiko, Japan) Mass analysis was conducted
with Quattro micromassTM (Waters, France). The dynamic light
scattering particle size measurements were performed on a
Zetasizer Nano ZS (Malvern instruments, England). UV-irra-
diation was performed by UV light source (TUV 15W/G15 T18
lamp; Philips, Holland).
General Procedure for Synthesis of Iodoalkyne (2-3). A
solution of morpholine (33.25 mL, 381.60 mmol) in toluene
(300 mL) was treated with iodine (13.56 g, 53.42 mmol), shielded
from light and stirred for an hour at 45 °C. A solution of
1-nonyne (6.26 mL, 38.15 mmol) in toluene (30 mL) was then
added and the reaction mixture kept stirring at 45 °C for an
hour. The reaction mixture was cooled to room temperature and
filtered to remove the iodomorpholine salt. The filtrate was
poured over a mixture of diethyl ether (200 mL) and saturated
aqueous solution of Na2S2O3 (100 mL) and shaken until the
organic layer was colorless. The organic layer was separated,
washed again with saturated aqueous solution of Na2S2O3 (100
mL), dried over anhydrous Na2SO4, filtered, concentrated, and
purified by column chromatography with hexane as an eluent to
afford 1-Iodo-1-nonyne (2) as colorless oil (6.85 g, 72% yield).
1H NMR (400 MHz, CDCl3) δ (ppm): 2.35 (t, J = 7.1 Hz, 2H;
ICCCH2), 1.50 (m, 2H; ICCCH2CH2), 1.35-1.25 (m, 8H; CH2),
0.88 (t, J = 6.7 Hz, 3H; CH3).
1-Iodo-1-dodecyne (3). This was synthesized according to the
above general procedure from morpholine (33.25 mL, 381.60
mmol), iodine (13.56 g, 53.42 mmol) in 300 mL of toluene and
solution of 1-dodecyne (8.16 mL, 38.17 mmol) in 30 mL of

7546 Macromolecules, Vol. 43, No. 18, 2010
Phollookin et al.
toluene, purified by column chromatography with hexane as
colorless oil (8.76 g, 79%yield).1H NMR (400 MHz, CDCl3)
δ (ppm): 2.35 (t, J = 7.1 Hz, 2H; ICCCH2), 1.50 (m, 2H;
ICCCH2CH2), 1.35-1.25 (m, 14H; CH2), 0.88 (t, J = 6.6 Hz,
3H; CH3).
Anal. Found: C, 78.22; H, 10.58 (Calcd for C18H28O2: C, 78.21;
H, 10.21).
6,8-Nonadecadiynoic Acid (6,8-19DA) (12). 12 was synthe-
sized according to the above general procedure from 6-hepty-
noic acid (6) (0.38 mL, 3.0 mmol), 1-iodo-1-dodecyne (3) (1.10 g,
3.6 mmol) and copper(I) iodide (0.01 g, 0.05 mmol) in pyrroli-
dine (1.24 mL, 15.0 mmol), purified by column chromatography
with hexane:ethyl acetate (90:10 v/v) as white solid (0.57 g, 65%
yield); mp 57-59 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 2.31
(t, J = 7.4 Hz, 2H; COCH2), 2.22 (t, J = 6.9 Hz, 2H; COCH2-
CH2CH2CH2), 2.17 (t, J = 7.1 Hz, 2H; CCCH2), 1.68 (m, 2H;
COCH2CH2), 1.52 (m, 2H; COCH2CH2CH2), 1.43 (m, 2H;
CCCH2CH2), 1.30-1.28 (m, 14H; CH2), 0.81 (t, J = 6.8 Hz,
3H; CH3) MS (ESI-): [M - H]- found, 289.26 (calcd for C19-
H30O2, 290.44). Anal. Found: C, 78.71; H, 10.53 (Calcd for
C19H30O2: C, 78.57; H, 10.41).
General Procedure for Synthesis of Bis(diynamide) (1a-1f).
N,N0-Dicyclohexylcarbodiimide (0.46 g, 2.25 mmol) in chloroform
(20 mL) was added into 4,6-tetradecadiynoic acid (7) (0.33 g, 1.5
mmol) in chloroform 20 mL and stirred for 1 h. Ethylenediamine
(0.05 mL, 0.75 mmol) was then added dropwise into the reaction
mixture and stirred for 48 h. The reaction mixture was concen-
trated under reduced pressure to yield the crude product as a
light yellow solid. Recrystallization with methanol afforded
N,N0-ethylenebistetradeca-4,6-diynamide (EB-4,6-14DA) (1a) as
white solid (0.10 g, 59% yield). 1H NMR (400 MHz, CDCl3) δ
(ppm): 6.09 (br, 2H; CONH), 3.35 (m, 4H; CONHCH2), 2.54 (t,
J = 7.1 Hz, 4H; COCH2), 2.33 (t, J = 7.1 Hz, 4H; COCH2CH2),
2.18 (t, J = 7.1 Hz, 4H; CCCH2), 1.44 (m, 4H; CCCH2CH2),
1.30-1.20 (m, 16H; CH2), 0.81 (t, J = 7.0 Hz, 6H; CH3).
N,N0-Ethylenebispentadeca-5,7-diynamide (EB-5,7-15DA) (1b).
1b was synthesized according to the above general procedure
from N,N0-dicyclohexylcarbodiimide (0.83 g, 4.02 mmol), 5,7-
pentadecadiynoic acid (0.63 g, 2.69 mmol) (8) and ethylenedia-
mine (0.09 mL, 1.34 mmol) as a white solid (0.34 g, 51% yield);
mp 148-150 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 6.13 (br,
2H; CONH), 3.39 (m, 4H; CONHCH2), 2.32 (m, 8H; COCH2
and COCH2CH2CH2), 2.24 (t, J = 7.0 Hz, 4H; CCCH2), 1.85
(q, J = 6.9, 7.1 Hz, 4H; COCH2CH2), 1.52 (m, 4H; CCCH2CH2),
1.38-1.27 (m, 16H; CH2), 0.88 (t, J = 7.0 Hz, 6H; CH3).
N,N0-Ethylenebishexadeca-6,8-diynamide (EB-6,8-16DA) (1c).
1c was synthesized according to the above general procedure
from N,N0-dicyclohexylcarbodiimide (0.92 g, 4.47 mmol), 6,8-
hexadecadiynoic acid (9) (0.74 g, 2.98 mmol), and ethylenedia-
mine (0.1 mL, 1.49 mmol) as a white solid (0.42 g, 54% yield). 1H
NMR (400 MHz, CDCl3) δ (ppm): 6.16 (br, 2H; CONH), 3.39
(m, 4H;CONHCH2), 2.24 (m, 12H; COCH2 COCH2CH2CH2CH2
and CCCH2), 1.73 (m, 4H; COCH2CH2), 1.53 (m, 8H; COCH2-
CH2CH2 and CCCH2CH2), 1.37-1.27 (m, 16H; CH2), 0.88 (t,
J = 6.7 Hz, 6H; CH3).
N,N0-Ethylenebisheptadeca-4,6-diynamide (EB-4,6-17DA) (1d).
1d was synthesized according to the above general procedure
from N,N0-dicyclohexylcarbodiimide (1.18 g, 5.72 mmol), 4,6-
heptadecadiynoic acid (10) (1.00 g, 3.81 mmol) and ethylene-
diamine (0.13 mL, 1.91 mmol) as a white solid (0.57 g, 55%
yield). 1H NMR (400 MHz, CDCl3) δ (ppm): 6.16 (br, 2H;
CONH), 3.41 (m, 4H; CONHCH2), 2.60 (t, J = 7.1 Hz, 4H;
COCH2), 2.39 (t, J = 7.1 Hz, 4H; COCH2CH2), 2.23 (t, J = 7.0
Hz, 4H; CCCH2), 1.50 (m, 4H; CCCH2CH2), 1.36-1.24 (m,
28H; CH2), 0.87 (t, J = 6.53 Hz, 6H; CH3) MS (ESIþ): [M þ H]þ
found, 549.69 (calcd for C36H56N2O2, 548.84).
N,N0-Ethylenebisoctadeca-5,7-diynamide (EB-5,7-18DA) (1e).
1e was synthesized according to above general procedure from
N,N0-dicyclohexylcarbodiimide (1.12 g, 5.43 mmol), 5,7-octa-
decadiynoic acid (11) (1.00 g, 3.62 mmol) and ethylenediamine
(0.12 mL, 1.81 mmol) as a white solid (0.56 g, 54% yield); mp
154-155 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 6.14 (br, 2H;
CONH), 3.38 (m, 4H; CONHCH2), 2.31 (m, 8H; COCH2 and
COCH2CH2CH2), 2.24 (t, J = 7.0 Hz, 4H; CCCH2), 1.84 (q,
J = 6.9, 6.9 Hz, 4H; COCH2CH2), 1.51 (m, 4H; CCCH2CH2),
General Procedure for Synthesis of Diynoic Acid Diacetylene
Lipid Monomers (7-12). To a stirred solution of 4-pentynoic
acid (4) (0.29 g, 3.0 mmol) and 1-iodo-1-nonyne (2) (0.90 g, 3.6
mmol) in pyrrolidine purum (g98%) (1.24 mL, 15.0 mmol),
copper(I) iodide was added. After that, the reaction mixture was
stirred at room temperature for 3 h, a saturated aqueous solu-
tion of ammonium chloride (50 mL) was added and then extr-
acted with diethyl ether (3 ꢀ 50 mL). The combined organic
layers were dried over anhydrous Na2SO4 and filtered, and sol-
vent was removed by rotary evaporator. The crude product was
purified by column chromatography with hexane:ethyl acetate
(90:10 v/v) to yield 4,6-tetradecadiynoic acid (4,6-14DA) (7) as
1
white solid (0.33 g, 49% yield); mp 61-63 °C. H NMR (400
MHz, CDCl3) δ (ppm): 2.59 (m, 4H; COCH2 and COCH2CH2),
2.23 (t, J = 6.9 Hz, 2H; CCCH2), 1.50 (m, 2H; CCCH2CH2),
1.36-1.25 (m, 8H; CH2), 0.87 (t, J = 6.6 Hz, 3H; CH3). Anal.
Found: C, 76.23; H, 9.11 (Calcd for C14H20O2: C, 76.33; H,
9.15).
5,7-Pentadecadiynoic acid (5,7-15DA) (8). This was synthe-
sized according to the above general procedure from 5-hexynoic
acid (5) (0.34 mL, 3.0 mmol), 1-iodo-1-nonyne (2) (0.90 g, 3.6
mmol), and copper(I) iodide (0.01 g, 0.05 mmol) in pyrrolidine
(1.24 mL, 15.0 mmol), purified by column chromatography with
hexane:ethyl acetate (90:10 v/v) as white solid (0.41 g, 58%
yield); mp 52-53 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 2.49
(t, J = 7.3 Hz, 2H; COCH2), 2.35 (t, J = 6.75 Hz, 2H;
COCH2CH2CH2), 2.23 (t, J = 7.0 Hz, 2H; CCCH2), 1.84 (q,
J = 7.1 Hz, 2H; COCH2CH2), 1.50 (m, 2H; CCCH2CH2),
1.36-1.25 (m, 8H; CH2), 0.87 (t, J = 6.6 Hz, 3H; CH3). Anal.
Found: C, 76.49; H, 9.21 (Calcd for C15H22O2: C, 76.88; H,
9.46).
6,8-Hexadecadiynoic acid (6,8-16DA) (9). 9 was synthesized
according to the above general procedure from 6-heptynoic acid
(6) (0.38 mL, 3.0 mmol), 1-iodo-1-nonyne (2) (0.90 g, 3.6 mmol),
and copper(I) iodide (0.01 g, 0.05 mmol) in pyrrolidine (1.24
mL, 15.0 mmol), purified by column chromatography with
hexane:ethyl acetate (90:10 v/v) as white solid (0.42 g, 57%
yield). 1H NMR (400 MHz, CDCl3) δ (ppm): 2.37 (t, J = 7.4 Hz,
2H; COCH2), 2.28 (t, J = 7.0 Hz, 2H; COCH2CH2CH2CH2),
2.23 (t, J = 7.1 Hz, 2H; CCCH2), 1.74 (m, 2H; COCH2CH2),
1.58 (m, 2H; COCH2CH2CH2), 1.50 (m, 2H; CCCH2CH2),
1.36-1.25 (m, 8H; CH2), 0.87 (t, J = 6.7 Hz, 3H; CH3).
4,6-Heptadecadiynoic acid (4,6-17DA) (10). 10 was synthe-
sized according to above general procedure from 4-pentynoic
acid (4) (0.29 g, 3.0 mmol), 1-iodo-1-dodecyne (3) (1.10 g, 3.6
mmol), and copper(I) iodide (0.01 g, 0.05 mmol) in pyrrolidine
(1.24 mL, 15.0 mmol), purified by column chromatography with
hexane:ethyl acetate (90:10 v/v) as white solid (0.58 g, 67%
yield); mp 76-78 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 2.59
(m, 4H; COCH2 and COCH2CH2), 2.24 (t, J = 6.9 Hz, 2H;
CCCH2), 1.51 (m, 2H; CCCH2), 1.36-1.25 (m, 14H; CH2), 0.88
(t, J = 6.0 Hz, 3H; CH3) MS (ESI-): [M - H]- found, 261.30
(calcd for C17H26O2, 262.39).
5,7-Octadecadiynoic Acid (5,7-18DA) (11). 11 was synthesized
according to the above general procedure from 5-hexynoic acid
(5) (0.34 mL, 3.0 mmol), 1-iodo-1-dodecyne (3) (1.10 g, 3.6
mmol), and copper(I) iodide (0.01 g, 0.05 mmol) in pyrrolidine
(1.24 mL, 15.0 mmol), purified by column chromatography with
hexane:ethyl acetate (90:10 v/v) as white solid (0.46 g, 55%
yield); mp 57-59 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 2.44
(t, J = 7.4 Hz, 2H; COCH2), 2.29 (t, J = 6.9 Hz, 2H;
COCH2CH2CH2), 2.17 (t, J = 7.0 Hz, 2H; CCCH2), 1.78 (q,
J = 7.1 Hz, 2H; COCH2CH2), 1.45 (m, 2H; CCCH2CH2),
1.30-1.19 (m, 14H; CH2), 0.81 (t, J = 6.8 Hz, 3H; CH3) MS
(ESI-): [M - H]- found, 275.33 (calcd for C18H28O2, 276.41).

Article
Macromolecules, Vol. 43, No. 18, 2010 7547
1.36-1.25 (m, 28H; CH2), 0.87 (t, J = 6.7 Hz, 6H; CH3) MS
(ESIþ): [M þ H]þ found, 577.76 (calcd for C38H60N2O2, 576.90).
Anal. Found: C, 79.05; H, 9.76 (Calcd for C38H60N2O2: C,
79.11; H, 10.48).
graphs of the bisdiynamide sols (S15), and absorption spectra of
the bisdiynamide sols upon thermal incubation (S16). This
material is available free of charge via the Internet at http://
pubs.acs.org.
N,N0-Ethylenebisnonadeca-6,8-diynamide (EB-6,8-19DA) (1f ).
1f was synthesized according to above general procedure from
N,N0-dicyclohexylcarbodiimide (1.07 g, 5.16 mmol), 6,8-non-
adecadiynoic acid (12) (1.01 g, 3.44 mmol) and ethylenediamine
(0.12 mL, 1.72 mmol) as a white solid (0.48 g, 46% yield); mp
139-140 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 6.17 (br, 2H;
CONH), 3.39 (m, 4H; CONHCH2), 2.24 (m, 12H; COCH2-
COCH2CH2CH2CH2 and CCCH2), 1.73 (m, 4H; COCH2CH2),
1.52 (m, 8H; COCH2CH2CH2 and CCCH2CH2), 1.36-1.25 (m,
28H; CH2), 0.87 (t, J = 6.7 Hz, 6H; CH3) MS (ESIþ): [M þ H]þ
found, 605.77 (calcd for C40H64N2O2, 604.95)
Typical Method for the Preparation of Polydiacetylene Vesi-
cles. Monomers were dissolved in chloroform (0.5 mL) in a test
tube and the solvent was removed under reduced pressure. A
volume of Milli-Q water was added to provide the lipid con-
centration of 1.0 mM. The suspensions were heated to 75-85 °C
and sonicated in an ultrasonicating bath for 30-40 min forming
a semitransparent or transparent vesicle solution. Then solution
was kept at 4 °C for overnight. The vesicle solution was
irradiated with UV light (254 nm) for 5 min at room temperature
and filtered through a filter paper (no. 1) to give a clear intense
blue-colored vesicle solution.
Study of Thermochromism. The color transition of the po-
lymerized sols at various temperatures was observed by naked
eye and photographed by a digital camera. The electronic ab-
sorption spectra of the sols were recorded by the temperature
variable UV-visible spectrophotometer. The quantitative eva-
luation of the colorimetric response (% CR) was determined as
the percentage of the change of the blue color fraction (FB0 -
FB) against the initial blue color fraction (FB0) according to the
following equation: % CR = 100 ꢀ (FB0 - FB)/FB0. FB is the
blue fraction calculated from Ablue/(Ablue þ Ared) where Ablue
and Ared are the absorbance at the λmax of the blue and the red
forms of the polydiacetylenes, respectively. The degree of ther-
mochromic reversibility (% DR) was determined from the per-
centage ratio of the average absorbance change from the second
to the tenth heating (ΔAavg) against the absorbance change in
the first heating (ΔA1) according to the following equation: %
DR = 100 ꢀ ΔAavg/ΔA1. The absorbance change ΔA = A20 °C
- A90 °C where the absorbances at the λmax of the initial blue
form are used for both temperatures.
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Preparation of Polydiacetylene Films. Diacetylene monomer
and screen ink base resin (GPV0906, Chaiyaboon brothers Co.,
LTD) was mixed into 10 mL vial. The diacetylene monomer
used was 5-10% w/w compare with the resin weight. Screen ink
was screened into commercial transparent sheet by using stencil.
After screening, the film was kept in a refrigerator for 2-4 h. The
film was polymerized by UV irradiation in an ice bath.
Acknowledgment. This study was financially supported by
the grants from National Nanotechnology Center, National
Science and Technology Development Agency (NANOTEC,
NSTDA, Project NN-B-22-FN9-10-52-06) and the Thailand
Research Fund (TRF). The work is part of the Project for
Establishment of Comprehensive Center for Innovative Food,
Health Products and Agriculture supported by the Thai government
stimulus package 2 (TKK2555, SP2)”. We would also like to thank
Center for Petroleum, Petrochemicals and Advanced Materials,
Chulalongkorn University, the 90th Anniversary of Chulalongkorn
University Fund (Ratchadaphiseksomphot Endowment Fund)
and the Thailand Graduate Institute of Science and Technology
(TGIST) for student scholarships.
Supporting Information Available: Figures showing 1H
NMR spectra of all synthesized compounds (S1-S14), photo-

7548 Macromolecules, Vol. 43, No. 18, 2010
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