X. Chen, J. Yoon / Dyes and Pigments 89 (2011) 194e198
195
NH2
H
N
CF3
O
HO
CH2Cl2
NHS, DCC
CH2Cl2
O
F3C
OH
HO
2
H
N
CF3
O
O
SOCl2
2
OH
O
O
7
7
CH2Cl2, DMF
7
7
1
Scheme 1. Synthesis of monomer 1.
2.2. Synthesis
for 12 h. Polymerization was carried out at room temperature by
irradiating the solution with 254 nm UV light (1 mW/cm2) for 5 min.
2.2.1. 2,2,2-Trifluoro-N-(4-hydroxyphenyl)acetamide
To a solution containing 2.0 g (17.7 mmol) of trifluoroacetic acid in
20 mL of CH2Cl2 was added 2.1 g (18.3 mmol) of N-Hydroxysuccinimide
(NHS) and 4.2 g (20.4 mmol) of N,N0-Dicyclohexylcarbodiimide (DCC).
The resulting solution was stirred for overnight at room temperature
under N2. The solvent was evaporated after the white precipitate was
filtered and trifluoroacetate was removed by flash column chroma-
tography (silica gel, eluent CHCl3). The ensuing activated ester was
added to a solution of 4-aminophenol (2.0 g, 18.3 mmol) in CH2Cl2
(10 mL) and the resulting mixture was stirred for 24 h. After the solvent
was evaporated, the residue was purified using silica gel column
(CHCl3/CH3OH, 100:2) to give 2,2,2-trifluoro-N-(4-hydroxyphenyl)
acetamide (2.65 g, 69% yield) as white solid.1HNMR(CD3OD, 250MHz)
2.4. Color reversibility (CR) values
For thermochromic properties experiments, all UV spectroscopy
measurements were carried out using a 1 cm optical path length
cell. The blue polymer was first transformed to a purple phase using
a heatingecooling cycle. UVeVis spectra were collected from the
second cycle. To quantify the extent of the purple-to-red transitions
within the polymer, the % color reversibility (CR) was calculated
using the following equation [30]:
CR ¼ ½ðPB0 ꢁ PB1Þ=PB0ꢂ ꢃ 100
d
(ppm): 7.32 (d, 2H, J ¼ 12.5 Hz), 6.78 (d, 2H, J ¼ 12.5 Hz); 13C NMR
where PB ¼ Ablue/(Ablue þ Ared), Ablue and Ared are the absorbance
values at 625 nm and 535 nm in the UVeVis spectrum, respectively.
PB0 and PB1 are pre- and post-thermal perturbations values, respec-
tively. The different temperature of PDA solution was controlled by
a water-bath system.
(CD3OD, 62.5 MHz) d (ppm): 155.43, 155.31, 127.83, 122.62, 114.99.
2.2.2. Monomer 1
To a solution containing 0.50 g (1.34 mmol) of 10,12-pentacosa-
diynoic acid in 10 mL of methylene chloride was added dropwise
0.55 g (4.32 mmol) of oxalyl chloride at room temperature. The
resulting solution was stirred at room temperature for 3 h. To the
ensuing solution was added a catalytic amount (one drop) of DMF
and the mixture was stirred for one additional hour. After concen-
trating in vacuo, the residue was redissolved in 10 mL of methylene
chloride. The resulting solution was added dropwise to a solution
containing 0.29 g (1.42 mmol) of 2,2,2-trifluoro-N-(4-hydrox-
yphenyl)acetamide in 10 mL of THF. The resulting mixture was
stirred overnight at room temperature. The solvent was removed
under vacuum and the residue purified by silica gel column chro-
matography (CHCl3 as an eluent) to give 0.32 g (42%) of the desired
diacetylene monomer 1 as a white solid. 1H NMR (CDCl3, 250 MHz)
2.5. Fabrication of PDA-embedded PVA film
A 5 mL of self-assembled DA aqueous solution (ca. 1 mM, 5%
DMSO) was mixed with an aqueous PVA solution (10 wt %, 5 mL)
with stirring. The resultant mixture solution was cast into a Petri
dish (diameter 6.5 cm) and dried at room temperature for five days.
During the drying process, the solutions were protected from light.
The resulting transparent film was irradiated with 254 nm UV light
to induce polymerization. The heating or cooling of film by a water-
bath system can lead to desired temperature.
d
(ppm): 7.93 (s, 1H), 7.48 (d, 2 H, J ¼ 12.5 Hz), 7.25 (d, 2 H,
J ¼ 12.5 Hz), 2.49 (t, 2H, J ¼ 7.5 Hz), 2.20e2.16 (m, 4H), 2.17e1.65 (m,
2H), 1.44e1.19 (m, 30H), 0.81 (t, 3H, J ¼ 6.25 Hz). 13C NMR (CDCl3,
62.5 MHz)
d (ppm): 172.56, 148.32, 132.68, 122.41, 121.56, 65.30,
65.17, 34.27, 31.90, 29.62, 29.47, 29.33, 29.08, 28.87, 28.73, 28.33,
28.27, 24.79, 22.68, 19.19, 14.11. FAB MS m/z ¼ 562.3504 [M þ H]þ,
calc. for C33H47O3NF3 ¼ 562.3508.
2.3. Preparation and polymerization of micelle
Preparation of PDA vesicles in aqueous solution was achieved by
the following method. Diacetylene monomer (11.2 mg, 0.02 mmol)
was dissolved in a small amount of DMSO (1 mL), and the organic
solution was injected into 19 mL deionized water while shaking the
mixed solution to yield a total monomer concentration of 1 mM. The
sample was sonicated at 80 ꢀC for 25 min and the resulting solution
was filtered through a 0.8
m
m filter and the filtrate cooled at 4 ꢀC
Fig. 1. Photographs of different color stages at 30 ꢀC and 70 ꢀC.