682
Chemistry Letters Vol.36, No.5 (2007)
A Polydiacetylene Supramolecular System that Displays Reversible Thermochromism
Cheol Hee Lee,1 Jong Seung Kim,2 Sun Young Park,2 Dong June Ahn,3 and Jong-Man KimÃ1
1Department of Chemical Engineering, Hanyang University, Seoul 133-791, Korea
2Department of Chemistry, Dankook University, Seoul 140-714, Korea
3Department of Chemical and Biological Engineering, Korea University, Seoul 136-701, Korea
(Received March 8, 2007; CL-070252; E-mail: jmk@hanyang.ac.kr)
A reversible blue-to-red color transition of polydiacetylene
supramolecules derived from an oligoethylene glycol-bridged
bisdiacetylene was observed upon thermal stress.
the diacetylenic units close together. If the bisdiacetylene 1
can adopt a conformation as described above, facile polymeriza-
tion would occur in aqueous solution and should result in poly-
merized diacetylene vesicles.
The synthetic procedures employed for the preparation of
the bisdiacetylene 1 are shown in Scheme 1. The amine group
of 4-aminophenol (2) was protected with a di-tert-butyl dicar-
bonate and the resulting protected aminophenol 3 was treated
with pentaethylene glycol di(p-toluenesulfonate) to yield the
oligoethylene glycol 4. The desired bisdiacetylene 1 was readily
prepared by removal of the protecting group followed by
coupling with 10,12-pentacosadiynoyl chloride (PCDA-Cl).
Having prepared the desired bisdiacetylene 1, next phase of
current investigation focused on the preparation of PDA supra-
molecules in aqueous solution. For this purpose, a probe-sonica-
tion method was employed. Briefly, the bisdiacetylene monomer
1 was dissolved in a small amount of DMF (ca. 100 mL) and the
clear solution was added to a hot deionized water to make a
1 mM of dispersed monomer suspension. The resultant suspen-
sion was probe-sonicated for 10 min, filtered, and kept in a
refrigerator for overnight to stabilize the self-assembled diacety-
lene vesicles. Photopolymerization of the suspension with 254-
nm-UV light (1 mW/cm2) for 15 min afforded a blue-colored
PDA solution. Efficient formation of PDAs and polymer
particles was confirmed by visible absorption spectroscopy,
color change, and scanning electron microscopic (SEM) images
(see Supporting Information).14
Polydiacetylenes (PDAs) are very intriguing materials in
terms of their method of preparation and output signals associat-
ed with the conjugated ene–yne backbones.1–5 Unlike most
conjugated polymers, PDAs are readily prepared by irradiation
(UV- or gamma-ray) of closely packed diacetylene supramole-
cules. Since no chemical initiators or catalysts are required
for the polymerization process, the polymers are generally not
contaminated with impurities and, consequently, additional
purification steps are not required. Owing to their intriguing
stress-induced chromic transition (blue-to-red), PDAs have been
extensively investigated as potential chemosensors.6–12
The majority of PDA-based chemosensors reported thus far
function in an irreversible fashion. Accordingly, the blue-to-red
color change that takes place when an external stimulus is
applied is not reversed when the external stimulus is removed.
PDA systems displaying colorimetric reversibility, especially,
in aqueous solution are very rare. Although colorimetric reversi-
bility of PDA supramolecules derived from a diacetylenic phos-
pholipid was reported,13 the reversible thermochromism was
observed only in the narrow temperature range. Very recently,
we have described a new strategy for the preparation of colori-
metrically reversible PDAs.12b We found strong headgroup
interactions (both hydrogen-bonding and aromatic interaction)
were essential for the complete colorimetric reversibility. In this
communication, we report a novel colorimetrically reversible
PDA supramoleular system derived from a bisdiacetylene 1
(Chart 1).
In order to investigate the reversibility of colorimetric tran-
sition, a solution of the PDA particles were gradually heated to
95 ꢀC while monitoring color changes by using UV–vis spectros-
copy (Figure 1). At 20 ꢀC, the PDA solution shows the typical
blue color corresponding to a visible absorption maximum
wavelength at 630 nm. When the temperature is raised from 20
to 95 ꢀC, the absorption maximum of the solution undergoes a
The bisdiacetylene 1 has several important features such as a
hydrophilic ethylene glycol moiety, two internal amide groups,
two phenyl groups, and two diacetylene units. The hydrophilic
ethylene glycol group should favor water molecules and force
the two diacetylene-containing hydrophobic alkyl chains to
locate close together in aqueous solution. In addition, the amide
groups of 1 are expected to interact with one another by hydro-
gen bonding. The aromatic interaction between the two phenyl
groups could serve as an additional attractive force to bring
OH
OH
TsO
OTs
O
Di-tert-butyl dicarbonate
4
TEA, DMF
CH3CN, K2CO3
HN
t-Boc
NH2
2
3
O
O
O
4
O
O
1. TFA, MC
2. PCDA-Cl, TEA, THF
1
O
O
O
N
H
O
t-Boc
HN
HN
t-Boc
O
O
4
N
H
O
Cl
PCDA-Cl =
1
Chart 1.
Scheme 1. Preparation of the bisdiacetylene monomer 1.
Copyright ꢀ 2007 The Chemical Society of Japan
Cheol, Hee Lee
