Cation Complexation, Photochromism, and Photoresponsive Ion-Conducting Behavior of Crowned Spirobenzopyran Vinyl Polymers

Article abstract of DOI:10.1021/ma035644g

Vinyl polymers incorporating a crowned spirobenzopyran moiety at the side chain were synthesized, and their alkali metal-ion complexation, photochromism, and photoresponsive ion-conducting behaviors were studied in comparison with similar polymers incorpo

Full text of DOI:10.1021/ma035644g

Macromolecules 2004, 37, 1871-1876
1871
Cation Complexation, Photochromism, and Photoresponsive
Ion-Conducting Behavior of Crowned Spirobenzopyran Vinyl Polymers
,
†
†
‡
Keiich i Kim u r a ,* Hid efu m i Sa k a m oto, a n d Ryok o M. Ud a
Department of Applied Chemistry, Faculty of Systems Engineering, Wakayama University,
Sakae-dani 930, Wakayama, Wakayama 640-8510, J apan, and Nara National College of Technology,
2
2 Yata-cho, Yamatokoriyama, Nara 639-1080, J apan
Received November 1, 2003; Revised Manuscript Received December 16, 2003
ABSTRACT: Vinyl polymers incorporating a crowned spirobenzopyran moiety at the side chain were
synthesized, and their alkali metal-ion complexation, photochromism, and photoresponsive ion-conducting
behaviors were studied in comparison with similar polymers incorporating crown ether and spirobenzo-
pyran moieties independently. The metal-ion complexation by their crown ether moiety significantly
affected the photochromism of their spirobenzopyran moiety. The crowned spirobenzopyran polymers
are similar to their corresponding monomeric analogue in their metal-ion complexing property and
photochromism, with some difference induced by polymer effect. Almost no significant aggregation of the
photoinduced merocyanine moiety was found in the crowned spirobenzopyran polymer, unlike the polymers
carrying spirobenzopyran and crown ether moiety independently. The crowned spirobenzopyran polymers
were applied successfully as components of photoresponsive ion-conducting materials.
In tr od u ction
immobilization of crowned spirobenzopyran and high
processability. An easy way to obtain polymers carrying
both crown ether and spirobenzopyran moieties is
copolymerization of vinyl monomers carrying the cor-
Considerable efforts have been invested in the design
of photochromic compounds. Specifically, organic pho-
tochromism has found its wide application in devices
for display, memory, and printing. We have applied
organic photochromic compounds to photochemical
switching of metal-ion complexation and ionic conduc-
tion by combining photochromism with the metal-ion
1
1
3
responding moieties. The crown ether-spirobenzo-
pyran copolymers, however, lose the original property
of photoresponsive metal-ion complexing ability for the
monomeric crowned spirobenzopyran, although they
undergo photoreversible precipitate formation on the
basis of the interpolymer aggregation of photoinduced
2
binding property of crown ether derivatives. For in-
stance, incorporation of a monoazacrown ether moiety
in a nitrospirobenzopyran moiety at the 8-position
produced a photocontrol reagent of metal-ion complex-
1
3
merocyanine moiety instead.
We have designed vinyl polymers carrying a crowned
spirobenzopyran moiety at the side chain 1, and we call
these crowned spirobenzopyran vinyl polymers. Here we
describe their metal-ion complexing property, photo-
chromism in the presence of metal ions, and their
applicability to photoresponsive ion-conducting materi-
als. A comparison is also made with the corresponding
monomeric crowned spirobenzopyran 2 and the copoly-
mers incorporating crown ether and spirobenzopyran
moieties independently 3.
3
ation. The crowned spirobenzopyran in the electrically
neutral form can bind an alkali metal ion with its crown
ether moiety, while its spirobenzopyran moiety isomer-
izes to the corresponding merocyanine form photo-
chemically. The zwitterionic merocyanine form of crowned
spirobenzopyran can bind a metal ion more powerfully
by intramolecular interaction of its phenolate anion with
a metal ion in the crown ether ring. In the crowned
spirobenzopyran, therefore, photoisomerization of its
spirobenzopyran moiety brings about a significant change
in the metal-ion binding ability. This attractive property
of crowned spirobenzopyran prompted us to apply the
Exp er im en ta l Section
Syn th esis of Cr ow n ed Sp ir oben zop yr a n Vin yl P oly-
m er . 1′-(2-Hydroxyethyl)-3′,3′-dimethyl-6-nitro-8-[10-(1,4,7-tri-
oxa-10-azacyclododecyl)methyl]spiro[2H-1-benzopyran-2,2′-in-
doline] or Hydroxyethyl Crowned Spirobenzopyran. A dry
4
compound to photoresponsive ion-conducting materials.
Vinyl polymers carrying a crown ether moiety at the
side chain exhibit not only powerful cation-binding
ability but also attractive polymer rheology.5-8 On the
other hand, polymers incorporating spirobenzopyran
3
ethanol solution (35 cm ) of 3a,4,4-trimethyloxazolidino[3,2-
14
a]indoline (10 mmol) and 10-(2-hydroxy-3-formyl-5-nitroben-
3
zyl)-1,4,7-trioxa-10-azacyclododecane (10 mmol) was refluxed
side chains are useful tools for photochemical control
for 7 h. The reaction mixture was allowed to stand overnight.
After filtration of the unreacted substrate, the solvent evapo-
ration yielded a crude product of hydroxyethyl crowned
spirobenzopyran. Purification by recrystallization from benzene/
of polymer rheology.9
-12
Therefore, the combination of
crown ether and spirobenzopyran moieties in a polymer
molecule is a promising approach. Also, the polymeri-
zation of crowned spirobenzopyran provides its polymers
with some advantages over their corresponding mono-
meric analogue in materials applications, i.e., easy
1
hexane(1/10) afforded a dark red glass (78%); mp 71 °C. H
NMR (270 MHz, CDCl
.18 (1H, s, OH), 2.81 (4H, m, N(CH
m, NCH CH OH, PhCH , and CH OCH
2
3
) δ: 1.17 and 1.42 (3H each, s, C(CH
CH ), 3.68-3.86 (18H,
), 6.48 (1H, d, J ) 16.2
3 2
) ),
2
2
2 2
)
2
2
2
2
Hz, CCHdCHPh), 6.76 (1H, d, J ) 7.6 Hz, 7′-H of indoline),
6.80 (1H, d, J ) 7.6 Hz, CCHdCHPh), 6.94 (1H, t, J ) 6.5 Hz,
5′-H of indoline), 7.09 (1H, d, J ) 7.6 Hz, 4′-H of indoline),
7.17 (1H, t, J ) 6.8 Hz, 6′-H of indoline), 7.85 (1H, d, J ) 2.7
Hz, 5-H of benzopyran), 8.29 (1H, d, J ) 2.7 Hz, 7-H of
†
Wakayama University.
Nara National College of Technology.
Corresponding author: Fax +81-73-457-8255; Ph +81-73-457-
‡
*
8
254; e-mail kkimura@sys.wakayama-u.ac.jp.
1
0.1021/ma035644g CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/07/2004

1
872 Kimura et al.
Macromolecules, Vol. 37, No. 5, 2004
+
benzopyran). MS, m/e (% relative intensity): 540 (M , 51), 307
100). Anal. Calcd for C29 : C, 55.83; H, 6.36; N, 6.70.
Found: C, 55.51; H, 5.94; N, 6.45.
′-(2-Methacryloyloxyethyl)-3′,3′-dimethyl-6-nitro-8-[10-(1,4,7-
Sch em e 1. Der iva tives In cor p or a tin g Cr ow n Eth er
a n d Sp ir oben zop yr a n Moieties Em p loyed in Th is
P a p er
(
37 3 7
H N O
1
trioxa-10-azacyclododecyl)methyl]spiro[2H-1-benzopyran-2,2′-
indoline] or Methacryloyloxyethyl Crowned Spirobenzopyran.
A mixture of hydroxyethyl crowned spirobenzopyran (6 mmol)
and triethylamine (9 mmol) dissolved in anhydrous THF (50
3
cm ) was cooled in an iced bath under an argon atmosphere.
Methacryloyl chloride (7 mmol) was added to the mixture
dropwise while stirring. The mixture was then stirred at room
temperature for 3 h. After the reaction, the resulting triethyl-
amine hydrochloride was filtered off. The solvent of the filtrate
was replaced with chloroform, and the solution was then
washed with water and dried over MgSO . The solvent
4
evaporation afforded a crude product of crowned spirobenzo-
pyran vinyl monomer. Purification by preparative gel perme-
ation chromatography (solvent: CHCl
3
) yielded dark-red glass
24%); mp 52 °C. H NMR (270 MHz, CDCl ) δ: 1.14 and 1.41
3H each, s, C(CH ), 2.08 (3H, s, CH CdC), 2.73 (4H, m,
CH ), 3.61-3.78 (18H, m, NCH CH OH, PhCH , and
OCH ), 5.87 and 6.44 (1H each, s, CH dC), 6.36 (1H, d, J
15.8 Hz, CCHdCHPh), 6.78 (1H, d, J ) 8.6 Hz, 7′-H of
1
(
(
3
3
)
2
3
N(CH
CH
2
2
)
2
2
2
2
2
2
2
)
indoline), 6.87 (1H, d, J ) 3.3 Hz, CCHdCHPh), 6.95 (1H, t,
J ) 8.1 Hz, 5′-H of indoline), 7.07 (1H, d, J ) 7.3 Hz, 4′-H of
indoline), 7.17 (1H, t, J ) 8.3 Hz, 6′-H of indoline), 8.30 (1H,
without an appropriate concentration of alkali metal per-
chlorate were irradiated by UV light in a 1 mm quartz cell
for 2 min. The absorbance for the corresponding open colored
form at 550 nm was followed at 40 °C, immediately after
photoirradiation. The first-order rate constants of thermal
decoloration (k) were determined from the slope in the plots
d, J ) 3.0 Hz, 5-H of benzopyran), 8.77 (1H, d, J ) 2.6 Hz,
+
7
1
-H of benzopyran). MS, m/e (% relative intensity): 608 (M ,
00). Anal. Calcd for C33
41 3 8
H N O : C, 65.22; H, 6.80; N, 6.92.
Found: C, 64.95; H, 6.71; N, 6.70.
P olym er iza tion . Radical copolymerization of the crowned
spirobenzopyran vinyl monomer with methyl methacrylate
of log[(A
t
- A
∞
)/(A
0
∞ t 0 ∞
- A )] vs time (T), where A , A , and A
are referred to as the absorbance at 550 nm for T ) t, T ) 0,
(MMA) was carried out in toluene at 70 °C for 36 h, using a
and T ) infinity, respectively.
glass tube sealed after several freeze-pump-thaw cycles
Fluorescence spectra for THF solutions containing a crowned
under a vacuum. The total monomer concentration ranged
-
4
-3
-3
spirobenzopyran polymer (4 × 10 mol dm for spirobenzo-
from 0.35 to 2.5 mol dm . R,R′-Azobis(isobutyronitrile) (AIBN)
was used as the initiator (0.5 mol % to the total monomer).
After the polymerization, the reaction mixture was evaporated
to dryness. The crude polymer was purified by fractionation
to appropriate portions by gel-permeation chromatography
pyran unit) with and without an alkali metal perchlorate
-
4
-3
(
4 × 10 mol dm ) were followed by 560 nm excitation at
room temperature after UV-light irradiation.
Com p osite F ilm F a br ica tion . PVC-based composite films
for ionic conductivity measurements were prepared on in-
dium-tin oxide-coated (ITO) glasses (2 × 2.5 cm) by spin-
coating from THF solutions and then dried at 60 °C overnight
under a nitrogen stream and thereafter at room temperature
3
(GPC, J AIGEL-1H and 2H, CHCl ) to yield dark red or red
powder of copolymers. The molecular weights (in polystyrene
standard) were determined by GPC (Shodex KF-2003) using
THF as the eluent.
Oth er Ma ter ia ls. Alkali metal salts (perchlorate and
hydroxide) and picric acid were of analytical grade. Poly(vinyl
chloride) (PVC) (average polymerization degree: 1020) was
purified by repeated reprecipitation from THF in methanol.
3
for 12 h under a vacuum. An aliquot (0.1 cm ) of a THF solution
3
(
0.6 cm ) containing PVC (30 mg), DOS (25 mg), crowned
spirobenzopyran polymer [0.8 mg for polymers 1(x ) 0.59)],
and LiClO (0.25 mg) was used for the spin-coating on an ITO
4
glass, affording a composite film with about 2 mm thickness.
Composite films containing polymer 3 [PVC (30 mg), DOS (25
2
-Ethylhexyl sebacate (DOS) was distilled under a vacuum.
The solvents used for the measurements and composite film
fabrication were of spectroscopy grade (Dojindo Lab., J apan).
Water was deionized.
mg), crown ether-spirobenzopyran polymer (1 mg), and LiClO
4
3
3
(
0.25 mg) dissolved in THF (1 cm ), 0.1 cm for each coating]
3
-3
were also fabricated in a similar way. For the self-supporting
Ca tion Extr a ction . Equal volumes (3 cm ) of 2.1 × 10
-
3
composite films containing polymer 1(x ) 0.04) (without PVC),
mol dm (concentration of crown ether unit in the case of the
polymer) crown ether 1,2-dichloroethane solution and an
aqueous solution containing a mixture of 0.1 mol dm alkali
0
.2 cm3 of a THF solution containing polymers 1(x ) 0.04)
-
3
4
(9 mg), DOS (2 mg), and LiClO (0.5 mg) was used for the
-
5
-3
spin-coating. For ionic conductivity measurements, gold was
evaporated as a disk electrode (4.5 mm diameter, about 40 nm
thickness) on the composite films.
Ion ic Con d u ctivity Mea su r em en ts. Ac impedance of
composite films was measured under an argon stream, as
reported previously.16 Ionic conductivity calculation was made
by the Cole-Cole plot method.
metal hydroxide and 7.0 × 10 mol dm picric acid were
introduced into a stoppered vial and shaken vigorously by a
reciprocating shaker under dark conditions for 15 min.15 After
phase separation, the organic and aqueous phases were
subjected to absorption-spectral measurements. The percent
of extraction was calculated as 100 × (A
0
0 0
- A)/A , where “A ”
and “A” denote the absorbance of picrate ion (350 nm) for the
aqueous phase before and after the extraction, respectively.
Sp ectr op h otom etr ic Mea su r em en ts. THF solutions con-
Resu lts a n d Discu ssion
-
4
taining a crowned spirobenzopyran polymer (4 × 10 mol
Syn t h esis of Cr ow n ed Sp ir oben zop yr a n Vin yl
P olym er s. The synthesis of a spirobenzopyran deriva-
tive incorporating a monoaza-12-crown-4 moiety and a
methacryloyloxyethyl group at the 8- and 1′-position,
respectively, is shown in Scheme 1.
The corresponding 1′-hydroxylethyl derivative was
synthesized by the condensation of 1,3,3-trimethyl-2-
methyleneindoline with 5-nitrosalicylaldehyde possess-
ing a monoaza-12-crown-4 moiety. The crowned nitro-
-3
dm for spirobenzopyran unit) and an appropriate concentra-
tion of an alkali metal perchlorate were prepared, and their
absorption spectra were then measured under dark conditions.
Photoirradiation was made by using UV light (300-400 nm)
and visible light (>500 nm), which were obtained by passing
a light from a 500 W Xe lamp through Toshiba UV-D35 and
Y-50 color filters, respectively. For the thermal decoloration
measurements, crowned spirobenzopyran polymer THF solu-
-
4
-3
tions (4 × 10 mol dm for spirobenzopyran unit) with and

Macromolecules, Vol. 37, No. 5, 2004
Crowned Spirobenzopyran Vinyl Polymers 1873
Sch em e 2. Syn th etic Dia gr a m for Cr ow n ed
Sp ir oben zop yr a n Vin yl Mon om er
F igu r e 1. Alkali-metal-ion extraction with crown ether
derivatives under dark conditions: circle, 1(x ) 0.16); square,
2
; triangle, 3.
Li+ not only fits well into the 12-crown-4 ring but also
interacts strongly with the phenolate anion due to its
high charge density. This is the reason why crowned
+
spirobenzopyran 2 possesses high Li selectivity, which
is also true in crowned spirobenzopyran polymer 1(x )
0
.16). On the other hand, crown ether-spirobenzopyran
polymer 3 exhibited a different metal-ion selectivity
from that for crowned spirobenzopyran polymer 1,
+
+
+
salicylaldehydes were in turn obtained by chloromethyla-
having a selectivity order of Na > K > Li . Since the
crown ether and spirobenzopyran moieties are not very
close to each other in the polymer carrying the two
moieties independently at the side chain, 3, the moieties
have difficulty in cooperating on the metal-ion binding,
unlike crowned spirobenzopyran derivatives 1 and 2.
1
7
tion of 5-nitrosalicylaldehyde, followed by the reaction
with a monoazacrown ether18 in the presence of triethyl-
amine. The reaction of the 1′-hydroxyethyl crowned
spirobenzopyran with methacrylic chloride in the pres-
ence of triethylamine afforded the methacryloyloxyethyl
derivative, that is, the crowned spirobenzopyran vinyl
monomer.
+
The high Na selectivity for crown ether-spirobenzopy-
ran polymer 3 suggests that the neighboring crown
ether rings cooperate on the metal-ion binding to form
sandwich-type 2:1 (crown ether ring/metal) complexes
instead. Actually, this was the case with polymers
carrying a 12-crown-4 moiety at the side chain19 and
their corresponding dimers, bis(12-crown-4) deriva-
Radical polymerization of the crowned spirobenzopy-
ran vinyl monomer was carried out in toluene using a
sealed glass tube. We tried homopolymerization of the
vinyl monomer, but this failed probably due to the high
steric hindrance of the crowned spirobenzopyran side
chain on the polymerization. Therefore, we copolymer-
ized the crowned spirobenzopyran monomer with meth-
yl methacrylate (MMA) to obtain three crowned spiroben-
zopyran polymers with a different composition of crown
ether and spirobenzopyran moieties, 1(x ) 0.59, 0.16,
2
0
tives.
The absorption spectra for organic phases after the
cation extraction explains the cooperation of the crown
ether and spirobenzopyran moieties on the metal-ion
complexation. The absorption spectra for the extraction
system with crowned spirobenzopyran polymer 1(x )
0.16) are shown in Figure 2, together with those for the
extraction systems with 2 and 3 for comparison. Figure
2a shows that there is significant absorption between
500 and 600 nm for the 1(x ) 0.16) system even under
dark conditions, which can be assigned to the merocya-
nine form of the crowned spirobenzopyran moiety. The
organic phase after cation extraction with both 1(x )
0.16) and 2 turned purple. The merocyanine absorption
3
and 0.04), the molecular weight of which was 5.7 × 10 ,
3
4
8
.1 × 10 , and 5.1 × 10 , respectively, in polystyrene
standards.
Meta l-Ion Com p lexin g P r op er ty. Alkali metal
picrate extraction was used to assay the cation-com-
plexing abilities of crowned spirobenzopyran derivatives
toward alkali metal ions. Cation extraction was carried
out with a 1,2-dichloroethane solution of a crowned
spirobenzopyran polymer, 1(x ) 0.16), from an alkali
metal picrate aqueous solution. The results are com-
pared with those for the corresponding monomeric
derivative 2 and crown ether-spirobenzopyran copoly-
mer 3 in Figure 1. The metal-ion selectivity for polymer
+
was the most intense on Li extraction with crowned
spirobenzopyran polymer 1(x ) 0.16), as was the case
with the system of the monomeric derivative 2. On the
contrary, there was hardly any significant absorption
based on the merocyanine in an organic phase of crown
ether-spirobenzopyran polymer 3 in extracting any
metal ion. This means that in crown ether-spiroben-
zopyran polymer 3 the metal-ion complexation with its
crown ether moiety does not induce the isomerization
of its spirobenzopyran moiety to the corresponding
merocyanine form and thereby the additional ionic
interaction between its phenolate anion and a metal ion
in the crown ether ring.
+
+
+
1
(x ) 0.16) is in the order Li > Na > K . This finding
is similar to the metal-ion selectivity of monomeric
+
+
+ 3
crowned spirobenzopyran 2 (Li . Na > K ). In
crowned spirobenzopyran 2, the crown ether moiety of
which binds an alkali metal ion, the isomerization of
its spirobenzopyran moiety proceeds even without pho-
toirradiation due to the cation-complexation-induced
polarization of the molecule. In the metal-ion complex
of the merocyanine form of 2, the phenolate anion
interacts with a metal ion in the crown ether ring, owing
to the stable six-membered chelate formation of the oxy
anion and the nitrogen atom in the crown ether ring.
Thus, the polymeric and monomeric derivatives con-
+
taining a crowned spirobenzopyran moiety show Li
selectivity due to the efficiently cooperative action of the

1
874 Kimura et al.
Macromolecules, Vol. 37, No. 5, 2004
F igu r e 2. Absorption spectra for the organic phase after alkali-metal-ion extraction without photoirradiation: (a) crowned
spirobenzopyran polymer 1(x ) 0.16); (b) monomeric crowned spirobenzopyran 2; (c) crown ether-spirobenzopyran polymer 3.
F igu r e 3. UV-light-induced absorption-spectral changes for THF solutions of crowned spirobenzopyran polymer 1(x ) 0.16)
+
+
without metal ion (a), with Li (b), and with Na (c). Photoirradiation time: (1) 0 min; (2) 1 min; (3) 3 min.
crown ether and spirobenzopyran (merocyanine) moi-
eties. Such cooperative action cannot be realized in
polymer carrying crown ether and spirobenzopyran
moieties independently 3. Instead, the cooperation of
two adjacent crown ether rings resulted in Na+ selectiv-
ity in polymer 3. A similar cooperative effect by two
neighboring crown ether rings might contribute to the
+
enhanced Na extractability by crowned spirobenzopy-
ran polymer 1(x ) 0.16) as compared to that by its
corresponding monomeric analogue 2.
P h otoch r om ism in th e P r esen ce of Alk a li Meta l
Ion s. The spirobenzopyran moiety of crowned spiroben-
zopyran polymers 1 isomerizes photochemically in the
absence and presence of an alkali metal ion, as dem-
onstrated by the typical UV-light-induced absorption-
spectral changes of polymer 1(x ) 0.16) THF solution
F igu r e 4. Plots of log[(A
t
- A
∞
)/(A
0
- A
∞
)] vs time for thermal
(
Figure 3). However, hardly any significant blue shift
time-course changes of the absorption peak) in the
decoloration 1(x ) 0.16) without metal ion (square), with 4 ×
-
4
-3
+
-4
-4
+
(
10 mol dm Li (triangle), and with 4 × 10 mol dm Na
-
4
-3
merocyanine peak was observed in any system of the
crowned spirobenzopyran polymers 1. The present
crowned spirobenzopyran polymers are very different
from crown ether-spirobenzopyran polymer 3 in that
a marked blue shift, assigned to the merocyanine
aggregate formation, can be found in the prolonged
photoirradiation of THF solutions of polymer 3, espe-
(circle). Concentration of 1(x ) 0.16): 4 × 10 mol dm (for
spirobenzopyran unit).
form, and the purple color of the solutions disappeared
with time. The thermal decoloration reaction was fol-
lowed in order to estimate the thermal stability of the
merocyanine forms in the absence and presence of an
alkali metal ion. The slopes in the plots in Figure 4
indicate first-order rate constants for the thermal de-
coloration. Adding an equimolar amount of Na to a
THF solution of polymer 1(x ) 0.16) decreased the
thermal decoloration rate, and the addition of Li
+
+
cially in the presence of Li or Na . Also, no polymer
precipitation induced by the merocyanine aggregation
as seen in polymer 3 was observed in any of the crowned
spirobenzopyran polymers 1. Probably, the merocyanine
aggregation in polymers 1 is suppressed by the steric
hindrance of their crown ether moiety and/or by the
powerful interaction between their phenolate anion and
a metal ion in the crown ether ring.
+
+
enhanced the reaction depression. The rate constants
for polymers 1(x ) 0.59, 0.16, and 0.04), monomeric
derivative 2, and polymer 3 are summarized in Table
1. The tendency in the thermal decoloration rate for the
crowned spirobenzopyran polymers 1 (no metal ion >
After UV-light irradiation on THF solutions of poly-
mers 1, turning off the light caused the thermal isomer-
ization from the merocyanine to return to its spiropyran
+
+
Na > Li ) is similar to that for the corresponding

Macromolecules, Vol. 37, No. 5, 2004
Crowned Spirobenzopyran Vinyl Polymers 1875
Ta ble 1. F ir st-Or d er Ra te Con sta n t (k) for Th er m a l
Decolor a tion of UV-Ligh t-In d u ced Mer ocya n in e Moiety
k (10- s-1)a
3
spirobenzopyran
derivative
without metal ion
Li+
Na+
1
(x ) 0.59)
(x ) 0.16)
(x ) 0.04)
5.0
5.2
4.6
7.0
17.3
3.5
2.3
2.4
3.5
8.6
4.2
3.5
3.3
6.1
9.1
1
1
2
3
a
Values determined in THF at 40 °C after UV-light irradiation
for 2 min.
monomeric analogue 2. This means that the stable
metal-ion complex formation by the crowned spiro-
benzopyran moiety as described above augments the
thermal stability of its merocyanine form in crowned
spirobenzopyran derivatives 1 and 2. In general, the
polymeric derivatives 1 are slightly smaller in the rate
constant than the monomeric analogue 2. Some polymer
rheology change accompanied by the isomerization
might somewhat affect the thermal decoloration of
crowned spirobenzopyran polymers, but the difference
in the copolymer composition (x) did not change their
rate constants very much.
F igu r e 5. Photoinduced ionic conductivity changes in com-
posite films containing crowned spirobenzopyran polymer 1(x
) 0.59) (a) and crown ether-spirobenzopyran polymer 3 (b).
spirobenzopyran polymer 1(x ) 0.59). Accordingly, the
ionic conductivity was increased by UV light and
decreased by visible light. This profile in the photoin-
duced ionic conductivity switching is certainly not based
on the mechanism for metal-ion complexation photo-
control for the crowned spirobenzopyran derivatives 1.
Also, the polymer 3 system was smaller in its magnitude
of photoinduced ionic conductivity changes than the
polymer 1(x ) 0.59) system. A plausible explanation for
the photoinduced ionic conductivity changes is that UV-
light-induced formation of the ionic merocyanine may
bring about some polarity increase in the bulk of the
composite film, which results in the ionic conductivity
enhancement by promoting the migration of ion-
conducting carriers.
In contrast, the thermal decoloration proceeds very
fast at the measurement temperature (40 °C) in the
polymer carrying crown ether and spirobenzopyran
+
moieties independently, 3, even in the presence of Li
+
and Na , although one can find some thermal stabiliza-
tion of the merocyanine moiety on the basis of the
merocyanine aggregation.13 This indicates strongly that
there is little merocyanine stabilization derived from the
interaction between its phenolate anion and a metal ion
in the crown ether ring.
A great advantage of the crowned spirobenzopyran
polymers 1 over the corresponding monomeric derivative
2 as the photocontrol reagents for photoresponsive ion-
conducting materials is that the polymers have the
capability to form films by themselves. Since polymer
1(x ) 0.04) is able to form transparent self-supporting
films thanks to its relatively high molecular weight
P h otoin d u ced Sw itch in g of Ion ic Con d u ctivity.
As already described, the crowned spirobenzopyran
moiety in polymers 1 binds an alkali metal ion power-
fully not only by the complexation with its crown ether
ring but also by the additional ionic interaction of a
phenolate anion of its merocyanine form. Also, visible-
light irradiation forces the merocyanine form to isomer-
ize back to the corresponding electrically neutral spiro-
pyran form and thus eliminates the additional inter-
action. One can, therefore, expect photocontrol of metal-
ion binding and thereby ionic conduction by using
crowned spirobenzopyran polymer 1, as has also been
seen in crowned spirobenzopyran 2. We fabricated
photoresponsive ion-conducting composite films contain-
ing PVC, a plasticizer, crowned spirobenzopyran poly-
mer 1, and LiClO4. Crown ether-spirobenzopyran
polymer 3 was also tested as the photocontrol reagent
for comparison. Figure 5 depicts typical profiles of
photoinduced ionic conductivity changes for both sys-
tems of 1(x ) 0.59) and 3. The ionic conductivity for the
composite films containing crowned spirobenzopyran
polymer 1(x ) 0.59) was decreased by UV-light irradia-
tion and increased by visible-light irradiation. UV light
enhanced the isomerization of the spirobenzopyran
moiety to its corresponding merocyanine form and thus
the metal-ion binding. This in turn diminished the
4
(about 5 × 10 ), we fabricated ion-conducting films
consisting of polymer 1(x ) 0.04), a plasticizer, and
LiClO4 without using PVC. The self-supporting films of
crowned spirobenzopyran polymer contained more crown
ether unit and less plasticizer than the corresponding
PVC-based composite films, so a greater amount of
lithium salt can be dissolved in the former films with a
help of the cation binding ability of the crown ether
moiety. This has in turn realized photochemical switch-
ing in the higher order of ionic conductivity (Figure 6).
In the self-supporting films as cast, a considerable
amount of spirobenzopyran moiety was isomerized to
its merocyanine form due to the high electric constant
in the bulk film. Visible-light irradiation allowed the
merocyanine moiety to isomerize back to the spiropyran
form, thus increasing the ionic conductivity. The sub-
sequent UV-light irradiation again promotes the ionic
conduction, as was the case with the corresponding
4
PVC-based composite films.
In conclusion, the present polymers carrying a crowned
spirobenzopyran moiety at the side chain, 1, showed
similar behaviors to their corresponding monomeric
analogue, 2, in terms of metal-ion complexation, photo-
chromism, and photoresponsive ionic conduction, al-
though some polymer effect was observed in the poly-
meric analogues. Crowned spirobenzopyran vinyl poly-
mers 1 are quite different from polymer 3 carrying
crown ether and spirobenzopyran moieties indepen-
+
concentration of uncomplexed Li that can contribute
to ionic conduction, thus decreasing the ionic conductiv-
ity. Subsequent visible-light irradiation induced reverse
isomerization from the merocyanine to spiropyran forms,
restoring the ionic conductivity.
The profile in the photoinduced ionic conductivity
switching for the system of crown ether-spirobenzopy-
ran polymer 3 is the opposite of that for crowned

1
876 Kimura et al.
Macromolecules, Vol. 37, No. 5, 2004
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F igu r e 6. Photoinduced ionic conductivity changes in self-
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Ack n ow led gm en t. Financial support by a Grant-
in-Aid for Scientific Research (B) (No. 15350043) from
the Ministry of Education, Culture, Sports, Science, and
Technology, J apan, is gratefully acknowledged.
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