Intercalation and Photochemical Behavior of Azobenzene Derivatives with Layered Polymer Crystals as the Organic Host

Article abstract of DOI:10.1246/cl.2003.712

A photofunctional organic solid was fabricated by the intercalation of azobenzene derivatives containing an amino group into poly(muconic acid) as the layered polymer crystals. The organic intercalation and photoisomerization behaviors depended on the str

Full text of DOI:10.1246/cl.2003.712

712
Chemistry Letters Vol.32, No.8 (2003)
Intercalation and Photochemical Behavior of Azobenzene Derivatives with Layered
Polymer Crystals as the Organic Host
Shinya Oshitay and Akikazu MatsumotoÃy;yy
yDepartment of Applied Chemistry, Graduate School of Engineering, Osaka City University,
Sugimoto, Sumiyoshi-ku, Osaka 558-8585
yyPRESTO-JST, Convention and Control by Advanced Chemistry, Sugimoto, Sumiyoshi-ku, Osaka 558-8585
(Received May 12, 2003; CL-030410)
A photofunctional organic solid was fabricated by the inter-
Table 1. Intercalation of azobenzene derivatives containing an ami-
no group with PMA
calation of azobenzene derivatives containing an amino group
into poly(muconic acid) as the layered polymer crystals. The or-
ganic intercalation and photoisomerization behaviors depended
on the structure of the spacer between the azobenzene and ami-
no groups of the guest.
Guest
amine
[-NH2]/
[-CO2H]
Conversion
Methoda Time/h
ꢀ
d/A
/%
0
0
81
48
93
89
1
1
2
2
3
A
B
A
B
A
B
2
0.5
36
0.5
48
0.5
10
10
3
1
4
>1
—
—
26.5
—
36.0
>44
Supramolecular materials including the photochromic moi-
ety imply a possibility of application to novel photoresponsive
materials and optical devices.1 The intercalation of photoactive
species into layered inorganic solids has been investigated in or-
der to construct photofunctional intercalation compounds; for
examples, the photochromic reactions of viologens, fulgide,
spiropyrans, diarylethene, and azobenzene in the interlayer
space of host materials.2 In contrast, there is no example of con-
structing photoactive materials using layered organic materials
coupled with any photochromic organic compounds.
Recently, we reported that poly(muconic acid) (PMA) func-
tioned as a unique organic host compound for intercalation with
various amines (Scheme 1).3,4 The organic intercalation system
consisting of layered organic polymers and guest amines has
characteristics different from known intercalation compounds
with an inorganic host. The former has a crystalline structure,
in which carboxylic acids are orderly arranged along the poly-
mer chain in a high density. A combination of the organic host
crystal with organic guest molecules can induce any specific
feature through not only host–guest but also guest–guest inter-
actions. In this study, we carried out the intercalation of four
kinds of azobenzene derivatives (1-4) containing different
spacer groups between the azobenzene and amino groups
(Scheme 2) to investigate the structure of the layers, the assem-
bly of guest molecules, and the photochemical bahavior of the
dyes intercalated into the PMA.
4
a
A: stirred in methanol as dispersant. B: ground in a mortar in the
solid state.
ious azobenzene derivatives. We first attempted the intercala-
tion of 1 as a commercially available azobenzene by both dis-
persion and solid-state methods.5 However,
1 was not
incorporated into PMA due to the low basicity of the guest ani-
line (pKa = 4.6 for unsubstituted aniline). The intercalation of
aniline derivatives with an electron-donating substituent such as
methoxy and hydroxy groups was also attempted, but failed.
Therefore, three azobenzene derivatives with a suitable spacer
group were synthesized (2-4).6
From the diffraction peak at a low angle in powder XRD
profiles for PMA intercalated with the azobenzene derivatives
(X-PMAs) shown in Figure 1, the interlayer spacing (d) was
evaluated. The d-value increased with an increase in the size
of the guest, although the d-value for 4-PMA could not be de-
termined due to the diffraction at a lower angle. Considering the
d-values and the size of the guest molecules, it is postulated that
the azobenzene ammoniums are arranged in the interlayer space
with a structure inclined to the PMA sheets, but not interdigitat-
ed (Figure 2). A similar inclined structure of the guests has also
been formed for the intercalation with n-alkylamines, as previ-
ously reported.4 The guest amines are regularly aligned along
Table 1 shows the conversion of the intercalation with var-
Layered Ammonium
Host Polymer Crystals
Polymer Crystals
CO2-+NH3R
CO2H
d2
RNH2
H+
d1
n
n
CO2-+NH3R
CO2H
Scheme 1.
R'-NH2 = -NH2 (1)
-CH2NH2 (2)
-O(CH2)3NH2 (3)
-O(CH2)6NH2 (4)
N
N
R' NH2
Figure 1. XRD diffraction profiles of PMA and X-PMAs. (a)
PMA (before intercalation), (b) 2-PMA, and (c) 3-PMA.
Scheme 2.
Copyright ꢀ 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.8 (2003)
713
PMA was completed within 1-min of UV irradiation accompa-
nying a slight change in the absorbance, and the photoreaction
was reversible. The length of the spacer between the azoben-
zene and amino groups causes different behaviors of the azo
group in the X-PMAs. 2 and 3 are strongly fixed near the car-
boxylate of the PMA sheets, while azobenzene as the photo-
reaction part is more flexible in 4-PMA. As a result, the photo-
isomerization feature of 4-PMA is similar to those observed for
the azobenzene-containing polymer8 and an azobenzene inter-
calated into inorganic layered materials.2g,2h No significant
change in the interlayer spacing was observed for the X-PMAs
upon photoirradiation under the conditions in this work. Further
investigation is now continued.
Figure 2. Models of stacking structure. (a) Interdigitated
and (b) inclined structures.
ꢀ
the polymer chain at a stacking distance of 5 A, and no interdi-
In conclusion, we succeeded in the design of azobenzene
derivatives as the guest suitable for organic intercalation with
layered polymer crystals as the host. The intercalation of three
kinds of azobenzene derivatives with an amino group through a
spacer group into the interlayer space of poly(muconic acid)
crystals occurs. It has been revealed that the azobenzene mole-
cules form H-like aggregates in the interlayer space of the 2-
and 3-PMAs. We also confirmed the different isomerization be-
haviors depending on the position of the azobenzene guest inter-
calated into the polymer sheets.
gitated structure is observed. Tilt angles (ꢀ) are estimated to be
57 ꢀ and 71 ꢀ for 2 and 3, respectively. According to the McRae
and Kasha theory,7 a blue shift is observed when an angle be-
tween the dipole direction of a dye molecule and the line which
connects the center of an aggregating dye is greater than 54.7 ꢀ
(H aggregate). In fact, the absorption band due to the trans-azo-
benzene chromophore was observed at 314and 316 nm for the
2- and 3-PMAs, respectively, which are shifted toward a shorter
wavelength relative to that of a monomeric azobenzene in a di-
lute solution of the corresponding guests. These results suggest
that the H-like aggregates of the azobenzene molecules are
quite consistent with a tilt guest structure of the 2- and 3-PMAs.
The photochemical behavior of the X-PMAs was investi-
gated under UV irradiation using a high-pressure Hg lamp. Fig-
ure 3 shows the change in the diffusion reflectance spectra of
the 2- and 4-PMAs in the solid state. For both cases, an absorp-
tion intensity at around 450 nm due to the cis-isomer of the azo-
benzene moiety increased according to the photoirradiation
time. It strongly indicates that the azobenzenes isomerize in
the constrained interlayer spacing of the polymer crystals. How-
ever, the isomerization rate and the reversibility of the 2- and 4-
PMAs were different from each other. In the case of 2-PMA, the
isomerization proceeded at a lower rate and the equilibrium was
not yet achieved after a 1020-min irradiation. Furthermore, the
original adsorption band due to the trans isomer was not recov-
ered even after heating at 80 ꢀC for 10 h or visible ray irradia-
tion for 2 days. Thus, the E=Z isomerization of 2-PMA pro-
ceeds very slowly and is apparently irreversible under these
conditions. 3-PMA also showed a photoreaction behavior simi-
lar to that of 2-PMA. On the other hand, the isomerization of 4-
References and Notes
1
a) G. S. Kumar and D. C. Neckers, Chem. Rev., 89, 1915 (1989). b) S. Xie,
A. Natansohn, and P. Rochon, Chem. Mater., 5, 403 (1993). c) M. Irie,
Chem. Rev., 100, 1685 (2000). d) M. Ogawa and K. Kuroda, Bull. Chem.
Soc. Jpn., 70, 2593 (1997).
2
a) H. Miyata, Y. Sugihara, K. Kuroda, and C. Kato, J. Chem. Soc., Faraday
Trans. 1, 83, 1851 (1987). b) J. M. Adams and A. J. Gabbutt, J. Inclusion
Phenom., 9, 63 (1990). c) T. Seki and K. Ichimura, Macromolecules, 23,
31 (1990). d) H. Tomioka and T. Ito, J. Chem. Soc., Chem. Commun.,
1991, 532. e) K. Takagi, T. Kurematsu, and Y. Sawaki, J. Chem. Soc., Per-
kin Trans. 2, 1991, 1517. f) R. Sasai, H. Ogiso, T. Shichi, and K. Takagi,
Tetrahedron, 56, 6979 (2000). g) M. Ogawa, J. Mater. Chem., 12, 3304
(2002). h) T. Fujita, N. Iyi, and Z. Klapyta, Mater. Res. Bull., 33, 1693
(1998).
3
A. Matsumoto and T. Odani, Macromol. Rapid Commun., 22, 1195 (2001)
and references cited therein.
4A. Matsumoto, S. Oshita, and D. Fujioka,
(2002).
J. Am. Chem. Soc., 124, 13749
5
6
T. Odani and A. Matsumoto, Polym. J., 34, 841 (2002).
2: 4-Phenylazobenzoyl chloride was reacted with ammonia, and then the re-
sulting amide was reduced with LiAlH4 to obtain 2. mp 75 ꢀC; 1H NMR
(400 MHz, CDCl3) d 7.92-7.90 (m, 4H, Ar), 7.54-7.45 (m, 5H, Ar), 3.95
(s, 2H, CH2); 13C NMR (100 MHz, CDCl3) d 152.61, 151.57, 146.39,
130.85, 129.05, 127.66, 123.07, and 122.74(Ar), 46.18 (CH 2); UV (EtOH)
ꢁN=N 323 nm (e ¼ 22600). 3: 4-Phenylazophenol was reacted with a large
excess of 1,3-dibromopropane, and then with sodium azide to obtain the cor-
responding azide, which was reduced with LiAlH4 to obtain 3. mp 88-90 ꢀC;
1H NMR (400 MHz, CDCl3) d 7.94-7.86 (m, 4H, Ar), 7.52-7.41 (m, 3H, Ar),
7.04-7.00 (m, 2H, Ar), 4.15 (t, J ¼ 6:0 Hz, 2H, CH2), 2.95 (t, J ¼ 6:8 Hz,
2H, CH2), 1.97 (m, 2H, CH2); 13C NMR (100 MHz, CDCl3) d 161.49,
152.74, 146.93, 130.33, 129.01, 124.73, 122.53, and 114.66 (Ar), 66.16,
39.12, and 32.97 (CH2); UV (EtOH) ꢁN=N 344 nm (e ¼ 19100). 4: 6-Bro-
mo-n-hexanoic acid protected with 3,4-dihydro-2H-pyrane was reacted with
4-phenylazophenol.9 After, removed the protecting group, the resulting azo-
benzene-containing carboxylic acid was reacted with thionyl chlorides. The
following reactions were performed similarly to the method for 2. 1H NMR
(400 MHz, CDCl3) d 7.93-7.86 (m, 4H, Ar), 7.52-7.41 (m, 3H, Ar), 7.02-
6.98 (m, 2H, Ar), 4.05 (t, J ¼ 6:4 Hz, 2H, CH2), 2.72 (t, J ¼ 7:2 Hz, 2H,
CH2), 1.84(m, 2H, CH 2), 1.55-1.22 (m, 6H, CH2); 13C NMR (100 MHz,
CDCl3) d 161.54, 152.66, 146.73, 130.23, 128.93, 124.65, 122.43, and
114.58 (Ar), 68.10, 41.94, 33.43, 29.05, 26.55, and 25.81 (CH2).
E. G. MacRae and M. Kasha, in ‘‘Physical Processes in Radiation Biology,’’
Academic Press, New York (1964).
7
8
9
a) T. Seki and K. Ichimura, Polym. Commun., 30, 108 (1989). b) T. Seki,
Kobunshi Ronbunshu, 5, 253 (2002) and references cited therein.
T. Seki, T. Fukuchi, and K. Ichimura, Bull. Chem. Soc. Jpn., 71, 2807
(1998).
Figure 3. Changes in absorption spectra of X-PMAs in the solid
state. (a) 2-PMA during UV irradiation for 1020 min and (b) 4-
PMA during UV irradiation for 1 min.
Published on the web (Advance View) July 14, 2003; DOI 10.1246/cl.2003.712