AbstractIrradiation of colorless 1,3,3-trimethylspiro[indoline-2,3′-[3H]naphtho[2,1-b][1,4]oxazine] SO doped in PMMA and epoxy resin with UV light (at 366nm) results in the formation of an intensely colored zwitterionic photomerocyanine PMC. The reverse reaction was photochemically induced by irradiation with white light. Photocoloration and photobleaching reactions follow a first-order rate equation. It was found that photocoloration rate constant of SO in PMMA film is greater than that in epoxy resin. On the other hand, the photobleaching rate constant is almost identical in both matrices. Spirooxazine doped in epoxy resin shows much better fatigue resistance than that doped in PMMA

Al-Sehemi, Abdullah G.

Alsoliemy, Amerah M.

Asiri, Abdullah M.

Bahajaj, Abood A.

Elsevier - Publisher Connector 

Arabian Journal of Chemistry (2009) 2, 13–17King Saud University
Arabian Journal of Chemistry
www.ksu.edu.sa
www.sciencedirect.comORIGINAL ARTICLEPhotochromic properties of 1,3,3-trimethylspiro-
[indoline-2,30-[3H]naphtho[2,1-b][1,4]oxazine] doped
in PMMA and epoxy resin thin ﬁlmsAbdullah M. Asiri a,*, Abood A. Bahajaj b, Abdullah G. Al-Sehemi c,
Amerah M. Alsoliemy aa Chemistry Department, Faculty of Science, King Abdul Aziz University, Jeddah 21413, P.O. Box 80203, Saudi Arabia
b Chemistry Department, Faculty of Science, Hadhramout University of Science and Technology, P.O. Box 50512,
Mukalla, Republic of Yemen
c Chemistry Department, Faculty of Science, King Khalid University, Abha, Saudi ArabiaReceived 10 July 2009; accepted 10 July 2009
Available online 6 August 2009*
E-
18
re
doKEYWORDS
Spirooxazine;
Photochromism;
Polymer ﬁlm;
Epoxy resin;
Photobleaching;
Photocoloration;
Kinetics;
Fatigue resistanceCorresponding author.
mail address: aasiri2@kau.ed
78-5352 ª 2009 King Saud
view under responsibility of
i:10.1016/j.arabjc.2009.07.00
Production and hu.sa (A.
Univers
King Sau
9
osting by EAbstract Irradiation of colorless 1,3,3-trimethylspiro[indoline-2,30-[3H]naphtho[2,1-b][1,4]oxa-
zine] SO doped in PMMA and epoxy resin with UV light (at 366 nm) results in the formation of
an intensely colored zwitterionic photomerocyanine PMC. The reverse reaction was photochemi-
cally induced by irradiation with white light. Photocoloration and photobleaching reactions follow
a ﬁrst-order rate equation. It was found that photocoloration rate constant of SO in PMMA ﬁlm is
greater than that in epoxy resin. On the other hand, the photobleaching rate constant is almost iden-
tical in both matrices. Spirooxazine doped in epoxy resin shows much better fatigue resistance than
that doped in PMMA.
ª 2009 King Saud University. All rights reserved.M. Asiri).
ity. All rights reserved. Peer-
d University.
lsevier1. Introduction
The IUPAC deﬁnition of photochromism is ‘‘a reversible
transformation of a chemical species induced in one or both
directions by absorption of electromagnetic radiation between
two forms, A and B, having different absorption spectra’’
(Bouas-Laurent and Durr, 2001). This transformation is usu-
ally induced by electromagnetic radiation in the ultraviolet
wavelengths range, where a deeply colored specie B is gener-
ated from the uncolored or weakly colored specie A. The re-
verse reaction (bleaching) could be accomplished by thermal
and/or photochemical effects. Various organic systems were
found to show potential thermal and photochromic properties.
14 A.M. Asiri et al.The widest and most important groups of such systems are
those based on the reversible light-induced hexatriene/cyclo-
hexadiene pericyclic reactions such as in fulgides (Yokoyama,
2000), diarylethenes (Hu et al., 2006), spiropyrans (Ubukata
et al., 2007) and spirooxazines (Berkovic et al., 2000).
Spiropyrans and spirooxazines are much closed compounds
in their photochromism. The photochromism of these colorless
or weakly colored spiro compounds SO arises from the photo
cleavage of the C–O spiro bond upon the UV irradiation. Such
a cleavage results in the formation of an intensely colored zwit-
terionic open form known as photomerocyanine PMC which
absorbs in the visible region. The reverse reaction (fading) pro-
ceeds thermally or under irradiation with white light. The
immediate cleavage of the spiro carbon–oxygen bond upon
UV irradiation results in the formation of a highly unstable
intermediate cis–cisoid isomer (Glebov et al., 2006). This inter-
mediate isomerizes to the more stable zwitterionic open form
which in turn undergoes subsequent geometrical isomerism
to give several quinoidal forms (Scheme 1).
Time-resolved absorption spectroscopy (Tamai and Miya-
saka, 2000) and NMR studies (Berthet et al., 2006) reveal
the coexistence of four geometrical isomers (TTC, CTT,
CTC, and TTT) which are in thermal equilibrium at room tem-
perature. Takahashi et al. (1988) has found that TTC isomer
(trans–trans–cis isomer) is more stable in aliphatic hydrocar-
bons, while CTT and CTC are more stable in polar solvents.
The recent interest in the photochromism of spiropyrans and
spirooxazines is due to their fast coloration rate under UV
irradiation, fast thermal fading, and excellent fatigue resis-
tance. These criteria are indispensable for applications to opto-
electronic devices, such as memories and switches, and
nonlinear optics (Berkovic et al., 2000). Spiropyrans and spi-
rooxazines have been recently used as nucleic acid hybridiza-
tion probes (Guo et al., 2005).
2. Experimental
1,3,3-Trimethylspiro[indoline-2,30-[3H]naphtho[2,1-b][1,4]oxa-
zine] was prepared according to the general procedure reportedO
N
N
N
N O
N
N
O
N
N
N N
N N
O
O
O
+ -
UV
Vis or heat
(TTT)
(TTC)
(CTT)
(CTC)
colorless spirooxazine
Colored photomerocyanine
(zwitterionic form)
(quinoidal forms of photomerocyanine)
(SO) (PMC)
Scheme 1 Photochemical reactions of spiroindolinenapht-
hooxazine.previously (Tan and Chen, 2005). The ﬁlms were prepared as
follows: 2.23 g of PMMA (Aldrich product) was dissolved in
20 mL of chloroform and warmed to ensure complete dissolu-
tion. The solution was then cooled. Two blank ﬁlms were pre-
pared by taking 0.3 mL of the above-mentioned solution and
spread over a quartz plate. These plates were covered and left
overnight in the dark. About 1 mg of spirooxazine SO was
added to the remaining solution and mixed well. Then
0.3 mL of the mixture was added to each of the quartz plates
which were then covered and left overnight in the dark. The
epoxy resin ﬁlm was prepared as follows: 10 mL of epoxy resin
(diglycidyl ether of bisphenol A) and 1 mL of diamine hard-
ener were added and mixed thoroughly to ensure complete dis-
solution. Two blank ﬁlms were prepared by taking 0.3 mL of
the above-mentioned solution and spread over each quartz
plate. To the remaining mixture, a solution of 2 mg of SO dis-
solved in 15 mL of chloroform was added and mixed. Then
0.3 mL of the mixture was added to each of the quartz plates
which were then covered and left overnight in the dark.
Ultraviolet and visible spectra were measured using Perkin–
Elmer lambda EZ210 spectrophotometer. Photocoloration (at
366 nm) was carried out using Blak–Ray lamp model UVL-56
and photobleaching was carried out using a tungsten ﬁlament
lamp. Two fresh ﬁlms of SO in PMMA and epoxy resin were
annealed for 3 h at 75 C. The fatigue resistant of the annealed
SO doped PMMA and epoxy resin ﬁlms was carried out by
photocoloring and photobleaching SO, consecutively for 9 cy-
cles. In each cycle, the ﬁlm was irradiated with UV lamp for
30 min and photobleached with white light for 20 min.
3. Results and discussion
3.1. Photocoloration
1,3,3-Trimethylspiro[indoline-2,30-[3H]naphtho[2,1-b][1,4]oxa-
zine] SO doped in PMMA polymer ﬁlm was irradiated
with mercury lamp (366 nm) and the photocoloration
process was followed spectrophoto-metrically by monitoring
the absorption of the intense purple colored open form0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
250 300 350 400 450 500 550 600 650 700
Wavelength (nm)
A
bs
or
ba
nc
e
Figure 1 Photocoloration of SO doped in PMMA polymer ﬁlm.
The arrow direction indicates the increase of absorbance with
increasing exposure time (s), 0; 20; 40; 100; 120; 140; 200; 240; 280;
340; 520; 560; 600.
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
250 300 350 400 450 500 550 600 650 700
Wavelength (nm)
A
bs
or
ba
nc
e
Figure 2 Photocoloration of SO doped in epoxy resin polymer
ﬁlm. The arrow direction indicates the increase of absorbance with
increasing exposure time (s), 0; 20; 40; 60; 100; 140; 180; 220; 300;
480; 540.
0
0.5
1
1.5
2
2.5
0 100 200 300 400 500 600
Time (sec.)
Photocoloration in PMMA polymer
Photocoloration in epoxy resin
ln
 (A
∞
 
-
 
A
0) 
-  l
n (
A ∞
 
-
 
A
t)
Figure 3 First-order plot of the photocoloration of SO doped in
PMMA and epoxy resin.
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
250 300 350 400 450 500 550 600 650 700
Wavelength (nm)
A
bs
or
ba
nc
e
Figure 4 Photobleaching reaction of PMC in PMMA polymer
ﬁlm. The arrow direction indicates the decrease of absorbance
with increasing exposure time (s), 0; 20; 100; 120; 200; 240; 280;
340; 560.
Photochromic properties of 1,3,3-trimethylspiro-[indoline-2,30-[3H]naphtho[2,1-b][1,4]oxazine] 15photomerocyanine PMC at its kmax (555 nm) at intervals of
time as shown in Fig. 1.
The ﬁlm of SO doped in an epoxy resin was similarly trea-
ted. The resulting PMC has its kmax at 560 nm (Fig. 2). The ob-
served red shift of the absorption band of PMC in epoxy resin
compared to that in PMMA ﬁlm is a result of increasing the
polarity of the medium. It is well known that this absorption
band shows a bathochromic shift as the solvent polarity
increases (Chu, 1983; Shin et al., 2000; Kopelman
et al., 2008; Lafuma et al., 2003) which represents a positive
solvatochromism.
Kinetics of spiropyrans and spirooxazines have been stud-
ied in solutions (Chu, 1983; Shin et al., 2000; Kopelman
et al., 2008; Lafuma et al., 2003), in phospholipid bilayers
(Wohl and Kuciauskas, 2005), in solid polymer matrices
(Fua et al., 2007; Lin and Chiu, 2003) and in the crystalline
state (Be´nard and Yu, 2000). They show, in general, ﬁrst-order
rate dependence, especially in solutions (Shin et al., 2000; Kop-
elman et al., 2008). However, in polymer matrices deviation
from the simple ﬁrst-order reaction was observed. Such nonlin-
earity of the ﬁrst-order plots was attributed to several factors
such as the effects of the polymer matrix on the photochromic
compound, the presence of more than one conformer or the
dye that might be conﬁned in the solid polymer matrix (Rap-
pon and Ghazalli, 1995).
The integrated form of the ﬁrst-order rate law for the
photocoloration process is:
ln
A1  A0ð Þ
A1  Atð Þ ¼ kt
where k is the rate constant, A1, At, and, A0 are the absor-
bance of the PMC at inﬁnite time, at time t, and at zero time,
respectively. Plot of [ln(A1  A0)/(A1  At)] against time
gives a straight line with slope equals as shown in k (Fig. 3).
From the graph the apparent ﬁrst-order rate constant (k) for
the photocoloration of spirooxazine SO doped PMMA and
epoxy resin ﬁlms was found to be 0.0040 s1 and 0.0021 s1,
respectively. It is clear that the photocoloration of SO in
PMMA is almost twice faster than that in epoxy resin. This
could be attributed to the larger free volume of the PMMA
compared to that of epoxy resin which offers a large space
for the dye to undergo isomerization. Another factor couldbe the possible hydrogen bonding between the epoxy resin
and the spirooxazine which stabilizes the latter.
3.2. Photobleaching
Spiropyrans and spirooxazines are known (Lafuma et al.,
2003) to be thermally reversible photochromic compounds.
This thermal reversibility is due to the sigma bond cleavage
of the spiro C–O single bond. The open form photomerocya-
nine reverts thermally to the closed form spiro compound.
The rate of thermal fading of photomerocyanine to spiro form
was found to decrease with increasing solvent polarity
(Lafuma et al., 2003) and metal complexation (Kopelman
et al., 2008; Zhang et al., 2008). This trend was attributed to
the stabilization of the polar zwitterionic photomerocyanine
through complexation and hydrogen bonding.
00.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
250 300 350 400 450 500 550 600 650 700
Wavelength (nm)
A
bs
or
ba
nc
e
Figure 5 Photobleaching reaction of PMC in epoxy resin ﬁlm.
The arrow direction indicates the decrease of absorbance with
increasing exposure time (s), 0; 20; 40; 60; 80; 140; 180; 320; 400;
440; 500; 540; 680; 720.
16 A.M. Asiri et al.Photobleaching and thermal fading of PMC–SO follow
simple ﬁrst-order rate law. When the open form PMC was
irradiated with white light, it was converted to the colorless
spirooxazine SO. Thus, the purple color gradually disappeared
with time. Figs. 4 and 5 show the absorption spectrum of the
photobleaching reaction of photomerocyanine PMC doped
in PMMA and epoxy resin polymer ﬁlms, respectively.
The integrated form of the ﬁrst-order rate law for the
photobleaching process is
ln
At
A0
¼ kt
where k is the rate constant, A0 is the absorbance of the PMC
at zero time and At is the absorbance at time t. Plot of
[ln(At  ln(A0)] against time gives a straight line with slope
equals (k). Fig. 6 shows the simple ﬁrst-order plots of the
photobleaching reaction of PMC doped in PMMA and epoxy
resin polymer ﬁlms, respectively. The apparent ﬁrst-order rate-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0 100 20 0 30 0 40 0 50 0 60 0 70 0 80 0
Time (sec.)
Photobleaching in PMMA polymer
Photobleaching in epoxy resin
ln
 A
t 
/ A
0
Figure 6 First-order plot of the photobleaching reaction of
PMC in PMMA and epoxy resin ﬁlms.constant (k) for the photobleaching of spirooxazine SO doped
in PMMA equals 0.0012 s1 and that for SO doped in epoxy
resin equals 0.0013 s1. The rate of photobleaching reaction
of PMC in both ﬁlms is almost the same. We found that the
reaction rate for the photobleaching process is slower than that
of the photocoloration process in both matrices. This is ex-
pected because PMMA and epoxy resin are both polar and
could form hydrogen bond with photomerocyanine and thus
stabilize the latter which results in the retardation of photoble-
aching rate.
3.3. Photochemical fatigue resistance of spirooxazine in PMMA
and epoxy resin polymer ﬁlms
One of the indispensable properties that should be fulﬁlled by
a photochrome to be used as a data-storage medium is its high
resistance to photochemical degradation. The fatigue resis-
tance of spirooxazine SO doped in PMMA and epoxy resin
polymer ﬁlms is reported as the changes in An/A0 with UV/vis-
ible irradiation cycles numbers, A0 and An are the absorbance
of the open form PMC at its kmax obtained on the ﬁrst and nth
cycles, respectively (Fig. 7). As it is clear from Fig. 7, the fati-
gue resistance of spirooxazine doped in epoxy resin is much
better than that of spirooxazine doped in PMMA. Similar re-
sults were reported with fulgides (Bahajaj and Asiri, 2005,
2006; Lafond et al., 2002; Lessard et al., 2003). This was attrib-
uted to the decrease of available polymer-free volume due to
increasing cross-linkage in the epoxy resin (Lessard et al.,
2003).
4. Conclusion
The photochromic properties of 1,3,3-trimethylspiro[indoline-
2,30-[3H]naphtho[2,1-b][1,4] oxazine] SO doped in epoxy resin
and PMMA ﬁlms were investigated. Kinetics of photocolor-
ation and photobleaching reactions were followed spectro-
photo-metrically. Irradiation of colorless spirooxazine SO
doped in PMMA and epoxy resin with UV light (366 nm) re-
sults in the formation of the intensely colored zwitterionic
photomerocyanine PMC.
The reverse reaction was photochemically induced by irra-
diation with white light. It was found that the visible absorp-
tion band is red shifted of the PMC doped in epoxy resin
compared to that doped in PMMA. Such a bathochromic shift0
0.2
0.4
0.6
0.8
1
1.2
1 2 3 4 5 6 7 8 9
Number of irradiation cycles
A
(n
) /
 A
(0
)
SO doped in PMMA polymer
SO doped in epoxy resin
Figure 7 Photochemical fatigue resistance of SO doped in
PMMA and epoxy resin polymer ﬁlms.
Photochromic properties of 1,3,3-trimethylspiro-[indoline-2,30-[3H]naphtho[2,1-b][1,4]oxazine] 17was attributed to the higher polarity of epoxy resin compared
to PMMA. Photocoloration and photobleaching reactions fol-
low a ﬁrst-order rate equation. It was found that photocolor-
ation rate constant of SO in PMMA ﬁlm is greater than that in
epoxy resin. On the other hand, photobleaching rate constant
is almost identical in both matrices. This was attributed to the
higher stability of the zwitterionic photomerocyanine PMC in
both matrices compared to the colorless closed spirooxazine
SO. Spirooxazine doped in epoxy resin shows much better fa-
tigue resistance than that doped in PMMA.Acknowledgements
The authors wish to thank King Abdul Aziz City for Science
and Technology (KACST) for funding this research work via
Grant No. At-27-68.
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Photochromic properties of 1,3,3-trimethylspiro[indoline-2,3′-[3H]naphtho[2,1-b][1,4]oxazine] doped in PMMA and epoxy resin thin films 

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Photochromic properties of 1,3,3-trimethylspiro[indoline-2,3′-[3H]naphtho[2,1-b][1,4]oxazine] doped in PMMA and epoxy resin thin films

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