Phototriggered micromanufacturing using photoresponsive amorphous spirooxazine films

Article abstract of DOI:10.1039/c2jm32149a

In this study, a series of spirooxazine molecules possessing bulky substituents was synthesized. These molecules readily formed amorphous glasses and their glass transition temperatures increased with the bulkiness of substitution. Their amorphous thin films exhibited apparent photochromism due to the spirooxazine-merocyanine isomerism and high durability to UV light in a nitrogen atmosphere. When the amorphous spirooxazine films were irradiated with spatially patterned UV light, surface relief gratings were produced because of the lateral material transfer from the shaded areas to the irradiated areas around their glass transition temperatures. Surface relief structure growth rate has a good relationship with the amount of photogenerated merocyanine formed at the irradiated area. A mechanism based on the diffusion of the spiro form for surface relief formation in this system has been proposed.

Full text of DOI:10.1039/c2jm32149a

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ISSN 0959-9428
PAPER
M. Vallet-Regí et al.
Supramolecular mechanisms in the synthesis of mesoporous magnetic
nanospheres for hyperthermia
0959-9428(2012)22:1;1-2
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ARTICLE
Phototriggered Micromanufacturing Using Photoresponsive Amorphous
Spirooxazine Films
Takashi Ubukata,* Shohei Fujii, Kento Arimatsu, and Yasushi Yokoyama
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
In this study, a series of spirooxazine molecules possessing bulky substituents was synthesized. These
molecules readily formed amorphous glasses and their glass transition temperatures increased with the
bulkiness of substitution. Their amorphous thin films exhibited apparent photochromism due to the
spirooxazine-merocyanine isomerism and high durability to UV light in a nitrogen atmosphere. When the
10 amorphous spirooxazine films were irradiated with spatially patterned UV light, surface relief gratings
were produced because of the lateral material transfer from the shaded areas to the irradiated areas around
their glass transition temperatures. Surface relief structure growth rate has a good relation with the
amount of photogenerated merocyanine form at the irradiated area. A mechanism based on the diffusion
of the spiro form for surface relief formation in this system has been proposed.
50 On the other hand, easy fabrication of SRGs of non-azobenzene
photochromic compounds has remained challenging and only
some papers have been published so far.37-42 In order to broaden
the application field of SRGs as optical elements, our study
focuses on photoinduced SRG formation on films containing
55 photochromic compounds other than azobenzenes in which one
of the two stable isomers is colorless.39-42 Recently, reversible
SRG formation, in which SRG can be erased by heating and
reconstructed by spatially patterned irradiation, has been attained
by using low-molecular-weight spirooxazine (SO), which can
60 form an amorphous film without a polymer matrix.41 Thus, the
SRG formed on the SO film can be used as a dynamic optical
application that deals with visible light.
It is well known that SO derivatives are one of the most widely
studied classes of representative thermally reversible
65 photochromic compounds, which exhibit extraordinarily high
resistance to photodegradation.43 Although various SO
derivatives have been reported so far,44 most of them are
15 1. Introduction
Photochromism is referred to as ‘‘a reversible transformation of a
single chemical species being induced in one or both directions
by electromagnetic radiation between two states having different
distinguishable absorption spectra.”1 Upon photoirradiation,
20 photochromic compounds change their structures. Therefore,
their physical and chemical properties, as well as absorption
spectra, may be changed by photochromic transformation.2,
3
Photochromism has been fascinating academic as well as
industrial researchers because of not only the simple phenomenon
25 of color change but also the wide variety of potential applications.
Recently, it has attracted further attention because the molecular
structure change is amplified to the change at mesoscopic4 or
macroscopic scales5-8 in properly sophisticated solid state systems.
In addition, since two pioneering reports in 1995,9, 10 reversible
30 formation of topographical features on the so-called surface relief
gratings (SRGs) of photochromic thin films has been widely
studied as the amplified motion at a mesoscopic scale. Upon
irradiation with interfering laser beams, SRGs are formed on
azobenzene functionalized polymer films at temperatures well
35 below the glass transition temperatures (Tgs) of the polymers.11-17
The key to SRG formation is thought to be the repeatable trans-
cis-trans isomerization cycling of the azobenzene chromophore
upon irradiation with light of an appropriate wavelength. It is
widely accepted that SRG formation is based on a directional
40 flowing process.18 Although several models have been
proposed,19-22 the mechanism has not been completely elucidated
yet.
composed of indoline and oxazine rings, which are linked by a
46
spiro-carbon atom and aligned vertically;45,
thus, stable
70 structures of SO molecules are often called spiro (SP) form.
Because the electrons localize in each ring, the stable SP form
absorbs light whose wavelength is shorter than the visible region.
Upon UV light irradiation, the SP form undergoes bond cleavage
between the spiro carbon atom and the oxygen atom to produce
75 the planar merocyanine (MC) form (Fig. 1). Because of the
delocalization of electrons in the planar MC form, the MC form
can absorb the light in the visible regions and becomes colored.
When UV irradiation is discontinued and the colored MC form is
kept in the dark, it rapidly reverts to the initial SP form. Such
80 back reaction is accelerated by visible light irradiation. Thus, SO
molecules undergo thermally reversible photochromism between
the colorless closed SP form and colored open MC form.
Although various azobenzene-pendant amorphous polymers23
have been extensively explored since the first two reports,9, 10 the
45 phenomena of photoinduced SRGs have also been observed in
various azobenzene-containing systems including liquid
crystalline polymers,24-26 main-chain polymers,27 hyperbranched
polymers,28 supramolecular polymers,29 host–guest hybrids,30 sol-
gel matrices,31 molecular glasses,32-35 and crystal surfaces.36
Our first attempt to produce SRG was conducted using
unmodified SO, SO1 (Fig. 1). However, the amorphous nature of
85 SO1 is not sufficient to be used as an application because the film
crystallizes at the edge of the film in one day unless the film is
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2.2 General properties of SO derivatives
preirradiated with UV light. Shirota and coworkers have
developed the concept of “amorphous molecular materials,”
which are small organic molecules that can form stable
amorphous glasses under room temperature if their molecular
structures are properly designed.47 For example, they reported
that a newly synthesized bulky ditolyl amino-substituted SO1,
SO4, readily forms amorphous glass and exhibits photochromism
as an amorphous film as well as in solution.48 In the present study,
various SO derivatives with bulky substituents have been
10 synthesized to improve the amorphous nature. Thus, SRG
formation properties have been investigated using films of SO
derivatives. We consider that the comparison of the efficiency of
phototriggered mass transfer among the SO derivatives should
support and clarify the suitable molecular structures for SRG
15 forming materials. Furthermore, we propose the mechanism of
SRG formation adopted in the study.
60 All these SO derivatives formed amorphous glasses with well-
defined Tg when the melt samples were cooled on standing in air
(Fig. S1). The value of Tg increased with the molecular weight by
the introduction of rigid moieties. Introduction of one phenyl
substituent to SO1 increased Tg by approximately 30 K, as shown
65 in the Tgs of SO2 and SO5, and two phenyl substituents increased
Tg by approximately 40–50 K, as shown in the Tgs of SO3 and
SO4. The value of Tg in SO1 in our previous report was found to
be mistaken with the melting point of incorporated water and the
value has been corrected in Table 1.41
5
70
Table 1 Property of amorphous SO1–SO5 films
SO1
328.41
1 day ~
308
SO2
SO3
SO4
SO5
404.50
495.61
523.67
378.47
Mw
Stability of glassy state
Tg / K
2,3 day ~ 2 month ~ 2 month ~ 2,3 day ~
335
622
346
635
359
337
75
 max / nm
612
641
598
X
Y
Z
3.7 x 101
5.0 x 100
1.6 x 102
3.5 x 103 9.6 x 102
4.7 x 101 8.3 x 101
6.7 x 102 6.9 x 102
2.9x 103
6.5 x 101
3.7 x 102
3.7 x 103
3.7 x 101
9.2 x 102
t
1/2 / s
UV
X
N
H
H
H
H
H
H
H
H
H
SO1
SO2
SO3
Air
N2
X
Photodurability*
/ J cm–2
N
Z
Ph
N(Ph)2
N
O
Vis, 
CH3
N
O
Y
SO4 N(p-Tol)2
SO5
Y
Z
20
CH3
80
H
* Irradiation energy until 20 % SO degradation.
SP
MC
Fig. 1. Schematic of the reversible isomerization between spiro
(SP) and merocyanine (MC) forms used in this study.
The amorphous thin films of SO derivatives were prepared by
spin coating from the chloroform solution on clean glasses. The
films’ thicknesses were in the range 100–125 nm. The films were
85 transparent and isotropic, as revealed by polarized optical
microscopy and UV-visible absorption spectroscopy. Before SRG
experiments, various properties such as the stability of the glassy
state, photochromic properties, and photodurability were
investigated. These are summarized in Table 1. The stability of
90 the glassy state is defined as the period for which the film
maintains the amorphous glass state at room temperature after the
spin coating. After the period, the SO films exhibited
crystallization from the edge of the film. The stability of the
resulting amorphous glass considerably depends on molecular
95 structures and Tg, and is improved in SO3 and SO4 as they
remain stable as amorphous glass for two months.
Next, the films’ photochromic properties were investigated. Upon
irradiation with UV light (365 nm, 12 mWcm−2) at room
temperature, the colorless films changed to blue because of the
100 generation of the colored form, and new absorption bands
ascribed to MC forms were detected in the visible region (Fig.
S2). When the UV light irradiation was ceased, the original
absorption spectrum was recovered completely, indicating that
the backward ring-closing reaction occurred thermally.
25 2. Results and Discussion
2.1 Molecular design and synthesis
As mentioned above in the introduction, the crystallization of
SO1 is challenging. Using Shirota’s concept, we synthesized a
series of SO derivatives with bulky substituents, including SO4,
30 to improve the amorphous glass nature of the resultant films.
However, this previously reported route of SO4 synthesis from 4-
amino-N,N-bis(4-methyl-phenyl)aniline involves three steps.
Moreover, the synthesis of another SO derivative requires
retracing the other three steps. Therefore, we first synthesized a
35 precursor of brominated SO (Br-SO) from SO1 according to the
literature.49 Accordingly, we synthesized SO2–4 from Br-SO, as
shown in Scheme 1. SO2 was obtained by Suzuki coupling
reaction with phenylboric acid in 44% yield. SO3 and SO4 were
obtained by Buchwald–Hartwig coupling reaction in 77% and
40 91% yields, respectively. Thus, the Br-SO precursor enables us to
synthesize various SO derivatives readily. Compounds of SO2–4
1
were identified by H NMR and FT-IR spectroscopies and mass
105 Comparison of a sequence of SO1 and SO4 reveals that the
addition of electron-donating substituents on the 5-position of the
indoline ring has the effect of bathochromic shift on the visible
absorption peak (max) of the MC form, which is probably due to
the increment of contribution of a zwitterionic structure in the
110 MC form.46 When wavelengths, max, of SO1 (612 nm) and SO5
(598 nm) in the amorphous film are compared with those in
solution,50 they are very similar to those in the polar solvent of
ethanol (613 nm and 600 nm, respectively) rather than in
nonpolar solvent of methylcyclohexane (585 nm and 566 nm,
115 respectively). The results suggest that the matrix environment
surrounding the molecules in the amorphous film is similar to that
in polar solvents.
spectrometry. SO5 was purchased and used without further
purification.
45
N
N
O
CH3
SO2
N
N
N
N
Br
50
N
N
N
O
O
O
CH3
CH3
CH3
SO1
Br-SO
SO3
N
N
N
O
Next, the behavior of thermal back isomerization of the MC form
was investigated. Although this can generally be analyzed in
120 solution by regarding it as first order kinetics, the analysis in an
amorphous film requires the consideration of at least two
different rate constants. For simplicity, we analyzed the
CH3
55
SO4
Scheme 1. Synthesis of spirooxazine derivatives
2
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irradiated convex is higher, and the bottom of the depression is
lower, than the initial surface level. The results clearly show that
lateral material transfer occurred from the shaded areas to the
65 irradiated areas regardless of the type of SO derivative (Fig. 3).
decoloration kinetics with a half-life (t1/2). Half-lives for the
modified SO5 were prolonged by 100 times compared to those
for SO1, although the kinetic constant for SO5 is larger than that
for SO1 in ethanol solution.50 It is well known that the thermal
(a)
(b)
(c)
5
decoloration reaction rate decreases when SOs are placed in solid
52
matrices such as polymer films.51,
Prolonged half-lives
observed for SO2–SO5 are thought to be ascribed to their
relatively large volume for isomerization. They may also be
ascribed to their increased Tgs since the decoloration experiments
10 were performed at room temperature (300–306 K).
To verify the durability of the SO films against UV light, the
visible absorption band ascribed to the colored MC form was
monitored during UV light irradiation (12 mWcm−2). Although
SO derivatives exhibit extraordinarily high photostability
15 compared to spiropyran derivatives,43, 44 the visible absorption
band ascribed to the MC form gradually disappeared with the
contentious UV irradiation after the photostationary state (pss),
probably due to the oxidative degradation of the MC from.53
Photodurability was analyzed with irradiation energy until the
20 visible absorption band decreased to 80% of the absorbance of
the pss. As already reported in the preceding paper, SO1’s
photodurability is dramatically improved under a nitrogen
atmosphere compared to that in air;41 the other SO derivatives
had same tendency as SO1. Thus, the following experiments
25 using UV light were performed under a nitrogen atmosphere.
(d)
(e)
Fig. 3. AFM images of surface relief structures in amorphous SO
films after UV light irradiation (12 or 60 mW cm−2) through a
photomask of pattern with a single 2.5-m-wide slit for various
70 times at various temperatures: (a) SO1, 12 mW cm−2, 12 min, 300
K; (b) SO2, 12 mW cm−2, 60 min, 310 K; (c) SO3, 60 mW cm−2,
60 min, 344 K; (d) SO4, 60 mW cm−2, 60 min, 349 K; (e) SO5,
12 mW cm−2, 60 min, 333 K.
150
360
(b)
(a)
75
SO1
SO2
SO3
SO4
SO5
SO1
SO2
SO3
SO4
SO5
350
340
330
320
310
300
100
50
0
2.3 Phototriggered surface relief formation
80
Figure 2 shows the surface relief structures of SO derivative films
produced by the patterned UV (365 nm) irradiation through a
30 grating photomask with a period of 5 m. When the films were
irradiated with spatially patterned UV light under controlled
temperature, regular surface modulations were produced on all
SO derivative films, and its spatial period was coincident with
that of the photomask. The photomodulated structures were stable
35 and remained unchanged as long as the films were kept below the
Tg of each SO derivative.
280
300
320
340
360
380
300 310 320 330 340 350 360
Glass transition temperature / K
Temperature / K
85 Fig. 4. (a) Plots of relief height as a function of film temperature
for five SO films after UV light irradiation through a photomask
under constant irradiation conditions (circles: SO1, 7.9 mW cm−2,
30 min; squares: SO2, 12 mW cm−2, 60 min; diamonds: SO3, 60
mW cm−2, 180 min; triangles: SO4, 60 mW cm−2, 60 min;
90 inverted triangles: SO5, 12 mW cm−2, 30 min). (b) Relationship
between the optimal temperature and glass transition temperature.
(a)
(b)
(c)
40
During spatially patterned light irradiation, the transfer efficiency
depended considerably on the type of SO derivative and the
95 temperature of the SO films. Figure 4a shows the temperature
dependence of the resulting relief height using the SO derivative
films. The height of the relief produced on the SO films increased
gradually to a maximum and then decreased with increasing
temperature, although the optimal temperature and height of the
100 maximum vary among the SO derivatives. This temperature
dependence may be due to the competition between increasing
molecular mobility and the smoothing effect of surface tension
with increasing temperature since optimal temperature is related
to Tg (Fig. 4b). Details will be presented in the following section.
105 The higher the Tg of the SO derivatives, the higher the optimal
temperature. Optimal temperatures for SO derivatives (SO1–
SO5) were 305, 310, 338, 349, and 333 K, respectively, and
corresponded to slightly lower temperatures than their Tgs, except
for SO2. In the case of SO2, the optimal temperature was
110 observed to be considerably lower (310 K) than its Tg of 335 K.
This may be because partial crystallization was observed in the
SO2 film after the patterned irradiation above the optimal
temperature. That is, since SO2 exhibits the property that
(d)
(e)
45
50 Fig. 2. AFM images of surface relief structures in the amorphous
SO films after UV light irradiation (12 or 60 mW cm−2) through a
photomask of stripes with a period of 5 m for various times at
various temperatures: (a) SO1, 12 mW cm−2, 12 min, 300 K; (b)
SO2, 12 mW cm−2, 60 min, 310 K; (c) SO3, 60 mW cm−2, 60 min,
55 338 K; (d) SO4, 60 mW cm−2, 60 min, 349 K; (e) SO5, 12 mW
cm−2, 60 min, 333 K.
In order to investigate the direction of material transfer,
irradiation experiments through a photomask possessing a single
60 2.5-m-wide slit line were performed. All cross-sectional
topographies of the SO derivatives show that the top of the
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crystallization occurs easily at a temperature higher than its Tg, 65 surface relief is mainly constructed as a result of the movement of
SRG formation ability was suppressed at elevated temperatures
by crystallization, leading to the much lower optimal temperature.
Next, we examined the relief heights of the SRGs formed near the
optimal temperatures. For each SO derivative, the relief
the SP form from the shaded area to the irradiated area, where the
concentration of the MC form is high considering the direction of
mass transfer (Fig. 3). The following experiment was conducted
to ascertain whether the essence of mass transfer is in the
5
formation process was conducted by plotting relief height as a 70 movement of the SP form to the exposed area or to a place of
function of irradiation time (Fig. 5a). For all SO derivatives, the
relief height of SRG was almost proportional to the irradiation
time at the early stages of irradiation. The growth rate of SRG
10 was obtained from the slope of the straight line calculated by the
least squares method. Although the growth rate of SRG has a
linear relationship with irradiation intensity in the azobenzene
polymer system,54 this is not the case in this system.41 Thus, the
growth rate of each SO derivative was examined in accordance
15 with the increment in conversion ratio (CR) between the
irradiated and dark states. CR is expressed as
high concentration of the MC form.
(a)
350
10
8
(b)
SO1, 2.5 mW cm-2
300
SO1
SO2
SO3
SO4
SO5
SO1, 12 mW cm-2
SO1, 60 mW cm-2
SO2, 12 mW cm-2
SO3, 60 mW cm-2
SO4, 60 mW cm-2
SO5, 12 mW cm-2
250
200
150
100
50
6
75
4
2
0
0
80
0
50
100 150 200 250 300 350 400
Irradiation time / min
0.0
0.1
0.2
0.3
 Conversion ratio
CR = CMC/CSO (1)
Fig. 5. (a) Plots of relief height as a function of irradiation time
for five SO films after UV light irradiation through a photomask
under constant irradiation conditions (circles: SO1, 2.5 or 12 or
where CMC is an increment in the concentration of the MC form
in the amorphous SO film exposed at the SRG forming condition
20 and CSO is the concentration of the SO molecule in the initial
amorphous SO film. Moreover, CMC and CSO are expressed as
CMC (mol/dm3) = A/l (2)
85 60 mW cm−2, 301 ± 1 K; squares: SO2, 12 mW cm−2, 310 K;
diamonds: SO3, 60 mW cm−2, 338 K; triangles: SO4, 60 mW
cm−2, 349 K; inverted triangles: SO5, 12 mW cm−2, 333 K). (b)
Relationship between the growth rate of the relief height and the
change in conversion ratio during irradiation.
CSO (mol/dm3) = d/Mw (3)
where A is a change in absorbance in the visible band at pss
25 during UV light irradiation under the SRG forming conditions, 
is the molar absorption coefficient of the MC form at the
maximum in the visible band, l is the path length, that is, the film
thickness, d is density, and Mw is molecular weight. Thus, CR is
expressed as
90
As shown in Fig. 6a, the thin film of SO1 was uniformly
irradiated with UV (365 nm) light from the glass substrate surface
to gain pss, and was irradiated with visible light (>520 nm)
through the photomask possessing one slit line to locally induce
95 back photoisomerization from the MC form to SP form. This
experimental setup allows us to make the film state such that the
part irradiated with visible light is in the low concentration of the
MC form compared to the other parts, although the total light
intensity is higher than the other parts. After the irradiation, a
100 concave surface relief structure was observed at the visible light
exposed area in contrast to that observed in Fig. 3a, which
indicates the mass transfer from the irradated to the shaded area
(Fig. 6b). As a result, it was confirmed that the origin of the relief
structure formation is the molecular movement of the SP form to
105 the parts where the concentration of the MC form is high.
30 CR = MwA/ld (4)
where the molar absorption coefficients are assumed to be equal
to those of the ethanol solution (6.1 × 10−3 and 8.1 × 10−3 dm3
mol−1 nm−1 for SO1 and SO5, respectively)50 since the visible
absorption peaks of the films are very similar to those of the
35 ethanol solution. The molar absorption coefficients of SO2–SO4
are assumed to have the same values as those for SO1 because of
the same SO skeleton. The densities of SO1 and SO5 (1.198 and
1.221 × 103 g dm−3) are adopted from a free chemical database.55,
56
The densities of SO2–SO4 are assumed to have the same
40 values as those for SO1, similar to that for the molar absorption
coefficient.
Figure 5b shows the relationship between SRG growth rate and
CR for SO derivatives under the SRG forming conditions.
Although the value of CR estimated in the present study may
45 include varying deviations due to approximation, Fig. 5b
indicates that the more MC form generated, the greater the
increase in SRG growth rate. This can be regarded as a roughly
proportional relation. It can be considered that the SRG formation
efficiency of SO2 is lower than that of the other derivatives as the
50 observed plot for SO2 appeared at under deviation to linearity.
Again, this is probably because the SRG formation experiment
for SO2 was performed at a relatively low temperature compared
to its Tg since it crystalizes easily; thus, molecular mobility was
suppressed in the environment. On the other hand, the SRG
55 formation efficiency of SO5 is higher than that of the other
derivatives as the observed plot for SO5 appeared at over
deviation to linearity. The molecular skeleton of SO5, the
phenanthrooxazine ring, may be appropriate for efficient SRG
formation compared to the naphthooxazine ring, although a
60 greater degree of overestimation of the molar absorption
coefficient of an MC in the film should be considered.
110
115
120
Fig. 6. (a) Schematic of setup for simultaneous irradiation with
uniform UV light (365 nm, 2 mW cm−2) and patterned (a single
2.5-m-wide slit) visible light (>520 nm, 100 mW cm−2). (b)
AFM image of surface relief structure in the amorphous SO1 film
125 after the simultaneous irradiation shown in (a) for 4 h at 300 K.
The fact that the formation efficiency increases with the amount
of MC forms indicates that the spatial distribution of SP and MC
forms is important for SRG formation. It is determined that
4
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2.4 Proposed mechanism for SRG formation in this system
4. Experimental Section
From the knowledge obtained here and precedent our
communication,41 we consider the mechanism of SRG formation
in the amorphous SO films. The material transport in this system
exhibits characteristic features such as (i) the process is
insensitive to light polarization and (ii) the growth rate is not
proportional to the irradiation intensity. These features are rather
60 4.1 Materials
1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3′-[3H]naphth[2,1-
b][1,4]oxazine] (SO1) and 1,3-dihydro-1,3,3-trimethylspiro[2H-
indole-2,3′-[3H]phenanthro[9,10-b][1,4]oxazine] (SO5) were
purchased from Sigma-Aldrich Co. and Tokyo Chemical Industry
65 Co., Ltd. and used without further purification. Chloroform for
film preparation was of spectroscopic grade (Wako Pure
Chemical Industries Ltd.).
5
different from those of the well-studied system involving
57, 58
amorphous azobenzene.54,
Thus, it is considered that the
10 given photons and the resultant electromagnetic force are not
directly used to induce material transfer. Seki and coworkers
reported phototriggered mass migration motion in a liquid
crystalline azobenzene polymer system in which the
photochemically induced phase transition and the resulting spatial
15 modulations in the physical properties of the film play essential
roles for SRG formation.59, 60 The present system is similar to the
Seki system since the present system is recognized as a
phototriggered process rather than a photoinduced one. As shown
in Fig. 5, the growth rate depends on the concentration of the MC
20 form at the irradiated region, that is, the degree of the
concentration gradient that generates at the boundary between the
irradiated and shaded regions. This result reminds us that the
driving force for material transfer is diffusion. According to
Fick’s first law, the diffusive flux goes from high concentration
25 regions to low concentration regions, with a magnitude that is
proportional to the concentration gradient and diffusivity.
4.2 Film preparation
70 Thin amorphous films of SO derivatives were prepared by spin
coating from chloroform solutions (100 or 80 l, 1.1 wt%) on a
clean glass (26 × 10 × 1 mm3) or quarts (20 × 10 × 1 mm3)
substrate. A spincoater (Mikasa Co. Ltd., 1H-D7) was used with
two program steps (step 1: 1000 rpm, 50 s; step 2: 3000 rpm, 2 s).
75 Film thickness was calculated by curve fitting the reflection
fringe obtained from a UV-vis-near-infrared spectrometer (Jasco
Co., V-670) equipped with an absolute reflectance measurement
unit (ARSN-733). The thicknesses of the films were in the range
100–125 nm.
80
J = −D grad C (5)
where J is the diffusion flux, D is diffusivity, and C is
concentration. If the diffusivities of the SP form (DSP) and MC
30 form (DMC) are same, no SRG will be produced. However, SRG
was produced because of the transfer of the SP form, as shown in
Figs. 3 and 6. These results imply that DSP is much larger than
DMC under the SRG forming conditions. Thus, the difference in
diffusivity between the SP and MC forms should induce diffusion
35 flux at the boundary between the irradiated and unirradiated
regions, where the concentration gradient is generated.
4.3 Photoirradiation
UV LED (Keyence Co., UV-400) or Hg–Xe lamp (SAN-EI
Electronic Co. Ltd., UVF-204S) through a combination of glass
filters (UV-35 and UV D36B) were used as UV light sources. UV
85 light intensity was evaluated at a wavelength of 365 nm using a
power meter (Newport Co., 1830-C) equipped with a detector
(818-UV) over the entire exposed area. Patterned light irradiation
(stripes with a period of 5 µm) was performed using the above-
described light source through a custom-made photomask
90 (Toppan Printing Co. Ltd.) attached to the film. A gap was
produced between the photomask and the film surface by a bump
in the film near the edge of the film. During irradiation, the film
was set on a chamber (Imoto Machinery Co., Ltd., N33067)
equipped with nitrogen gas serve to control the temperature and
95 atmosphere. After irradiation, the film was immediately returned
to room temperature. Photoirradiation with >520-nm light was
conducted using a 500-W high-pressure mercury lamp (Ushio
Inc.), separated by filters (a 5-cm water filter, a Pyrex glass filter,
and a Y-52 glass filter).
3. Conclusions
40 We have readily synthesized three SO molecules possessing
bulky substituents from a precursor of brominated SO in one step.
All SO derivatives formed transparent amorphous molecular
films by a spin coating method. The stability of the resulting
amorphous films and their Tgs increased with increasing
45 bulkiness of substitution, maintaining the photoresponsive
property. When amorphous SO films were irradiated with
spatially patterned UV light under controlled temperature, surface
relief structures were produced because of the lateral material
transfer from the shaded areas to the irradiated areas regardless of
50 the type of SO derivative. The optimal temperature to produce the
surface relief structure efficiently has a good relation to the bulk
Tg of each SO derivative. SRG growth rate has a linear relation to
the amount of photogenerated MC form at the irradiated area. We
can conclude that the SO molecule whose increment of
55 conversion ratio is high near its Tg is suitable for efficient SRG
formation. Moreover, the SRG formation mechanism in this
system is proposed on the basis of the diffusion of the SP form.
100
4.4 Physical measurements
UV-vis spectra were recorded on a UV-vis spectrometer
(Shimadzu Co., Multispec-1500) to confirm film quality. Surface
relief structures were observed with an atomic force microscope
105 (AFM; Shimadzu Co., 9500 equipped with an Olympus Co.,
OMCL-TR800PSA-1 cantilever) in the contact mode. Relief
height is defined as the difference in the vertical distance between
the central part of the exposed and unexposed areas. Values of Tg
for each SO derivative were obtained with a differential scanning
110 calorimeter (Seiko Instruments Inc., DSC6100) equipped with an
instrument controller (Extra6000) at heating and cooling rates of
5 and 20 K min−1, respectively, for SO1 and at a heating/cooling
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rate of 10 K min−1 for SO2–SO5. Amorphous specimens were
prepared by casting from chloroform solution for SO1, SO3, and
SO4, and by rapid quenching from melt for SO2 and SO5. All
procedures were conducted in dimmed red light.
1486, 1460, 1388, 1363, 1308, 1273, 1250, 1171, 1137, 1119,
1078, 1036, 1011, 979, 950, 917, 879, 836, 816, 778, 750, 697,
65 654, 624, 593, 560
LRMS (EI, 70 eV) m/z (rel intensity), 495 (M+, 100), 480 ((M-
CH3)+, 27), 326 ((M-C11H7NO)+, 43)
5
Found: m/z 495.23006, Calcd for C34H29N3O: M, 495.23107.
4.5 Synthesis
70 5-di-p-tolylamino-1,3,3-trimethylspiro{indole-2,3′-(3H-
naphtho[2,1-b][1,4]oxazine)} (SO4)
To a microwave vial (2–5 ml) with a spinner, 5-bromo-1,3,3-
5-phenyl-1,3,3-trimethylspiro{indole-2,3′-(3H-naphtho[2,1-
b][1,4]oxazine)} (SO2)
To a microwave vial (2–5 ml) with a spinner, 5-bromo-1,3,3-
trimethylspiro{indole-2,3′-(3H-naphtho[2,1-b][1,4]oxazine)}
(Br-
SO) (70.0 mg, 0.172 mmol, 1.00 eq.), di-p-tolylamine (39.7 mg,
75 0.201 mmol, 1.17 eq.), palladium (II) acetate (4.1 mg, 0.018
mmol, 0.11 eq.), tri-t-butylphosphine (4.0 mg, 0.020 mmol, 0.12
eq.), sodium t-butoxide (53.1 mg, 0.553 mmol, 3.22 eq.), and
toluene (5.0 ml) were added. The mixture was allowed to react by
using a microwave reactor (120 °C, 0 bar) for 10 min. After the
80 solvent was removed by evaporation, the resulting mixture was
extracted with chloroform. The combined organic layer was
washed with water three times and dried over anhydrous
magnesium sulfate. The drying agent was filtered off and the
solvent evaporated. The residue was purified by column
85 chromatography on silica gel using ethyl acetate/hexane (3%) as
the eluent to give SO4 (82.2 mg, 0.157 mmol, 91%) as a yellow
solid.
10 trimethylspiro{indole-2,3′-(3H-naphtho[2,1-b][1,4]oxazine)}
(Br-
SO) (155.1 mg, 0.381 mmol, 1.00 eq.), phenylboric acid (54.9 mg,
0.450 mmol, 1.18 eq.), tetrakis(triphenylphosphine)palladium(0)
(48.1 mg, 0.0416 mmol, 0.11 eq.), sodium carbonate (125.2 mg,
1.18 mmol, 3.10 eq.), THF (4.0 ml), and water (1.0 ml) were
15 added. The mixture was allowed to react by using a microwave
reactor (130 °C, 5 bar) for 10 min and the resultant mixture was
extracted with chloroform. The combined organic layer was
washed with water three times and dried over anhydrous
magnesium sulfate. The drying agent was filtered off and the
20 solvent evaporated. The residue was purified by column
chromatography on silica gel using ethyl acetate/hexane (3%) as
the eluent to give SO2 (67.6 mg, 0.167 mmol, 44%) as a pale
yellow solid.
1H NMR (300MHz, CDCl3, TMS) /ppm; 1.26 (3 H, s), 1.33 (3 H,
s), 2.30 (6 H, s), 2.75 (3 H, s), 6.45 (1 H, d, J/Hz = 8.1), 6.89–6.98
90 (6 H, m), 7.02–7.09 (5 H, m), 7.37–7.42 (1 H, tm, J/Hz = 7.4),
7.55–7.58 (1 H, tm, J/Hz = 7.4), 7.69 (1 H, d, J/Hz = 8.9), 7.73 (1 H,
s), 7.76 (1 H, d, J/Hz = 8.1), 8.55 (1 H, d, J/Hz = 7.9)
Mp: 205–207 °C
25 1H NMR (300 MHz, CDCl3, TMS) /ppm; 1.40 (3 H, s), 1.41 (3 H,
s), 2.81 (3 H, s), 6.65 (1 H, d, J/Hz = 8.1), 7.05 (1 H, d, J/Hz = 8.9),
7.27–7.33 (2 H, m), 7.38–7.48 (4 H, m), 7.56–7.61 (3 H, m), 7.68
(1 H, d, J/Hz = 8.9), 7.76 (1 H, d, J/Hz = 7.7), 7.77 (1 H, s), 8.56 (1
H, d, J/Hz = 7.3)
IR (ATR: diamond prism, neat) /cm−1 = 2925, 2868, 1606, 1593,
1505, 1485, 1460, 1385, 1352, 1313, 1269, 1248, 1169, 1111,
95 1080, 1034, 1000, 956, 880, 811, 748, 710, 690, 631, 579, 563
LRMS (EI, 70 eV) m/z (rel intensity), 523 (M+, 100), 508 ((M-
CH3)+, 58), 354 ((M-C11H7NO)+, 39)
30 IR (ATR: diamond prism, neat) /cm−1 = 2967, 2818, 1609, 1592,
1506, 1480, 1457, 1428, 1385, 1351, 1333, 1315, 1268, 1245,
1209, 1195, 1170, 1148, 1139, 1112, 1080, 1033, 1019, 980, 960,
890, 863, 836, 815,796, 779, 764, 749, 699, 680, 645, 583, 560
LRMS (EI, 70 eV) m/z (rel intensity), 404 (M+, 100), 389 ((M-
35 CH3)+, 56), 235 ((M-C11H7NO)+, 61), 220 ((M-C12H10NO)+, 18)
Found: m/z 404.18730, Calcd for C28H24N2O: M, 404.18886.
Found: m/z 523.26168, Calc. for C29H20N2O2S2: M, 523.26237.
100 Acknowledgments
5-diphenylamino-1,3,3-trimethylspiro{indole-2,3′-(3H-
naphtho[2,1-b][1,4]oxazine)} (SO3)
This study was supported in part by a Grant-in-Aid for Scientific
Research (23750153) from the Ministry of Education, Culture,
Sports, Science, and Technology and the Foundation for the
Promotion of Material Science and Technology of Japan (MST
105 Foundation). The authors wish to express their thanks to the
Instrumental Analysis Center, Yokohama National University, for
the use of the NMR and mass spectrometers. The authors would
like to thank Enago (www.enago.jp) for the English language
review.
40 To a microwave vial (10–20 ml) with a spinner, 5-bromo-1,3,3-
trimethylspiro{indole-2,3′-(3H-naphtho[2,1-b][1,4]oxazine)}
(Br-
SO) (200 mg, 0.491 mmol, 1.00 eq.), diphenylamine (100.2 mg,
0.592 mmol, 1.21 eq.), palladium (II) acetate (11.3 mg, 0.0503
mmol, 0.10 eq.), tri-t-butylphosphine (12.1 mg, 0.0598 mmol,
45 0.12 eq.), sodium t-butoxide (143.5 mg, 1.493 mmol, 3.04 eq.),
and toluene (15 ml) were added. The mixture was allowed to
react by using a microwave reactor (120 °C, 0 bar) for 15 min.
After the solvent was removed by evaporation, the resulting
mixture was extracted with chloroform. The combined organic
50 layer was washed with water three times and dried over
anhydrous magnesium sulfate. The drying agent was filtered off
and the solvent evaporated. The residue was purified by column
chromatography on silica gel using ethyl acetate/hexane (3%) as
the eluent to give SO3 (186.4 mg, 0.376 mmol, 77%) as a yellow
55 solid.
110 Rreferences
Department of Advanced Materials Chemistry, Graduate School of
Engineering, Yokohama National University 79-5, Tokiwadai, Hodogaya,
Yokohama 240-8501, Japan. Fax: +81-45-339-3970; Tel: +81-45-339-
3970; E-mail: ubukata@ynu.ac.jp
115 † Electronic Supplementary Information (ESI) available: Electronic
supplementary information (ESI-1-3) depicting DSC charts, changes in
absorption spectra and 1H-NMR spectra. See DOI: 10.1039/b000000x/
Mp: 187–191 °C
1H NMR (300 MHz, CDCl3, TMS) /ppm; 1.26 (3 H, s), 1.33 (3 H,
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