Synthesis and photochromic properties of substituted naphthopyran compounds

Article abstract of DOI:10.1016/j.tet.2011.01.078

A group of 3,3-diaryl-3H-naphtho[2,1-b]pyran compounds with functional substituents at the 5- and 6-positions of the naphthopyran skeleton and the para positions at the 3-aryl moieties were prepared through condensation reactions between 2-naphthol derivatives and 1,1-diarylprop-2-yn-1-ol derivatives. The chemical structures of the compounds were confirmed by NMR and MS. The crystal structure of 3,3-diphenyl-6-morpholino-3H-naphtho[2,1-b]pyran (4b) was determined and the relationship between the pyran substructure and photochromism was discussed. The photochromic properties were studied as well, and decoloration kinetics of colored forms was fitted to the biexponential model. Among these compounds, 4b was considered to be the best one due to the large ΔOD of colored form, which is one of the most important properties used in the photochromic material.

Full text of DOI:10.1016/j.tet.2011.01.078

Tetrahedron 67 (2011) 2246e2250
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Tetrahedron
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Synthesis and photochromic properties of substituted naphthopyran compounds
,
b
a
a,
Zhen Wang a, Qinghua Meng a , Zhihui Zhang , Dingliang Fu , Wanbin Zhang
*
*
a School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, PR China
b Department of Chemistry, Changzhou University, Changzhou 213164, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A group of 3,3-diaryl-3H-naphtho[2,1-b]pyran compounds with functional substituents at the 5- and 6-
positions of the naphthopyran skeleton and the para positions at the 3-aryl moieties were prepared
through condensation reactions between 2-naphthol derivatives and 1,1-diarylprop-2-yn-1-ol de-
rivatives. The chemical structures of the compounds were confirmed by NMR and MS. The crystal
structure of 3,3-diphenyl-6-morpholino-3H-naphtho[2,1-b]pyran (4b) was determined and the re-
lationship between the pyran substructure and photochromism was discussed. The photochromic
properties were studied as well, and decoloration kinetics of colored forms was fitted to the biexpo-
Received 17 December 2010
Received in revised form 20 January 2011
Accepted 26 January 2011
Available online 2 February 2011
Keywords:
Photochromism
Naphthopyran
Decoloration kinetics
Crystal structure
nential model. Among these compounds, 4b was considered to be the best one due to the large
DOD of
colored form, which is one of the most important properties used in the photochromic material.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
yellowish or reddish color and a photochromic compound that
develops blue color. Recently, our research interest has been fo-
cused on the naphthopyran compounds. The reversible color gen-
eration mechanism of the naphthopyran compounds operates
through a facile electrocyclic ring-opening of the 2H-pyran moiety
to afford an equilibrium mixture of colored geometrical isomers
that gradually electrocyclise to the colorless pyran ring on cessation
of irradiation.19,26 Compared to other photochromic families, the
naphthopyran compounds have the advantages of the low initial
color, low solvachromism, high color density and large color gamut
provided by the ring open form when substituted with various
electron donating and withdrawing groups.20 Furthermore, we
realize that it will be great beneficial to the composites compati-
bility in the formula and the color balance at steps of developing
and fading, if the neutral tint is obtained by the mixture of com-
pounds selected from the same structural family. In order to ac-
complish the above object, the present paper has conducted keen
study concerning on the synthesis of a number of naphthopyran
compounds with various substituted groups and the effects of these
groups on the optical properties of the compounds.
Thus, we prepared the 3,3-diaryl-3H-naphtho[2,1-b]pyran
compounds (Scheme 1), with substituents at the 5- and 6-positions
of the naphthopyran skeleton and the para positions of the 3-aryl
moieties. The substituents were selected form the substituted
amino groups and heterocyclic groups bonded to the skeleton
structure of chromophores through the nitrogen atom, and the
substituted amido groups as well. The starting materials, such as
naphthol derivatives and ketones were commercially available. The
chemical structures and photochromic properties were character-
ized, and the decoloration kinetics was studied as well.
The photochromism is an interesting phenomenon that has been
drawing various attentions for several decades. It is a reversible
photochemical reaction of a compound, which quickly changes its
color when irradiated with light, such as UV light, sunlight or light
from a fluorescent lamp and resumes its initial color when no irra-
diation. Various compounds have so far been synthesized and used
in ophthalmic lenses,1e5 imaging devices, and smart windows.6,7
The photochromic compounds working through external light
stimulus can also be the basis for molecular photoswitches,8e11
sensors,12e14 and the photo-control nano surface topology.15 Fur-
thermore, the application of photochromic compounds in other
fields, e.g., fuel markers16 and security markers,17 continues to grow.
In the field of photochromic ophthalmic lenses, there are many
requirements on photochromic dyes, such as optical density and
fading speed in the dark, and so on.18 In particular, the color tone
that greatly affects the liking of the customers serves as an im-
portant factor, and a neutral tint like grey or brown is generally
considered to be the most desired color tone for most people at any
step of developing and fading during photochromism. However, it
is difficult to obtain the above neutral tint relying upon one pho-
tochromic compound only. Practically, it could be obtained by
mixing two or more photochromic compounds, which acts as the
complimentary colors in the color gamut. For example, a neutral
tint was obtained from a photochromic compound that develops
* Corresponding authors. Tel./fax: þ86 021 54743265; e-mail address: qhmeng@
sjtu.edu.cn (Q. Meng).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.01.078

Z. Wang et al. / Tetrahedron 67 (2011) 2246e2250
2247
Scheme 1. Preparation of the 3,3-diaryl-3H-naphtho[2,1-b]pyran compounds.
2. Results and discussion
the naphthopyran plane, which indicated an unconjugation re-
lationship of them and assured the colorless state of naphthopyran
compound in the closed form. On the other hand, it would prevent
2.1. Synthesis and structures
the intermolecular
pep interaction, which often leading to the
The preparation of the 3,3-diaryl-3H-naphtho[2,1-b]pyran
compounds as outlined in Scheme 1, With the purpose of en-
hancement of the color density, the benzophenone was replaced by
4,40-bis(diethylamino)benzophenone (1b) at the case of 2b, which
having diethylamino groups at the para positions of both phenyl
moieties. Interestingly, 4,40-bis(diethylamino)diphenylmethane
(2bb) was identified as a minor amount of byproduct as well as the
principal intermediate product of propargyl alcohol (2b) in the
reaction mixture using analysis methods of ESI-MS and HR-ESIMS
(2bb, calcd for C21H31N2, 311.2482, found 311.2486.), which might
result from reduction of 4,40-bis(diethylamino)benzophenone (1b)
with sodium acetylide, perhaps in a similar way of reduction using
LiAlH4.21
compact stacking and poor solubility in solvents or polymer matrix.
The morpholinyl group was directly substituted to the naphthalene
backbone, which led to the pep conjugation and therefore resulted
in an enhanced hyperchromic effect with the value of
DOD in-
creasing to six times than that of 4a (Table 1).
A carbocation generated by the protonation of the propynol and
following loss of water acts as an important intermediate to interact
with 2-naphthol, then continues to undergo the Claisen rearrange-
ment, tautomerisation to the allenyl naphthol, a 1,5-hydrogen shift
and finally a 6p electrocyclisation to complete the sequence to afford
the 3H-naphtho[2,1-b]pyran.22 The yields of 4d and 4e were rela-
tively low, which may be explained by the resonance-stabilized
carbocation affected by diethylamino groups at the para positions of
the phenyl groups. Obviously, the positive charge was delocalized
Fig. 1. The molecular configuration of 4b.
throughout the resonance system, which extended by pep conju-
gation (Scheme 2), and the selectivity of the reaction was decreased
when reaction with 2-naphthol and then led to the low yield.
Table 1
The photochromic characteristics of the colored (open) forms
Entry
lmax (nm)
Colors
D
OD
s1/2 (min)
4a
4b
4c
4d
4e
430
420
490
580
640
Yellow
Yellow
Red
Violet
Blue
0.06
0.36
0.18
0.01
0.01
17
15
11
6
<1
Scheme 2. The resonance of carbocation stabilized by electron donating substituted
amino groups.
The X-ray crystal analysis was a good tool to investigate the
effect of substitutes on the geometrical configuration and thus the
single crystal of 4b among the naphthopyran compounds was for-
tunately obtained by slow evaporation of the solvent. The molec-
ular configuration was shown in Fig. 1 and the two phenyl groups
substituted at the spiro carbon atom were repelling to both sides of
In the molecular structure of naphthopyran compounds, the
pyran ring did not fit into a perfect plane like the naphthalene plane
and the rms deviation of fitted atoms from the least-squares plane
was as large as 0.1307, which actually indicated as a non-aromatic
ring but as the core unit for photochromism. The pyran ring of 4b,
as well as the bond lengths, were clarified and shown in Fig. 2. The

2248
Z. Wang et al. / Tetrahedron 67 (2011) 2246e2250
ꢀ
bond length of O(1)eC(1) was measured as 1.456 A, and O(1)eC(13)
ꢀ
was 1.362 A, which indicated the later one could be regarded as the
double bond and the previous one as a single bond. Thus the weak
bond of O(1)eC(1) was reasonably considered as the cleavable bond
during the photochromic process. The bond length of C(2)eC(3)
ꢀ
was 1.300 A, which was a typical double bond and conjugated to
the naphthalene plane. The angle of O(1)eC(1)eC(2) was measured
as 109.7ꢀ, which indicated a typical sp3 carbon structure for C(1)
and drove the C(2)eC(1) bond stretching outside from the main
p
conjugation plane of the molecule.
C3
1.300
C2
1.443
C4
1.376
1.505
C13
1.362
109.7o
C1
Fig. 3. The absorption spectra of 4c doped PS film in dark (a) and irradiated by UV
light (b).
1.456
O1
Fig. 2. The clarified structure of the pyran ring in 4b.
reaction. This is because the high rigidity of the polymer matrix
greatly restricted the degrees of freedom of the dye molecules at
room temperature, whereas the glass transition temperature (Tg) of
the polymer was measured as high as 107 ꢀC.
2.2. The photochromic properties
In the reversible transformation upon exposure to UV radiation
(Scheme 3), the derivatives of 3,3-diaryl-3H-naphtho[2,1-b]pyran
compounds indicated the typical absorption peaks in the visible
area like 4c shown in Fig. 3, and their photochromic characteristics
of the colored forms (open forms) were listed in Table 1. From the
wavelengths of the absorption maximum of 4d and 4e0s colored
forms in the visible area, the electron donating groups at the para
positions of both 3-phenyls gives a much bigger bathochromic shift
than those derivatives, which had substitutes on the naphthalene,
and this kind of shift seems additive. Interestingly, the electron
donating group, such as morpholinyl at the 6-position on the
naphthalene (4b) led to a minor hypsochromic rather than batho-
chromic shift, but the color density was still found to be enhanced
at the same case. However, the changes of color density (DOD) of 4d
and 4e were really low and the initial color densities were high,
which limit their practical application. From the data of the s1/2 of
the colored forms, the fading speeds were increased by in-
troduction of the electron donating groups not only at the para
positions of 3-phenyl, but also on the naphthalene.
Fig. 4. First-order plots for the decay of colored forms in PS film.
R1
The origins for the non-monoexponential decay kinetics could
be described by a kinetic model taking into account the simulta-
neous relaxation of the matrix and the colored form of the com-
pound,24 and a biexponential model was used for analyzing the
kinetic data of the thermal back reaction, which had been applied
to the spirooxazine-doped organically modified doped gels by
Boilot and co-workers.25 The basic assumption of the model is that
the distribution of rate constants, k, is due to a normal distribution
of free energies. In this case, the thermal ring closure of the com-
pound was described by the following equation:
R1
UV
O
R4
R3
Heat
R2
O
R4
R3
R2
Scheme 3. The reversible transformation upon exposure to UV radiation.
2.3. The decoloration kinetics
AðtÞ ¼ A1eꢁk t þ A2eꢁk t þ Ath
1
2
The colored form reverting back to the thermodynamically
stable closed form, with a decay kinetics strongly dependent on the
environment and kinetics in solid media is normally quite complex
due to the rigidity of the environment.23 Fig. 4 presented the first-
order plots for the decoloration of 4a, 4b, and 4c in PS coating at
room temperature and the kinetic behaviors of all three PS coatings
indicated the obvious deviation from the monoexponential decay
kinetics. It could be clearly seen that the decoloration was largely
retarded by the PS matrix and was by no means a first-order
where A(t) is the optical density at the wavelength of the absorp-
tion maximum and A1 and A2 are contributions to the initial optical
density A0, Ath reflects the thermal equilibrium between the two
forms, and k1, k2 are kinetic constants.
In our study of the PS coatings doped by 4a, 4b, and 4c, the decay
kineticsof colored formsindicated the excellent agreement between
this biexponential model and the experimental data, and the
agreement of thermal decoloration of 4c doped PS coating was

Z. Wang et al. / Tetrahedron 67 (2011) 2246e2250
2249
shown as an example in Fig. 5. Table 2 presented constant values
deduced from the fit of the experimental data of the 4a, 4b, and 4c
doped PS coating samples by using biexponential process. The ki-
netic constants of k1 and k2 were obtained in range of 0.74～0.96 and
0.13～0.16, respectively. From the viewpoint of the distribution of
freevolume, the separated constants k1 and k2 werethus understood
as empirical meanvalues of ‘the fast’ and ‘the slow’ kinetic constants,
which represented by different degrees of freedom for the colored
molecule restricted by the rigid polymer matrix. The contribution of
two different dynamic paths were approximately evaluated using
the values of the A1/A2 ratio in range of 0.44～0.58 for the three
samples, which might be considered that the slow kinetics was
relatively predominant dynamic path in the decoloration process.
Thus, the shrinking cage around the trapped molecules rendered the
thermal ring closure more difficult and less effect of substitutes on
the fading kinetics was observed in PS matrices.
in CDCl3 unless otherwise stated using (CH3)4Si as an internal
standard, and J values are given in Hertz. LCeMS was performed on
an HP 1100 HPLC (Agilent), interfaced with a tripleequadruple
mass spectrometer equipped with an ESI or EI ion source and an
in-line diode-array UVevis detector. HRMS were recorded on
a MAT95XP instrument (Thermo).
4.2. Preparation of 3,3-diaryl-3H-naphtho[2,1-b]pyrans (4),
general procedure
Preparation methods of 3,3-diaryl-3H-naphtho[2,1-b]pyrans
were generally based on condensation reactions taking place in the
apolar solvent as toluene under acid catalysis, which starting from
suitable naphthols and propargyl alcohols.26e28
Thepropargylalcohol (2) was preparedfromthe diaryl ketone (1)
as outlined in Scheme 1. 10 mmol diaryl ketone (1) was dissolved in
50 mL dry THF and was added dropwise to a solution of 50 mmol
sodium acetylide inTHF below0 ꢀC. Themixturewas then allowed to
stir at room temperature for about 3 h until none of the diaryl ketone
(1) remained by TLC examination of the reaction mixture. The re-
action mixture was poured into iced water for separation. The or-
ganic phase was collected and followed by washing with water
(3ꢂ50 mL) and then dried (anhyd Na2SO4). The propargyl alcohol
was then obtained in the yield of about 80% after the short flash
chromatography and was used for subsequent procedure directly.27
3 mmol propargyl alcohol (2), 3 mmol 2-naphthol derivative (3),
and 1.0 g p-toluenesulfonic acid (TsOH) were dissolved in 50 mL
toluene. The reaction mixture was refluxed for about 2 h until TLC
examination indicated that none of the propargyl alcohol
remained. The mixture was cooled to room temperature and
washed with 1 mol Lꢁ1 NaOH solution (2ꢂ50 mL) and water. After
drying with anhyd Na2SO4, removal of the toluene by vacuum
evaporation gave a dark gum. The pure naphthopyran product was
obtained by elution from silica using 10% ethyl acetate/hexane. The
following naphthopyrans were prepared using this method:
Fig. 5. The biexponential model and the experimental thermal decoloration of 4c
doped PS film ( : data measured; d: the biexponential model fitted).
4.2.1. 3,3-Diphenyl-3H-naphtho[2,1-b]pyran (4a). Compound 4a
was prepared from 2a and 3c as the white microcrystal, (0.75 g, 75%
yield), mp 158e160 ꢀC (Lit. mp 158e159 ꢀC28). 1H NMR (400 MHz,
Table 2
The parameters of fitted biexponential models for 4a, 4b, and 4c in PS film
CDCl3)
d
8.06 (d, J¼7.6 Hz, 1H), 7.76e7.80 (t, J¼8.0 Hz, 2H), 7.47 (m,
Entry
Fast path
Slow path
A1/A2
Ath
6H), 7.29e7.36 (m, 6H), 7.23 (m, 2H), 6.58 (d, J¼10 Hz, 2H); ESI-MS
k1/minꢁ1
s1/2∕min
k2/minꢁ1
s1/2∕min
(m/z): 334.2 (Mþ1).
4a
4b
4c
0.96
0.77
0.74
0.7
0.9
0.9
0.16
0.14
0.13
4.3
5.0
5.3
0.58
0.44
0.46
0.056
0.182
0.092
4.2.2. 3,3-Diphenyl-6-morpholino-3H-naphtho[2,1-b]pyran
(4b). Compound 4b was prepared from 2a and 3c as the light
yellow microcrystal, (0.74 g, 59% yield), mp 156e158 ꢀC. 1H NMR
(400 MHz, CDCl3)
d
8.07 (d, J¼8.8 Hz, 1H), 7.94 (d, J¼8.0 Hz, 1H),
3. Conclusion
7.42e7.50 (m, 2H), 7.24e7.30 (m,10H), 7.24 (d, J¼2.8 Hz,1H), 6.83 (s,
1H), 6.20 (d, J¼10.0 Hz, 1H), 3.95 (t, J¼5.2 Hz, 4H), 3.09 (t, J¼4.8 Hz,
Five photochromic naphthopyran compounds with functional
substituents were prepared. The chemical structures of the com-
pounds were confirmed by NMR and MS. The crystal structure of
3,3-diphenyl-6-morpholinyl-3H-naphtho[2,1-b]pyran (4b) was
determined and the relationship between the pyran structure and
photochromism was discussed. 4c, 4d, and 4e showed significant
bathochromic shifts in the spectra of the open forms. Among them,
4b was considered to be the best one due to the large DOD of col-
ored forms. The decoloration kinetics of colored forms of the 4a, 4b,
and 4c doped in PS coating were fitted to the biexponential model.
4H); 13C NMR (100 MHz, CDCl3)
d 151.6, 151.1, 145.2, 131.2, 128.3,
127.7, 127.2, 126.9, 125.9, 124.7, 124.1, 123.3, 122.1, 119.6, 110.1, 107.7,
82.9, 67.5, 53.6; ESI-MS (m/z): 420.1 (MþH); HR-EIMS calcd for
C29H25NO2, 419.1885, found 419.1884.
Slow evaporation of ethyl acetate solution of 4b gave crystals
after several days. The single crystal was collected by filtration and
used in the X-ray crystal analysis. X-ray diffraction data were col-
lected at 293 K on a CAD4 DIFFACTIS 586 diffractometer with
ꢀ
graphite monochromated Mo
Ka
radiation
(l
¼0.71073 A),
m
¼0.080 mmꢁ1. Crystal data for 4b: C29H25NO2, monoclinic, space
group P21/c, a¼16.110(5) Ǻ, b¼6.511(2) Ǻ, c¼23.934(6) Ǻ,
4. Experiment
4.1. General
b
¼119.984(15)ꢀ, Volume¼2174.5(11) Ǻ3, Z¼4, Dcalcd¼1.281 Mg/m3,
10099 reflections collected, 4677 reflections independent, R(int)¼
0.0919, 1874 observed reflections (>2
s
), R1¼0.1297 [F2>2
s
(F2)],
u
R2¼0.1591 (all data). The crystal structure was solved and refined
All chemicals were commercial available. NMR spectra were
recorded on a Mercury plus 400 instrument (Varian) for solutions
with standard techniques.29 All U values of H-atoms were refined to
realistic values. Crystallographic data for this structure have been

2250
Z. Wang et al. / Tetrahedron 67 (2011) 2246e2250
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC804456.
(PG Instruments Limited) coupled with flash photolysis and the
film was placed in a holder room temperature. The photochromic
optical density
DOD is defined as the change of absorbance (A) at
4.2.3. 3-(4-Piperidinophenyl)-3-phenyl–6-morpholino-3H-naphtho-
[2,1-b]pyran, (4c). Compound 4c was prepared from 2c and 3c as
the light orange microcrystal, 0.77 g, 51% yield, mp 170e172 ꢀC. 1H
the photostationary state under UV irradiation (8 W lamp, 365 nm).
The decoloration rate (k) and half-life time (s1/2) were deduced
from the coloring-fading curve.
NMR (400 MHz, CDCl3)
d
7.95 (d, J¼6.4 Hz, 1H), 7.20e7.60 (m, 8H),
7.02 (d, J¼8 Hz, 1H), 6.80 (d, J¼6 Hz, 1H), 6.14 (s, 1H), 6.10 (s, 1H),
3.96 (t, J¼10 Hz, 4H), 2.22 (t, J¼8 Hz, 8H), 1.56 (m, 6H); 13C NMR
Acknowledgements
(100 MHz, CDCl3) d 151.6,151.1,146.2, 131.2, 128.3, 127.5,127.1, 126.9,
This work was supported by the National Nature Science
Foundation of China (No. 20972095) and Science and Technology
Commission of Shanghai Municipality (No. 09JC1407800). We
thank Dr. Yanlong Wang and Wenjuan Yu (Instrumental Analysis
Center, Shanghai Jiao Tong University) for the provision of a mass
spectrometry service.
126.6, 124.6, 124.1, 123.3, 122.4, 119.1, 116.0, 110.2, 83.1, 67.5, 54.0,
50.4, 26.0, 24.2; ESI-MS (m/z): 503.2 (MþH); HR-ESIMS calcd for
C34H35N2O2, 503.2699, found 503.2697.
4.2.4. 3,3-Di(4-diethylaminophenyl)-3H-naphtho[2,1-b]pyran,
(4d). Compound 4d was prepared from 2b and 3a as the light green
solid, 0.25 g, 18%, yield, mp 193e195 ꢀC. 1H NMR (400 MHz, CDCl3)
d
7.95 (d, J¼6.4 Hz, 1H), 7.59e7.72 (m, 5H), 7.10e7.25 (m, 8H), 6.58
(d, J¼8 Hz, 1H), 6.24 (d, J¼8.8 Hz, 1H), 3.31 (m, 8H), 1.12 (t, J¼4.8 Hz,
12H); 13C NMR (100 MHz, CDCl3)
151.2, 147.3, 132.2, 130.1, 129.9,
References and notes
d
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44.6, 12.8; ESI-MS (m/z): 477.3 (MþH); HR-ESIMS calcd for
C33H37N2O, 477.2906, Found 477.2900.
4.2.5. 3,3-Di(4-diethylaminophenyl)-5-(N-phenylamido-3H-naphtho
[2,1-b]pyran), (4e). Compound 4e was prepared from 2b and 3b as
the light blue microcrystal, 0.21 g, 12%, yield, mp 180e182 ꢀC. 1H
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NMR (400 MHz, CDCl3) d 8.70 (s,1H), 7.98 (s,1H), 7.30e7.60 (m, 5H),
7.22 (m, 4H), 7.05 (m, 8H), 6.60 (d, J¼10 Hz,1H), 6.32 (d, J¼10 Hz,1H),
3.30 (m,8H),1.12 (t, J¼8 Hz,12H); 13C NMR (100 MHz, CDCl3)
d 162.6,
148.2,132.9,132.4,131.8,130.7,129.9,129.2,129.1,128.1,124.2,124.0,
122.0, 121.6, 121.0, 118.9, 111.4, 77.1, 44.5, 12.5; ESI-MS (m/z): 596.3
(MþH); HR-ESIMS calcd for C40H42N3O2, 596.3272, found 596.3264.
4.2.6. 4-(4-(Diethylamino)benzyl)-N,N-diethylbenzenamine,
(2bb). The byproduct of the less polar fraction during preparation
of 2b from 1b, brown oil, 0.11 g, 3%, yield. 1H NMR (400 MHz, CDCl3)
14. Glebov, E. M.; Smolentsev, A. B.; Korolev, V. V.; Plyusnin, V. F.; Chebunkova, A.
V.; Paramonov, S. V.; Fedorova, O. A.; Lokshin, V.; Samat, A. J. Phys. Org. Chem.
2009, 22, 537e545.
15. Irie, M.; Kobatake, S.; Horichi, M. Science 2001, 291, 1769e1772.
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17. Camus, M. Eur. Patent No. 488902, 1992.
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20. Gabbutt, C. D.; Heron, B. M.; Instone, A. C.; Horton, P. N.; Hursthouse, M. B.
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21. Arient, J.; Dvorak, J. Chem. Listy Vedu Prum. 1954, 48, 1581e1582.
22. Gabbutt, C. D.; Heron, B. M.; Instone, A. C.; Thomas, D. A.; Partington, S. M.;
Hursthouse, M. B.; Gelbrich, T. Eur. J. Org. Chem. 2003, 1220e1230.
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d
6.91 (d, J¼8 Hz, 4H), 6.50 (d, J¼8 Hz, 4H), 3.80 (s, 2H), 3.31 (m, 8H),
1.15 (t, J¼6 Hz, 12H); ESI-MS (m/z): 311.2 (MþH); HR-ESIMS, calcd
for C21H31N2, 311.2482, found: 311.2486.
4.3. Preparation of polymer films doped by the photochromic
compounds
The polystyrene (PS) with the Tg of 107 ꢀC and the photochromic
compoundswereweighted and dissolvedintoluene. Thesolutionwas
placed on a glass slide in horizontal and the solvent was allowed to
evaporate overnight at roomtemperature. Then thefilmwasremoved
from the glass slide and the film thickness was measured with a mi-
crometer. The thickness of the film was kept about 10 mm by con-
trollingthesolutionused,andtheconcentrationsofthephotochromic
compounds in the polymer film were maintained in 0.1% w/w.
25. Biteau, J.; Chaput, F.; Boilot, J. P. J. Phys. Chem. 1996, 100, 9024e9031.
26. Pozzo, J. L.; Samat, A.; Guglielmetti, R.; Dubest, R.; Aubard, J. Helv. Chim. Acta
1997, 80, 725e738.
27. Gabbutt, C. D.; Hepworth, J. D.; Heron, B. M.; Partington, S. E.; Thomas, D. A.
Dyes Pigm. 2001, 49, 65e74.
28. Alberti, A.; Teral, Y.; Roubaud, G.; Faure, R.; Campredon, M. Dyes and Pigments
2009, 81, 85e90.
4.4. The spectral and kinetic measurements
29. Sheldrick, G. M. SHELXS-90 Crystal Structure Solution Program; University of
Gottingen: Germany, 1990; Sheldrick, G.M. SHELXL-97 Crystal Structure Re-
finement Program; University of Gottingen: Germany, 1997.
The spectral and kinetic measurements were performed in
doped polymer films using a TU1901 UVevis spectrophotometer