Rapid fading of 3H-naphtho[2,1-b]pyrans with protonation of N,N-disubstituted group

Article abstract of DOI:10.1039/c1jm11267h

We present the rapid fading of photochromic 3H-naphtho[2,1-b]pyrans at ambient temperature by protonation of N,N-disubstituted group. It is found that photochromic 3H-naphtho[2,1-b]pyrans with a N,N-disubstituted group are converted to protonated 3H-naphtho[2,1-b]pyran by treatment with acid, and the protonated 3H-naphtho[2,1-b]pyrans show rapid fading in both solution and a rigid polymer matrix at ambient temperature. It is also found that the protonated 3H-naphtho[2,1-b]pyrans exhibit similar absorption and fatigue resistance compared to their original compounds.

Full text of DOI:10.1039/c1jm11267h

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PAPER
Rapid fading of 3H-naphtho[2,1-b]pyrans with protonation of N,N-
disubstituted group
*
Shulie Han and Yi Chen
Received 25th March 2011, Accepted 13th June 2011
DOI: 10.1039/c1jm11267h
We present the rapid fading of photochromic 3H-naphtho[2,1-b]pyrans at ambient temperature by
protonation of N,N-disubstituted group. It is found that photochromic 3H-naphtho[2,1-b]pyrans with
a N,N-disubstituted group are converted to protonated 3H-naphtho[2,1-b]pyran by treatment with
acid, and the protonated 3H-naphtho[2,1-b]pyrans show rapid fading in both solution and a rigid
polymer matrix at ambient temperature. It is also found that the protonated 3H-naphtho[2,1-b]pyrans
exhibit similar absorption and fatigue resistance compared to their original compounds.
original compounds in solution as well as in rigid polymer
Introduction
matrix, which provides a new strategy for increasing the fading
speed of 3H-naphtho[2,1-b]pyrans at ambient temperature
without changing their absorption and fatigue resistance.
Photochromic naphthopyrans with rapid fade at ambient
temperature are of great importance with regards to commercial
application used as ophthalmic lenses.1–8 Consequently, a variety
of strategies have been employed to achieve this purpose. There
are two strategies extensively explored for enhancement of fading
speed of naphthopyrans at ambient temperature, one is to
modify the intrinsic properties of molecules including electronic
nature of substituents and structure of naphthopyrans,9–11 the
other is to change the local host environment and the media that
incorporate them.12–15
Experimental
General
1H NMR spectra were recorded at 400 MHz with tetrame-
thylsilane (TMS) as an internal reference and CDCl3 as solvent.
Mass spectra were recorded with a GC–TOF MS spectrometer.
UV absorption spectra were measured on an absorption spec-
trophotometer (Hitachi U-3010). Coloration was carried out
One of the major interests in our group has focused on
developing new strategy for increasing fading speed of naph-
thopyrans at ambient temperature. In our previous studies,16,17
we found that 3H-naphtho[2,1-b]pyrans containing N,N-disub-
stituted group in the para position of aryl ring at 3-position
showed faster fade than that of 3H-naphtho[2,1-b]pyrans
without N,N-disubstituted group at ambient temperature.
Herein we disclose the first example of increasing the fading
speed of 3H-naphtho[2,1-b]pyrans by protonation of N,N-
disubstituted group in the para position of aryl ring at 3-position
at ambient temperature. As illustrated in Scheme 1, 3H-naphtho
[2,1-b]pyrans containing N,N-disubstituted group (1a–3a) are
easily converted to protonated 3H-naphtho[2,1-b]pyrans (1aH–
3aH) by protonation of N,N-disubstituent group with acid. It is
found that the protonated 3H-naphtho[2,1-b]pyrans exhibit
photochromism in both solution and a rigid polymer matrix, and
the fading speed of steady-state is significantly increased at
ambient temperature in comparison to the original compounds.
Moreover, it is also found that the protonated naphthopyrans
show similar absorption properties and fatigue resistance to their
Key Laboratory of Photochemical Conversion and Optoelectronic
Materials, Technical Institute of Physics and Chemistry, Chinese
Academy of Sciences, Beijing, 100190, China. E-mail: yichencas@yahoo.
com.cn; Fax: +86 10 6487 9375; Tel: +86 10 8254 3595
Scheme 1 Protonated 3H-naphtho[2,1-b]pyrans 1aH–3aH resulted from
the protonation of 3H-naphtho[2,1-b]pyrans 1a–3a by treatment
with acid.
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with a UV light (l ¼ 254 nm, intensity: 4.3 mW cmꢀ2). All
chemicals for synthesis were purchased from commercial
suppliers, and solvents were purified according to standard
procedures. Reactions were monitored by TLC silica gel plate
60F-254). Column chromatography was performed on silica gel
(Merck, 70–230 mesh). PMMA thin film was prepared as
following: naphthopyrans (1.0 mg) was dissolved in 2.0 ml
PMMA–cyclohexanone solution (10%, w/w). The film was
obtained by spin coating on quartz glass with a gradient of
700 rpm (10 s) followed 1200 rpm (30 s) (25 ꢁC) and dried in air
and kept in the darkness at room temperature. The concentration
of thin film is about 1.2 ꢂ 10ꢀ5 mol/g.
4H), 7.09 (dd, J ¼ 14.5, 8.2 Hz, 5H), 6.99 (t, J ¼ 7.9 Hz, 4H), 6.29
(d, J ¼ 9.9 Hz, 1H). HRMS: m/z (M+): 551.22.
Protonated compounds 1aH–3aH were prepared as follows:
To solution of 1a–3a (10 mmol) in CH2Cl2 (10 ml) was added
CF3COOH (1.2 mmol), the mixture solution was stirred at room
temperature for 10 min in the dark. The target compound 1aH–
3aH were obtained after evaporation of the solvent under
reduced pressure without further purification.
1aH: 1H NMR (400 MHz, CDCl3, d): 8.21 (d, J ¼ 8.6 Hz, 1H),
8.00 (d, J ¼ 8.5 Hz, 1H), 7.82 (t, J ¼ 8.9 Hz, 2H), 7.66 (ddd, J ¼
22.9, 14.8, 8.5 Hz, 5H), 7.54–7.31 (m, 8H), 7.09 (d, J ¼ 8.8 Hz,
1H), 3.19 (s, 6H). HRMS: 427.955.
2aH: 1H NMR (400 MHz, CDCl3, d): 8.45 (d, J ¼ 8.7 Hz, 1H),
8.27 (d, J ¼ 8.6 Hz, 1H), 7.99 (d, J ¼ 8.5 Hz, 1H), 7.89 (d, J ¼ 8.1
Hz, 1H), 7.72 (d, (d, J ¼ 8.2 Hz, 1H), 7.60 (t, J ¼ 8.9, 8.8 Hz, 1H),
7.62 (d, J ¼ 8.9 Hz, 1H), 7.50–7.34 (m, 10H), 7.07 (d, J ¼ 8.8 Hz,
1H), 6.17 (d, J ¼ 3.7 Hz, 1H), 3.40 (s, 6H).
Material
Naphthopyrans 1a18 and 2a17 were prepared previously in our
laboratory, and 3a was prepared according to the synthetic route
described in Scheme 2 and the detailed procedures were
according to the literature19 which summarized as follows: 1,2-
Diaryl-2-ol was synthesized by starting from 1-naphthoyl chlo-
ride, which reacted with N,N-diphenylaniline by Friedel–Crafts
reaction to afford 1,1-diarylketone, followed by treatment with
soldium acetylide in an ether solvent at ambient temperature.
The target compound 3a was obtained by the condensation of
1,2-diaryl-2-propyn-1-ol with 2-naphthol in the presence of
pyridinium para-toluenesulfonate (PPTS) as the catalyst. The
general procedure is as follows: treatment of 1,2-diaryl-2-pro-
pyn-1-ol (1.1 equiv) and 2-naphthol in 1,2-dichloroethane with 2
equivalent of (MeO)3CH and 5 mol % PPTS (pyridinium para-
toluensulfonate) furnished the desired product.
1a: Total yield: 28%. 1H NMR (400 MHz, CDCl3, d): 8.31 (d, J
¼ 8.6 Hz, 1H), 7.99 (d, J ¼ 8.5 Hz, 1H), 7.82 (d, J ¼ 8.0 Hz, 1H),
7.78 (d, J ¼ 8.1 Hz, 1H), 7.60 (d, J ¼ 7.6 Hz, 2H), 7.59 (d, J ¼ 8.9
Hz, 1H), 7.46–7.44 (t, J ¼ 3.7, 3.8 Hz, 1H), 7.39–7.36 (m, 2H),
7.34–7.30 (m, 5H), 7.12 (d, J ¼ 8.8 Hz, 1H), 6.66 (d, J ¼ 8.9 Hz,
2H), 6.31 (d, J ¼ 9.9 Hz, 1H), 2.91 (s, 6H). HRMS: m/z (M+ + 1):
428.2.
3aH: 1H NMR (400 MHz, CDCl3, d): 8.37 (d, J ¼ 8.4 Hz, 1H),
8.01 (d, J ¼ 8.4 Hz, 1H), 7.83 (d, J ¼ 8.6 Hz, 1H), 7.78 (d, J ¼
8.2 Hz, 1H), 7.71 (d, J ¼ 7.6 Hz, 2H), 7.60 (d, J ¼ 8.8 Hz, 1H),
7.48–7.31 (m, 8H), 7.22 (t, J ¼ 8.3, 8.1 Hz, 4H), 7.08–7.06 (m,
5H), 6.99–6.97 (m, 4H), 6.30 (d, J ¼ 9.9 Hz, 1H).
Results and discussion
Treatment of naphthopyrans 1a–3a with CF3COOH in CH2Cl2
yielded protonated naphthopyrans 1aH–3aH in quantitativity,
and their structures were characterized by 1H NMR spectra. As it
is known,20–22 the signals arising from the protons of N,N-
disubstituted groups shift downfield, and the signals arising from
the protons of benzene ring shift upfield when N,N-disubstituted
groups are protonated. As compared to 1a, the signals arising
from the protons of N,N-disubstituted groups of 1aH shifted
downfield from 2.91 ppm to 3.19 ppm, and the signals arising
from the protons of benzene ring of 1aH shifted upfield from 8.31
ppm to 8.21 ppm. Similar results were obtained with compounds
2aH and 3aH.
All protonated compounds 1aH–3aH showed photochromism
in both solution and PMMA thin film. The ring-opening and
ring-closing isomerization was illustrated in Scheme 3,23,24 and
their absorption data were presented in Table 1. By comparison
with the absorption of naphthopyrans 1b–3b, it was found that
the absorption spectral of protonated naphthopyrans 1bH–3bH
showed similar profile to these of 1b–3b in both solution and in
PMMA thin film (Fig. 1), and no significant change was detected
except for optical density (O.D.). As presented in Table 1, it was
found that the optical density of 1bH (O.D.a ¼ 0.390) is
much smaller than that of 1b (O.D.a ¼ 0.577) in the solution at
2a: Total yield: 38%. 1H NMR (400 MHz, CDCl3, d): 8.32 (d,
J ¼ 8.6 Hz, 1H), 8.23 (d, J ¼ 8.4 Hz, 1H), 7.99 (d, J ¼ 8.5 Hz,
1H), 7.69 (d, J ¼ 8.1 Hz, 1H), 7.58 (d, J ¼ 8.8 Hz, 1H), 7.54–7.27
(m, 11H), 7.10 (d, J ¼ 8.8 Hz, 1H), 6.91 (d, J ¼ 8.0 Hz, 1H), 6.22
(d, J ¼ 9.9 Hz, 1H), 2.85 (s, 6H). MS: m/z [M+ + 1]: 428.4.
3a: Total yield: 30%. 1H NMR (400 MHz, CDCl3, d): 8.36 (d,
J ¼ 8.5 Hz, 1H), 8.00 (d, J ¼ 8.4 Hz, 1H), 7.84–7.69 (m, 4H), 7.60
(d, J ¼ 8.9 Hz, 1H), 7.50–7.30 (m, 8H), 7.22 (dd, J ¼ 8.3, 7.5 Hz,
Scheme 3 Photochromism of 1a–3a and 1aH–3aH in both solution and
Scheme 2 Synthesis of 3a.
in PMMA thin film.
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Table 1 Absorption data of 1b–3b and 1bH–3bH in both solution
(CH3CN, 2 ꢂ 10ꢀ5 M) and in PMMA thin film (1.2 ꢂ 10ꢀ5 mol gꢀ1
experiments. As presented in Table 1, a little small decrease of
optical density of 1bH (O. D.b ¼ 0.553) was obtained as
compared to 1b (O.D.b ¼ 0.577) when optical density was
detected at local wavelength (lmax). Similarly, a small decrease in
optical density of 1bH–3bH was also obtained in PMMA thin
film as compared to their original compounds 1b–3b due to
slower fading speed in a rigid polymer matrix than in solution at
ambient temperature.
It is known23 that the colored forms of naphthopyrans fade
back to colorless forms via two steps: transoid-cis to colorless
form (k1) and transoid-trans to colorless form (k2). Convenient
measures of fade speed are the T1/2 and T3/4 values,25 which are
the time it takes from the optical density to reduce by 1/2 and 3/4
of the initial optical density of the colored form, and the smaller
T1/2 and T3/4, the faster the fade. Table 2 represents the fading
kinetics of 1bH–3bH in both solution and PMMA thin film at
ambient temperature. As compared to naphthopyrans 1b–3b, the
fading speed of protonated naphthopyrans 1bH–3bH was much
faster than that of 1b–3b in both solution and in PMMA thin
)
Compound
Media
lmax (nm)
O. D.a
O. D.b
1b
Solution
Film
Solution
Film
Solution
Film
Solution
Film
Solution
Film
Solution
Film
542
550
542
550
415
420
415
420
518
526
518
526
0.577
1.074
0.390
0.832
0.229
0.569
0.142
0.427
0.525
0.714
0.375
0.60
0.640
1.074
0.553
0.832
0.240
0.569
0.232
0.427
0.531
0.714
0.526
0.60
1bH
2b
2bH
3b
3bH
a
Optical density was measured by scanning the full absorption spectral
b
(200–700 nm) at ambient temperature (15 ꢁC). Optical density was
measured by detection of local maximum absorption (lmax) at ambient
temperature (15 ꢁC).
film. It was found that the fading time of 1bH (T1/2 ¼ 8 s, T3/4
¼
16 s) is much shorter than that of 1b (T1/2 ¼ 62 s, T3/4 ¼ 220 s),
and only about 1/8 original fading time was obtained. Similar
results were observed when the media was changed from solution
to a rigid polymer. The fading time of 1bH (T1/2 ¼ 24 s, T3/4 ¼ 43
s) was also much shorter than that of 1b (T1/2 ¼ 70 s and T3/4
¼
195 s) in PMMA thin film. The data presented in Table 2 indi-
cated that the protonated naphthopyrans show much faster fade
than their original naphthopyrans in both solution and in a rigid
polymer matrix.
The fading speed of protonated naphthopyrans 1bH–3bH
being much faster than that of naphthopyrans 1b–3b was also
confirmed by the fading rate constant. Comparing the kinetics of
fading speed found that the fading rate constants of 1bH (in
solution: k1 ¼ 6.0 ꢂ 10ꢀ2 sꢀ1, in film: k1 ¼ 2.3 ꢂ 10ꢀ2 sꢀ1) are
larger than these of 1b (in solution: k1 ¼ 0.92 ꢂ 10ꢀ2 sꢀ1, in film:
k1 ¼ 0.8 ꢂ 10ꢀ2 sꢀ1) in both solution and in PMMA thin film
(Fig. 2), which resulted in the fading speed of 1bH being much
faster than that of 1b. Similar results were obtained with other
protonated naphthopyrans 2bH and 3bH, as compared to
naphthopyrans 2b and 3b, the fading rate constants of 2bH and
3bH are much larger than these of 2b and 3b, respectively, in both
solution and a rigid polymer matrix (Table 2).
Further investigation of protonated naphthopyrans 1bH–3bH
being faster fade than that of 1b–3b at ambient temperature was
explored. Control experiments found that 1bH–3bH showed
more thermal instablity than that of 1b–3b at ambient tempera-
ture. As presented in Fig. 3, it took about 20 min for 1bH to
completely bleach to colorless in PMMA thin film at 20 ꢁC, but it
took 80 min for 1b to bleach to colorless under the same
conditions. The time for completed bleach of both is shortened
with raising the temperature, and it was found that the bleach
time is almost the same (less than 1 min) when the temperature is
over 70 ꢁC. It was noted that different results were obtained when
both the protonated compounds 1bH–3bH and their original
compounds 1b–3b were bleached with visible light irradiation, as
presented in Fig. 4, the fading rate constant of 1bH (k1 ¼ 5.1 ꢂ
10ꢀ2 sꢀ1) is smaller than that of 1b (k1 ¼ 7.6 ꢂ 10ꢀ2 sꢀ1) in the
same conditions with visible light irradiation, which is contrary
to that with thermal bleach. In addition, control experiments also
Fig. 1 Absorption of 1bH (white) and 1b (black) in solution (2 ꢂ 10ꢀ5
M, CH3CN) and in PMMA thin film (1.2 ꢂ 10ꢀ5 mol gꢀ1) at photo-steady
state.
photo-steady state, and similar results were obtained by
comparison of 2bH and 3bH with 2b and 3b. The large decrease
in optical density of 1bH is probably due to faster fade of 1bH
than that of 1b at ambient temperature, and time consumption of
scanning absorption spectrum results in the decrease of optical
density. The suggestion was confirmed by the control
12404 | J. Mater. Chem., 2011, 21, 12402–12406
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Table 2 Kinetics data of 1b–3b and 1bH–3bH in both solution (CH3CN, 2 ꢂ 10ꢀ5 M) and in PMMA thin film (1.2 ꢂ 10ꢀ5 mol gꢀ1
)
Compound
Media
lmax/nm
O. D.c
aT1/2 (s)
aT3/4 (s)
bK1 (ꢂ 10ꢀ2
)
bK2 (ꢂ 10ꢀ4
)
1b
Solution
Film
Solution
Film
Solution
Film
Solution
Film
Solution
Film
Solution
Film
542
550
542
550
415
420
415
420
518
526
518
526
0.640
1.074
0.553
0.832
0.240
0.569
0.232
0.427
0.531
0.714
0.526
0.60
62
70
8
24
58
64
7
14
110
420
31
115
220
195
16
0.9
0.8
6.0
2.3
1.0
0.9
6.4
4.0
0.6
0.2
2.2
0.5
1.8
2.0
7.2
2.9
4.5
4.6
4.1
2.8
1.1
0.7
1.9
3.2
1bH
2b
43
135
162
15
2bH
3b
32
238
1230
61
3bH
350
a
Samples initially irradiated at 254 nm till photo-steady state (40 s), then thermal decoloration monitored at lmax of the colored form at room
temperature in the dark. The fading rate constant was obtained using the biexponetial decoloration model according to the standard biexponential
b
c
equation.26,27 The optical density was obtained by measuring the local maximum wavelength at ambient temperature (15 ꢁC).
Fig. 3 The completed bleach of 1bH (black) and 1b (white) in PMMA
thin film at different temperature.
Fig. 2 The fading kinetics of 1bH (black) and 1b (white) in both solution
(CH3CN) and PMMA thin film at ambient temperature (15 ꢁC).
confirmed that the protonation of naphthopyran with amino
group also produced the protonated compound 4aH (Scheme 4),
Fig. 4 The fading kinetics of 1bH (black) and 1b (white) in PMMA thin
whose fading speed was also increased significantly in both
solution (4a: k1 ¼ 1.3 ꢂ 10ꢀ2 sꢀ1, 4aH: k1 ¼ 2.1 ꢂ 10ꢀ2 sꢀ1) and
PMMA thin film (4a: k1 ¼ 1.2 ꢂ 10ꢀ2 sꢀ1, 4aH: k1 ¼ 1.8 ꢂ 10ꢀ2
sꢀ1), but no significant change of fading speed was detected when
naphthopyrans without amino substituent group such as 5a and
6a (Scheme 4) were treated with acid.
film with visible light irradiation (l $ 400 nm).
1b–3b in both solution and a rigid polymer matrix. No significant
degradation was detected after 5 cycles of coloration/decolor-
ation when 1aH was irradiated up to photosteady state (1bH)
with UV light, and the colored 1bH was completely bleached
back (kept in the dark) to colorless (1aH) at ambient temperature
The preliminary investigation showed that the protonated
naphthopyrans 1bH–3bH exhibited similar fatigue resistance to
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enhancing the fading speed of naphthopyrans without changing
the color and fatigue resistance.
Acknowledgements
This work was supported by National Basic Research Program
of China (2010CB934103) and the National Nature Science
Foundation of China (21073214).
Scheme 4 Chemical structures of naphthopyrans 4a, 4aH, 5a and 6a.
Notes and references
1 M.-J. P. R. Queiroz, A. S. Abreu, P. M. T. Ferreira, M. Manuel
Olievira, R. Dubest, J. Aubard and A. A. Samat, Org. Lett., 2005,
7, 4811.
2 J. N. Moorthy, P. Venkatakrishnan, S. Samanta and D. K. Kumar,
Org. Lett., 2007, 9, 919.
3 W. Zhao and E. M. Carreira, J. Am. Chem. Soc., 2002, 124, 1582.
4 N. F. S. A. Cerqueria, A. M. F. Oliveria-Campos, P. J. Coelho,
L. H. Melode Carvalho, A. Samat and R. Gugliemetti, Helv. Chim.
Acta, 2002, 85, 442.
5 B. M. Heron, C. D. Gabbutt, J. D. Hepworth, S. M. Partington,
D. A. Clarke and S. N. Corns, WO, 2001/12619A1, 2001.
6 D. A. Clarke, B. M. Heron, C. D. Gabbutt, J. D. Hepworth,
S. M. Partington and S. N. Corns, US Pat., 6 248 264 B241, 2001.
7 D. B. Knowles, US Pat., 5384077, 1995.
8 B. Van Gemert, M. P. Bergomi, US Pat., 5066818, 1991.
9 M. Frigoli, C. Moustrou, A. Samat and R. Guglielmetti, Eur. J. Org.
Chem., 2003, 2799.
10 W. Zhao and E. M. Carreira, Chem.–Eur. J., 2007, 13, 2671.
11 J.-L. Coelho, M. A. Salvador, M. Manuel Oliveira and
L. M. Carvalho, J. Photochem. Photobiol., A, 2005, 172, 300.
12 R. A. Evans, T. L. Hanley, M. A. Skidmore, T. P. Davis, G. K. Such,
L. H. Yee, G. E. Ball and D. A. Lewis, Nat. Mater., 2005, 41, 249.
13 F. Ercole, N. Malic, S. Harrisson, T. P. Davis and R. A. Evans,
Macromolecules, 2010, 43, 249.
14 N. Malic, J. A. Campbell and R. A. Evans, Macromolecules, 2008, 41,
1206.
15 F. Ercole, T. P. Davis and R. A. Evans, Macromolecules, 2009, 42,
1500.
16 K. Guo and Y. Chen, J. Mater. Chem., 2010, 20, 4193.
17 S. Han and Y. Chen, J. Mater. Chem., 2011, 21, 4961.
18 K. Guo and Y. Chen, J. Phys. Org. Chem., 2010, 23, 207.
19 W. Zhao and E. M. Carreia, Org. Lett., 2006, 8, 99.
20 X. Meng, W. Zhu, Z. Guo, J. Wang and H. Tian, Tetrahedron, 2006,
62, 9840.
Fig. 5 The fatigue resistance of 1bH in CH3CN (white) and in PMMA
thin film (black) (detecting optical denisty at lmax ¼ 542 nm in solution,
and lmax ¼ 550 nm in PMMA thin film).
(Fig. 5). Similar results were obtained with other protonated
naphthopyrans 2aH and 3aH. In addition, control experiments
demonstrated that counter anion CF3COOꢀ had no effect on the
fading speed of naphthopyrans, and no significant change in
fading speed of 1bH was detected when CF3COONa was added
to the solution of 1a. Furthermore, 1aH–3aH could be obtained
by treatment of 1a–3a with other strong acids (acetic acid, 4-
chlorobenzoic acid, 4-nitrobenzoic acid), and the protonated
1bH–3bH also showed rapid fading speed at ambient tempera-
ture in both solution and a rigid polymer matrix.
21 K. Yang, L. P. Chen, Y. Q. Cai, N. Hiraoka, S. Li, J. F. Zhao,
D. W. Shen, H. F. Song, H. Tian, L. H. Bai, Z. H. Chen,
Z. G. Shuai and D. L. Feng, Phys. Rev. Lett., 2007, 98, 036404.
22 J. T. C. Wojtyk, A. Wasey, N.-N. Xiao, P. M. Kazmaier, S. Hoz,
C. Yu, R. P. Lemieux and E. Buncel, J. Phys. Chem. A, 2007, 111,
2511.
23 Organic Photochromic and Thermochromic Compounds. ed. J. C.
Crano and R. J. Gugliemetti, Plenum Press, New York, 1999.
24 Photochromism: Molecules and Systems, ed. H. Duerr and H. Bouas-
Laurent, Elsevier, Amsterdam, The Netherlands, 2003.
25 R. W. Walters and H. Van Gemert, WO, 2001/70719A2, 2001.
26 B. Schaudel, C. Guermeur, C. Sanchez, K. Nakatani and
J. A. Delaire, J. Mater. Chem., 1997, 7, 61.
Conclusion
A new strategy for increasing the fading speed of photochromic
3H-naphtho [2,1-b]pyrans with N,N-disubstituted groups has
been developed. It has demonstrated that 3H-naphtho [2,1-b]
pyrans with N,N-disubstituted groups can be converted to
protonated naphthopyrans whose fading speed is increased
significantly in both solution and in a rigid polymer matrix at
ambient temperature. The protonated naphthopyrans shows
similar absorption and fatigue resistance to their corresponding
naphthopyrans, which provides a simple and efficient method for
27 J. Hobley, U. Pfeifer-Fukumura, M. Bletz, T. Asahi, H. Masuhara
and H. Fukumura, J. Phys. Chem. A, 2002, 106, 2265.
12406 | J. Mater. Chem., 2011, 21, 12402–12406
This journal is ª The Royal Society of Chemistry 2011