Photochromic properties of naphthopyrans - PMMA thin film

Article abstract of DOI:10.1080/15421400802697566

A class of naphthopyran derivatives (3a-10a) with electron-donating and electron-acceptor substituent is prepared by condensation of 1,2-diaryl-2-propyn-1-ol with -naphthol in the presence of pyridinium para-toluenesulfonate (PPTS) as catalyst. All compounds go ring-opening isomerization in polymethylmethacrylate (PMMA) matrix with UV light irradiation (30watt) and the maximum absorption of ring-opening isomers is at the range of 426-556nm. Ring-opening isomers are completely back to ring-closing isomers when samples are kept in darkness, the bleach rate of ring-opening isomers in PMMA film increased significantly when temperature is more than 45C. Fatigue testing showed that no significant change of optical density was detected after 10cycles.

Full text of DOI:10.1080/15421400802697566

This article was downloaded by: [University of Haifa Library]
On: 04 October 2013, At: 08:24
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Molecular Crystals and Liquid
Crystals
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/gmcl20
Photochromic Properties of
Naphthopyrans – PMMA Thin
Film
Kunpeng Guo a & Yi Chen a
a Key Laboratory of Photochemical Conversion and
Optoelectronic Materials, Technical Institute of
Physics and Chemistry, The Chinese Academy of
Sciences, Beijing, China
Published online: 18 Mar 2009.
To cite this article: Kunpeng Guo & Yi Chen (2009) Photochromic Properties of
Naphthopyrans – PMMA Thin Film, Molecular Crystals and Liquid Crystals, 501:1,
62-71, DOI: 10.1080/15421400802697566
To link to this article: http://dx.doi.org/10.1080/15421400802697566
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or

indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Mol. Cryst. Liq. Cryst., Vol. 501, pp. 62–71, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802697566
Photochromic Properties of Naphthopyrans – PMMA
Thin Film
Kunpeng Guo and Yi Chen
Key Laboratory of Photochemical Conversion and Optoelectronic
Materials, Technical Institute of Physics and Chemistry, The Chinese
Academy of Sciences, Beijing, China
A class of naphthopyran derivatives (3a–10a) with electron-donating and electron-
acceptor substituent is prepared by condensation of 1,2-diaryl-2-propyn-1-ol with
b-naphthol in the presence of pyridinium para-toluenesulfonate (PPTS) as cata-
lyst. All compounds go ring-opening isomerization in polymethylmethacrylate
(PMMA) matrix with UV light irradiation (30 watt) and the maximum absorption
of ring-opening isomers is at the range of 426–556 nm. Ring-opening isomers are
completely back to ring-closing isomers when samples are kept in darkness, the
bleach rate of ring-opening isomers in PMMA film increased significantly when
temperature is more than 45ꢀC. Fatigue testing showed that no significant change
of optical density was detected after 10 cycles.
Keywords: naphthopyrans; photochromism; PMMA thin film; synthesis
INTRODUCTION
Interest in the photochromism of benzopyrans and naphthopyrans has
been sparked by commercialization of photochromic plastic ophthal-
mic lenses and glasses in the early 1990s [1]. Benzopyrans and
naphthopyrans display highly desirable photochromic properties and
have thus been the subject of intense investigations aimed at develop-
ing novel materials with useful applications [2]. Although there are
many publications [3–7] and patents [8–13] on benzopyrans and
naphthopyrans including the synthetic methodology, photochromism,
and applications, the design and synthesis of novel photochromic
benzopyrans and naphthopyrans with improved properties have
Address correspondence to Yi Chen, Key Laboratory of Photochemical Conversion
and Optoelectronic Materials, Technical Institute of Physics and Chemistry, The Chinese
Academy of Sciences, Beijing 100080, China. E-mail: yichencas@yahoo.com.cn
62

Photochromic Properties of Naphthopyrans
63
always been attracting attention because of their widespread use in
photon device applications [14–16]. In general, there are three
approaches to the preparation of benzopyrans and naphthopyrans:
1) the Kabbe synthesis, commences with chromanones and necessi-
tates a multistep sequence of reactions [17,18]; 2) the reaction of aryl
Grignard with benzocoumarins, followed by dehydrations [19]; and 3)
the Claisen rearrangement of propargyl-aryl ethers prepared in situ
from naphthol and a diaryl propargyl alcohol under acidic conditions
[20–23]. Among the three methodologies, the third one is most expedi-
tious and popular. The disadvantages of these approaches are in gen-
erality and in poor yields. Recently, E. M. Carreira, et al. reported a
facile one-pot synthesis of photochromic pyrans in excellent yields
with modification of reaction conditions by employing PPTS as cata-
lyst [24,25]. In contrast to synthesis, the properties of photochromic
naphthopyrans are less reported, especially in solid state. In this arti-
cle, we prepared a class of naphthopyran derivatives with electron-
donating and electron-acceptor substituted groups by condensation
of 1,2-diaryl-2-propyn-1-ol (1) with b-naphthol (2) (Scheme 1), and
we also present photochromic properties of naphthopyran derivatives
in solid state (PMMA film) including the absorption bands, the rate of
coloration and bleaching, and fatigue resistance. This may provide
useful information for further applications of photochromic naphtho-
pyran derivatives.
SCHEME 1 Synthesis of photochromic naphthopyran derivatives 3a–10a.

64
K. Guo and Y. Chen
EXPERIMENTAL
Instrumentation
1H NMR spectra were recorded at 400 MHz with Tetramethylsilane
(TMS) as an internal reference and CDCl3 as solvent. Mass spectra
(MS) were recorded with as Trio-2000 GC-MS spectrometer. UV
absorption spectra were measured on an absorption spectrophoto-
meter (Hitachi U-3010). Coloration was carried out with a UV light
(Power: 30 watt, k ¼ 254 nm).
Chemicals
All chemicals for synthesis were purchased from commercial suppli-
ers, and solvents were purified according to standard procedures.
Compounds 3a–10a were prepared according to the literature [9a],
and the general procedure for the preparation of compounds 3a–10a
is as follows: treatment of 1,2-diaryl-2-propyn-1-ol (1.1 equiv) and
b-naphthol (1 equiv) in 1,2-dichloroethane with 2 equivalant of
(MeO)3CH and 5 mol% PPTS furnished the desired product in high
yields (72–95%) except for 7a (10%) and 8a (18%).
3a: Yield: 88%. 1H NMR (400 MHz, CDCl3): d ¼ 7.96 (d, 1H, J ¼ 8.5 Hz),
7.72 (d, 1H, J ¼ 8.2 Hz), 7.67 (d, 1H, J ¼ 8.8 Hz), 7.50–7.44 (m, 5H),
7.33–7.30 (m, 6H), 7.25–7.22 (m, 2H), 7.21 (d, 1H, J ¼ 8.8 Hz), 6.29
(d, 1H, J ¼ 9.9 Hz). MS: m=z [Mþ]: 334. Anal. Calcd for C25H18O:
C, 89.80; H, 5.42. Found: C, 89.88; H, 5.40.
4a: Yield: 72%. 1H NMR (400 MHz, CDCl3): d ¼ 7.96 (d, 1H, J ¼ 8.5 Hz),
7.72 (d, 1H, J ¼ 8.3 Hz), 7.66 (d, 1H, J ¼ 8.8 Hz), 7.50–7.43 (m, 3H),
7.37–7.29 (m, 6H), 7.24–7.18 (m, 2H), 7.12 (d, 1H, J ¼ 8.1 Hz), 6.27
(d, 2H, J ¼ 9.9 Hz), 2.30 (s, 3H). MS: m=z [Mþ]: 348. Anal. Calcd
for C26H20O: C, 89.62; H, 5.78. Found: C, 89.58; H, 5.74.
5a: Yield: 73%. 1H NMR (400 MHz, CDCl3): d ¼ 7.97 (d, 1H, J ¼ 8.5 Hz),
7.72 (d, 1H, J ¼ 8.1 Hz), 7.66 (d, 1H, J ¼ 8.8 Hz), 7.49–7.46 (m, 3H),
7.44–7.38 (m, 2H), 7.33–7.29 (m, 4H), 7.25–7.24 (m, 1H), 7.20 (d, 1H,
J ¼ 8.8 Hz), 6.84 (d, 2H, J ¼ 8.8 Hz), 6.25 (d, 1H, J ¼ 9.9 Hz), 3.77 (s,
3H). MS: m=z [Mþ]: 364. Anal. Calcd for C26H20O2: C, 85.69; H, 5.53.
Found: C, 85.72; H, 5.49.
6a: Yield: 70%. 1H NMR (400 MHz, CDCl3): d ¼ 7.96 (d, 1H, J ¼ 8.4 Hz),
7.73 (d, 1H, J ¼ 8.1 Hz), 7.68 (d, 1H, J ¼ 8.8 Hz), 7.49–7.41 (m, 5H),
7.34–7.26 (m, 7H), 7.19 (d, 1H, J ¼ 8.8 Hz), 6.22 (d, 1H, J ¼ 9.9 Hz).
MS: m=z [Mþ]: 368. Anal. Calcd for C25H17ClO: C, 81.40; H, 4.64.
Found: C, 81.48; H, 4.60.

Photochromic Properties of Naphthopyrans
65
7a: Yield: 10%. 1H NMR (400 MHz, CDCl3): d ¼ 8.17 (d, 2H, J ¼ 8.9 Hz),
7.97 (d, 1H, J ¼ 8.4 Hz), 7.74 (d, 1H, J ¼ 8.2 Hz), 7.70 (d, 3H,
J ¼ 8.9 Hz), 7.49–7.44 (m, 3H), 7.41–7.28 (m, 5H), 7.21 (d, 1H,
J ¼ 8.9 Hz), 6.25 (d, 1H, J ¼ 9.9 Hz). MS: m=z [Mþ]: 363. Anal. Calcd
for C25H17NO2: C, 82.63; H, 4.71. Found: C, 82.58; H, 4.74.
8a: Yield: 18%. 1H NMR (400 MHz, CDCl3): d ¼ 7.96 (d, 1H, J ¼ 8.5 Hz),
7.71 (d, 1H, J ¼ 8.1 Hz), 7.65 (d, 1H, J ¼ 8.8 Hz), 7.51–7.44 (m, 3H),
7.32–7.23 (m, 8H), 7.19 (d, 1H, J ¼ 8.8 Hz), 6.66 (d, 1H, J ¼ 8.9 Hz),
6.25 (d, 1H, J ¼ 9.9 Hz), 2.91 (s, 6H). MS: m=z [Mþ]: 377. Anal. Calcd
for C27H23NO: C, 85.91; H, 6.14. Found: C, 86.11; H, 6.21.
9a: Yield: 78% 1H NMR (400 MHz, CDCl3): d ¼ 8.30 (d, 1H, J ¼ 8.6 Hz),
8.01 (d, 1H, J ¼ 8.5 Hz), 7.81 (d, 1H, J ¼ 8.0 Hz), 7.78 (d, 1H,
J ¼ 8.2 Hz), 7.72–7.68 (m, 2H), 7.59 (d, 1H, J ¼ 8.8 Hz), 7.50–7.48
(m, 3H), 7.46–7.10 (m, 8H), 7.11 (d, 1H, J ¼ 8.8 Hz), 6.26 (d, 1H,
J ¼ 9.9 Hz). MS: m=z [Mþ]: 384. Anal. Calcd for C29H20O: C, 90.59;
H, 5.24. Found: C, 90.68; H, 5.22.
10a: Yield: 95%. 1H NMR (400 MHz, CDCl3): d ¼ 7.97 (d, 1H,
J ¼ 8.4 Hz), 7.73 (d, 1H, J ¼ 8.1 Hz), 7.68 (d, 1H, J ¼ 8.8 Hz), 7.59–
7.57 (m, 2H), 7.47–7.45 (m, 1H), 7.36–7.27 (m, 5H), 7.21 (d, 1H,
J ¼ 8.8 Hz), 6.73 (d, 1H, J ¼ 3.5 Hz), 6.54 (d, 1H, J ¼ 3.6 Hz), 6.27
(d, 1H, J ¼ 9.9 Hz), 2.40 (s, 3H). MS: m=z [Mþ]: 354. Anal. Calcd
for C24H18OS: C, 81.32; H, 5.12. Found: C, 81.40; H, 5.15.
Naphthopyrans-PMMA Thin Film
Compounds 3a–10a (2.0 mg) were dissolved in PMMA-cyclohexanone
solution (10% w=w, 1.0 ml). The mixture solution was then spin-coated
on a glass substrate, which was then dried in air and kept in darkness
at room temperature. The thickness of the film was about 10 mm.
RESULTS AND DISCUSSION
Photochromic Properties of Naphthopyran Derivatives
3a–10a in PMMA Thin Film
Preliminary investigation showed that all compounds 3a–10a under-
went ring-opening and ring-closing photoisomerization in PMMA film.
The photoisomerization of 9a is described in Scheme 2, and absorption
spectra changes are presented in Fig. 1. Before irradiation, there are
three absorption bands at 360, 294, and 252 nm, respectively, which
are attributed to the ring-closing isomer 9a. Upon irradiation with
UV light, a new band appeared at 428 nm, which corresponds to the

66
K. Guo and Y. Chen
SCHEME 2 Ring-opening and ring-closing isomerization of 9a in PMMA
thin film.
ring-opening isomer 9b, and absorption intensity increased with
increasing the irradiation time until the photostationary state is
reached. The process was companied by the color change of PMMA
film from colorless to bright yellow. The new band at 428 nm decreased
and disappeared when the sample was kept in darkness, accompany-
ing the color change of PMMA film from bright yellow to colorless.
Similar results were obtained when other compounds performed
ring-closing and ring-opening isomerization. The absorption data of
ring-closing and ring-opening isomers in PMMA media are presented
in Table 1. As shown in Table 1, it is found that the absorption band of
ring-opening isomers occurred red shift when the substituent in the
benzene ring is changed from an electron-acceptor to an electron-dona-
tor, and the stronger the electron-donator, the greater the red shift. It
is probable because of decreasing the density of electron cloud of
FIGURE 1 Absorption changes of 9a–PMMA thin film with UV light irradia-
tion (0, 20, 40, 60s).

Photochromic Properties of Naphthopyrans
67
TABLE 1 Absorption Data of Ring-Opening and
Ring-Closing Isomers in PMMA Thin Film
kmax (nm)
kmax (nm)
Compounds Closing isomer (a) Opening isomer (b)
3
4
5
6
7
8
9
10
346
346
346
346
344
346
360
346
454
456
466
452
426
556
428
490
ring-opening isomers resulted from strong electronic properties, which
resulted in a decreasing energy gap between the ground states and the
excited states.
Coloration and Bleach of Naphthopyran Derivatives 3a–10a
in PMMA Thin Film
The investigation of coloration of naphthopyran derivatives 3a–10a
found that all compounds undergo coloration with UV light or sunlight.
It took about 1–2 min for naphthopyran derivatives to get photostation-
ary state with 30 watt UV light (it took much longer time under
sunlight), and the color of film changed from colorless to colored. The
bleaching of film was carried out in darkness at room temperature
(15ꢀC). It is found that the color of film was faded fast during the first
one to two minutes and one half optical density of colored isomer was
detected during that time. It took, however, much longer (10–30 min)
to completely bleach back to colorless, and one-tenth optical density of
colored isomer was detected in these cases. Generally, naphthopyrans
with electron-donating groups bleach faster than those with electron-
acceptor groups. It is worth noting that the bleach of 9b took much longer
time (2 hrs) to back to colorless at room temperature by comparison with
others although the mechanism is not clear. Both coloration and bleach of
the naphthopyran derivatives 9a are presented in Figs. 2a,b.
Temperature Influence on the Bleach of Naphthopyran
Derivatives 3a–10a in PMMA Thin Film
It is well known that temperature has great influence on the bleach
of photochromic pyrans and naphthopyrans. In this article, a

68
K. Guo and Y. Chen
FIGURE 2 Coloration and bleach of 9a–PMMA thin film (a: coloration;
b: bleach).
preliminary investigation of temperature effects the color fade was
carried out by the following way: a photostationary state naphtho-
pyran–PMMA thin film was covered with foil paper and placed in tem-
perature-controlled oven until the color of film faded completely.
Figure 3 shows the results of fade time of 9b at different temperature.
It is found that it took more than one and half hours for 9b to bleach
completely back to colorless at 25ꢀC (room temperature), but it only
took less than 5 min to do it when temperature is over 45ꢀC. It is also
found that the higher the temperature is, the less time the fade takes.
Similar results are obtained when other naphthopyrans–PMMA
thin films were measured in the same way and the fade is much
faster when the temperature is over 45ꢀC although the fade time to
colorless is somewhat different at room temperature with different
compounds.
Fatigue Resistance of Naphthopyran Derivatives 3a–10a
in PMMA Thin Film
Fatigue resistance is one of important factors to evaluate material
applications. It is known that photochromic naphthopyrans exhibit
good fatigue resistance. A preliminary investigation of fatigue resis-
tance for naphthopyran derivatives 3a–10a was performed by the
following way: a naphthopyrans–PMMA thin film was irradiated to
the photostationary state with UV light and the optical density of
ring-opening isomers was measured, then bleach the colored film to

Photochromic Properties of Naphthopyrans
69
FIGURE 3 The fade time of 9b–PMMA thin film at different temperature.
colorless (optical density of ring-opening isomer decreased to one tenth
of ring-opening isomer at photostationary state) at darkness, this is
defined one cycle. Figure 4 represented the fatigue testing results of
9a–PMMA thin film. It is found that no significant change of optical
density (ring-opening isomer) was detected after 10 cycles, suggesting
9a exhibited good fatigue resistance. Other naphthopyran derivatives
also showed good fatigue resistance and no significant change of
optical density was detected after 10 cycles.
FIGURE 4 Fatigue resistance of 9a–PMMA thin film.

70
K. Guo and Y. Chen
CONCLUSIONS
In summary, a class of naphthopyran derivatives with different elec-
tronic property substituent has been prepared by the condensation
of 1,2-diaryl-2-propyn-1-ol with b-naphthol, and their photochromic
behavior in PMMA thin film has been investigated. With UV light
or sunlight irradiation, the colorless ring-closed isomers transform to
the yellow or orange ring-opening isomers, and the yellow or orange
ring-opening isomers reverse back to the colorless ring-closed isomer
when they are kept in darkness. All ring-opening isomers are sensitive
to temperature and back to ring-closed isomers quickly when tempera-
ture is over 45ꢀC.
ACKNOWLEDGMENTS
This work was supported by the National Nature Science Foundation
of China (No. 60337020) and Beijing Natural Science Foundation
(No. 4082033).
REFERENCES
[1] Durr, H., & Bouas-Laurent, H. (1990). Photochromism: Molecules and Systems,
Elsevier: Amsterdam.
[2] Crano, J. C., & Guglielmetti, R. (1999). Organic Photochromic and Thermochromic
Compounds, Plenum Press: New York.
[3] Pozzo, J. L., Samat, A., Guglielmetti, R., Lokshin, V., & Minkin, V. (1996). Can. J.
Chem., 74, 1649.
[4] Harie, G., Samat, A., & Guglielmetti, R. (1997). Tetrahedron Lett., 28, 3075.
[5] Moustrou, C., Rebiere, N., Samat, A., Guglielmetti, R., Yassar, A. E., Dubest, R., &
Aubard, J. (1998). Helv. Chim. Acta., 81, 1293.
[6] Tanaka, K., Aoki, H., Hosomi, H., & Ohba, S. (2000). Org. Lett., 2, 2133.
[7] Oliveira, M. M., Carvalho, L. M., Moustrou, C., Samat, A., Guglielmetti, R., &
Oliveira-Campos, A. M. F. (2001). Helv. Chim. Acta., 84, 1163.
[8] Kumar, A. (1995). U.S. Patent 5411679.
[9] Knowles, D. B., & Von Gemert, B. (1995). U.S. Patent 5464567.
[10] Von Gemert, B. (1997). U.S. Patent 5645767.
[11] Momodam, J., & Hara, T. (1998). U.S. Patent 5808100.
[12] Heller, H. G., & Levell, J. R. (1999). U.S. Patent 5955520.
[13] Frigoli, M., Moustrou, C., Samat, A., & Guglielmetti, R. (2001). WO0104233.
[14] Feringa, B. L. (2001). Molecular Switches, Wiley-VCH: Weinheim.
[15] Durr, H., & Bouas-laurent, H. (2003). Photochromism: Molecules and Systems,
Elsevier: Amsterdam.
[16] Zhao, W., & Carreira, E. M. (2002). J. Am. Chem. Soc., 124, 1582.
[17] Gabbutt, C. D., Hartley, D. J., Hepworth, J. D., Heron, B. M., Kanjia, M., &
Rahman, M. (1994). Tetrahedron, 50, 2507.
[18] Kabbe, H., & Widdig, A. (1982). Angew. Chem., Int. Ed. Engl., 21, 247.
[19] Cottam, J., & Livingstone, R. (1965). J. Chem. Soc., 6646.

Photochromic Properties of Naphthopyrans
71
[20] Coelho, P. J., Carvalho, L. M., Abrantes, S., Oliveira-Campos, A. M. F., Dubest, R.,
Samat, A., & Guglielmetti, R. (2002). Tetrahedron, 58, 9505.
[21] Coelho, P. J., Carvalho, L. M., Rodrigues, S., Oliveira-Campos, A. M. F., Dubest, R.,
Aubard, J., Samat, A., & Guglielmetti, R. (2002). Tetrahedron, 58, 925.
[22] Yassar, A., Jaafari, H., Galy, N. R., Frigoli, M., Moustrou, C., Samat, A., &
Guglielmetti, R. (2002). Eur. Phys. J. Appl. Phys., 18, 3.
[23] Martin, C. I., Coelho, P. J., Carvalho, L. M., Oliveira-Campos, A. M. F., Samat, A.,
& Guglielmetti, R. (2003). Helv. Chim. Acta., 86, 570.
[24] Zhao, W., & Carreira, E. M. (2003). Org. Lett., 5, 4153.
[25] Zhao, W., & Carreira, E. M. (2006). Org. Lett., 8, 99.