ISSN 1070-4272, Russian Journal of Applied Chemistry, 2017, Vol. 90, No. 4, pp. 501−506. © Pleiades Publishing, Ltd., 2017. Original Russian Text © T.M. Valova, A.M. Gorelik, V.A. Barachevsky, 2017, published in Zhurnal Prikladnoi Khimii, 2017, Vol. 90, No. 4, pp. 399−405.

INORGANIC SYNTHESIS AND INDUSTRIAL INORGANIC CHEMISTRY

Synthesis of Photochromic Optically Transparent Polycarbonate Glasses and Study of Their Properties T. M. Valovaa, A. M. Gorelika, and V. A. Barachevskya,b* a

Center of Photochemistry, Crystallography and Photonics Federal Research Center, Russian Academy of Sciences, ul. Novatorov 7a, Moscow, 119421 Russia b Interdepartmental Center of Analytical Research, Russian Academy of Sciences, ul. Profsoyuznaya 65, 117997, Moscow, Russia *e-mail: [email protected] Received April 17, 2017

Abstract—Procedure was developed for surface dyeing of polycarbonate glass with photochromic thermally relaxing compounds from the classes of spiropyrans, spirooxazines, and chromenes via diffusion of photochromic molecules from solutions in cyclohexanone. It was shown that the highest diffusion efficiency of photochromic compounds without loss of the optical surface quality of polycarbonate glass is reached at a temperature of 80°C. Samples of photochromic polycarbonate glasses were obtained and their photochromic properties were studied. DOI: 10.1134/S1070427217040012

In this communication, we present the results obtained in the development of such photochromic polymeric materials on the basis of polycarbonate (PC) glasses and thermally relaxing compounds belonging to the classes of spiropyrans, spirooxazines, and chromenes.

As photonics is being developed, particular role is acquired by photochromic materials experiencing reversible transformations of the coloration and other optical properties, which accompany the photochromic transformations. To be used in photonic devices, photochromic materials, especially those of organic type, must possess acceptable optical properties. At present, organic photochromic materials are, as a rule, fabricated with the use of polymeric binders by the method of casting onto a polymeric base or silicate glass substrates, including that by the spin-coating (centrifugation) method, casting in molds, extrusion, and diffusion of photochromic compounds from solution into a polymeric matrix [1]. The last method is especially attractive for obtaining photochromic glasses with photochromic compounds introduced into their surface layers and an internal waveguide layer containing no photochromic molecules. Materials of this kind can be used in fast optical modulators that reversibly attenuate the intensity of passing light under the action of UV radiation introduced into the waveguide from another source of light.

EXPERIMENTAL Photochromic samples were produced from 2 × 3 cm PC glass plates with thickness of 3.2 mm, manufactured by Bayer (Germany). Photochromic compounds were introduced into PC glass by the diffusion method with the use of commercial substances from the class of spiropyrans, 1-phenyl-3,3-dimethyl-8'-methoxy-6'-nitrospiro[1Hindole-2(3H)]2'-[2H-benzopyrane (compound 1), spirooxazines 1,3',3'-trimethylspiro(indoline-2',3[3H]anthracene[2,1-b][1,4- oxazine (compound 2), and the newly synthesized chromene, 2-phenyl-2-ferrocenyl5-(2-fluorobenzoyloxy)-2H-naphtho[1,2-b]pyrene (compound 3): 501

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Chromene 3 was synthesized by Scheme 1. The acylation of 1,3-dihydroxynaphthalene (I) with ortho-fluorobenzoyl chloride (II) in the presence of triethylamine yielded an acetoxy derivative, 3-(2-fluorobenzoyloxy)-1-naphthol (III). The formation of two more compounds: products of acylation at two oxy groups and at the oxy group in the α-position of 1,3-dihydroxynaphthalene required a chromatographic

separation of the products, with III isolated in 18% yield. Propargilic alcohol, 1-phenyl-1-ferrocenyl-2-propin-1-ol (IV), was formed in the interaction of potassium acetylide produced in situ by passing acetylene into a KOH suspension in THF with benzoylferrocene. Further interaction of III with alcohol IV produced 2-phenyl-2-ferrocenyl5-(2-fluorobenzoyloxy)-2H-naphtho[1, 2-b]pyrene 3 in 17% yield.

Scheme 1.

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3-(2-Fluorobenzoyloxy)-1-naphthol (III). A solution of 4.5 g (45 mmol) of triethylamine in 40 mL of abs. THF was added dropwise in the course of 1 h to a solution of 6 g (38 mmol) of 1,3-dihydroxynaphthalene (I) and 4.48 g (38 mmol) of 2-fluorobenzoyl chloride (II) in 100 mL of abs. THF. A 5-mL portion of water was added, the mixture was extracted with EtOAc, and the extract was dried with Na2SO4. The inorganic precipitate was filtered off, the filtrate was evaporated in a vacuum, and the residue was chromatographed on silica gel, with a 10 : 1 toluene–EtOAc mixture as eluent. The yield was 18%. 1-Phenyl-1-ferrocenyl-2-propin-1-ol (IV). Acetylene was passed through a suspension of 23 g (410 mmol) of KOH in abs. THF for 1 h at 20–25°C. A solution of 10 g (35 mmol) of benzoylferrocene in 70 mL of abs. THF was added dropwise to the reaction mass at 30–40°C. The mixture was agitated for 1.5 h at 30–40°C, with acetylene passed through it, and poured into 500 mL of water, the mixture was extracted with EtOAc, the extract was dried with Na2SO4, and the organic precipitate was filtered off. The filtrate was evaporated in a vacuum, 15 mL of hexane was added to the residue, and the hardened precipitate was filtered off. In what follows, IV was used without preliminary purification. 2-Phenyl-2-ferrocenyl-5-(2-fluorobenzoyloxy)-2Hnaphtho[1, 2-b]pyran 3. To a solution of 0.7 g (2.5 mmol) of 3-(2-fluorobenzoyloxy)-1-naphthol (III) and 0.078 g (2.5 mmol) of 1-phenyl-1-ferrocenyl-2-propin-1-ol (IV) in 20 mL of abs. toluene were added at 20–25°C catalytic amounts of para-toluene sulfonic acid. The reaction mixture was agitated for 4 h at 50–60°C, the precipitate was filtered off, the filtrate was evaporated in a vacuum, the residue was chromatographed on silica gel with toluene as eluent, and recrystallized from ethanol. The yield of 3 was 17%. 1H NMR spectrum, DMSO-d6, δ, ppm.: 3.90 s (5H, Fe), 4.23 s (1H, Fc ), 4.27 s (1H, Fc), 4.54 s (1H, Fc), 4.61 s (1H, Fc), 6.71 s (1H, Ar), 6.77 s (1H, Ar), 7.18 t (1H, Ar), 7.26 t (2H, Ar), 7.42–7.65 m (7H, Ar), 7.79–7.89 m (2H, Ar), 8.19 t (1H, Ar), 8.40 d (1H, Ar). The 1H NMR spectra were recorded with a Bruker AMX 400 spectrometer in DMSO-d6, with Me4Si as internal standard and values of δ measured to within 0.01 ppm. The reactions were monitored with TLC on Kieselgel 60 F254 plates. The 60-mesh Silica Gel ASTM was used for the column chromatography. Solutions of photochromic compounds were prepared with cyclohexanone from Aldrich serving as solvent. The concentrations of the compounds in the solutions were

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5 × 10–3, 1 × 10–2, and 2 × 10–2 M (compound 1); 1 × 10–3, 5 × 10–3, and 1 × 10–2 M (compound 2); and 5 × 10–3 and 1 × 10–2 (compound 3). Samples of PC glasses were prepared by casting of photochromic solutions of various concentrations onto the surface of PC glasses, followed by drying first at room temperature and then at elevated temperatures in a drying box for 1 h. Spectrophotometric measurements on the polymeric samples of the photochromic materials under study were made with an Ocean Optics USB2000 spectrophotometer. Samples of photochromic PC glasses were irradiated with light from an L8253 xenon lamp in a Hamamatsu LC-8 light source. RESULTS AND DISCUSSION The photochromic transformations of the compounds under study have been well examined [1–4]. According to schemes (a) (spiropyrans, where Z = C, and spirooxazines, where Z = N) and (b) (chromenes), these compounds demonstrate in solution reversible photoinduced transformations between two states, namely, the colorless A and colored merocyanine B forms (Scheme 2). Molecules are returned from the photoinduced state B into the starting state A under the action of visible light spontaneously. The process becomes faster under heating. The photochromic compounds introduced via diffusion into the surface layer exhibited transformations similar to those observed in solutions. Figure 1 shows as an example the photoinduced and spontaneous relaxation

λ, nm Fig. 1. Absorption spectra of compound 1 introduced into a PC glass via diffusion from a solution with photochromic compound concentration c = 1 × 10–2 M (1) before the irradiation with unfiltered light in the photoequilibrium state, (2) after the irradiation, and (3–6) in the course of dark relaxation. (D) Optical density and (λ) wavelength; the same for Figs. 4. and 5.

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changes in the absorption spectra of spiropyrane 1 in a PC glass upon diffusion of its molecules into the surface layer from a solution with concentration c = 1 × 10–2 M. Under irradiation with UV light, a colorless PC glass sample with spiropyran 1 was colored, with an absorption band peaked at 410 and 620 nm appearing in the visible spectral range (see table). After the UV excitation was switched off, the coloration spontaneously disappeared. The discoloration process in the dark is described by two exponentials (see table). The photocoloration efficiency of PC glasses under the action of UV radiation grows with increasing spiropyran 1 concentration in solution (Fig. 2).

c, M Fig. 2. Optical density D of spiropyrane 1 at the peak of the absorption band of the photoinduced merocyanine form (620 nm) in the photoequilibrium state vs. the concentration c of the photochromic compound in the solution deposited onto the surface of PC glasses.

Also, a less pronounced dependence is observed of the photoinduced optical density on the residence time of the photochromic solution on the surface of a PC glass (Fig. 3). Further studies demonstrated that the diffusion of a photochromic compound into a PC glass is the most effective when the solution layer on the surface of a PC glass is dried at 60–80°C for 1 h. The samples are characterized by high optical quality and high concentration of the photochromic compound in the surface layer. A sample dried at 80°C has a more uniform photochromic surface layer, compared with a similar sample dried at 60°C.

τ, s Fig. 3. Optical density D of spiropyran 1 at the peak of the absorption band of the photoinduced merocyanine form (620 nm) in the photoequilibrium state vs. the time τ of contact between the solution of the photochromic compound (c = 1 × 10–2 M) with the surface of a PC glass.

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Spectral-kinetic characteristics of samples of photochromic PC glasssa

a

Compound

max λW , nm

max ΔDW

А0

kdo, s–1

1

620

1.9

A1 = 1.16 A2 = 0.48

k1 = 1.2 × 10–1 k2 = 6.5 × 10–3

2

610

1.8

A1 = 1.30 A2 = 1.74

k1 = 6.2 × 10–1 k2 = 2.9 × 10–2

3

475 640

0.5 0.5

A1 = 0.11 A2 = 0.18

k1 = 2.8 × 10–2 k2 = 2.0 × 10–3

max max λW is the peak wavelength of the absorption band of the photoinduced merocyanine form; ΔDW , maximum change in the optical density of the photoinduced merocyanine form; A0, pre-exponential factor; and kdo, rate constant of the reaction in which the photoinduced optical density of the merocyanine form changes in the dark.

A comparative study of the photodegradation of spiropyran 1 introduced by the diffusion method into the surface layer of a PC glass from solutions with various concentrations of the photochromic compound demonstrated that the service life of a photochromic material of this kind under exposure to light simulating the solar radiation grows with increasing concentration of compound 1 in the surface layer of the PC glass. This is due to the different concentrations of the photochromic compound in the surface layer. The time in which the photoinduced optical density becomes twice lower is about 100 s for all the samples. Photochromic spirooxazine 2 introduced into the surface layer of a PC glass is characterized by photoinduced and dark relaxation spectral changes similar to those observed for spiropyran 1 in a PC glass (see table and Figs. 1 and 4). The only difference is that the peak of the highest intensity absorption band of the photoinduced merocyanine form is shifted to shorter wavelengths by 10 nm to 610 nm. In addition, a higher dark relaxation rate is characteristic of this photochromic PC glass (see table), compared with the PC glass with spiropyran 1. The PC glasses with spirooxazine 2 also have a higher stability against irreversible photoinduced transformations, compared with glasses containing spiropyran 1. In contrast to PC glasses containing spiropyran 1 and spirooxazines 2, samples based on chromene 3 are characterized by a broad band of photoinduced absorption, which is peaked at 475 and 640 nm and covers the whole visible spectral range (Fig. 5). The appearance of the broad band of photoinduced absorption is accounted for by the introduction of a ferrocenyl fragment into the structure of chromene [5–7].

The process of the dark relaxation of this compound in the PC glass is characterized by smaller rate constants as compared with PC glass samples containing spiropyran 1 and spirooxazines 2 (see table). It was found that chromene 3 in a PC glass is the most stable against photodegradation, compared with other compounds (Fig. 6). This compound surpasses the sample with spiropyran 1 by a factor of 16 in the stability against irreversible photoinduced transformation, evaluated by the time in which the photoinduced optical density becomes twice lower. It was shown with the use of chromene 3 that the concentration of the photochromic compound in the surface layer of a PC glass can be raised, without loss of the optical quality of PC glasses, via multiple deposition of a solution of the photochromic compound in cyclohexanone onto the surface of the PC glass and its subsequent drying.

λ, nm

Fig. 4. Absorption spectra of compound 2 introduced into a PC glass via diffusion from a solution with photochromic compound concentration c = 1 × 10–2 M (1) before the irradiation with unfiltered light in the photoequilibrium state, (2) after the irradiation, and (3–6) in the course of dark relaxation.

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τ, s

λ, nm

Fig. 5. Absorption spectra of compound 3 introduced into a PC glass via diffusion from a solution with photochromic compound concentration c = 1 × 10–2 M (1) before the irradiation with unfiltered light in the photoequilibrium state, (2) after the irradiation, and (3–6) in the course of dark relaxation.

CONCLUSIONS A procedure was developed with the use of a spectralkinetic method, for obtaining photochromic polycarbonate glasses with surface photochromic layers via thermal diffusion of molecules of photochromic thermally relaxing spiropyrans, spirooxazines, and chromenes from solutions of the photochromic compounds in cyclohexanone into the surface layer of a polycarbonate glass. It was shown that the procedure is versatile and applicable to photochromic compounds of varied structure. Samples of photochromic polycarbonate glasses of high optical quality were obtained and their photochromic properties were studied. It was found that, owing to their high stability against irreversible photoinduced transformation, samples of photochromic polycarbonate glass samples containing molecules of spirooxazines and chromen in the surface layer are of practical interest for development of fast light-protective devices with reversible change in the optical transmission in the visible spectral range. This is provided by the use of pulsed UV light-emitting diodes and lasers whose emission, propagating in the waveguide layer of a glass, causes an effective coloration of large-area photochromic materials. The glasses based on spirooxazines 2 are characterized by selective photoinduced absorption

Fig. 6. Normalized kinetic curves of the photodegradation of PC glass samples containing spiropyran 1, spirooxazine 2, and chromene 3, measured at the peaks of the absorption bands of the merocyanine form at 620, 610, and 610 nm, respectively, in the course of irradiation with unfiltered light.(D) Optical density and (τ) time. The samples were produced by casting solutions of the compounds with concentration c = 2 × 10–2 M onto the surface of PC glasses.

in the visible spectral range, and the samples with a photochromic layer composed of chromene 3 attenuate the emission in the whole visible range. The procedure for obtaining photochromic polycarbonate glasses with waveguide layers provides development of photochromic devices for eye protection from pulsed light, which has not been done so far. REFERENCES 1. Barachevskii, V.A., Lashkov, G.I., and Tsekhomskii, V.A., Fotokhromizm i ego primenenie (Photochromism and Its Application), Moscow: Khimiya, 1977. 2. Bertelson, R.C., Photochromism, Brown, G.H., Ed., New York: Wiley Interscience, 1971, p. 45. 3. Photochromism. Molecules and Systems, Durr, H. and Bouas-Laurent, H., Eds., Amsterdam: Elsevier, 1990. 4. Organic Photochromic and Thermochromic Compounds, Crano, J.C. and Guglielmetti, R.J., Eds., NewYork: Plenum Press, 1999, vol. 1. 5. Anguille, S., Brun, P., and Guglielmetti, R., Heterocycl. Commun., 1998, vol. 4, pp. 63–66. 6. Barachevsky, V.A., Strokach, Y.P., Ignatin, A.A., et al., Mol. Cryst. Liq. Cryst., 2000, vol. 344, pp. 119–124. 7. Anguille, S., Brun, P., Guglielmetti, R., et al., J. Chem. Soc., Perkin Trans. II, 2000, pp. 639–644.

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