Photoconversion of a Protonated Diarylethene Derivative - The

Article pubs.acs.org/JPCA

Photoconversion of a Protonated Diarylethene Derivative Huan-huan Liu, Xu Zhang, Zeng Gao, and Yi Chen* Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, China ABSTRACT: A photochromic diarylethene with N,N-dimethyl substituted group 1a was prepared. 1a showed ring-opening and ring-closing photoisomerization with UV/vis light irradiation. Treatment of 1a with CF3COOH produced a protonated diarylethene 1aH. With UV light irradiation, 1aH photoconverted to protonated ring-closed isomer 1c, which is photoinactive. It is found that 1c is hydrophilic and 1aH is hydrophobic.

1. INTRODUCTION Photoactive molecules have currently attracted considerable attention because of wide potentials in chemistry,1−5 biochemistry,6−10 environmental science,11−14 and material science.15−19 Integrating an external stimulus to regulate targets affords a means to control chemical processes and modulate the behavior of functional materials containing them. Light is a particularly effective stimulus to spatially and temporally trigger changes in structure and function of molecules and materials.20−23 Diarylethenes display excellent photochromic properties and are one of the most promising photochromic compounds for photoelectronic applications such as optical memory media and photoswitching devices because of their fatigue resistant and thermally irreversible properties.24−29 Photochromic diarylethenes act as photoswitching and have been extensively studied for controlling various chemical and physical properties, including absorption spectral and fluorescence spectral,30−35 molecular chirality,36,37 magnetic interactions,38,39 electronic conduction,40−43 chemical reactivity,44,45 and self-assembling behavior.46,47 Diarylethenes that can be protonated have been attracting interest48,49 because their photochromic reactivity can be modulated by simple pH stimulus. Protonated diarylethenes usually exhibit different photoreactivity and physical and chemical properties from their original diarylethenes such as inhibiting photochromism of ring-opened isomers or ringclosed isomers or both, which provides a stragety for controlling or regulating photoreactivity. Controllability and selectivity in photochromism would endow such molecules with the ability to act as controllable photoactive molecules and be used for selective functionalization. In this paper, a photochromic diarylethene with an N,N-dimethyl substitutent group 1a is empolyed as a model compound (Scheme 1); by simple protonation with CF3COOH, a protonated diarylethene derivative 1aH (Scheme 1) is prepared. As compared to reported protonated diarylethenes, the presented protonated diarylethene 1aH herein shows some novel and meritorious properties including: (1) 1aH is photoactive and photoconverted to a protonated ring-closed isomer 1c upon irradiation with UV light, and (2) 1c is photoinactive and © 2012 American Chemical Society

Scheme 1. Chemical Structures of 1a and 1aH

differs from its precursor 1aH in solubility. The finding may be beneficial to insight into the relationship between molecular structure and properties and provides information of designing artificial molecules for controlling or regulating reactivity and function of molecules.

2. EXPERIMENTAL SECTION 2.1. General Methods. The 1H NMR spectrum and 13C NMR spectrum were recorded at 400 and 100 MHz with tetramethylsilane (TMS) as an internal reference, respectively. Both CDCl3 and DMSO-d6 are used as solvents. MS spectra were recorded with a GC-TOF MS spectrometer. Absorption spectra were measured with an absorption spectrophotometer (Hitachi U-3010). Coloration was carried out with a UV light (λ = 254 nm, intensity: 4.3 mW/cm−2). All chemicals for synthesis were purchased from commercial suppliers, and solvents were purified according to standard procedures. Reaction was monitored by TLC silica gel plates (60F-254). Column chromatography was performed on silica gel (Merck, 70−230 mesh). A 360 nm lamp (36W) and a Xenon light (500 W), with different wavelength filters, were used as light sources for photocoloration and photobleaching, respectively. 2.2. Material. Diarylethene 1a was prepared according to synthetic route shown in Scheme 2, and the detailed procedures and spectra data were as follows: To a solution of 3,4-bis(5iodo-2-methylthien-3-yl)-2,5-dihydrothiophene50 (270 mg, 0.5 mmol) in anhydrous THF (15 mL) were added Pd(PPh3)4 (40 mg, 3 mol %) and a solution of K2CO3 solution (2.5 M, 2 mL). Received: July 16, 2012 Revised: August 27, 2012 Published: September 18, 2012 9900

dx.doi.org/10.1021/jp3070163 | J. Phys. Chem. A 2012, 116, 9900−9903

The Journal of Physical Chemistry A

Article

Scheme 2. Synthesis of Diarylethene 1a

The resulting solution was stirred for 10 min at ambient temperature. To the resulting solution was added (4(dimethyamino)phenyl)boronic acid (248 mg, 1.5 mmol) under nitrogen, and the reaction was monitored by TLC. After the starting material disappeared, H2O (20 mL) was added to the residue, and the product was extracted with Et2O (3 × 20 mL). The combined organic phase was washed with H2O (30 mL) and a saturated solution of NaCl (30 mL), respectively, and dried over MgSO4. After evaporation of the solvent, the crude product was purified by flash column chromatography (petroleum ether−ethyl acetate = 1:1, v/v) to give diarylethene 1a in 33% yield (170 mg). Mp = 196−197 °C. 1 H NMR (400 MHz, CDCl3): 7.37 (d, 4H, J = 7.8 Hz), 6.86 (s, 2H), 6.71 (d, 4H, J = 8.8 Hz), 4.18 (s, 4H), 2.95 (s, 12H), 1.96 (s, 6H). 13C NMR: 150.0, 141.1, 134.2, 133.7, 133.1, 126.5, 123.0, 121.4, 112.8, 43.1, 40.7, 14.4. TOF-MS EI (m/z) calcd for C30H32N2S3: 516. 1728. Found: 516.1728. Protonated diarylethene 1aH was prepared as follows: To solution of 1a (10 mmol) in CH2Cl2 was added CF3COOH (21 mmol), and the mixture was stirred at room temperature for 10 min. The target compound 1aH was obtained quantitatively after evaporation of the solvent under reduced pressure without further purification. Mp ≥ 300 °C. 1H NMR (400 MHz, CDCl3): 7.90 (d, 4H, J = 9.8 Hz), 7.73 (d, 4H, J = 8.7 Hz), 7.08 (s, 2H), 4.12 (s, 4H), 3.06 (s, 12H), 1.98 (s, 6H). Dye 1c was prepared as follows: 1aH (10 mg, 0.02 mmol) was dissolved in CH3CN (50 mL). The resulting solution was then irradiated for 30 min under a high pressure Hg lamp (500 W). After the conversion was completed (detection by TLC, starting material disappeared), the solvent was evaporated under reduce pressure, and the target compound 1c was obtained without further purification. Mp ≥ 300 °C. 1H NMR (400 MHz, DMSO-d6): 7.87 (d, 4H, J = 9.1 Hz), 7.22 (d, 4H, J = 8.9 Hz), 6.86 (s, 2H), 4.14 (s, 4H), 3.15 (s, 12H), 2.26 (s, 6H). 13C NMR (100 MHz, DMSO-d6): 159.6, 146.8, 146.5, 133.6, 131.5, 125.8, 119.8, 117.4, 60.9, 42.7, 40.9, 14.6. IR (KBr) ν: 3452, 3213, 1687, 1412, 1216, 1108 cm−1.

Figure 1. Absorption change of 1a (20 μM, CH3CN) with 254 nm light irradiation until the photosteady state (periods: 0, 20, 40, 60, 80, 100 s).

Figure 2. Absorption change of 1aH (20 μM, CH3CN) with 254 nm light irradiation (periods: 0, 30, 60, 90, 100 s).

3. RESULTS AND DISCUSSION 3.1. Photochromism of 1a with 254 nm Light Irradiation. Spectral photochromic properties of 1a were studied in acetonitrile solution. 1a showed ring-opening and ring-closing photoisomerization with UV/vis light irradiation.

Figure 3. Absorption spectral of 1b with addition of CF3COOH in CH3CN (before, black; after, red).

Scheme 3. Ring-Opening and Ring-Closing Photoisomerization of 1a with UV/Vis Light Irradiation

9901

dx.doi.org/10.1021/jp3070163 | J. Phys. Chem. A 2012, 116, 9900−9903

The Journal of Physical Chemistry A

Article

Scheme 4. Conversion of 1c from 1aH and 1b

irradiation time and completed after irradiation of 100 s. This process was accompanied by a color change of solution from colorless to dark blue-green. The conversion of 1aH to 1c was ca. 80% (determined by 1H NMR). As presented in Figure 2, there is an isosbestic point at 345 nm, the clear isosbestic point indicated that only two isomers existed when protonated diarylethene 1aH underwent the photoconversion reaction. Further study found that the dark green-blue solution could not be bleached back to colorless solution with visible light (≥400 nm) irradiation, which suggested that 1c did not exhibit photochromism. 3.3. Structure of 1c. To find out the species whose absorption corresponded to the new absorption in the range of 400−750 nm, the photoproduct 1c resulted from the photoconversion of 1aH was obtained, and its structure was determined by 1H NMR and 13C NMR spectroscopy. It was found that the proton of CH3 group linked in the thiophene ring shifted downfield from 1.98 ppm (1aH) or 1.96 ppm (1a) to 2.26 ppm. It is known that the protons of CH3 linked in thiophene rings usually shift downfield when ring-opened isomers of diarylethenes photoconvert to their ring-closed isomers. The result suggested that 1c possessed a ring-closed structrue. Comparing both 13C NMR data (1a and 1c) found that the signal arising from the CS in thiophene ring shifted upfield from 112.8 (1a) to 60.9 (1c) ppm, which confirmed that the double bond (CC−S) in thiophene ring was changed to single bond (C−C−S) when 1aH was photoconverted to 1c. Moreover, it was found that 1c was also obtained from 1b by addition of acid. Addition of CF3COOH to the solution of 1b produced the color of solution changed immediately from purple to dark green-blue, and maximum absorption shifted from 546 to 610 nm (Figure 3). As compared to Figure 2, Figure 3 showed very similar spectral profile, which implied that 1b was converted to 1c in the presence of acid. Besides, control experiments demonstrated the following points: (1) the photoconversion of 1aH to 1c could also be performed in the atmosphere of N2, and no significant change was observed as compared in the air, which indicated that no oxidation occurred when 1aH photoconverted to 1c. (2) 1c was transformed to 1b by the addition of NaOH solution. It was found that the color of solution changed from dark green-blue to purple when NaOH solution

Figure 4. Photographs of 1aH, 1b, and 1c in a mixture of solution (top, toluene; bottom, water).

The photoiosmerization of 1a is described in Scheme 3, and changes in the absorption spectra are presented in Figure 1. Upon irradiation with UV light, the absorption band (λmax = 330 nm, ε = 5.4 × 104 L mol−1 cm−1), which is attributed to the ring-opened isomer 1a, decreased in intensity, and a new band (λmax = 546 nm), which corresponds to the ring-closed isomer 1b, appeared at the same time. The band at 546 nm increased in intensity with the increase of irradiation time until the photostationary state (PSS) was reached. This process was accompanied by a color change of solution from colorless to purple. The conversion of 1a to 1b was ca. 90% (determined by 1 H NMR) in PSS. As presented in Figure 1, the figure showed the typical absorption spectra changes of photochromic diarylethene derivatives in solution, and the clear isosbestic point indicated that only two isomers existed when diarylethene 1a underwent the photoisomerization reaction. The purple solution was bleached completely back to colorless solution with visible light (≥400 nm) irradiation, and the coloration and decoloration can be repeated. 3.2. Photoconversion of 1aH with 254 nm Light Irradiation. Spectral examination of the photoconversion of 1aH was studied in acetonitrile solution with UV light irradiation, and changes in the absorption spectra are presented in Figure 2. Upon irradiation with UV light, the absorption band (λmax = 320 nm, ε = 3.3 × 104 L mol−1 cm−1), which is attributed to 1aH, decreased in intensity, and a new absorption covering the full visible light wavelength range (400−750 nm), which corresponds to 1c (Scheme 4), appeared at the same time. The new band increased in intensity with the increase of 9902

dx.doi.org/10.1021/jp3070163 | J. Phys. Chem. A 2012, 116, 9900−9903

The Journal of Physical Chemistry A

Article

(11) Lee, C.; Choi, W.; Yoon, J. Environ. Sci. Technol. 2005, 39, 9702−9709. (12) Hou, Y.; Li, X.; Zhao, Q.; Quan, X.; Chen, G. Environ. Sci. Technol. 2010, 44, 5098−5103. (13) Herath, A. C.; Rajapakse, R. M. C. Environ. Sci. Technol. 2009, 43, 176−180. (14) Hernandez-Alanso, M. D.; Fresno, F.; Suarez, S.; Coronado, J. M. Energy Environ. Sci 2009, 2, 1231−1257. (15) Kang, D. J.; Bae, B. S. Acc. Chem. Res. 2007, 40, 903−912. (16) Faustini, M.; Nicole, L.; Boissire, C.; Innocenzi, P.; Sanchez, C.; Grosso, D. Chem. Mater. 2010, 22, 4406−4413. (17) Zhu, J.; Sun, G. J. Mater. Chem. 2012, 22, 10581−10588. (18) Jayalakshmi, V.; Hegde, G.; Nair, G. G.; Prasad, S. K. Phys. Chem. Chem. Phys. 2009, 11, 6450−6454. (19) Ye, C.; Li, M.; Luo, J.; Chen, L.; Tang, Z.; Pei, J.; Jiang, L.; Song, Y.; Zhu, D. J. Mater. Chem. 2012, 22, 4299−4305. (20) Kawamoto, M; Sassa, T.; Wada, T. J. Phy. Chem. B 2010, 114, 1227−1232. (21) Kawatsuki, N.; Tsutsumi, T.; H. Takatsuka, H. Macromolecules 2007, 40, 6355−6360. (22) Yu, H.; Ikeda, T. J. Am. Chem. Soc. 2006, 128, 11010−11011. (23) Sharma, G. D.; Suresh, P.; Mikroyannides, J. A.; Stylianakis, M. J. Mater. Chem. 2010, 20, 561−567. (24) Irie, H. Chem. Rev. 2000, 100, 1685−1716. (25) Tian, H.; Yang, S. Chem. Soc. Rev. 2004, 33, 85−97. (26) Kawata, S.; Kawata, Y. Chem. Rev. 2000, 100, 1777−1788. (27) Natali, M.; Giordani, S. Chem. Soc. Rev. 2012, 41, 4010−4029. (28) Morinaka, K; Ubukata, T.; Yokoyama, K. Org. Lett. 2009, 11, 3890−3893. (29) Zhu, W.; Yang, Y.; Metivier, R.; Zhang, Q.; Guillot, R.; Xie, Y.; Tian, H.; Nakatani, K. Angew. Chem., Int. Ed. 2011, 50, 10986−10990. (30) Tan, W.; Zhang, Q.; Zhang, J.; Tian, H. Org. Lett. 2009, 11, 161−164. (31) Yamaguchi, T.; Irie, M. J. Mater. Chem. 2006, 16, 4690−4694. (32) Taguchi, M.; Nakagawa, T.; Nakashima, T.; Kawai, T. J. Mater. Chem. 2011, 21, 17425−17432. (33) Norsten, T.; Branda, N. R. J. Am. Chem. Soc. 2001, 123, 1784− 1785. (34) Zou, Q.; Li, X.; Zhang, J.; Zhou, J; Sun, B.; Tian, H. Chem. Commun. 2012, 48, 2095−2097. (35) Chen, S.; Yang, Y.; Wu, Y.; Tian, H.; Zhu, W. J. Mater. Chem. 2012, 22, 5486−5494. (36) Shiozawa, T.; Hossain, M. K.; Ubukata, T.; Yokoyama, Y. Chem. Commun. 2010, 46, 4785−4787. (37) Feringa, B. L.; van Delden, R. A.; Koumura, N.; Geertsema, E. M. Chem. Rev. 2000, 100, 1789−1816. (38) Tanifuji, N.; Irie, M.; Matsuda, K. J. Am. Chem. Soc. 2005, 127, 13344−13353. (39) Nakatsuji, S. Chem. Soc. Rev. 2004, 33, 348−353. (40) Kawai, T.; Nakashima, Y. Adv. Mater. 2005, 17, 309−314. (41) Kudernac, T.; Katsonis, N.; Browne, W. R.; Feringa, B. L. J. Mater. Chem. 2009, 19, 7168−7177. (42) Matsuda, K.; Yamaguchi, H.; Sakano, T.; Ikeda, M.; Tanifuji, N.; Irie, M. J. Phys. Chem. C 2008, 112, 17005−17010. (43) Uchida, K.; Yamanoi, Y.; Yonezawa, T.; Nishihara, H. J. Am. Chem. Soc. 2011, 133, 9239−9241. (44) Sud, D.; Wigglesworth, T. J.; Branda, N. R. Angew. Chem., Int. Ed. 2007, 46, 8017−8019. (45) Fujimoto, Y.; Ubukata, T.; Yokoyama, Y. Chem. Commun. 2008, 5755−5757. (46) Hirose, T.; Matsuda, K.; Irie, M. J. Org. Chem. 2006, 71, 7499− 7508. (47) Lucas, L. N.; van Esch, J.; Kellogg, R. M.; Feringa, B. L. Chem. Commun. 2001, 759−760. (48) Yumoto, K.; Irie, M.; Matsuda, K. Org. Lett. 2008, 10, 2051− 2054. (49) Li, Z. X.; Liao, L. Y.; Sun, W.; Xu, C. H.; Zhang, C.; Fang, C. J.; Yan, C. H. J. Phy. Chem. C 2008, 112, 5190−5196. (50) Xie, N.; Zeng, D. X.; Chen, Y. Synlett 2006, 5, 737−740.

was added to the solution of 1b. Further study found that the recovered 1b could be bleached back to 1a with visible light irradiation. In light of the above results, the structure of 1c was proposed to be a protonated ring-closed isomer (it should be emphasized that the structure is only a prediction based on limited evidence). The conversion of 1c from both 1aH and 1b was outlined in Scheme 4. 3.4. Stability and Solubility of 1c. Both stability and solubility of 1c were investigated. Preliminary experiments showed that 1c is photoinactive and no significant change (detection by absorption spectral) was detected when the solution of 1c was irradiated with UV light or visible light for more than 10 min. 1c is also thermal stable at ambient temperature and no decompose was observed when the solution of 1c was kept at ambient temperature for several weeks. In addition, it was found that 1c is hydrophilic whereas both 1aH and 1b are hydrophobic (1a is also insoluble in water). As presented in Figure 4, 1aH or 1b dissolved in toluene (up), after irradiation with UV light (for the solution of 1aH) or addition of acid (for the solution of 1b), both 1aH and 1b converted to 1c, which was soluble in water (bottom). The change of solubility from hydrophilic to hydrophobic with light irradiation probably provides a simple way to transfer hydrophobic dye to hydrophilic dye by phototrigger, which is beneficial to application such as photoresist.

4. CONCLUSIONS In summary, a protonated diarylethene derivative has been synthesized. It has been demonstrated that the protonated diarylethene derivative is photoactive and converted to a photoinactive protonated ring-closed isomer upon irradiation with UV light. It has also been demonstrated that the protonated ring-closed isomer is hydrophilic whereas the protonated ring-opened isomer is hydrophobic.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported the National Nature Science Foundation of China (91123032) and Beijing Natural Science Foundation (Synthesis and properties of recording material for multilevel memory).

■

REFERENCES

(1) Zimmerman, H. E.; Shorunov, S. J. Org. Chem. 2009, 74, 5411− 5416. (2) Rudolf, P.; Buback, J.; Aulbach, J. J. Am. Chem. Soc. 2010, 132, 15213−15222. (3) Sarma, S. J.; Jones, P. B. J. Org. Chem. 2010, 75, 3806−3813. (4) Nagarathinam, M.; Vittal, J. J. Chem. Commun. 2008, 438−440. (5) Saha, S.; Stoddart, J. F. Chem. Soc. Rev. 2007, 36, 77−92. (6) Ostrowshi, A. D.; Deakin, S. J.; Azhar, B.; Miller, T. W.; Franco, N.; Cherney, M. M.; Lee, A. J.; Burstyn, J. N.; Fukuto, J. M.; Megson, I. L.; et al. J. Med. Chem. 2010, 53, 715−722. (7) Shieh, Y. A.; Yang, S. J.; Wei, M. F.; Shieh, M. J. ACS Nano 2010, 4, 1433−1442. (8) Morgan, J.; Jackson, D.; Zheng, X.; Pandey, S. K.; Pandey, R. K. Mol. Pharm. 2010, 7, 1789−1804. (9) Shao, Q.; Xing, B. Chem. Soc. Rev. 2010, 39, 2835−2846. (10) Sortino, S. J. Mater. Chem. 2012, 22, 301−318. 9903

dx.doi.org/10.1021/jp3070163 | J. Phys. Chem. A 2012, 116, 9900−9903