苏艺博　王明盛　郭国聪

(中国科学院福建物质结构研究所，结构化学国家重点实验室，福州350002)

首例含4，4′-联吡啶和乙酸锌的光致变色化合物

苏艺博王明盛郭国聪＊

(中国科学院福建物质结构研究所，结构化学国家重点实验室，福州350002)

采用一种新方法得到一维配位聚合物[Zn(CH3COO)2(4，4′-bipy)]n(1)。配合物1的晶体结构和荧光性质已经有详细报道，但光致变色性质还没有相关的研究工作发表。通过研究化合物1在光照前后的紫外吸收光谱和顺磁共振谱，表明化合物1具有电子转移光致变色性能。实验结果验证了我们提出的利用非光致变色单元设计电子转移光致变色材料的新方法是有效可行的。

羧酸锌；4，4′-联吡啶；配位聚合物；光致变色；电子转移

Photochromic materials have drawn wide attentions for their reversible color change that irradiated by light in the one or two directions[1-2].Especially, electron-transfer(ET)photochromic materials such as viologens[3],naphthalene diimides[4],dibenzobarrelenes[5],salicylidene anilines[6]and tetrathiafulvalenes[7-8], provide various potential applications,for instance smart windows,optical data storage,solar cell,etc[9]. Most of ET photochromic compounds were synthesized using the well-known ET photoactive units,such as viologen cation or inner salts and polyoxometallates[10-12]. We have previously proposed a new design strategy for ET photochromic metal-organic complexes by the coordination between nonphotochromic units with lone pairs of electrons and those with large π-conjugate structures,and developed a new class of ET photochromic compounds[9].4,4′-bipyridine(4,4′-bipy)shows no ET photochromic behavior itself,and has been proved to be a good candidate to synthesize photochromic compounds by using the new strategy[13-15].

The crystal structure and some physical properties of the 1D coordination polymer[Zn(CH3COO)2(4,4′-bipy)]n(1)have been clearly studied previously, revealing intraligand fluorescence emission and good thermal property[16-17].In this article,we elucidate the electron-transfer photochromic behavior of 1 for the first time,which demonstrates again the effectiveness ofourpreviouslyproposeddesignstrategyforelectron-transfer photochromic materials.

1　Experimental

1.1Material and instrument

Chemicals were commercially obtained and used without further purification.Water was deionized and distilled before use.

A PLS-SXE300C 300 W xenon lamp system equipped with an IR filter was used to prepare colored samples for FTIR,UV-Vis absorption spectra(UVVis),Powder X-ray diffraction(PXRD),and electron spin resonance(ESR)studies.The distances between the samples and the xenon lamp were around 25 cm. TheFTIRspectrawererecordedonaBruker VERTEX 70 FT-IR spectrometer using KBr pellets in the range of 4 000～450 cm-1.The UV-Vis spectra were recorded at room temperature on a PerkinElmer Lambda 950 UV/Vis/NIR spectrophotometer equipped with an integrating sphere in the wavelength range of 200～1 200 nm.BaSO4plates were used as a reference (100%reflection),on which the finely ground powder of the sample was coated.The PXRD patterns were collected with a Rigaku MiniFlex II diffractometer powered at 30 kV and 15 mA for Cu Kα(λ=0.154 18 nm).The simulated pattern was produced using the Mercury Version 3.5.1 software(http://www.ccdc.cam. ac.uk/products/mercury/)andthereportedsingle crystal reflection diffraction data.The ESR spectra wererecordedonaBrukerELEXSYSE500 spectrometer with a 9.847 GHz magnetic field in X band at room temperature.The elemental analyses of C,H,and N were measured on an Elementar Vario EL III microanalyzer.

1.2Preparation of 1

Colorlesscompound1hasbeenpreviously synthesized by Zn(CH3COO)2·2H2O and 4,4′-bipy by a solvent evaporation or hydrothermal method[16-17].In this work,a mixture of Zn(CH3COO)2·2H2O(220 mg,1.0 mmol),(NH4)2SO3·H2O(136 mg,1.0 mmol),4,4′-bipy (156 mg,1.0 mmol)and trimethylamine(0.1 mL,0.7 mmol)was solved in an aqueous solution(5 mL)and sealed into a 20 mL Teflon-lined stainless steel vessel under autogenous pressure and then heated at 120℃ for 84 h.Yellow block crystals of 1 were collected and dried in air with 33%yield(based on Zn).Anal. Calcd.(%)for ZnC14H14N2O4:C:49.51;H:4.15;N: 8.25%.Found:C:49.46,H:4.18,N:8.48%.IR(KBr pellet,cm-1):3 042(w)1 602(s br),1 586(sh),1 487 (w),1 422(s br),1 332(w sh),1 218(m),1 067(m),1 044 (m),1 005(m),931(w),818(s),731(w),673(m),624(s), 469(w).

As reported,compound 1 features a 1D ladderlike chain structure,where[Zn(OAc)2]2dimers are double-bridged by 4,4′-bipy ligands along the[011] direction(Fig.1).The distance between N1 and O1 is about 0.286 8 nm,which is short enough to allow electron transfer happens[18].The phase purity of the crystalline samples used in this work was proved by the PXRD determination(Fig.2),elemental analysis and IR.

Fig.1　1D ladder structure of 1

Fig.2　PXRD patterns of 1

2　Results and discussion

Unlike traditional ways building ET photochromicmetal-organic complexes by choosing N-substitutedbipyridinium[12],N,N′-disubstitutedbipyridinium[10]or other photochromic units as electron acceptor,the new design strategy chooses nonphotochromic units such as 4,4′-bipy[14-15]and tris(4-pyridyl)triazine[13].To the best of our knowledge,the photochromic behavior of 1 has never been reported.We found that the yellow sample of 1 turned to purple after irradiation by a 300 W Xenon lamp under ambient condition.The UV-Vis spectra after irradiation,demonstrated in Fig.3,show that the absorption has obviously change between 320 and 630 nm.The new generated peaks at 380 and 554 nm are the typical absorption bands of oneelectron reduced species of 4,4′-bipy[19-20].After 120 minutesirradiation,theabsorptionturnstobe saturated and comes to a stable state.The colored sample could be easily bleached after annealing at 100℃for 30 min.

Fig.3　Time-dependent UV-Vis spectra of 1 upon irradiation by the Xe lamp under ambient condition,New absorption bands at 380 and 554 nm are the characteristic of 4,4′-bipy radical

An ESR study confirms the existence of radicals after light irradiation,suggesting that the photochromism of 1 is caused by an electron-transfer process. Before irradiation,the crystalline sample shows small ESR signal,which is caused by the ambient light during the determination since the samples are highly sensitive to the light.After irradiation,the one singleline signal at g=2.003 becomes multiple larger,which is characteristic of the free radical.After annealing at 100℃for 30 min,the radical signal decreases apparently,illustrating that radical is generated during theirradiationanddisappearedafterthermal bleaching.The appearance of radical signals after annealing is also caused by the ambient light during the determination.

Fig.4　ESR spectra of 1

3　Conclusions

In conclusion,wereportheretheelectrontransfer photochromic behavior of 1.This work proves that our previously proposed method for synthesis and design of electronic-transfer photochromic materials is relatively effective.

References:

[1]Exelby R,Grinter R.Chem.Rev.,1965,65:247-260

[2]Raymo F M,Tomasulo M.Chem.Soc.Rev.,2005,34:327-336

[3]Mercier N.Eur.J.Inorg.Chem.,2013:19-31

[4]Matsunaga Y,Goto K,Shinmyozu T,et al.Chem.Eur.J., 2014,20:7309-7316

[5]Sajimon M C,Ramaiah D,Suresh C H,et al.J.Am.Chem. Soc.,2007,129:9439-9445

[6]Jacquemin P L,Robeyns K,Garcia Yann,et al.Chem. Commun.,2014,50:649-651

[7]Tanaka K,Ishiguro F,Chujo Y.Langmuir,2010,26:10254-10258

[8]Tanaka K,Ishiguro F,Chujo Y.Langmuir,2010,26:1152-1156

[9]Wang M S,Xu G,Guo G C,et al.Chem.Commun.,2010, 46:361-376

[10]Xu G,Guo G C,Wang M S,et al.Angew.Chem.Int.Ed., 2007,46:3249-3251

[11]Chen Z W,Wang M S,Guo G C,et al.Cryst.Growth Des., 2014,14:2527-2531

[12]Lü X Y,Wang M S,Guo G C,et al.Inorg.Chem.,2012,51: 4015-4019

[13]Fu Z Y,Chen Y,Zhang J,et al.J.Mater.Chem.,2011,21:7 895-7897

[14]Zhu Q L,Sheng T L,Wu X T,et al.Chem.Eur.J.,2011, 17:3358-3362

[15]Zhang C J,Wang M S,Guo G C,et al.Inorg.Chem.,2014,53: 847-851

[16]Amiri M G,Morsali A.Z.Anorg.Allg.Chem.,2006,632: 2491-2494

[17]Conerney B,Kruger P E,Murray K S,et al.CrystEngComm., 2003,5:454-458

[18]Wu J,Tao C,Li Y,et al.Chem.Sci.,2014,5:4237-4241

[19]Braterman P S,Song J I.J.Org.Chem.,1991,56:4678-4682

[20]Bockman T M,Kochi J K.J.Org.Chem.,1990,55:4127-4135

The First Photochromic Compound Containing 4,4′-Bipyridine and Zinc Acetate

SU Yi-BoWANG Ming-ShengGUO Guo-Cong＊
(Fujian Institute of Research on the Structure of Matter,Chinese Academy of Sciences,Fuzhou 350002,China)

The 1D coordination polymer[Zn(CH3COO)2(4,4′-bipy)]n(4,4′-bipy=4,4′-bipyridine)has been synthesized under a new way.Previous studies have revealed its crystal structure and luminescent properties.In this article, we demonstrate its electron-transfer photochromic behavior,which is conformed to our previously proposed design strategy for electron-transfer photochromic materials.

zinc carboxylate;4,4′-bipyridine;coordination polymer;photochromism;electronic transfer

O614.24+1；O612.2

A

1001-4861(2015)09-1881-04

10.11862/CJIC.2015.259

2015-06-04。收修改稿日期：2015-08-04。

国家自然科学基金(No.21373225、21221001、21471149)和福建自然基金(No.2014J07003、2014J01065)资助项目。

＊通讯联系人。E-mail：gcguo@fjirsm.ac.cn