photochromic copolymers containing bisthienylethene units

Photochromic Copolymers Containing

Bisthienylethene Units

Sheng Wang, Xiaochuan Li, Bingzhi Chen, Qianfu Luo, He Tian*

Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai,200237 P. R. ChinaFax: þ86-21-64252288; E-mail: [email protected]

Received: March 17, 2004; Revised: May 25, 2004; Accepted: May 26, 2004; DOI: 10.1002/macp.200400106

Keywords: copolymerization; luminescence; photochromic; synthesis

Introduction

Organic photochromic materials attract much attention

because of their numerous potential applications for optical

devices, such as ultra-high-density optical information

storage, variable-transmission filters, and photoregulated

molecular switches. Among various types of photochromic

compounds, bisthienylethene (BTE) derivatives are the

most promising compounds because of their excellent

fatigue resistance and thermal stability in both isomeric

forms.[1–4] In particular, photochromic bisthienylethene

polymers may meet the requirements in many practical

applications because of their excellent photoresponsive

behavior in the solidsor crystals.Variousmethodshavebeen

employed to prepare the photochromic diarylethene poly-

mers.[5–8] For example, Branda et al.[5a] synthesized

1,2-dithienylcyclopentene photochromic polymers with

ultra-high content in the main-chain by ring-opening meta-

thesis polymerization (ROMP). Irie et al.[7] prepared an

amorphous photochromic polymer by oxidation poly-

merization closed-ring isomers of 1,2-bis[2-methyl-6-

(o-hydroxyphenyl)-1-benzothiophen-3-yl]hexafluorocy-

clopentene. Recently, diarylethene dimer linked through a

phenyl ring was reported to show better photochromic

reactivity.[9]

Here we use two simple methods to prepare the photo-

chromic copolymers. One is Wittig polycondensation

reaction; the other is radical polymerization. By employing

the above methods two families of photochromic copoly-

mers containing bisthienylethene units were synthesized

(as illustrated Scheme 1) and the photochromism of the

copolymers was investigated in solution and in solid film.

For the copolymer containing fluorene fluorophore unit and

BTEunit, appreciable fluorescence changes could beobserv-

ed along with the photochromic reaction, which might be

used as a potential readout method for erasable information

storage.[6,14a,10] In addition, the recording density for two-

wavelength recording using a two-component photochro-

mic crystal is twice as high as for common one-component

crystal systems.[11] In order to obtain high performance

Summary: Two simple yet effective strategies (Wittig con-densation reaction and radical polymerization) for thesynthesis of photochromic copolymers containing bisthieny-lethene units are presented. A new family of photochromiccopolymer containing bisthienylethene and fluorophores

units in the main chains was synthesized by Wittig conden-sation reaction. Another novel photochromic copolymerwithmulti-component photochromic pendent groups was prepar-ed by radical polymerization. Photochromism of the copoly-mers was investigated in solid film and in solution.

Photochromic copolymers containing bisthienylethene units.

Macromol. Chem. Phys. 2004, 205, 1497–1507 DOI: 10.1002/macp.200400106 � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper 1497

photochromic solid film, multi-component photochromic

copolymers should be explored. Here, a novel multi-

photochromic copolymer (copolymer 3 shown inScheme1)

has been obtained by radical polymerization and introduc-

tion of different kinds of photochromic units into the poly-

mer. This procedure might offer a route towards capability

in high-density optical memory data storage.

Results and Discussion

The synthesis of photochromic copolymer poly[{9,90-dio-ctylfluorene-2,7-ylenevinylene}-alt-{5,50-[bis(2-methyl-

3-thienyl)cyclopentene]enevinylene}]P(BTE-PF)and poly-

[{2,5-dioctyloxy-1,4-phenylenevinylene}-alt-{5,50-[bis(2-methyl-3-thienyl)cyclopentene]enevinylene}] P(BTE-

PPV) were performed byWittig polycondensation reaction

as shown in Scheme 2. The copolymer P(BTE-PF) was

synthesized by 1,2-bis(5-formyl-2-methyl-3-thienyl)cyclo-

pentene (this compound was synthesized according to the

literature procedure[12]) reaction with 2,7-bis(bromo-

methyl)-9,90-dioctanylfluorene triphenyl phosphonium salt

in the solution of sodium ethoxide (EtONa). After the reac-

tion was completed, the mixture was poured into methanol

and precipitated three times. The resulting polymer P(BTE-

PF) was dried in vacuum to give yellow solid. The copoly-

mer P(BTE-PPV) was prepared by 1,2-bis(5-formyl-2-

methyl-3-thienyl)cyclopentene reaction with 2,5-bis(bro-

momethyl)-1,4-dioctyloxybenzene triphenyl phosphonium

salt according to the same procedure. Two copolymers

containing bisthienylethene units in the main-chain were

obtained with satisfactory yields as yellow solids. They are

identified by FTIR and 1HNMRanalyses. Both copolymers

were founded readily to dissolve in common organic sol-

vents such as tetrahydrofuran (THF), chloroform and

toluene and so on.

The basic strategic employed for the synthesis of photo-

chromic Copolymer 3 was based on the radical polymeriza-

tion reaction as shown in Scheme 3. The key intermediate

1-(5-benevinyl-2-methyl-3-thienyl)-2-[5-benevinyl-(40-methacrylate-propyl-ether)-2-methyl-3-thienyl]cyclo-

pentene11wassynthesizedby1,2-bis(5-formyl-2-methyl-3-

thienyl)cyclopentene via Wittig reaction, etherification. The

other key intermediate 2,3-bis(2,4,5-trimethyl-3-thienyl)-N-

(methacrylate ether)propyl maleic imide 6 was prepared by2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydrides by sub-

stituting with propanolamine, then etherification with meth-

acrylic chloride. Finally compound6 and compound 11werecopolymerized with methyl methacrylate (MMA) in the

Scheme 1. The structures of photochromic copolymers containing bisthienylethene units.

1498 S. Wang, X. Li, B. Chen, Q. Luo, H. Tian

Macromol. Chem. Phys. 2004, 205, 1497–1507 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

presence of 2,20-azoisobutyronitrile (AIBN) as radical initi-ator in toluene solutions. The Copolymer 3 was dissolved

in toluene and precipitated with methanol four times. The

resulting copolymerwas dried invacuum to give satisfactory

yields as buff powder and its glass transition temperature (Tg)

was 138.9 8C, determined by DSC.

The chemical structure of Copolymer 3was also verifiedby 1H NMR. The polydispersity index of copolymers was

determined by gel permeation chromatography (GPC)

against the polystyrene standards and the data of GPC

analysis are listed in Table 1.

The copolymers P(BTE-PF) and P(BTE-PPV) were

found to exhibit photochromic properties in the solution

as well as fluorescence with high fluorescence quantum

yield. Figure 1 shows absorption spectral changes of poly-

mer P(BTE-PF) in THF. The absorption peak of the open-

ring form was observed at 392 nm and its threshold

wavelength was around 450 nm. Upon irradiation with UV

light (365 nm), the yellow solution of polymer P(BTE-PF)

in THF turned to dark green and an absorption band

appeared at 592 nm. The red-shift of the absorption maxi-

mum in the polymer P(BTE-PF) from open-ring form to

closed-ring form is attributed to larger p-conjugation in thepolymer.[14] In the open-ring form, an effective conjugation

interruption at 3-thiophene existed in the backbone of

the polymer and p-electrons are localized in the two

thiophene units, while in the closed-ring form p-electronsdelocalize along the whole main chain in the copolymer.

The absorption maximum for the closed-ring form of co-

polymer P(BTE-PF)was quite comparable to that ofmodel 4compoundand the smalldifferenceobservedbetween themis

within the range of the expected substitute effect. The similar

absorption and emission profiles further suggest the nearly

same electronic band structures exist between the model 4

and the polymer P(BTE-PF) of about 80 repeating units.[14]

Figure 2 shows absorption spectral changes of copolymer

P(BTE-PPV) in THF. The absorption peak of the open-ring

form was observed at 272 and 360 nm. Upon irradiation

with UV light (365 nm), the yellow color solution of co-

polymer P(BTE-PPV) in THF turned to dark green and an

absorption band appeared at 590 nm. The bathochromic

shift of the closed-ring form is attributed to large p-electrondelocalization along the main chain in copolymer P(BTE-

PPV). Figure 3 shows fluorescence spectra of copolymer

Scheme 2. Synthetic routes of photochromic copolymers P(BTE-PF) and P(BTE-PPV).

Photochromic Copolymers Containing Bisthienylethene Units 1499


P(BTE-PF) in THF. The open-ring form of copolymer

P(BTE-PF) exhibited intense fluorescence emission be-

cause of the introduction of an appropriate fluorophore,

namely, fluorene. In copolymer P(BTE-PF), 9,90-dioctyl-fluorene derivatives act as a fluorophore bridge between two

bisthienylethene units. The relative fluorescence quantum

yield for the open-ring form of copolymer P(BTE-PF) was

determined as 0.36 (Rhodamine 6G in ethanol as a refer-

ence), which is quite high as compared to that of other

photochromic bisthienylethene systems.[10] For the open-

ring form of copolymer P(BTE-PF), whose strong emission

with lmax at 442 nm and 466 nm was observed, when

excited at 392 nm. The emission profile was similar to that

of the polyfluorene. Upon irradiation with UV light

(365 nm), an interesting phenomenon was observed in

view of fluorescence intensity changes. For the long-term

irradiation, the fluorescence intensity decreased upon the

photocyclization and the fluorescence was quenched by the

Scheme 3. The synthesis of photochromic Copolymer 3.



photochromic photostationary state. However, the fluores-

cence intensity of copolymer P(BTE-PF) firstly increased to

the maximum value for the initial irradiation, and then

decreased to the minimum value with the increasing of the

irradiation time. Figure 3a shows the increasing of fluo-

rescence intensity on the initial irradiation. Figure 3b shows

the decrease of fluorescence intensity upon the irradiation

time.

The possible explanation for this interesting phenom-

enon is based on two different mechanisms.[15,16] One, the

aggregation form (A) of the copolymer, turns off certain

non-radiative decay processes of the fluorophores, but it

results in the formation of new emitting species having a

stronger fluorescence character than its origin. The other,

the closed-ring form (C) of copolymer P(BTE-PF) produ-

ced by UV irradiation, appears to behave as a fluorescence

quencher and to be responsible for the decrease of the fluo-

rescence. The fluorescence quenching by the closed form is

attributed to the efficient energy transfer from the excited

fluorophore core to the attached closed-ring BTE unit that

has lower energy level. At the earlier stage upon the irra-

diation, the fluorescence intensity researched to the maxi-

mum because that the molecular ratio (A/C) would be high.

Thus, the fluorescence enhancement is observed. The

fluorescence intensity maximum is obtained upon initial

irradiation for about 2.5 min. The prolong irradiation in-

creases the extent of the closed-ring form (C) gradually, the

intramolecular fluorescence quenching mechanism plays a

key role to compensate for the resulting decrease of the

fluorescence intensity.At the photostationary state, the fluo-

rescence intensity minimum was observed. Figure 4 shows

the changes of the fluorescence intensity vs the irradiation

time for copolymer P(BTE-PF) in THF.

Figure 5 shows fluorescence spectra of copolymer

P(BTE-PPV) in THF. For the open-ring form of copolymer

P(BTE-PPV), strong emission with lmax at 460 nm and

485 nmwas observed in THF. The fluorescence intensity of

copolymer P(BTE-PPV) in THF has very similar changes

as that of copolymer P(BTE-PF) upon UV irradiation. Both

photochromic copolymers P(BTE-PF) and P(BTE-PPV)

have relative high cyclization converting efficiency as

listed in Table 1, which is ascribed to the increase of the

Table 1. Molecular number-average (Mn) and weight-average (Mw) of the copolymers and absorption and emission spectral data as wellas photocyclization converting efficiency ZO–C of the open-ring forms.

Copolymer Mn Mw Mw=Mn lmax lem ZO–Cc) Quantum yield

nm nm cyclization cycloreversion

P(BTE-PF) 6 996 9 268 1.33 392a) 422 0.81a) 0.26 0.06466

P(BTE-PPV) 3 323 5 634 1.69 360a) 460 0.71a) 0.38 0.14485

Copolymer 3 33 709 61 655 1.83 343b) 0.67b) 0.25 0.12

a) In THF.b) In toluene.c) Photocyclization converting efficiency ZO–C calculated according to the method used in Ref. [13].

Figure 1. Absorption changes of copolymer P(BTE-PF) in THF(1.2� 10�5 mol �L�1) upon irradiation with 365 nm light.

Figure 2. Absorption changes of copolymer P(BTE-PPV) inTHF (1.2� 10�5 mol �L�1) upon irradiation with 365 nm light.



anti-parallel conformation in the backbone of the copoly-

mers.[17] However, they exhibit low cycloreversion quan-

tumyield, it is because the bigp-conjugated systemenhance

the energy of closed-ring carbon-carbon single bond, which

leads the cycloreversion quantum yield to reduce.[18]

Regretfully, the obvious photochromic behavior of above

copolymers was not observed in solid film. It was inferred

that the relatively low photochromic reactivity in this

p-conjugated main-chain type diarylethene polymer ap-

peared to originate from intramolecular interaction or the

free rotation of the polymer chain and the repeat units were

suppressed in amorphous films. Excited state energy trans-

fer from the one diarylethene site to the other site seems

to suppress further photochromic ring-cyclization reac-

tion from the open-ring form to the closed-ring form. In

addition, the absorption of the polymeric main chain

(polyfluorene or PPV) in UV region would reduce or filter

partially the excitation energy for the photochromic reac-

tion of the BTE units in the copolymers.

A colorless solution of Copolymer 3 in toluene turned

brick-brown color upon irradiation with 402 nm light, as

shown in Figure 6 (sample 2). Then the solution reverted to

the initial state upon irradiation with 521 nm light. Upon

further irradiation on colorless sample 1 with 342 nm light,

the solution turned blue (Figure 6, sample 3). When the

Figure 3. Fluorescence spectral changes of copolymer P(BTE-PF) in THF (1.2� 10�5 mol �L�1).

Figure 4. Change curve of the fluorescence intensity at 466 nmvs the irradiation time.

Figure 5. Fluorescence changes of copolymer P(BTE-PPV) inTHF (1.2� 10�5 mol �L�1).



solutionwas exposed simultaneously by342nmand402nm

light, it turned bluish violet (Figure 6, sample 4). Based on

the experiments, it is inferred that the above color changes

originates from the photoreaction of Copolymer 3 as shownin Scheme 4. When two kinds of dithienylethene units in

Copolymer 3 are open-ring state (3 (OO)), the solution

shows colorless of the initial state. Upon irradiation with

402 nm, 2,3-bis(2,4,5-trimethyl-3-thienyl)-N-hydroxy-

propyl maleic imide units in Copolymer 3 convert their

closed-ring forms, while 1-(5-benevinyl-2-methyl-3-thie-

nyl)-2-[5-benevinyl-(40-methacrylate-propyl-ether)-2-

methyl-3-thienyl]cyclopentene units still remain in their

open-ring state (3 (CO)), the solution shows the color

of closed isomers of 2,3-bis(2,4,5-trimethyl-3-thienyl)-

N-hydroxypropyl maleic imide. Upon irradiation with

342 nm, 1-(5-benevinyl-2-methyl-3-thienyl)-2-[5-benevi-

nyl-(40-methacrylate-propyl-ether)-2-methyl-3-thienyl]cy-

clopentene units in Copolymer 3 convert their closed-ring

isomers, but 2,3-bis(2,4,5-trimethyl-3-thienyl)-N-hydroxy-

propyl maleic imide units are inactive to this irradiation

wavelength, the solution of 3 (OC) shows the color of theclosed isomers of 1-(5-benevinyl-2-methyl-3-thienyl)-

2-[5-benevinyl-(40-methacrylate-propyl-ether)-2-methyl-

3-thienyl]cyclopentene. When the solution was exposed

simultaneously to 342 nm and 402 nm light, the solution

shows the color of the both closed-ring isomers of 2,3-

bis(2,4,5-trimethyl-3-thienyl)-N-hydroxypropyl maleic

imide and 1-(5-benevinyl-2-methyl-3-thienyl)-2-[5-bene-

vinyl-(40-methacrylate-propyl-ether)-2-methyl-3-thienyl]-

cyclopentene 3 (CC).In addition, the Copolymer 3 shows also excellent photo-

chromic reaction by irradiationwith 365 nm light in toluene

and in solid film as shown in Figure 7a and Figure 7b, res-

pectively. When upon 365 nm light irradiation, the toluene

solution of Copolymer 3 turned from the colorless to bluish

violet and a new absorption band appeared at 570 nm.

Copolymer 3 retains its photochromic behavior in the thin

film when spin-coated from its toluene solution onto quartz

substrates. Upon the irradiation with 365 nm the thin film

of the Copolymer 3 results in the similar color change,

indicating that the photochromic property of theCopolymer

3 was conserved in proceeds.

Conclusions

In summary, we applied Wittig polycondensation and radi-

cal polymerization to synthesize two types of photochromic

copolymers containing bisthienylethene units. A family of

highly fluorescent photochromic copolymers was synthe-

sized by Wittig polycondensation reaction containing the

fluorophore (for example, polyfluorene) and the photo-

chromic units in the main chain. Appreciable fluorescence

changes were observed, which indicated the potential

application of the polymer in a readout system by means of

Figure 6. Color changes of Copolymer 3 in toluene uponirradiation with different light. Sample 1: initial state; Sample2 and 3 with 402 and 342 nm, respectively; Sample 4: uponirradiation with 402 and 342 nm light alternatively.

Scheme 4. Photoreaction of Copolymer 3 with multi-component photochromic groups.



luminescence. Wittig polycondensation is a simple method

to prepare the main-chain copolymer containing fluoro-

phore and photochromophore. In addition, a novel photo-

chromic copolymer (Copolymer 3) with multi-component

photochromic pendent groups was also prepared by radical

polymerization method, which is an ideal method to syn-

thesize the photoresponsive copolymerhavingmulti-compo-

nent photochromic groups. Copolymer 3 shows multi-color

photochromic processes upon irradiation with different light

sources and it retains obvious photochromic behavior in the

thin film formed from the solution spin-coated.

Experimental Part

Instruments

Absorption spectra were measured on a Varian Cary500 UV-Vis spectrophotometer. Fluorescence spectra were measuredon a Varian Cary Eclipse Fluorescence spectrophotometer. 1HNMR spectra were recorded on a Bruker AM500 spectrometer

with tetramethyl silane as internal reference. Mass spectrawere obtained on a HP5989 mass spectrometer. The averagemolecular weight of copolymer was determined with a Waters410 gel permeation chromatograph (GPC). Differential scan-ning calorimetry (DSC, Waters 1040) was used to determinethe glass transition temperature (Tg). The optical switch ex-periments were carried out using a photochemical reactionapparatus (British Applied Photophysics, Limited) with a200 W Hg lamp. Quantum yields were determined by withmonochromatic light of Hg lamp and 200WXe lamp at differ-ent absorption maximum of the samples at room temperature.

Synthesis of Copolymers P(BTE-PF) and P(BTE-PPV)

Synthesis of 2,7-Bis(bromomethyl)-9,90-dioctylfluorene 1

Amixture of 9,90-dioctylfluorene (1.6 g, 53 mmol) and 30% of3.6 ml hydrogen bromide in acetic acid (10 ml) was stirred at80 8C for 24 h. After the reaction mixture cooled to roomtemperature, it was slowly poured into saturated sodium bicar-bonate aqueous solution (50 ml). The mixture was extractedwith dichloromethane (3� 30 ml) and washed with water,saturated aqueous sodium bicarbonate solution and brine. Thecombined organic extracts were dried over anhydrous magne-sium sulfate and evaporated. The residue was purified bycolumn chromatography on silica gel (petroleum ether) to giveproduct 1 in 66% yield.

1H NMR (CDCl3): d¼ 0.59 (t, 6H,CH3), 0.72–1.04 (m,22H, –CH2–), 1.95 (m, 4H, –CH2–), 4.60 (s, 4H, –CH2Br),7.28–7.30 (m, 2H, benzene), 7.34–7.43 (m, 4H, benzene),7.64 (m, 2H, benzene).

MS (EI): m/z¼ 574.3 (Mþ).

Synthesis of 2,7-Bis(bromomethyl)-9,90-dioctanylfluoreneTriphenyl Phosphonium Salt 2

Amixtureof2,7-bis(bromomethyl)-9,90-dioctylfluorene (2.6g,0.5 mmol), triphenyl phosphine (3.93 g, 15 mmol) and 30 mlanhydrous N,N0-dimethylformamide (DMF) was heated toreflux with stirring for 12 h. The mixture was cooled to roomtemperature and added slowly to 150 ml ether while beingstirred. The white precipitate was filtered, washed with etherand dried in vacuum to afford product 2 in 56% yield.

Synthesis of 2,5-Bis(bromomethyl)-1,4-dioctyloxybenzeneTriphenyl Phosphonium Salt 3

A mixture of 2,5-bis(bromomethyl)-1,4-dioctyloxybenzene(2.6 g, 0.5 mmol), triphenyl phosphine (3.93 g,15 mmol) and30 ml anhydrous toluene was heated to reflux with stirring for12 h. The white solid was precipitated out and filtered, washedwith toluene and dried in vacuum to afford product 3 in 56%yield.

Synthesis of 1,2-Bis(5-formyl-2-methyl-3-thienyl)cyclopentene 4

2.5 ml butyl lithium (2.5 M in hexane) was slowly dropped to astirred solution of 1,2-bis(5-chloro-2-methylthien-3-yl)cyclo-pentene (1.0 g, 5mmol) in 10ml anhydrous THF at�78 8Cand

Figure 7. Absorption changes of Copolymer 3 in toluene(3.0� 10�5 mol �L�1) and in solid film upon irradiation with365 nm.



under nitrogen. After 15 min stirring at �78 8C, anhydrousDMF 3 ml was added and the mixture was allowed warm toroom temperature. The reaction mixture was poured into adilute solution of HCl and extracted with dichloromethane.The organic phase was washed with water, dried over anhy-drous magnesium sulfate and evaporated under reduced pres-sure. The residue was purified by column chromatography onsilica gel (dichloromethane/petroleum ether: 3/1) to giveproduct 4 in 21% yield.

1HNMR (CDCl3): d¼ 2.05 (s, 6H,CH3), 2.12 (m, 2H, –CH2,J¼ 7.54 Hz), 2.84 (s, 4H, –CH2, J¼ 7.41 Hz), 7.43 (s, 2H,thiophene-H), 9.74 (s, 2H, –CHO).

Synthesis of Poly[{9,90-dioctylfluorene-2,7-ylenevinylene}-alt-{5,50-[bis(2-methyl-3-thienyl)cyclopentene]-enevinylene}] P(BTE-PF)

2,7-Bis(bromomethyl)-9,90-dioctanylfluorene triphenyl phos-phonium salt 2 (132 mg, 0.12 mmol) and 1,2-bis(5-formyl-2-methyl-3-thienyl)cyclopentene 4 (38 mg, 0.12 mmol) weredissolved in a mixture of anhydrous ethanol (10 ml) and THF(10 ml) at room temperature. To the above solution was addeddropwise a solution of EtONa (0.213 M in ethanol solution,1.5ml) under argon.After stirring for 12 h, themixture solutionwas poured into methanol with stirring. The precipitate wascollected by filtration. This operationwas repeated three times.The resulting polymer was dried in vacuum to give yellowfibrous solid in 61% yield.

1H NMR (CDCl3): d¼ 0.61–1.17 (br, 28H) 1.90–2.01 (br,6H), 2.05–2.10 (br, 6H), 2.70–2.85 (br, 6H), 6.5–6.85 (br, m,4H), 7.09–7.20 (br, 2H), 7.27–7.64 (br, 6H).

IR (KBr): 3052.2, 3012.9, 2951.0, 2923.4, 2849.9, 1671.0,1622.0, 1459.6, 1438.7, 1373.6, 1308.2, 1248.5, 1211.1,1159.7, 1143.3, 1026.1, 1004.7, 943.6, 887.6, 826.9, 806.4,745.2, 719.5 cm�1.

Synthesis of Poly[{2,5-dioctyloxy-1,4-phenylenevinylene}-alt-{5,50-[bis(2-methyl-3-thienyl)cyclopentene]-enevinylene}] P(BTE-PPV)

Synthesis of 2,5-Bis(bromomethyl)-1,4-dioctyloxybenzenetriphenyl phosphonium salt 3 (96.6 mg, 0.092 mmol) and1,2-bis(5-formyl-2-methyl-3-thienyl)cyclopentene 4 (29 mg,0.092mmol) were dissolved in a mixture of anhydrous ethanol(15 ml) and THF (15 ml) at room temperature. The abovesolution was added dropwise a solution of EtONa (0.213 M inethanol solution, 1.5 ml) under argon. After stirring for 12 h,the mixture solution was poured into methanol with stirring.The precipitate was collected by filtration. This operation wasrepeated three times. The resulting polymer was dried invacuum to give yellow fibrous solid in 20% yield.

1H NMR (CDCl3): d¼ 0.8� 1 (6H), 1.2� 1.5 (24H),1.6� 2 (6H), 2.2 (2H), 2.8 (4H), 3.5� 4.0 (4H), 6.3� 7.2 (8H).

Model Compound 4

2,7-Bis(bromomethyl)-9,90-dioctanylfluorene triphenyl phos-phonium salt 2 (0.45 mmol) and 2-formylthiophene (50 mg,0.45 mmol) were dissolved in a mixture of anhydrous THF(10 ml) and anhydrous ethanol (5 ml). 6.4 ml of freshlyprepared EtONa ethanol solution (conc. 0.23 M) was added

dropwise to the reaction flask via a syringe at room temperatureunder argon atmosphere. The mixture was poured into 50 mlwater, and then the aqueous layer was extractedwith ether. Thecombined organic extracts were dried with ether (30 ml� 3)and evaporated to give a yellow liquid. The crude product waspurified by column chromatography on silica gel using petro-leum ether as eluent to obtain compound 8 with yield of 58%.

1HNMR (CDCl3): d¼ 0.80 (t, 6H, J¼ 7.2Hz, –CH3), 1.01–1.08 (m, 20H, –CH2–), 1.09 (m, 4H, –CH2–), 1.99 (m, 4H,–CH2–), 7.00–7.05 (m, 4H, thiophene-H and –CH CH–),7.09 (d, 2H, J¼ 3.4 Hz, thiophene-H), 7.20 (d, 2H, J¼ 5.0 Hz,thiophene-H), 7.29 (d, 2H, J¼ 16.0 Hz, –CH CH–), 7.41 (s,2H, benzene-H), 7.45 (dd, 2H, J¼ 7.9Hz, J¼ 0.9Hz, benzene-H), 7.60 (d, 2H, J¼ 8.0 Hz, benzene-H).

IR (KBr): 3022.5, 3001.5, 2953.5, 2924.8, 2853.0, 1786.4,1624.9, 1465.7, 1417.4, 1376.5, 1360.3, 1305.1, 1260.5,1133.2, 1078.2, 1042.7, 947.4, 888.0, 854.0, 820.8, 753.8,722.1, 692.8 cm�1.

Synthesis of Copolymer 3

Synthesis of 2,3-Bis(2,4,5-trimethyl-3-thienyl)-N-hydroxypropyl maleic imide 5

A mixture of 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhy-dride (3.5 g, 10 mmol) and propanolamine (20.1 g, 270 mmol)in hexahydropyridine (15 ml) was refluxed for 14 h. The mix-ture was poured into the ice water and extracted with dich-loromethane andwashedwith hydrochloride aqueous solution,water and brine. The combined organic layer was dried overMgSO4, filtrated, and concentrated. The residue was purifiedby column chromatography (silica gel, CH2Cl2/ether 1:1) andafforded the compound 5 (3.3 g, 81%).

1H NMR (CDCl3) d¼ 1.74 (s, 3H), 1.86 (m, 2H) 1.89 (s,3H), 1.90 (s, 3H), 2.06 (s, 3H), 2.24 (s, 3H), 2.27 (s, 3H), 3.64 (t,2H, J¼ 5.89 Hz), 3.8 (t, 2H, J¼ 5.86 Hz).

Synthesis of 2,3-Bis(2,4,5-trimethyl-3-thienyl)-N-(methacrylate ether)propyl Maleic Imide 6

Compound 5 (2.0 g, 4.96 mmol) was dissolved in anhydrousdichloromethane (30 ml) and then triethylamine (3.0 g,29.7 mmol) was added. Methacrylic chloride (1.5 g) in anhy-drous dichloromethane (10 ml) was added dropwise at roomtemperature. After stirring for 12 h, the mixture solution waspoured intowater and extracted with dichloromethane (30ml),the organic layer was dried over MgSO4, filtrated, and concen-trated. The residue was purified by column chromatography(silica gel, CH2Cl2/petroleum ether 1:2) and afforded com-pound 6.

1HNMR (CDCl3) d¼ 1.73 (s, 3H), 1.88 (s, 3H), 1.89 (s, 3H),1.96 (s, 3H), 2.05 (s, 3H), 2.09 (m, 2H), 2.23 (s, 3H), 2.26 (s,3H), 3.76 (t, 2H), 4.19 (t, 2H, J¼ 6.14Hz), 5.57 (s, 1H), 6.15 (s,1H).

MS (EI): m/z¼ 471.2.

Synthesis of 1-(5-Chloro-2-methyl-3-thienyl)-2-(5-formyl-2-methyl-3-thienyl)cyclopentene 7

1,2-Bis(5-chloro-2-methylthien-3-yl)cyclopentene (1.0 g,3 mmol) was dissolved in anhydrous THF (10 ml) and butyl



lithium (1.25 ml of 2.5 M solution in hexane) was addeddropwise under nitrogen at �78 8C using a syringe. The mix-ture was stirred for 15 min at�30 8C and then the addition thereaction mixture was quenched with anhydrous dimethylfor-mamide (3 ml). The mixture was stirred for an addition hour atroom temperature, before it was poured into HCl (2 M, 25 ml).The mixture was extracted with ether. The organic layer wasdried overMgSO4, filtrated, and concentrated. The residuewaspurified by column chromatography (silica gel, CH2Cl2/petroleum ether 1:2) and afforded compound 7 (0.5 g, 51%).

1H NMR (CDCl3): d¼ 1.84 (s, 3H), 2.01 (m, 2H,J¼ 7.46 Hz), 2.05 (s, 3H), 2.77 (t, 4H, J¼ 8.00 Hz), 6.57 (s,1H), 7.44 (s, 1H), 9.74 (s, 1H).

MS (EI): m/z¼ 322.

Synthesis of 1-(5-Chloro-2-methyl-3-thienyl)-2-(5-benevinyl-2-methyl-3-thienyl) cyclopentene 8

Amixture of chloro benzyl triphenyl phosphonium salt (1.5 g,11.85 mmol) and compound 7 (1.5 g, 4.65 mmol) wasdissolved in anhydrous THF (20 ml) and anhydrous ethanol(20 ml) and stirred at room temperature. To the above solutionwas added dropwise EtONa (6 ml of 1 M solution in ethanol)under argon. After stirring for 1 h, the mixture solution waspoured into water and extracted with ether (50 ml), the organiclayer was dried over MgSO4, filtrated, and concentrated. Theresidue was purified by column chromatography (silica gel,petroleum ether) and afforded compound 8 (1.0 g, 54.3%).

1H NMR (CDCl3): d¼ 1.87 (s, 3H), 1.97 (s, 3H), 2.02 (m,2H, J¼ 7.43 Hz), 2.69 (t, 4H, J¼ 6.52), 6.61 (s, 1H), 6.65 (s,1H), 6.75 (s, 1H), 7.29 (s, 1H), 7.31–7.42 (m, 5H).

MS (EI): m/z¼ 396.

Synthesis of 1-(5-Formyl-2-methyl-3-thienyl)-2-(5-benevinyl-2-methyl-3-thienyl)cyclopentene 9

Compound 8 (1.2 g, 3 mmol) was dissolved in anhydrous THF(10 ml) and butyl lithium (1.25 ml of 2.5 M solution in hexane)was added dropwise under nitrogen at�78 8C using a syringe.The mixture was stirred for 15 min at �30 8C and then theaddition the reaction mixture was quenched with anhydrousDMF (3 ml). The mixture was stirred for an addition hour atroom temperature, before it was poured into HCl (2 M, 25 ml).The mixture was extracted with ether. The organic layer wasdried overMgSO4, filtrated, and concentrated. The residuewaspurified by column chromatography (silica gel, CH2Cl2/petroleum ether 1:1) and afforded compound 9 (0.5 g, 51%).

1H NMR (CDCl3): d¼ 1.78 (s, 3H), 1.94 (s, 3H), 2.04 (m,2H, J¼ 7.92 Hz,), 2.79 (t, 4H, J¼ 7.63 Hz), 6.64 (s, 1H), 6.71(s, 1H), 7.22 (s, 1H), 7.30–7.41 (m, 5H), 7.46 (s, 1H), 9.75 (s,1H).

MS (EI) m/z¼ 390.

Synthesis of 1-(5-Benevinyl-2-methyl-3-thienyl)-2-[5-benevinyl-(40-bromopropyl-ether)-2-methyl-3-thienyl]-cyclopentene 10

A mixture of p-bromopropyl-ether bromomethyl-benzenetriphenylphosophonium salt (1.0 g, 1.81mmol) and compound9 (0.7 g, 1.79 mmol) was dissolved in anhydrous THF (10 ml)

and anhydrous ethanol (10ml) and stirred at room temperature.To the above solution was added dropwise to EtONa (1 ml of1 M solution in ethanol) under argon. After stirring for 2 h, themixture solution was poured into water and extracted withether (30 ml), the organic layer was dried over MgSO4, filtrat-ed, and concentrated. The residue was purified by columnchromatography (silica gel, CH2Cl2/petroleum ether 1:1) andafforded compound 10 (0.4 g, 36.3%).

1H NMR (CDCl3): d¼ 1.85 (s, 3H), 1.91 (s, 3H), 2.02 (m,2H), 2.32 (m, 2H), 2.76 (t, 4H), 3.60 (t, 2H), 4.10 (t, 2H), 6.66 (s,2H), 6.75 (s, 2H), 7.10 (s, 2H), 7.30–7.43 (m, 9H), 9.75 (s, 1H).

MS (EI): m/z¼ 602.

Synthesis of 1-(5-Benevinyl-2-methyl-3-thienyl)-2-[5-benevinyl-(40-methacrylate-propyl-ether)-2-methyl-3-thienyl]cyclopentene 11

A mixture of compound 10 (0.33 g, 0.55 mmol) and meth-acrylic acid (0.06 g, 0.69 mmol) was dissolved in anhydrousDMF (15 ml). The solution was stirred for 20 h at 75 8C. Afterthe reactionmixture cooled to room temperature, it was pouredinto the water. The mixture was extracted with dichlorome-thane and washed with water and brine. The combined organiclayer was dried over MgSO4, filtrated, and concentrated. Theresidue was purified by column chromatography (silica gel,CH2Cl2/petroleumether 2:3) and afforded the compound 11(0.26 g, 80%).

1HNMR (CDCl3): d¼ 1.55 (s, H), 1.84 (s, 3H), 1.94 (s, 3H),2.01 (m, 2H), 2.74 (t, 4H), 2.31 (m, 2H), 3.60 (t, 2H), 4.06 (m,2H), 4.34 (t, 2H), 5.56 (s, 1H), 6.11 (s, 1H), 6.67 (s, 2H), 6.79 (s,2H), 7.08 (s, 2H), 7.34–7.4 (m, 9H).

MS (EI): m/z¼ 606.

Synthesis of Copolymer 3

In an ampoule flushed with argon, methyl methacrylate(MMA) (1.8 g, 25 mmol), compound 6 (0.01 g, 0.021 mmol),compound 11 (0.013 g, 0.021 mmol) and AIBN (0.01 g) weredissolved in toluene (5ml). The ampoulewas sealed and heatedfor 4 d at 65 8C. The copolymer thus obtainedwere dissolved intoluene and precipitated with methanol. This operation wasrepeated four times. The polymer was dried in vacuum to givethe buff powder.

1H NMR (CDCl3): d¼ 7.23 (br), 6.80 (br), 6.40–6.67 (m),4.08 (br), 3.95 (br), 3.38 (m), 2.20–2.67 (m), 1.52–1.99 (m).

Tg¼ 138.94 8C.

Acknowledgement: This work was supported by NationalScience Foundation of China and Education Committee ofShanghai.

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photochromic copolymers containing bisthienylethene units

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