Patent Application: US-82875610-A

Abstract:
this invention relates to novel photochromic and electrochromic monomers and polymers based on 1 , 2 - dithienylcyclopentene derivatives and method of using and synthesizing same . the compounds are reversibly interconvertible between different isomeric forms under suitable photochromic or electrochromic conditions . the electrochromic conversion may be catalytic . the application also relates to ultra - high density homopolymers prepared using ring - opening methathesis polymerization where the central ring of the 1 , 2 - bis - cyclopentene is incorporated directly into the polymer backbone . the monomer units may be readily functionalized to enable the synthesis of polymers with diverse structural and electronic properties . the compounds have many potential applications including high - density optical information storage systems , photoregulated molecular switches , reversible holographic systems , ophthalmic lenses , actinometry and molecular sensors , photochromic inks , paints and fibers and optoelectronic systems such as optical waveguides , bragg reflectors and dielectric mirrors .

Description:
throughout the following description specific details are set forth in order to provide a more thorough understanding of the invention . however , the invention may be practiced without these particulars . in other instances , well known elements have not been shown or described in detail to avoid unnecessarily obscuring the present invention . accordingly , the specification and drawings are to be regarded in an illustrative , rather than a restrictive , sense . this application relates to 1 , 2 - dithienylcyclopentene derivatives having the general structure shown in scheme 1 below : as described in detail below , this application also relates to methods of synthesizing and using the compounds , including both polymer and monomer precursors . the compounds are reversibly convertible between the ring - open isomer ( i ) and the ring - closed isomer ( ii ) under photochemical and / or electrochemical conditions . for example , reversible photocyclization between the ring - open and ring - closed forms ( i , ii ) may occur when the compounds are irradiated with the appropriate wavelengths of light or electrochemically oxidized or reduced . for example , some compounds undergo photochemical ring - closing ( with uv light ) and both photochemical ( with visible light ) and electrochemical ( oxidation ) ring - opening . conversely other compounds undergo photochemical ring - opening under photochemical conditions and ring - closing under both photochemical and electrochemical conditions . accordingly , some of the compounds exhibit a dual - mode action combining both photochromism and electrochromism . as used in this patent application “ photochromism ” refers to the capacity of a compound to reversibly change color when subjected to radiant energy and “ electrochromism ” refers to the capacity to change color when subjected to a positive or negative charge . the general methodology for synthesizing the fluorinated derivatives of the invention is shown in scheme 2 . in this case octafluorocyclopentene is used as a reagent and r 1 and r 2 are f . as shown in table 1 , and as described in detail below , the following fluorinated monomeric compounds have been shown synthesized using the methodology of scheme 2 and have been shown to exhibit both photochromic and electrochromic properties as discussed above , the need to incorporate these compounds into workable materials such as films , sheets , fibers or beads demands that the compounds be in polymeric rather than monomeric forms . the fluorinated compounds may be polymerized using ring - opening methathesis polymerization ( romp ) as described in patent cooperation treaty application no . pct / ca01 / 01033 ( wo 02 / 06361 ) and as shown generally in scheme 3 below : another significant advantage of the invention is that the electrochromism of the photochromic compounds described herein is catalytic as shown in scheme 4 below . in particular , in an electrochemical cell the ring - closed form ( ii ) loses an electron to the anode ( i . e . it is oxidized ) and forms its radical cation . this radical cation undergoes a rapid ring - opening reaction to produce the radical cation of isomer ( i ). because the neutral form of isomer ( i ) requires a substantially more positive potential to undergo oxidation ( 1 . 27 v ), its radical cation immediately oxidizes a neighboring molecule of ( ii ) and is effectively neutralized . accordingly , only a small amount of the ring - closed form ( ii ) needs to be oxidized because this will ring - open to ( i ), which will subsequently remove an electron from another molecule of ( ii ) regenerating its radical cation . the continuation of this oxidize / ring - open / reduce cycle will eventually result in the complete conversion of ( ii ) to ( i ). the fact that the conversion between photochromic forms may be catalysed electrochemically may be advantageous in many applications of the invention , such as thin film displays . first , the need for diffusion of counterions is minimized which is often a kinetic bottleneck in conventional electrochromic systems . for example , in the case of an oxidation process , anions must be incorporated from the surrounding medium or cations must be ejected from the film to maintain charge balance . typically this is accomplished by adding a secondary electrochrome and a charge - carrying layer to the system . this step is not required in the present case . the catalytic system needs minimal movement of ions because there is no net change in charge in the reactions or a buildup of charge . as described above , when the radical cation of the ring - open isomer forms , it removes an electron from a neighbouring molecule of the ring - closed isomer and hence the process will propagate throughout the entire system . secondly , the catalytic process is very energy efficient since only a small amount of charge needs to be applied to initiate the catalytic cycle . thirdly , the colouration value will be very large . the colouration value is proportional to the change in absorpitivity and inversely proportional to the charge injected per unit area . this is particularly important when constructing devices from indium tin oxide ( ito ) electrodes which are semiconducting and have a very small number of charge carriers . in the case of films , very thin films such as monolayers do not contain a sufficient amount of active material to generate a satisfactory change in optical absorbance . thicker films would require the diffusion of ions through all of the layers . the catalytic system of the present invention does not require diffusion since the transfer process can be relayed throughout the entire film . in other words the electrochemical trigger does not need to be highly efficient since it is only required to initiate the catalytic cycle . the general methodology for synthesizing the non - fluorinated dithienylalkene derivatives using 2 , 3 - dibromobicyclo [ 2 . 2 . 1 ] hepta - 2 , 5 - diene as a reagent is shown in scheme 5 below . as shown in table 2 , and as described in detail below , the following non - fluorinated monomeric and polymeric compounds have been shown synthesized using the methodology of scheme 5 . an important advantage of the polymerization approach shown in scheme 5 ( for example , yielding polymerized compounds 10 , 11 12 and 13 ) is that the cyclopentene ring of the 1 , 2 - bis ( 3 - thienyl ) cyclopentene unit is incorporated directly into the polymer backbone . this results in a polymer having an ultra - high density of active photochromic / electrochromic components ( i . e . higher densities are achieved by decreasing the size of the linker that connects the dithienylethene to the polymer backbone ). higher density polymers offer the opportunity to express or store a greater amount of information per unit volume or surface area . for example , the percent mass of the active photochromic component in the side - chain polymers shown in scheme 3 ranges from 60 - 68 %. by way of comparison , the new generation main - chain polymers of scheme 5 have a percent mass of the active photochromic component ranging up to 93 %. this is primarily due to the romp reaction of the strained olefin producing the requisite cyclopentene backbone that has been shown to be very versatile . as described below , both lipophilic and hydrophilic versions of the polymers have been prepared . as described below , the photochromic polymers of table 2 have been shown to undergo induced isomerization both in solution and in solid state form . these functional polymers are therefore well suited for incorporation into workable materials such as films , sheets , fibers or beads . the following examples will further illustrate the invention in greater detail although it will be appreciated that the invention is not limited to the specific examples . all solvents were dried and degassed by passing them through steel columns containing activated alumina under nitrogen using an mbraun solvent purification system . solvents for nmr analysis ( cambridge isotope laboratories ) were used as received . all synthetic precursors were purchased from aldrich with the exception of pd ( pph 3 ) 4 and bis ( tricyclohexylphosphine ) benzylidene ruthenium ( iv ) dichloride ( grubb &# 39 ; s catalyst ) which were purchased from strem . octafluorocyclopentene was obtained from nippon zeon corporation . column chromatography was performed using silica gel 60 ( 230 - 400 mesh ) from silicycle inc . 1 h nmr characterizations were performed on a bruker amx 400 instrument working at 400 . 103 mhz . 13 c nmr characterizations were performed on a bruker amx 400 instrument working at 100 . 610 mhz . chemical shifts ( δ ) are reported in parts per million relative to tetramethylsilane using the residual solvent peak as a reference standard . coupling constants ( j ) are reported in hertz . ft - ir measurements were performed using a nexus 670 or a nicolet magna - ir 750 instrument . uv - vis measurements were performed using a varian cary 300 bio spectrophotometer . low resolution mass spectrometry measurements were performed using a hp5985 with isobutane as the chemical ionization source . standard lamps used for visualizing tlc plates ( spectroline e - series , 470 μw / cm 2 ) were used to carry out the ring - closing reaction of all photochromic compounds using a 365 - nm , a 313 - nm or a 254 - nm light source when appropriate . the compositions of all photostationary states were detected using 1 h nmr spectroscopy . the ring - opening reactions were carried out using the light of a 150 - w tungsten source that was passed through a 490 - nm or a 434 - nm cutoff filter to eliminate higher energy light . as used herein , a bold numeral ( e . g . 1 ) denotes the ring - open isomeric form of a compound and a bold , primed numeral ( e . g . 1 ′) denotes the ring - closed isomeric form of the same compound . a solution of 3 ′- bromo - 2 , 2 ′; 5 ′ 2 ′ terthiophene ( 0 . 749 g , 2 . 3 mmol ) in anhydrous et 2 o ( 25 ml ) cooled to − 20 ° c . was treated with n - buli ( 0 . 91 ml of a 2 . 5 m solution in hexane ) dropwise under an argon atmosphere . after stirring the solution for 30 min , octafluorocyclopentene ( 0 . 13 ml , 1 . 15 mmol ) was added dropwise using a cooled gas tight syringe and the solution immediately turned dark red in colour . after stirring for 1 h , the cooling bath was removed and the solution was allowed to warm to room temperature and stirred for 16 h when it was quenched with 5 % hcl ( 10 ml ). the aqueous layer was separated and extracted with et 2 o ( 2 × 10 ml ). all organic extracts were combined , washed with h 2 o ( 2 × 10 ml ), followed by brine ( 10 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 175 mg of pure product as a yellow crystalline solid . yield : 23 %. m . p . 116 - 117 ° c . ; 1 h nmr ( 300 mhz , cd 2 cl 2 ) δ7 . 30 ( dd , j = 5 , 1 hz , 2h ), 7 . 19 ( dd , j = 5 , 1 hz , 2h ) 7 . 11 ( dd , j = 4 , 1 hz , 2h ), 7 . 04 ( dd , j = 5 , 4 hz , 2h ), 6 . 83 ( dd , j = 5 , 3 hz , 2h ), 6 . 74 ( dd , j = 3 , 1 hz , 2h ), 6 . 41 ( s , 2h ); 13 c nmr ( 125 mhz , cd 2 cl 2 ) δ137 . 9 , 136 . 3 , 136 . 2 , 133 . 0 , 128 . 3 , 128 . 2 , 127 . 9 , 127 . 0 , 125 . 7 , 125 . 0 , 124 . 9 , 123 . 8 ( 12 of 15 carbons found ); ft - ir ( chcl 3 cast ) 3105 , 1695 , 1685 , 1651 , 1644 , 1616 , 1576 , 1561 , 1538 , 1505 , 1467 , 1415 , 1384 , 1328 , 1274 , 1244 , 1225 , 1191 , 1130 , 1096 , 1046 , 1028 , 976 , 952 , 877 , 833 , 757 , 696 , 581 , 553 , 472 , 458 cm − 1 ; hrms ( ei ) calcd for m + ( c 29 h 14 f 6 s 6 ): 667 . 9324 . found : 667 . 9337 . compound 1 ( 5 mg ) was dissolved in ch 2 cl 2 ( 20 ml ) and placed in a quartz glass cell . the solution was irradiated at 365 nm for 10 min . the solvent was evaporated off under reduced pressure and the crude product was recrystallized ( hexanes ) to afford the pure product as a blue powder . 1 h nmr ( 500 mhz , cd 2 cl 2 ) δ 7 . 49 ( d , j = 5 hz , 2h ), 7 . 38 ( dd , j = 4 , 1 hz , 2h ), 7 . 30 ( dd , j = 5 , 1 hz , 2h ), 7 . 28 ( d , j = 4 hz , 2h ), 7 . 07 ( dd , j = 5 , 4 hz , 2h ), 6 . 92 ( dd , j = 5 , 4 hz , 2h ), 6 . 58 ( s , 2h ). irradiation of a ch 2 cl 2 solution ( 2 × 10 − 5 m ) of compound 1 with 365 nm light resulted in an immediate increase in the absorption band in the visible spectral region ( λ max = 632 nm ) due to the production of the ring - closed isomer 1 ′ of compound 1 ( fig1 ). a visual change in colour from light yellow to blue accompanied this transformation . subsequent irradiation of the solution with visible light ( greater than 490 nm ) resulted in the complete disappearance of the absorption band at 632 nm and regeneration of the original uv - vis absorption trace representing the ring - open isomer 1 . the thermal stability of the ring - closed isomer 1 ′ was studied by storing a sample containing 80 % of the ring - closed isomer 1 ′ ( i . e . the photostationary state ) in cd 2 cl 2 at room temperature in the dark . 1 h nmr analysis was performed on this solution periodically and the ring - closed isomer 1 ′ was thermally stable at 25 ° c . for over one month . the cyclic voltammogram of ring - open isomer 1 shows an irreversible oxidation peak at 1 . 27 v for all scan rates tested ( 50 - 3000 mv / s ) ( fig2 a ). the voltammogram of the ring - closed isomer of compound 1 ′, obtained after irradiation of a ch 3 cn ( 1 × 10 − 3 m ) solution of compound 1 with 365 nm light for 5 minutes , showed a very small irreversible oxidation peak at 0 . 85 v that is almost too small to measure ( fig2 b ). increasing the sweep rate in the cyclic voltammetry experiments resulted in a subsequent increase in the intensity of the oxidation peak at 0 . 85 v . however , there is insignificant growth in the reduction peak on the return sweep ( fig2 c ). this implies that the rate of the ring - opening reaction of the radical cation compound 1 ′ (+·) is faster than the limitations of our instrument . the sweep rate was increased up to a maximum speed of 5000 mv / s without a significant change in the intensity of the reduction peak on the return sweep . 1 . 6 catalytic ring - opening of compound 1 ′ monitored using uv - vis absorption spectroscopy a ch 2 cl 2 solution of ring - open isomer 1 was irradiated with 365 nm light until 75 % of the ring - closed form 1 ′ was produced as determined by 1 h nmr spectroscopy . the uv - vis absorption spectrum of a ch 2 cl 2 solution containing 75 % of the ring - closed isomer 1 ′ is shown in fig3 . an aliquot of a ch 2 cl 2 solution ( 2 × 10 − 5 m ) of the one - electron - accepting radical cation [( 4 - brc 6 h 4 ) 3 n ][ sbcl 6 ] ( e ox = 1 . 15 v ), corresponding to one mol % was added to the blue ch 2 cl 2 solution containing 75 % of the ring - closed isomer 1 ′. the uv - vis absorption spectrum taken immediately after the addition of one mol % of [( 4 - brc 6 h 4 ) 3 n ][ sbcl 6 ] showed the complete disappearance of the absorption band in the visible region ( λ max = 632 nm ) corresponding to the ring - closed isomer 1 ′ and regeneration of the spectrum that is consistent with the ring - open isomer 1 ( fig3 and fig4 ). irradiation of the solution with 365 nm light resulted in no change of the uv - vis spectrum , which would accompany the formation of the ring - closed product , since the radical cation [( 4 - brc 6 h 4 ) 3 n ][ sbcl 6 ] still remained in solution . inducing the ring - opening reaction using a catalytic amount of the chemical oxidant was very efficient since only a small percent was needed to initiate the ring - opening process . the π - electrons are delocalized throughout the photochromic backbone only in the ring - closed state 1 ′ due to the linearly π - conjugated pathway that is created upon photocyclization . on the other hand , these electrons are forced to reside on the two thiophene rings in the ring - open form 1 due to the lack of linear π - conjugation between the two heterocycles . therefore , any π - electrons of the two r 3 groups can only interact with each other through the conjugated pathway in the ring - closed state 1 ′. accordingly , incorporating the photochromic dithienylethene backbone into polyene molecular wires should permit the reversible switching of conductive properties by photoirradiation . although there are several reports that describe how this structural modification can regulate electronic communication between various r 3 substituent groups , the inventors are unaware of any that take advantage of the skeletal alteration between the groups r 3 and r 4 within the two isomers : upon photochemical ring closure , the two carbon atoms involved in forming the new single bond ( the 2 ′- positions of the heterocycles ) change their hybridization from sp 2 to sp 3 . in accordance with the invention two terthiophene units have been modified so that the central thiophene rings of each make up the photochromic dithienylethene backbone . because oligo and polythiophenes display promising semi - conducting properties and are being considered as prototype molecular - scale wires , the inventors chose to use terthiophene as a model oligothiophene to incorporate into the photochromic 1 , 2 - dithienylcylcopentene . complete delocalization of the π - electrons in this manner results in the ring - closed structure 1 ′. using this approach , π - conjugation is not just regulated on command , but also re - routed . single crystals of compound 1 suitable for x - ray crystallographic analysis were grown by slowly cooling a hot hexane solution of the compound . the structure of 1 in the crystal reveals that the two peripheral heterocycles of each terthiophene are rotated an average of 20 ° and 48 ° for the outer and inner rings respectively . despite this deviation from coplanarity with the central heterocycle in the solid - state , the recorded uv - vis absorption spectra , described above , show that , in solution , π - conjugation is still extended throughout each terthiophene arm of the photochromic system . this work clearly demonstrates that while the ring - open isomer 1 has two π - conjugated terthiophene arms , the ring - closed isomer 1 ′ has the linearly π - conjugated pathway extending throughout the backbone of the photochrome . the original conjugated pathways have been destroyed . this is clearly evidenced by the similarity of the absorption spectrum in the visible region between the ring - closed forms of 1 ′ and 5 ′ ( described further below ), the latter possessing an identical linear π - conjugation backbone but is lacking the additional thiophene heterocycles . the absorption spectra of ring - open 1 and 5 are different due to the extended conjugation in 1 as compared to 5 . similar principles apply in respect of the other compounds described below where r 3 and r 4 are aryl . a solution of 3 - bromo -[ 2 , 2 ′] bithiophenyl ( 0 . 500 g , 2 . 3 mmol ) in anhydrous et 2 o ( 25 ml ) cooled to − 20 ° c . was treated with n - buli ( 0 . 82 ml of a 2 . 5 m solution in hexane ) dropwise under an argon atmosphere . after stirring the solution for 30 min , octafluorocyclopentene ( 0 . 13 ml , 1 . 0 mmol ) was added dropwise using a cooled gas tight syringe and the solution immediately turned dark red . after stirring at this temperature for 1 h , the cooling bath was removed and the reaction mixture was allowed to warm to room temperature and stirred for 16 h when it was quenched with 5 % hcl ( 5 ml ). the aqueous layer was separated and extracted with et 2 o ( 2 × 10 ml ). all organic extracts were combined , washed with h 2 o ( 2 × 10 ml ), followed by brine ( 10 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 75 mg of pure product as a white solid . yield : 8 %. m . p . 160 - 162 ° c . ; 1 h nmr ( 400 mhz , cd 2 cl 2 ) δ7 . 23 ( dd , j = 5 , 1 hz , 2h ), 7 . 03 ( d , j = 5 hz , 2h ), 6 . 89 ( dd , j = 5 , 4 hz , 2h ), 6 . 64 ( dd , j = 4 , 1 hz , 2h ), 6 . 41 ( d , j = 5 hz , 2h ); 13 c nmr ( 125 mhz , cdcl 3 ) δ137 . 1 , 133 . 2 , 127 . 7 , 127 . 5 , 126 . 9 , 126 . 3 , 125 . 4 , 124 . 3 ( 8 of 11 carbons found ); ft - ir ( ch 2 cl 2 cast ) 3110 , 2924 , 2841 , 1337 , 1275 , 1241 , 1189 , 1130 , 1088 , 963 , 942 , 852 , 737 , 699 , 651 cm − 1 ; lrms ( ci ) calcd for m + ( c 21 h 10 f 6 s 4 ) 504 . found : 505 [ m + h ] + . anal . calcd for c 21 h 10 f 6 s 4 : c , 49 . 99 ; h , 2 . 00 . found : c , 50 . 40 ; h , 2 . 11 . compound 2 ( 10 mg ) was dissolved in ch 2 cl 2 ( 20 ml ) and placed in a quartz glass cell . the solution was irradiated with 313 nm light for 4 min . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes : ch 2 cl 2 , 9 : 1 ) to afford pure 2 ′ as a purple solid . 1 h nmr ( 600 mhz ; cd 2 cl 2 ) δ7 . 42 ( dd , j = 3 . 6 , 1 . 2 hz , 2h ), 7 . 34 ( dd , j = 4 . 8 , 1 . 2 hz , 2h ), 7 . 14 ( d , j = 6 . 0 hz , 2h ), 6 . 96 ( dd , j = 5 . 4 , 1 . 2 hz , 2h ), ( d , j = 5 . 4 hz , 2h ), 6 . 28 ( d , j = 6 . 0 hz , 2h ). the bis ( dithiophene ) 2 exhibits a low - energy absorption band at λ max = 320 nm ( fig5 ). the absorption band of bis ( dithiophene ) 2 ′ appears at λ max = 545 nm after irradiation of a ch 2 cl 2 solution ( 2 × 10 − 5 m ) with 313 nm light and reaches a photostationary state of 38 % in cd 2 cl 2 ( 1 × 10 − 3 m ) as monitored by 1 h nmr spectroscopy ( fig5 ). the voltammogram of 2 shows an irreversible oxidation peak at 1 . 54 v . irradiation of the solution of 2 with 313 nm light generated 38 % of the ring - open isomer ( as determined by 1 h nmr spectroscopy ) and the cyclic voltammogram shows a small irreversible oxidation peak at 1 . 16 v due to the ring - closed isomer 2 ′ ( fig6 ). phenylboronic acid ( 0 . 756 g , 6 . 2 mmol ) was added to flask containing deoxygenated thf ( 10 ml ) and a 20 % w / w na 2 co 3 solution ( 10 ml ) under a nitrogen atmosphere and stirred vigorously . 2 , 3 , 5 - tribromothiophene ( 1 . 022 g , 3 . 1 mmol ) and pd ( pph 3 ) 4 ( 0 . 107 g , 0 . 096 mmol ) were added and the solution was heated at reflux under a nitrogen atmosphere for 24 h . the heat source was removed , the reaction mixture was allowed to cool to room temperature and extracted with ch 2 cl 2 ( 3 × 20 ml ). the combined organic extracts were washed with h 2 o ( 2 × 20 ml ) followed by brine ( 2 × 20 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 0 . 553 g of pure product as a white solid . yield : 57 %. m . p . 43 - 44 ° c . ; 1 h nmr ( 400 mhz , cd 2 cl 2 ) δ7 . 72 - 7 . 69 ( m , 2h ), 7 . 63 - 7 . 60 ( m , 2h ), 7 . 49 - 7 . 32 ( m , 7h ), 7 . 31 ( s , 1h ); 13 c nmr ( 100 mhz ; cdcl 3 ) δ143 . 2 , 137 . 3 , 133 . 1 , 132 . 8 , 129 . 0 , 128 . 9 , 128 . 5 , 128 . 3 , 128 . 2 , 127 . 4 , 107 . 9 ( 11 of 16 carbons found ); ft - ir ( ch 2 cl 2 cast ) 3062 , 3014 , 1600 , 14844 , 1443 , 1326 , 1076 , 1028 , 825 , 759 , 756 , 690 cm − 1 ; lrms ( ci ) calcd for m + ( c 16 h 11 brs ): 314 . found : 317 ([ m + h ] + , [ 81 br ], 100 %), 315 ([ m + h ] + , [ 79 br ], 94 %); anal . calcd for c 16 h 11 brs : c , 60 . 96 ; h , 3 . 32 . found : c , 61 . 11 ; h , 3 . 56 . a solution of 3 - bromo - 2 , 5 - diphenylthiophene ( 0 . 200 g , 0 . 63 mmol ) in anhydrous et 2 o ( 10 ml ) cooled to − 20 ° c . was treated with n - buli ( 0 . 25 ml of a 2 . 5 m solution in hexane ) dropwise under a nitrogen atmosphere . a white precipitate formed after stirring for 5 min . this reaction mixture was stirred at − 20 ° c . for a total of 15 min followed by addition of octafluorocyclopentene ( 40 μl , 0 . 31 mmo ) using a cooled gas tight syringe . the precipitate remained therefore anhydrous thf ( 3 ml ) was added to dissolve the precipitate . after stirring for 30 min , the cooling bath was removed and the reaction was allowed to warm to room temperature and stirred for 1 h when it was quenched with 5 % hcl ( 5 ml ). the aqueous layer was separated and extracted with et 2 o ( 2 × 10 ml ). all organic extracts were combined , washed with h 2 o ( 2 × 10 ml ), followed by brine ( 10 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 59 mg of pure product as a yellow crystalline solid . yield : 30 %. m . p . 223 - 225 ° c . ; 1 h nmr ( 400 mhz , cd 2 cl 2 ) δ7 . 38 ( m , 8h ), 7 . 33 ( m , 2h ), 7 . 09 ( m , 6h ), 7 . 01 ( m , 6h ), 6 . 31 ( s , 2h ); 13 c nmr ( 100 mhz , cdcl 3 ) δ144 . 3 , 143 . 7 , 133 . 3 , 132 . 3 , 128 . 7 , 128 . 7 , 128 . 0 , 127 . 8 , 127 . 8 , 125 . 6 , 124 . 4 , 122 . 8 ( 12 of 15 carbons found ); ft - ir ( ch 2 cl 2 cast ) 3069 , 3014 , 2924 , 1600 , 1490 , 1448 , 1324 , 1269 , 1186 , 1124 , 1097 , 979 , 924 , 751 , 690 cm − 1 ; lrms ( ci ) calcd for m + ( c 37 h 22 f 6 s 2 ): 644 . found : 645 [ m + h ] + . anal . calcd for c 37 h 22 f 6 s 2 : c , 68 . 93 ; h , 3 . 44 . found : c , 69 . 20 ; h , 3 . 50 . compound 3 ( 0 . 8 mg ) was dissolved in cd 2 cl 2 ( 1 . 2 ml ) and placed in an nmr tube . the solution was irradiated with 365 nm light for 4 min . this resulted in a photostationary state containing 42 % of the ring - closed isomer 3 ′. 1 h nmr ( 600 mhz , cd 2 cl 2 ) δ7 . 80 ( d , j = 7 . 2 hz , 4h ), 7 . 44 ( d , j = 6 . 0 hz , 4h ), 7 . 40 - 7 . 38 ( m , 8h ), 7 . 23 ( m , 2h ), 6 . 69 ( s , 2h ). upon irradiation of a ch 2 cl 2 solution ( 2 × 10 − 5 m ) of compound 3 using 365 nm light , the colourless ring - open isomer 3 ( λ max = 292 nm ) was converted to the blue ring - closed isomer 3 ′ ( λ max = 604 nm ) ( fig7 a ). 1 h nmr spectroscopic analysis of the ring - closing reaction determined that the photostationary state contained 42 % of the ring - closed isomer 3 ′ when a cd 2 cl 2 solution of 3 was irradiated with 365 nm light for 2 minutes . the cyclic voltammogram of a ch 2 cl 2 solution ( 1 × 10 − 3 m ) of compound 3 shows an irreversible oxidation peak at 1 . 62 v due to the oxidation of the ring - open isomer ( fig8 a ). irradiation of the solution with 365 nm light generated the blue ring - closed isomer and the cyclic voltammogram of this solution showed a very small irreversible oxidation peak at 0 . 89 v which is assigned to the ring - closed isomer 3 ′. electrolysis of cd 3 cn solutions ( 1 × 10 − 3 m ) containing the blue ring - closed isomer 3 ′ at 1 . 0 v resulted in decolourization of the solutions and 1 h nmr analysis showed that complete conversion from the ring - closed isomer 3 ′ to the ring - open isomer 3 resulted . addition of only 2 mol % of the catalyst [( 4 - brc 6 h 4 ) 3 n ][ sbcl 6 ] to a solution containing 3 ′ at the photostationary state ( as determined by uv - vis spectroscopy ) resulted in complete conversion to the ring - open isomer 3 indicating that the ring - opening process of this molecule is also catalytic . a solution of 3 - bromo - 2 - phenylthiophene ( 0 . 4565 g , 1 . 9 mmol ) in anhydrous et 2 o ( 25 ml ) cooled to − 20 ° c . was treated with n - buli ( 0 . 76 ml of a 2 . 5 m solution in hexane ) under a nitrogen atmosphere . after stirring for 45 min , a white precipitate formed . octafluorocyclopentene ( 0 . 119 ml , 0 . 95 mmol ) was added via a cooled gas - tight syringe and the solution was stirred at − 20 ° c . for 1 h . the cooling bath was removed , the reaction mixture was allowed to slowly warm to room temperature and the mixture was stirred for 16 h when it was quenched with 5 % hcl ( 10 ml ). the aqueous layer was separated and extracted with et 2 o ( 2 × 10 ml ). all organic extracts were combined , washed with h 2 o ( 2 × 10 ml ), followed by brine ( 10 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 83 mg of pure product as a white solid . yield : 19 %. m . p . 117 - 118 ° c . ; 1 h nmr ( 500 mhz , cd 2 cl 2 ) δ7 . 26 - 7 . 18 ( m , 6h ), 6 . 92 ( m , 4h ), 6 . 90 ( d , j = 5 hz , 2h ), 6 . 15 ( d , j = 5 hz , 2h ); 13 c nmr ( 125 mhz , cd 2 cl 2 ) δ145 . 6 , 133 . 0 , 129 . 0 , 128 . 5 , 128 . 2 , 127 . 6 , 125 . 6 , 123 . 8 ( 8 of 13 carbons found ); 19 f nmr ( 470 mhz , cd 2 cl 2 ) δ − 107 . 20 ( q , j = 5 hz , 2f ), − 112 . 67 ( t , j = 5 hz , 4f ); ft - ir ( ch 2 cl 2 cast ) 3057 , 1651 , 1600 , 1493 , 1445 , 1384 , 1338 , 1278 , 1237 , 1188 , 1130 , 1087 , 1074 , 1023 , 1000 , 965 , 941 , 842 , 761 , 746 , 711 , 692 , 668 , cm − 1 ; hrms ( ei ) calcd for m + ( c 25 h 14 f 6 s 2 ): 492 . 0441 . found : 492 . 0445 . anal . calcd for c 25 h 14 f 6 s 2 : c , 60 . 97 ; h , 2 . 87 . found : c , 60 . 94 ; h , 2 . 99 . compound 4 (˜ 5 mg ) was dissolved in ch 2 cl 2 ( 20 ml ) and placed in a quartz glass cell . the solution was irradiated with 313 nm light for 5 min . the solvent was removed under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes : chcl 3 , 9 : 1 ) to afford 4 ′ as a purple solid . 1 h nmr ( 300 mhz , cd 2 cl 2 ) δ7 . 69 ( dt , j = 7 , 2 hz , 4h ), 7 . 39 - 7 . 22 ( m , 5h ), 7 . 01 ( d , j = 6 hz , 2h ), 6 . 22 ( d , j = 6 hz , 2h ). upon irradiation of a ch 2 cl 2 solution ( 2 × 10 − 5 m ) of 4 with 313 nm light , the colourless ring - open form 4 ( λ max = 251 nm ) was converted to the purple ring - closed isomer 4 ′ ( λ max = 541 nm ) ( fig7 b ). 1 h nmr spectroscopic analysis determined that the photostationary state contained 27 % of the ring - closed isomer 4 ′ when a cd 2 cl 2 solution ( 1 × 10 − 3 m ) of 4 was irradiated with 313 nm light for 2 minutes . the ring - opening reactions of both 3 ′ and 4 ′ could be done by irradiating the solutions with light using wavelengths greater than 490 nm . the cyclic voltammogram of a ch 3 cn solution ( 1 × 10 − 3 m ) of 4 shows an irreversible oxidation peak at 1 . 86 v due to the oxidation of the ring - open isomer ( fig8 b ). irradiation of the solution with 313 nm light generated the purple ring - closed isomer and the cyclic voltammogram of this solution showed a very small irreversible oxidation peak at 1 . 05 v which is assigned to the ring - closed isomer 4 ′. electrolysis of a cd 3 cn solution ( 1 × 10 − 3 m ) of 4 ′ containing 27 % of the ring - closed isomer 4 ′ at 1 . 1 v for 10 minutes resulted in the decolourization of the solution and subsequent regeneration of the 1 h nmr spectrum of the ring - open isomer 4 . addition of 8 mol % of the one - electron accepting radical cation [( 4 - brc 6 h 4 ) 3 n ][ sbcl 6 ] to a cd 2 cl 2 solution ( 1 × 10 − 5 m ) of 4 ′ at the photostationary state ( as determined by uv - vis spectroscopy ) resulted in the complete disappearance of the absorption band in the visible region of the uv - vis absorption spectrum and regeneration of the spectrum for the ring - open 4 indicating that the ring - opening process of this molecule is also catalytic . a solution of dichloride dte - cl ( 0 . 500 , 1 . 14 mmol ) in anhydrous et 2 o ( 40 ml ) cooled to − 78 ° c . was treated with t - buli ( 1 . 34 ml of a 1 . 7 m solution in pentane ) dropwise under an argon atmosphere . after stirring for 30 min , a solution of br 2 ( 0 . 117 ml , 2 . 29 mmol ) in anhydrous et 2 o ( 10 ml ) was added dropwise and the mixture was stirred for 20 min at − 78 ° c . the cooling bath was removed and the reaction mixture was allowed to warm to room temperature . the reaction mixture was washed with h 2 o ( 2 × 15 ml ) followed by brine ( 15 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 0 . 452 g of the pure product as a colorless crystalline solid . yield : 75 % m . p . 146 - 148 ° c . ; 1 h nmr ( 300 mhz , cdcl 3 ) δ6 . 99 ( s , 2h ), 1 . 87 ( s , 6h ); 13 c nmr ( 100 mhz , cdcl 3 ) δ143 . 3 , 129 . 1 , 125 . 2 , 110 . 0 , 14 . 4 ( 5 of 8 carbons found ); ft - ir ( ch 2 cl 2 cast ) 3110 , 3076 , 2924 , 1514 , 1425 , 1322 , 1220 , 1152 , 1079 , 1003 , 839 , 812 , 785 , 692 cm − 1 ; lrms ( ei ) calcd for m + ( c 15 h 8 br 2 f 6 s 2 ): 524 . found : 524 ( m + , [ 79 br ][ 79 br ], 52 %), 526 ( m + , [ 79 br ][ 81 br ], 100 %), 528 ( m + , [ 81 br ][ 81 br ], 58 %). anal . calcd for c 15 h 8 br 2 f 6 s 2 : c , 34 . 23 ; h , 1 . 53 . found : c , 34 . 07 ; h , 1 . 56 . a solution of 2 - bromothiophene ( 0 . 080 g , 0 . 50 mmol ) in anhydrous et 2 o ( 10 ml ) was treated with magnesium turnings ( 0 . 014 g , 0 . 57 mmol ) and heated at reflux for 45 min . the heat source was removed and the reaction mixture was allowed to cool to room temperature when it was added to a solution of dibromide dte - br ( 0 . 100 g , 0 . 20 mmol ), pd ( dppf ) cl 2 ( 0 . 6 mg , 0 . 004 mmol ) and anhydrous et 2 o ( 10 ml ) cooled to 0 ° c . dropwise via a canula . the reaction was stirred at this temperature for 1 h , then allowed to come to room temperature and stirred for 16 h when it was quenched with 5 % hcl ( 10 ml ). the aqueous layer was separated and extracted with et 2 o ( 3 × 10 ml ). all organic extracts were combined , washed with h 2 o ( 3 × 10 ml ), followed by brine ( 10 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 0 . 056 g of pure product as a white solid . yield : 55 % a solution of 2 - bromothiophene ( 1 . 44 g , 8 . 8 mmol ) in anhydrous et 2 o ( 25 ml ) was treated with magnesium turnings ( 0 . 257 g , 10 . 6 mmol ) and heated at reflux for 45 min under a nitrogen atmosphere . the heat source was removed and the reaction mixture was allowed to cool to room temperature when it was added to a cooled ( 0 ° c .) solution of 3 , 5 - dibromo - 2 - methylthiophene ( 2 . 0 g , 8 . 8 mmol ), pd ( dppf ) cl 2 ( 13 mg , 0 . 018 mmol ) and anhydrous et 2 o ( 10 ml ) dropwise via a canula . the reaction was stirred at this temperature for 1 h , the cooling bath was removed , the mixture was allowed to slowly come to room temperature and stirred for 16 h when it was quenched with 5 % hcl ( 10 ml ). the aqueous layer was separated and extracted with et 2 o ( 2 × 20 ml ). all organic extracts were combined , washed with h 2 o ( 3 × 20 ml ), followed by brine ( 20 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 1 . 69 g of pure product as a white solid . yield : 78 %. m . p . 36 - 37 ° c . ; 1 h nmr ( 400 mhz , cd 2 cl 2 ) δ7 . 24 ( dd , j = 5 , 1 hz , 1h ), 7 . 13 ( dd , j = 4 , 1 hz , 1h ), 7 . 02 ( dd , j = 5 , 4 hz , 1h ), 7 . 00 ( s , 1h ), 2 . 39 ( s , 3h ); 13 c nmr ( 100 mhz , cdcl 3 ) 136 . 4 , 133 . 1 , 127 . 8 , 125 . 9 , 124 . 6 , 123 . 7 , 109 . 5 , 14 . 7 ( 8 of 9 carbons found ); ft - ir ; lrms ( ci ) calcd for m + ( c 9 h 7 brs 2 ): 258 . found : 261 ([ m + h ] + , [ 81 br ], 92 %), 259 ([ m + h ] + , [ 79 br ], 100 %). anal . calcd for c 9 h 7 brs 2 : c , 41 . 71 ; h , 2 . 72 . found : c , 41 . 96 ; h , 2 . 66 . a solution of 4 - bromo - 5 - methyl -[ 2 , 2 ′] bithienyl bt2 ( 0 . 395 g , 1 . 5 mmol ) in et 2 o ( 20 ml ) cooled to − 20 ° c . was treated with n - buli ( 0 . 61 ml of a 2 . 5 m solution in hexane ) dropwise under a nitrogen atmosphere . after stirring for 30 min at this temperature , octafluorocyclopentene ( 95 μl , 0 . 7 mmol ) was added using a cooled gas - tight syringe and the solution immediately turned dark red in color . the reaction was stirred at − 20 ° c . for 1 h , the cooling bath was removed , the solution was slowly warmed to room temperature and stirred for an additional 16 h at this temperature . the reaction was quenched with 5 % hcl ( 10 ml ), the layers were separated and the aqueous layer was extracted with et 2 o ( 2 × 10 ml ). the combined organic extracts were washed with h 2 o ( 2 × 10 ml ), brine ( 1 × 10 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ). the isolated product was recrystallized ( hexanes ) yielding 0 . 115 g of pure product as a white crystalline solid . yield : 30 %. m . p . 126 - 127 ° c . ; 1 h nmr ( 600 mhz , cd 2 cl 2 ) δ7 . 28 ( dd , j = 5 , 1 hz , 2h ), 7 . 16 ( dd , j = 3 . 6 , 1 . 2 hz , 2h ), 7 . 15 ( s , 2h ), 7 . 03 ( dd , j = 5 . 1 , 3 . 6 hz , 2h ), 1 . 97 ( s , 6h ); 13 c nmr ( 125 mhz , cdcl 3 ) δ140 . 8 , 136 . 2 , 135 . 5 , 127 . 9 , 125 . 5 , 124 . 9 , 124 . 1 , 122 . 8 , 14 . 4 ( 9 of 12 carbons found ); ft - ir ( ch 2 cl 2 cast ) 3117 , 3076 , 2952 , 2910 , 1440 , 1426 , 1338 , 1275 , 1192 , 1138 , 1115 , 1053 , 986 , 837 , 818 , 742 , 696 cm − 1 ; lrms ( ci ) calcd for m + ( c 23 h 14 f 6 s 4 ): 532 . found : 533 [ m + h ] + ; anal . calcd for c 23 h 14 f 6 s 4 : c , 51 . 87 ; h , 2 . 65 . found : c , 52 . 05 ; h , 2 . 59 . compound 5 ( 5 mg ) was dissolved in ch 2 cl 2 ( 50 ml ) and placed in a quartz glass cell . the solution was irradiated at 365 nm for 10 min . the solvent was evaporated off under reduced pressure and the crude product purified using hplc ( hexanes ) to afford the pure product 5 ′ as a blue powder . 1 h nmr ( 300 mhz , cd 2 cl 2 ) δ 7 . 51 ( dd , j = 5 , 1 hz , 2h ), 7 . 31 ( dd , j = 4 , 1 hz , 2h ), 7 . 11 ( dd , j = 5 , 4 hz , 2h ), 6 . 54 ( s , 2h ), 2 . 16 ( s , 6h ). a solution of 5 ( 2 × 10 − 5 m ) in ch 2 cl 2 appears at λ max = 316 nm ( fig9 ). irradiation of 5 with 365 nm light produces 5 ′ with an absorption band at λ max = 625 nm . the photostationary state upon irradiation of a solution ( 1 × 10 − 3 m ) in cd 2 cl 2 of 5 with 365 nm light is & gt ; 97 %. irradiation with light greater than 490 nm resulted in the loss of colour and regeneration of the spectrum corresponding to 5 . the voltammogram of a ch 3 cn solution ( 1 × m ) of 5 shows an irreversible oxidation peak at 1 . 41 v ( fig1 a , top trace ). the voltammogram of 5 ′ performed on a ch 3 cn ( 1 × 10 − 3 m ) solution of 5 after irradiation with 365 nm light for 6 minutes shows a clear reversible anodic wave at 0 . 85 v due to the oxidation of the ring - closed isomer 5 ′ ( fig1 a , bottom trace ). when the cyclic voltammetry experiment of the ring - open isomer 5 is swept through several oxidation / reduction cycles , a reversible peak appears at the same potential as that for the ring - closed isomer 5 ′ ( fig1 a , inset ) revealing that the ring - closing reaction is induced electrochemically . a solution of 2 - bromo - 5 - methylthiophene ( 0 . 124 g , 0 . 70 mmol ) in anhydrous et 2 o ( 10 ml ) was treated with magnesium turnings ( 0 . 02 g , 0 . 83 mmol ) and heated at reflux for 45 min under a nitrogen atmosphere . the heat source was removed and the reaction mixture was allowed to cool to room temperature when it was added to a cooled ( 0 ° c .) solution of dibromide dte - br ( 0 . 15 g , 0 . 29 mmol ), pd ( dppf ) cl 2 ( 0 . 6 mg , 0 . 004 mmol ) and anhydrous et 2 o ( 10 ml ) dropwise via a canula . the reaction was stirred at this temperature for 1 h , then allowed to come to room temperature and stirred for 24 h when it was quenched with 5 % hcl ( 10 ml ). the aqueous layer was separated and extracted with et 2 o ( 3 × 10 ml ). all organic extracts were combined , washed with h 2 o ( 3 × 10 ml ), followed by brine ( 10 ml ), dried ( na 2 so 4 ) and filtered . the solvent was evaporated under reduced pressure and the crude product was purified using column chromatography through silica gel ( hexanes ) yielding 0 . 116 g of pure product as a white solid . yield : 72 % m . p . 124 - 125 ° c . ; 1 h nmr ( 400 mhz , cd 2 cl 2 ) δ7 . 05 ( s , 2h ), 6 . 94 ( d , j = 4 hz , 2h ), 6 . 69 ( dq , j = 3 , 1 hz , 2h ), 2 . 47 ( d , j = 1 hz , 6h ), 1 . 94 ( s , 6h ); 13 c nmr ( 125 mhz , cdcl 3 ) δ 140 . 2 , 139 . 7 , 135 . 9 , 133 . 9 , 126 . 0 , 125 . 4 , 123 . 9 , 122 . 0 , 15 . 3 , 14 . 4 ( 10 of 13 carbons found ); ft - ir ( microscope ) 3081 , 3063 , 2956 , 2923 , 2859 , 2740 , 1720 . 1622 , 1580 , 1559 , 1536 , 1500 , 1441 , 1380 , 1338 , 1308 , 1264 , 1241 , 1225 , 1183 , 1160 , 1132 , 1097 , 1050 , 987 , 901 , 867 , 849 , 839 , 827 , 817 , 794 , 747 , 738 , 697 , 678 , 662 , 623 cm − 1 ; hrms ( ei ) calcd for m + ( c 25 h 18 f 6 s 4 ): 560 . 0196 . found : 560 . 01982 . anal . calcd for c 25 h 18 f 6 s 4 : c , 53 . 56 ; h , 3 . 24 . found : c , 53 . 47 ; h , 3 . 26 . compound 6 ( 1 mg ) was dissolved in cd 2 cl 2 ( 2 ml ) and placed in an nmr tube . the solution was irradiated at 365 nm for 7 min . this resulted in a photostationary state consisting of & gt ; 97 % of the ring - closed isomer 6 ′. no attempts were made to isolate 6 ′. 1 h nmr ( 600 mhz , cd 2 cl 2 ) δ 7 . 09 ( d , j = 5 . 4 hz , 2h ), 6 . 77 ( dq , j = 5 . 4 , 1 . 2 hz , 2h ), 6 . 42 ( s , 2h ), 2 . 52 ( s , 6h ), 2 . 12 ( s , 6h ). compound 6 showed similar behaviour as compound 5 as described above . the voltammogram of 6 shows an irreversible oxidation peak at e ox = 1 . 26 v ( fig1 b , top trace ). irradiation of the solution with 365 nm generated the ring - closed form 6 ′ which shows a reversible anodic wave at e 1 / 2 = 0 . 74 v ( fig1 b , bottom trace ). a colourless solution of 6 was electrolyzed at 1 . 35 v . immediately after the electrolysis reaction was started , a red species was generated in the solution surrounding the platinum coil working electrode . after several seconds of electrolysis , the entire solution turned deep red in colour . although the red species produced upon electrolysis has not been characterized , we believe this to be the oxidized ring - closed form . reduction of the solution by applying a voltage of 200 - 400 mv or simply opening the reaction to the atmosphere resulted in a colour change of the solution from red to blue , suggesting that the neutral ring - closed isomer was produced . the deep blue solution of 6 ′ which was generated electrochemically can be photochemically bleached upon exposure to greater than 490 nm light for 15 minutes . thus compound 6 is reversibly convertible between a colourless form , a red form and a blue form . this is potentially important with respect to high - density data storage media , where the three colours can represent three digital states ( 0 , 1 , 2 ) at the same storage location on the medium . this way more information can be stored at a single site . a solution of 2 - methyl - 3 - bromo - 5 - chlorothiophene in anhydrous ether ( 75 ml ) was treated with n - butyllithium ( 3 . 6 ml , 2 . 5 m in hexane , 9 . 0 mmol ) dropwise at − 78 ° c . under an n 2 atmosphere . the resulting yellow solution was stirred for 30 min at this temperature then it was treated with a solution of anhydrous zncl 2 ( 1 . 23 g , 9 . 00 mmol ) in anhydrous ether ( 10 ml ) in one portion via a cannula ( scheme 5 , above ). after stirring for an additional 30 min at − 78 ° c ., the cooling bath was removed and the reaction mixture was transferred via a cannula into a frame - dried flask containing 2 , 3 - dibromobicyclo [ 2 . 2 . 1 ] hepta - 2 , 5 - diene ( 750 mg , 3 . 00 mmol ), pd ( pph 3 ) 4 ( 100 mg , 0 . 087 mmol ) and anhydrous thf ( 50 ml ). the resulting pale yellow solution was allowed to warm slowly to room temperature and heated at reflux for 18 h under an n 2 atmosphere . the heating source was removed , the reaction was allowed to slowly cool to room temperature and quenched with saturated nh 4 cl ( 50 ml ). the aqueous layer was removed and extracted with ether ( 3 × 50 ml ). the combined organic layers were dried ( na 2 so 4 ), filtered and concentrated to dryness in vacuo . the crude product was purified by column chromatography ( hexanes ) yielding 0 . 65 g of dichloride monomer 7 as a pale yellow solid . yield : 62 %. m . p . 67 - 69 ° c . ; 1 h nmr ( cdcl 3 , 400 mhz ) δ6 . 93 ( m , 2h ), 6 . 58 ( s , 2h ), 3 . 70 ( m , 2h ), 2 . 32 ( dt , j = 6 , 2 hz , 1h ), 2 . 09 ( dt , j = 6 , 2 hz , 1h ), 1 . 85 ( s , 6h ); 13 c nmr ( cdcl 3 , 100 mhz ) δ 145 . 8 , 142 . 9 , 134 . 6 , 132 . 6 , 125 . 9 , 71 . 6 , 56 . 3 , 14 . 1 . ft - ir ( kbr - cast ) 2970 , 2864 , 1545 , 1463 , 1294 , 1023 , 970 , 820 , 709 , 646 , 468 cm − 1 ; ms ( ci isobutane ) m / z = 353 [ m + h ] + ; anal . calcd for c 17 h 14 cl 2 s 2 ; c , 57 . 79 ; h , 3 . 99 ; n , 0 . 00 . found : c , 57 . 39 ; h , 3 . 84 ; n , 0 . 00 . as shown in scheme 5 , above , a solution of dichloride monomer 7 ( 300 mg , 0 . 85 mmol ) in anhydrous thf ( 40 ml ) was treated dropwise with t - butyllithium ( 1 . 40 ml , 1 . 7 m in pentane , 2 . 40 mmol ) at − 78 ° c . until no starting material was detected by tlc . after stirring at − 78 ° c . for 30 min , the cooling ice bath was removed and dry co 2 gas was bubbled through the solution for 30 min . a white suspension immediately formed . the reaction mixture was concentrated to dryness in vacuo and re - suspended in acetone ( 40 ml ). solid k 2 co 3 ( 236 mg , 1 . 7 mmol ) was added , followed by dimethylsulfate ( 0 . 2 ml , 2 . 13 mmol ). the reaction was heated at reflux under an n 2 atmosphere for 18 h . the heating source was removed , the reaction was allowed to slowly cool to room temperature and quenched with water ( 20 ml ). the acetone was removed in vacuo and the remaining aqueous solution was extracted with ether ( 5 × 30 ml ). the combined organic layers were washed sequentially washed with saturated nahco 3 ( 10 ml ) and brine ( 10 ml ), dried ( na 2 so 4 ), filtered and evaporated to dryness in vacuo . the crude product was purified by column chromatography ( 9 % etoac / hexane ) yielding 150 mg of diester monomer 8 as a white solid . yield : 44 %. m . p . 102 - 103 . 5 ° c . 1 h nmr ( cdcl 3 , 400 mhz ) δ7 . 49 ( s , 2h ), 6 . 97 ( m , 2h ), 3 . 84 ( s , 6h ), 3 . 75 ( m , 2h ), 2 . 37 ( d , j = 3 hz , 1h ), 2 . 12 ( d , j = 3 hz , 1h ), 1 . 86 ( s , 6h ); 13 c nmr ( cdcl 3 , 100 mhz ) δ162 . 6 , 146 . 2 , 143 . 0 , 142 . 1 , 136 . 4 , 134 . 5 , 129 . 5 , 71 . 8 , 56 . 7 , 52 . 0 , 14 . 7 ; ftir ( kbr - cast ) 2945 , 2848 , 1717 , 1648 , 1469 , 1303 , 1255 , 1082 , 745 , 717 cm − 1 . ms ( ci isobutane ) m / z = 401 [ m + h ] + , 369 [ m − och 3 ] 30 ; anal . calcd for c 21 h 20 o 4 s 2 : c , 62 . 98 ; h , 5 . 03 ; n , 0 . 00 . found : c , 62 . 64 ; h , 5 . 31 ; n , 0 . 00 . a solution of 2 - bromo - 5 - methylthiophene ( 4 . 00 g , 22 . 6 mmol ) in anhydrous ether ( 10 ml ) was treated with magnesium turnings ( 0 . 577 g , 23 . 7 mmol ) and heated at reflux for 45 min under an n 2 atmosphere . the heat source was removed and the reaction mixture was slowly allowed to cool to room temperature when it was transferred to a flame - dried addition funnel via a cannula . a solution of 3 , 5 - dibromo - 2 - methylthiophene ( 5 . 49 g , 21 . 5 mmol ) and pd ( dppf ) cl 2 ( 16 . 5 mg , 0 . 023 mmol ) in 75 ml anhydrous ether was treated dropwise with the solution of the grignard reagent over 30 min at 0 ° c . under an n 2 atmosphere using an addition funnel . the resulting solution was allowed to slowly warm to room temperature and stirred for 72 h under an n 2 atmosphere , when it was quenched with saturated nh 4 cl ( 50 ml ). the aqueous layer was separated and extracted with ether ( 3 × 75 ml ). the combined organic layers were dried over na 2 so 4 , filtered and evaporated to dryness in vacuo . the crude product was purified by flash chromatography ( hexanes ) yielding 4 . 32 g of pure bt3 as a white solid . yield : 74 %. m . p . 80 - 81 ° c . ; 1 h nmr ( cdcl 3 , 400 mhz ) δ6 . 89 ( m , 2h ), 6 . 64 ( m , 1h ), 2 . 47 ( s , 3h ), 2 . 37 ( s , 3h ); 13 c nmr ( cdcl 3 , 100 mhz ) δ139 . 5 , 134 . 9 , 132 . 5 , 125 . 9 , 125 . 2 , 123 . 5 , 109 . 3 , 15 . 3 , 14 . 7 ( 9 of 10 carbons found ). ms ( ci isobutane ) m / z = 273 [ m + h ] + . a solution of 4 - bromo - 5 , 5 ′- dimethyl - 2 , 2 ′- bithienyl bt3 ( 1 . 50 g , 5 . 49 mmol ) in anhydrous ether was treated dropwise with n - butyllithium ( 2 . 2 ml , 2 . 5 m in hexane , 5 . 5 mmol ) at − 40 ° c . under an n 2 atmosphere . the resulting yellow solution was stirred for 30 min at this temperature , then it was treated with a solution of anhydrous zncl 2 ( 0 . 75 g , 5 . 5 mmol ) in anhydrous ether ( 10 ml ) in one portion via a cannula . after stirring for an additional 30 min at − 40 ° c ., the cooling bath was removed and the reaction mixture was transferred via a cannula into a flame - dried flask containing 2 , 3 - dibromo [ 2 . 2 . 1 ] hepta - 2 , 5 - diene ( 0 . 500 g , 2 . 00 mmol ), pd ( pph 3 ) 4 ( 46 mg , 0 . 040 mmol ) and anhydrous thf ( 50 ml ). the resulting solution was allowed to slowly warm to room temperature and heated at reflux for 18 h under an n 2 atmosphere . the heat source was removed , the reaction was allowed to slowly cool to room temperature and quenched with saturated nh 4 cl ( 50 ml ). the aqueous layer was removed and extracted with ether ( 3 × 75 ml ). the combined organic layers were dried over na 2 so 4 , filtered and evaporated to dryness in vacuo . the crude product was purified by flash chromatography ( hexanes ) and crystallized from 30 % hexanes in ether yielding 500 mg of monomer 9 as white platelets . yield : 54 %. m . p . 129 - 130 ° c . ; 1 h nmr ( cd 2 cl 2 , 400 mhz ) δ6 . 98 ( t , j = 6 hz , 2h ), 6 . 83 ( d , j = 4 hz , 2h ), 6 . 61 ( m , 2h ), 3 . 77 ( m , 2h ), 2 . 43 ( d , j = 1 hz , 6h ), 2 . 36 ( dt , j = 6 , 2 hz , 1h ), 2 . 09 ( dt , j = 6 , 2 hz , 1h ), 1 . 89 ( s , 6h ); 13 c nmr ( cdcl 3 , 100 mhz ) δ 145 . 7 , 143 . 0 , 138 . 5 , 136 . 0 , 135 . 3 , 133 . 7 , 132 . 7 , 125 . 7 , 122 . 9 , 122 . 8 , 71 . 5 , 56 . 4 , 15 . 3 , 14 . 2 . a solution of bis ( tricyclohexylphosphine ) benzylidene ruthenium ( iv ) dichloride ( 0 . 003 - 0 . 01 mmol ) dissolved in dry deoxygenated thf ( 2 ml ) was added through a cannula into a thf solution of the appropriate monomer ( 0 . 2 - 0 . 5 mmol ) as shown in scheme 5 above . the final monomer concentrations were 0 . 05 m . after stirring at room temperature for 18 h under a n 2 atmosphere , excess ethyl vinyl ether was added and the resulting solutions were stirred while exposed to the atmosphere for 30 min . the crude reaction mixtures were evaporated to dryness in vacuo . to isolate the polymers in high purity the solid residues were re - dissolved in thf ( 2 ml ), triturated with cold methanol or ether and the precipitate collected by vacuum filtration . dichloride monomer 7 ( 137 mg , 0 . 37 mmol ) was polymerized with 0 . 02 molar equivalents of bis ( tricyclohexylphosphine ) benzylidene ruthenium ( iv ) dichloride ( 6 . 1 mg , 0 . 007 mmol ) to afford 105 mg of polymer 10 as an off - white solid . yield : 80 %. 1 h nmr ( cdcl 3 , 400 mhz ) δ6 . 5 ( br s ), 5 . 4 ( br s ), 3 . 7 ( br s ), 3 . 5 ( br s ), 2 . 5 ( br s ), 1 . 8 - 1 . 6 ( m ). diester monomer 8 ( 150 mg , 0 . 38 mmol ) was polymerized with 0 . 02 molar equivalents of bis ( tricyclohexylphosphine ) benzylidene ruthenium ( iv ) dichloride ( 6 . 2 mg , 0 . 008 mmol ) to afford 92 mg of polymer 11 as an off - white solid . yield : 60 %. 1 h nmr ( cdcl 3 , 400 mhz ) δ5 . 3 - 5 . 4 ( m ), 3 . 5 ( br s ), 3 . 8 ( br s ), 2 . 5 ( br s ), 1 . 9 - 1 . 7 ( m ). a solution of diester polymer 11 ( 31 mg ) in deoxygenated thf ( 3 ml ) was treated with deoxygenated water ( 1 . 5 ml ), followed by an aqueous koh solution ( 0 . 3 ml , 1m ). the resulting solution was heated at reflux under an n 2 atmosphere for 5 h , the heat source was removed , the reaction was allowed to cool slowly to room temperature and stirred there for 18 h . the crude reaction mixture was concentrated to 1 ml , and acidified with 3m hcl ( 3 drops ). the resulting precipitate was collected by vacuum filtration , washed sequentially with cold water ( 3 ml ), et 2 o ( 3 ml ) and chcl 3 ( 3 ml ) and dried in vacuo yielding 25 mg of dicarboxylate polymer 12 as an off - white solid . yield : 83 %. 1 h nmr ( ch 3 od , 400 mhz ) δ7 . 3 ( br s ), 5 . 4 ( br s ), 4 . 2 - 3 . 4 ( m ), 2 . 5 ( br s ), 1 . 8 ( br s ). representative uv spectra from typical photoisomerization studies are illustrated in fig1 in respect of monomer 8 and polymers 11 and 12 . all solutions were prepared at 2 × 10 − 5 m in the active photochromic component . polymer films were spin - coated onto 1 cm × 2 cm quartz substrates as chcl 3 solutions using a laurell ws - 400a - 6npp / lite spin - coater . table 3 below shows the results of gpc analysis on selected compounds described above . with respect to the polymers reported in table 1 . the glass transition temperatures and melting temperatures of polymers 10 and 11 , measured by differential scanning calorimetry ( dsc ), are also included . themogravimetic analysis of polymers 10 and 11 indicated they are stable at high temperature . the absorption spectra of thf solutions ( fig1 and table 3 ) of polymers 10 and 11 shows that in each case the λ max values of the ring - closed form of the polymers are red - shifted when compared to the corresponding monomers 7 and 8 respectively . this effect can be attributed to the relief of ring - strain in the polymer , a direct result of the romp process . the results of the photoinduced isomerization studies , carried out by irradiating the thf solutions at 254 nm or 313 nm with a hand - held uv lamp , are shown in fig1 . within the first 10 seconds of irradiation , absorption bands appear between 500 and 600 nm as the photochromic monomers and polymers are converted from their colorless ring - open to their colored - closed forms . after 120 seconds of irradiation at the concentration used , the increases in the visible absorption bands level off . the resulting colored solutions can be decolorized by irradiating them with broad - band light greater than 490 nm ( 434 nm for 7 and 10 ) resulting in the complete disappearance of absorption bands in the visible region . however , long irradiation times result in a small degree of photodegradation and the absorption spectra corresponding to the ring - open forms cannot be fully regenerated . this result is not surprising as we have reported how some non - fluorinated dithienylalkene derivatives are substantially less photo - fatigue resistant than their fluorinated counterparts . fig1 also shows the photochromic behavior of hydrophilic polymer 12 in aqueous solution ( phosphate buffer , ph 7 , 25 ° c .). this polymer can also be reversibly colorized and decolorized . polymers 10 and 11 retain their photochromic behavior when spin - coated from chcl 3 solutions onto quartz substrates ( fig1 ). irradiation of the films with uv light ( 254 nm for 10 and 313 nm for 11 ) resulting in the immediate change in color indicating that the photochromic properties of the polymers were conserved in the processed state the changes in the uv - vis absorption spectrum of each polymer were similar to those obtained in solution , with the exception that slightly longer irradiation times were required to reach the photostationary states ( 290 seconds compared to 120 seconds for polymer 11 , for example ). the percent mass of the active photochromic component in our original side - chain polymers ranges from 60 - 68 %. the new generation main - chain polymer ranges from 93 %. this is due to the romp reaction of the strained olefin producing the requisite cyclopentene backbone that has been shown to be so versatile . monomer 9 ( 99 mg , 0 . 21 mmol ) was polymerized as shown in scheme 5 with 0 . 02 molar equivalents of bis ( tricyclohexylphosphine ) benzylidene ruthenium ( iv ) dichloride ( 3 . 4 mg , 0 . 004 mmol ) to afford 40 mg of polymer 13 as an off - white solid ( 40 %). 1 h nmr ( cdcl 3 , 400 mhz ) δ6 . 8 - 6 . 5 ( m ), 5 . 4 ( br s ), 3 . 8 ( br s ), 3 . 5 ( br s ), 2 . 5 - 2 . 3 ( m ), 1 . 8 - 1 . 6 ( m ). it is expected polymer 13 will be electrochromic based on its structural similarity to compound 6 described above . polymer 12 is hydrophilic . polymers 10 , 11 , and 13 are lipophilic . as will be apparent to those skilled in the art in the light of the foregoing disclosure , many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof . accordingly , the scope of the invention is to be construed in accordance with the substance defined by the following claims . 1 molecular switches , feringa b . l ., ed . ; wiley - 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