Author's personal copy Benzofuran-terminated infrared dyes and their electro-optic properties in guest–host polymers

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Author's personal copy Benzofuran-terminated infrared dyes and their electro-optic properties in guest–host polymers

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  This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institutionand sharing with colleagues.Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third partywebsites are prohibited.In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further informationregarding Elsevier’s archiving and manuscript policies areencouraged to visit:http://www.elsevier.com/copyright  Author's personal copy Benzofuran-terminated infrared dyes and their electro-optic propertiesin guest–host polymers Andrew P. Chafin a , Matthew C. Davis a , William W. Lai a , Geoffrey A. Lindsay a, ⇑ , Dong H. Park b ,Warren N. Herman b a US Navy, NAWCWD Research Department, China Lake, CA 93555, USA b Laboratory for Physical Sciences, University of Maryland, College Park, MD 20740, USA a r t i c l e i n f o  Article history: Received 29 December 2010Received in revised form 4 March 2011Accepted 4 March 2011Available online 7 April 2011 Keywords: Electro-opticFirst hyperpolarizabilityDyesNonlinear optic a b s t r a c t Molecular first hyperpolarizabilities anddipole moments of newbenzo-fused dyes were calculated usingquantum–mechanical density functional theory (DFT). Two new infrared dyes were synthesized: eachone was terminated with 6-diethylaminobenzo[ b ]furan on one end, and with CF 3 -tricyanodihydrofuranon the other end. The midsection of the  p -electron framework for one dye contained a morpholino-substituted cyclohexenylene unit, and the other dye contained an ethoxysiloxane-substituted cyclohex-enylene unit. Guest–host films were deposited on ITO-glass and contact poled. Electro-optic coefficients( r  33 )weremeasuredatawavelengthof1550nmbytheattenuatedtotalreflectionmethodandbyamod-ified simple Teng-Man reflection method. The measured values of   r  33  were compared with values esti-mated from a well-known model that employs the molecular properties of the dyes and the filmpoling parameters. Thermal stability and electronic absorption spectra of the dyes were measured.Published by Elsevier B.V. 1. Introduction During the last decade, the science and technology of organicnonlinear optical materials has greatly advanced [1–3]. Theelectro-optic (EO) coefficient ( r  33 ) of high-bandwidth organic-dyematerialsnowexceedthat of lithiumniobate(LN) byat least a fac-tor of five when measured with a 1550nm optical carrier signal.Thesameorganicfilmoperatingat1310nmexceedsLNbyafactorofatleasteight(boostedbyresonanceenhancement[4]);however,1550nm is preferred for superior long-term stability [5]. Evenwhen operating at 1550nm, one is advised to protect these mate-rials from oxygen for long-term operation at elevated tempera-tures [6,7].The magnitude of   r  33  for films of these organic dyes is largelydetermined by the product of three molecular parameters [8,9]as shown in Eq. (1): r  33  /  b N  d h cos 3 ð h Þi ð 1 Þ where  b  is the first molecular hyperpolarizability of the dye;  N  d  isthe molar concentration of dye (the number density), and h cos 3 ( h ) i is the polar order parameter of the ensemble of dyes [10]. The present study was focused on improving the  b  of the dye.Successful strategies used in the past for increasing  b  have beento increase the length of the  p -electron conjugated conduit andto adjust the push–pull strength of the end groups, for example,see [11]. More recently, the incorporation of stronger push and/orpull groupsontheinternalmethinesof theselargepolyenedyeshas also been used to increase  b  [12,13]. Density functional theory(DFT) computations show that  b  is usually enhanced when elec-tron-withdrawing substituents are placed on even-numberedinternal methine carbons and electron-donating substituents areplaced on odd-numbered internal methines, the so-called eW/oDpattern (if the numbering system of the present paper is used)[14,15]. This placement effect is related to the spatial distributionof electron density in the dye, for example, the odd–even bond-order alternation [16], and to some extent it can be anticipatedfrom Dewar’s rules [17] and the two-state model [9]. For the last decade, dyes based on the 4-aminophenylene-tetraene-tricyanodihydrofuran motif (herein called the  Phenylene dyes) [18] have been amongst the best performers in optical mod-ulators operating with a near infrared (IR) carrier signal. One rea-son investigators have been reluctant to increase the length of these so-called tetraenic dyes, and also the length of similar dyeshaving a 2,5-divinylene-heterocyclodiene in their  p -frameworks[4,19,20], is because adding one more ene group (CH @ CH) nor-mally extends the low-energy side of the electronic absorptionband (the red tail). The problem arises when the red tail overlapswith the IR carrier signal, which leads to unacceptable opticalabsorption loss. For the Mach–Zehnder modulator, the typicalupper limit for acceptable propagation loss is   0.2dB/mm, which 0925-3467/$ - see front matter Published by Elsevier B.V.doi:10.1016/j.optmat.2011.03.004 ⇑ Corresponding author. Address: NAWCWD, C/4L4200D, MS 6303, 1900N. KnoxRoad, China Lake, CA 93555, USA, Tel.: +1 760 939 1630; fax: +1 760 939 1617. E-mail address:  geoffrey.lindsay@navy.mil (G.A. Lindsay).Optical Materials 33 (2011) 1307–1315 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat  Author's personal copy also sets the upper limit of dye concentration in the film(and thus r  33 ),whichisawell-knowntrade-off.Furthermore,red-shiftingthetail of the electronic absorption spectrum beyond 1550nm in-creases the rate of detrimental photo-chemical reactions.DFT is a practical desk-top tool for predicting the relativechanges in  b  for specific changes in the dye structure [21]. Theuse of DFT as a screening guide is especially time-saving when adozensteps arerequiredfor synthesis. Time-dependent DFTis alsoproving to be useful in predicting the absorption spectra and thefrequency dependence of   b  for large IR dyes [22,23].A strategy of the present study for increasing  b  was to add onemore ene group by replacing the  Phenylene  group in theelectron-donatingendofthedyeswithabenzo-fusedfive-memberheterocyclicgroup(hereaftercalledthe BFFH   dyes).Thisreducesoreliminatesthered-shiftintheIRabsorptionspectrabyintroducingadegree of ground-state aromaticity into the  p -conjugated charge-transfer conduit. The fused benzo group also rigidifies the polyeneconduit.Anotherstrategyofthepresentstudy,usingDFTasaguide,wastheplacementofheteroatomsinthebeneficialeW/oDpattern.Thisisthefirstreport(totheauthors’knowledge)ofaddingtheben-zofuranunittotheelectron-donatingendof high- b  dyes. 2. Experimental methods  2.1. Starting materials and analytical methods Unless otherwise stated, all reagents were purchased fromSigma–Aldrich (Milwaukee, WI) and were used as received. Pipe-ridinium acetate was prepared according to literature procedures[24]. The 2,3,5,6-tetrachloro-1,4-benzoquinone (p-chloranil, 99%)was recrystallized from toluene before use. The 4-(diethyl-amino)salicylaldehyde (98%) was purified before use by dissolvingin Et 2 O, stirring with 5g of activated carbon for 1h, filteringthrough diatomaceous earth, and rotary evaporating until a tanamorphous crystal was obtained.Two host polymers were used. One was poly(vinyl butyral- co -vinyl acetate- co -vinyl alcohol), hereafter called PV, which hada glass transition temperature ( T   g  ) of 72  C and weight-averagemolecular weight of 70kg/mol. The other host polymer wasbisphenol-A polycarbonate, called PC, which had a  T   g   of 149  Cand a weight-average molecular weight of 51.6kg/mol.NMR data were collected on a Bruker Avance II 300-MHz spec-trometer ( 1 H at 300MHz,  13 C at 75MHz); data were processedusing NUTS software from Acorn NMR (Livermore, CA); spectraarereferencedtotetramethylsilane.TheUV–Visabsorptionspectrawere recorded on a Cary 5 spectrometer at roomtemperature. Dif-ferentialscanningcalorimetry(DSC)wasperformedonaTAInstru-ments, Inc. Model Q100. The DSC  T   g   was taken as the midpoint of the change in heat capacity when transitioning from glass to rub-ber (heating at 10  C/min). The gel permeation chromatography(GPC) equipment used to measure polymer molecular weightswas a Viscotek, Inc., model 302 equipped with a refractive indexdetector;thecolumnswerecalibratedrelativetopolystyrenestan-dards; and the solvent was tetrahydrofuran (THF).  2.2. Synthesis of the various dye components The synthesis of 6- N,N  -diethylamino[ b ]benzofuran-2-carboxal-dehyde ( 4 ) (Scheme 1) was recently reported by Davis et al. [25], which is an improvement over prior reports [26]. A summary of the synthesis is as follows. Commercially available 4-diethylami-nosalicylaldehyde,  1 , was deprotonated using potassium  tert  -butoxide. This product was alkylated with diethyl bromomalonatein dimethylformamide to give compound  2 . Compound  2  wasdehydrated and decarboxylated by brief treatment in hot poly-phosphoricacidtogivethebenzofuranester, 3 .Theresultingaque-ous reaction mixture was kept cold during the slow neutralizationwith cold aqueous sodium hydroxide to prevent hydrolysis of theproduct. The benzofuran ester was reduced with lithiumtetrahyd-roaluminate to give the benzofuran alcohol, which was then oxi-dized to the aldehyde,  4 , with 2,3,4,5-tetrachlorobenzoquinone(p-chloranil). Compound  4  was purifed on silica gel to give a yel-low–brown oil in 77% yield (22.56g).  1 H (CDCl3): 9.63 (s, 1H),7.50 (d,  J   =9.2, 1H), 7.41 (d,  J   =1.0, 1H), 6.77 (dd,  J   =8.9 and2.3Hz, 1H), 6.71 (d,  J   =2.0Hz, 1H), 3.45 (q,  J   =7.2Hz, 4H), 1.23(t,  J   =7.1Hz, 6H);  13 C (CDCl3): 177.79, 159.92, 151.33, 150.14,124.18, 116.08, 111.49, 92.73, 45.22, 12.66.The method of Edgar [12,27] was used to prepare 4-bromo-isophorone, to which morpholine readily attached (Scheme 2).Isophorone (100g, 0.72mol),  N  -bromosuccinimide (128g,0.72mol) and carbon tetrachloride (300mL) were added to a1000mL round bottom flask and fitted with a stirbar and con-denser.Themixturewasplacedundernitrogenandstirredatroomtemperature for 30min and then refluxed for 30min. The filtratewas collected by vacuum filtration and the solvent was removedunder reduced pressure to yield a yellow oil. To this oil was addedpetroleum ether (250mL) and refrigerated overnight at 0  C. Theresulting crystals of 4-bromo-isophorone were collected by vac-uum filtration and dried (121g, 77%).  1 H NMR (CDCl 3 )  d  5.80 (t,1H,  J   =1.2Hz), 4.34, (d, 1H,  J   =1.5Hz) 2.59 (d, 1H,  J   =1.0), 2.53(d, 1H,  J   =1.0Hz), 1.27 (s, 3H), 1.16 (s, 3H);  13 C NMR (CDCl 3 )  d 198.2, 157.4, 126.0, 61.7, 46.2, 37.5, 29.9, 24.9, 22.6.4-Bromo-isophorone (20.0g, 18.4mmol) was added to freshlydistilled morpholine (40mL, 0.45mol) and allowed to stir at roomtemperature under nitrogen for 3days. The precipitate was col-lectedbyvacuumfiltrationanddried. The crudewas recrystallizedin ethanol/water to give white crystals of   5  (19.6g, 95%).  1 H NMR (CDCl 3 )  d  3.69 (t, 4H,  J   =3.9Hz), 2.95 (b, 4H), 2.26 (s, 2H), 2.23 (s,2H), 2.00 (s, 3H), 0.99 (s, 6H);  13 C NMR (CDCl 3 )  d  197.6, 153.4,141.9, 67.7, 53.0, 50.3, 46.2, 32.7, 28.0, 19.8.( E  )-3-(2-(6-(diethylamino)benzofuran-2-yl)vinyl)-5,5-dimethyl-2-morpholino-cyclohex-2-enone( 6 )waspreparedasfollows:2-Mor-pholino-isophorone ( 5 ) (1.40g, 6.28mmol), benzofuran carboxaldehyde (1.50g, 6.90mmol) and 0.1Msodiummethoxide inmethanol(25mL)wereaddedtoa50mLroundbottomflaskwhichwasfittedwith a stirbar and reflux condenser. The mixture was placed undernitrogenandrefluxedovernight.Theprecipitatewascollectedbyvac-uumfiltration,washedwithcoldmethanolanddried(2.40g,91%).Nofurtherpurificationof  6 wasnecessary. 1 HNMR(CDCl 3 ) d 7.80(d,1H,  J  =16.5Hz), 7.33 (d, 1H,  J   =8.7Hz), 6.74 (d, 1H,  J   =16.4Hz), 6.74 (d,1H,  J   =2.3Hz), 6.67 (dd, 1H,  J   =8.7Hz,  J   =2.3Hz), 6.63 (s, 1H), 3.86(t, 4H,  J  =4.7Hz), 3.44 (q, 4H,  J  =7.1Hz), 3.09 (b, 4H), 2.49 (s, 2H),2.33 (s, 2H), 1.23 (t, 6H,  J  =7.1Hz), 1.08 (s, 6H);  13 C NMR (CDCl 3 )  d 198.0, 158.0, 152.6, 147.5, 145.8, 142.2, 124.4, 121.6, 121.4, 118.2,109.8, 108.5, 93.5, 68.0, 52.8, 51.2, 44.9, 39.5, 32.3, 28.4, 12.6; IR (KBr)cm  1 =1649.( E  )-2-(3-(( E  )-2-(6-(diethylamino)benzofuran-2-yl)vinyl)-5,5-dimethyl-2-morpholinocyclohex-2-enylidene)acetonitrile ( 7 ) wasprepared as follows: diisopropylamine (3.3mL, 24mmol) wasaddedtoanhydrousTHF(40mL) placedundernitrogenandcooledto  78  C.Tothissolutionwasadded2.5Mbutyllithiuminhexanes(9.5mL,24mmol)dropwise.Thissolutionwasallowedtowarmupto0  Candmaintainedatthistemperaturefor10min.Thesolutionwas cooled back to   78  C and anhydrous acetonitrile (1.5mL,26mmol) was added dropwise. This solution was warmed to 0  Candheldfor 10minandcooledbackdownto  78  C. Tothisslurrywasaddedtheketone( 6 )(1.0g,2.37mmol)dropwiseinanhydrousTHF(10mL). The slurry was warmedto 0  Candallowedto stir for30min. The reaction was quenched with water (50mL) and ex-tracted with ethyl acetate (3  25mL). The extractions were com-bined, washed with water (3  25mL) and brine (3  25mL) and 1308  A.P. Chafin et al./Optical Materials 33 (2011) 1307–1315  Author's personal copy dried over magnesium sulfate. The solvent was removed under re-duced pressure and was refluxed overnight with glacial acetic acid(25mL).Themixturewascooledtoroomtemperatureandneutral-ized with sodium carbonate and extracted with ethyl acetate(3  25mL). The extractions were combined, washed with water(3  25mL)andbrine(3  25mL).Thesolventwasremovedunderreduced pressure and the residue was purified by columnchroma-tography (9:1, hexanes:ethyl acetate) to yield the nitrile  7  as a redsolid (0.77g, 73%).  1 H NMR (CDCl 3 )  d  7.28 (d, 1H,  J   =15.6Hz), 7.32(d, 1H,  J   =8.6Hz), 6.82 (d, 1H,  J   =1.8Hz), 6.66 (dd, 1H,  J   =8.7Hz,  J   =2.3Hz), 6.60 (s, 1H), 6.58 (d, 1H,  J   =15.8Hz), 5.91 (s, 1H), 3.80(t, 4H,  J   =4.3Hz), 3.43 (q, 4H,  J   =7.1Hz), 3.12 (b, 4H), 2.51 (s, 2H),2.35 (s, 2H), 1.23 (t, 6H,  J   =7.1Hz), 1.02 (s, 6H);  13 C NMR (CDCl 3 )  d 157.9, 157.4, 152.5, 147.3, 142.1, 136.4, 123.8, 121.2, 119.5, 119.4,118.3, 109.7, 107.9, 93.7, 91.9, 68.3, 50.8, 45.0,42.9, 40.5, 30.1,28.0, 12.7;IR(KBr)cm  1 =2202.( E  )-2-(3-(( E  )-2-(6-(diethylamino)benzofuran-2-yl)vinyl)-5,5-di-methyl-2-morpholinocyclohex-2-enylidene)acetaldehyde ( 8 ) wasprepared as follows: The nitrile  7  (0.4g, 0.9mmol) was dissolvedin toluene (15mL) and cooled to  78  C under a blanket of nitro-gen. DIBAL (1.5M, 1.3mL) was added to this solution and stirredfor 2h. Ethyl acetate (15mL) was added to the solution whichwas then allowed to slowly warm to room temperature. Saturatedammonium chloride solution (25mL) was added and stirred for30min. The organic layer was extracted and dried with brine(3  25mL) and magnesium sulfate. The solvent was removed un-der reduced pressure and the resulting oil, the extended aldehyde 8 , was used without further purification.The electron-accepting end of the dye was prepared accordingto the procedure of He et al. [28], Scheme 3. 2-(3-Cyano-4-methyl-5-phenyl-5-(trifluoromethyl)furan-2-(5 H  )-ylidene)-malononitrile ( 9 ) was prepared as follows: A mixture of 19.23gof4,4,4-trifluoro-3-hydroxy-3-phenylbutan-2-one(88mmol),12.81g malononitrile (194mmol, 2.2eq) and 0.2g DMAP in 30mL pyridinewasheatedto50  Candstirredovernight.Themixwascooledandpouredinto200mLCH 2 Cl 2 .Thiswaswashedwith100mL4NHCland brine then dried (MgSO 4 ) and concentrated in vacuum to give24.19g of a dark glass. This was recrystallized from 100mL tolueneto give 7.72g of   9 , a white solid (28%).  1 HNMR (Acetone-d 6 ): 7.8 (m,2H),7.63(m,3H),2.57(s,3H).2-(Cyano-4-((1 E  ,3 E  )-3-(3-(( E  )-2-(6-(diethylamino)benzofuran-2-yl)vinyl)-5,5-dimethyl-2-morpholinocyclohex-2-enylidene)prop-1-enyl)-5-phenyl-5-(trifluoromethyl)furan-2-(5 H  )-ylidene)malononitrile ( 10 ) was prepared as follows: The extended aldehyde  8 (300mg) and the CF 3 -TCF acceptor ( 9 ) (350mg) were added toethanol (30mL) which was refluxed under nitrogen. The progressof the reaction was monitored with TLC and no trace of startingmaterial was observed after 2h. The solution was cooled and theethanol solvent was removed by evaporation under reduced pres-suretoconcentratethesolution.Aprecipitateformedwhichwasfil- Et 2 NCHOOH Et 2 N OOHCO 2 EtCO 2 EtEt 2 N OCO 2 EtEt 2 N OCHOEt 2 NO NOEt 2 NO NCNEt 2 NO NCHOEt 2 NO NONCNCCNPh CF 3 OCNCNCNF 3 CPhNOO 1 OOOO 2 3 4 5 678910 Scheme 1.  The synthesis of morpholino dye  10 . O OBr ONO 5 Scheme 2.  Bromination of isophorone, and reaction with morpholine. OHOPh CF 3 + NC CN OCNCNF 3 CPhCN 9 Scheme 3.  Preparation of the trifluoromethyl(phenyl)-tricyanodihydrofuran (CF 3 -TCF).  A.P. Chafin et al./Optical Materials 33 (2011) 1307–1315  1309  Author's personal copy teredundervacuumanddriedundernitrogentogiveadarkpowder(290mg,58%).Nofurtherpurificationof  10 wasdeemednecessary. 1 HNMR(CDCl 3 ) d 7.95(dd,1H,  J   =12.9Hz,  J   =12.8Hz),7.53(m,5H),7.47 (d, 1H,  J   =16.3Hz), 7.32 (d, 1H,  J   =8.7Hz), 6.98 (d, 1H,  J   =12.6Hz), 6.76 (s, 1H), 6.68 (d, 1H,  J   =15.6Hz), 6.66 (s, 1H), 6.46(d, 1H,  J   =14.7Hz), 3.86 (t, 4H,  J   =4.4Hz), 3.45 (q, 4H,  J   =7.0Hz),3.12(b, 4H), 2.43 (m, 2H), 2.23 (m, 2H), 1.24(t, 6H,  J   =7.0Hz), 0.98(s, 3H), 0.90(s, 3H).The preparation of hydroxyethyloxy-isophorone was accom-plished by reacting isophorone oxide with excess ethylene glycol[17,29] (Scheme 4). 2-(2-Hydroxyethoxy)-3,5,5-trimethylcyclohex-2-enonewaspre-pared as follows: 20.0g 4,4,6-trimethyl-7-oxabicyclo [4.1.0] hep-tan-2-one (130mmol) was added to a solution of 3.0g sodium(130mmol) in 150mL ethylene glycol. The solution was heatedto 50  C and stirred for 18h then cooled and poured into 500mL water. This was extracted with 2  250mL CH 2 Cl 2 . The combinedextracts were washed with water then dried (MgSO 4 ) and concen-trated in vacuumto give 24.14g of a tan liquid (94%) This was dis-tilled at 0.13torr (collected 105  C to 110  C) to give 18.35g of   11, a light yellow liquid (71%).  1 H NMR (acetone-d 6 ): 4.0 (t, 1H), 3.79(t, 2H), 3.59 (m, 2H), 2.31 (s, 2H), 2.2 (s, 2H), 1.88 (s, 3H), 1.00 (s,6H).( E  )-3-(2-(6-(diethylamino)benzofuran-2-yl)vinyl)-2-(2-hydro-xy ethoxy)-5,5-dimethylcyclohex-2-enone ( 12 ) was prepared asfollows: 2.3g sodium (100mmol) was dissolved in 50mL MeOH.To this was added a solution of 6.35g  4  (29mmol) and 5.8g  11 (29mmol) in 150mL MeOH. The solution was heated to 60  Cand stirred overnight. The mixture was pouredinto 200mL CH 2 Cl 2 and washed with water and brine then dried (MgSO 4 ) and concen-trated in vacuum to give 10.78g of a red glassy solid. This waschromatographed on Silica Gel using 50% EtOAc/hexanes to give9.57g of a red glass (83%).  1 H NMR (Acetone-d 6 ): 7.5 (d, 1H), 7.4(d, 1H), 6.9 (d, 1H), 6.73 (s, 1H), 6.7 (m, 2H), 3.97 (t, 2H), 3.71 (q,2H), 3.48 (q, 4H), 2.57 (s, 2H), 2.34 (s, 2H), 1.2 (t, 6H), 1.1 (s, 6H).MS (EI): 397 (M + ), 324.( E  )-3-(2-(6-(diethylamino)benzofuran-2-yl)vinyl)-2-(2-( tert  -butyldiphenylsilyloxy)ethoxy)-5,5-dimethylcyclohex-2-enone( 13 )waspreparedasfollows:Toasolutionof12.48g 12 (31mmol)and9.0g chloro  t  -butyldiphenylsilane (33mmol) in 150mL dimethyl-formamide was added 2.23g imidazole (33mmol). The mixturewas stirred for 4h then poured into 300mL chloroform. This waswashed with 1N HCl and water then dried (MgSO 4 ) and concen-trated in vacuum to give 18.59g of a reddish solid. This was tritu-rated with ether to give 15.06g of an orange solid (76%). 8.0g of this was recrystallized from 200mL ethanol and 20mL water togive 6.19g of orange crystals (59%).  1 H NMR (Acetone-d 6 ): 7.7(m, 4H), 7.6 (d, 1H), 7.35 (m, 6H), 7.3 (d, 1H), 6.9 (d, 1H), 6.75 (s,1H), 6.6 (m, 1H), 6.5 (s, 1H), 4.12 (t, 2H), 3.94 (t, 2H), 3.38 (q,4H), 2.57 (s, 2H), 2.31 (s, 2H), 1.1 (m, 21H). MS (EI): 635 (M + ), 578.( E  )-2-(2-(2-( tert  -butyldiphenylsilyloxy)ethoxy)-3-(( E  )-2-(6-(diethylamino)benzofuran-2-yl)vinyl)-5,5-dimethylcyclohex-2-enylidene)acetonitrile( 14 )waspreparedasfollows:Asolutionof5mLdryCH 3 CN(96mmol)in100mLTHFwascooledto  70  Cwhile35mL2.5M n -BuLi(88mmol)wasaddeddropwise.After15minat  70  Casolutionof7.0g 13 (11mmol)in150mLTHFwasadded.Themixturewasstir-redat  70  Cfor10minthenallowedtowarmto0  C.100mLwaterwasthenaddedandthemixturewasconcentratedinvacuum.Theres-iduewastakenupin250mLCH 2 Cl 2 andwashedwithwaterthendried(MgSO 4 )andconcentratedinvacuumtogive8.71gofadarkredoilysolid. This was takenupin100mLHOAc. Thesolutionwas heatedto60  Cand stirredovernight. The solutionwas cooledandpoured into300mL CHCl 3 . This was washed well with water then dried (MgSO 4 )andconcentratedinvacuumtogive7.15gofaredglass.Thiswaschro-matographedonSilicaGelusing30%EtOAc/hexanestogive3.17gofaredglass(44%).MS(EI):658(M + ),635.( E  )-2-(2-(2-( tert  -butyldiphenylsilyloxy)ethoxy)-3-(( E  )-2-(6-(diethylamino)benzofuran-2-yl)vinyl)-5,5-dimethylcyclohex-2-enylidene)acetaldehyde( 15 )waspreparedasfollows:Asolutionof5.48g 14 (8.3mmol) in 60mL toluene was cooled to   70  C while 18mL 1.5MDibal-Hintoluenewasadded.Thesolutionwasstirredfor4hat   70  C then about 15g of wet silica gel was added along with30mLether.Themixturewasallowedtowarmtoroomtemperaturethenstirredovernight.Thesolidswerethenfilteredoffandthefiltrateconcentrated invacuumto give 5.55g of a red glass. This was chro-matographed on Silica Gel using 30% EtOAc/hexanes to give 2.69gofaredglass(52%). 1 HNMR(Acetone-d 6 ):10.1(d,1H,CHO).2-(4-((1 E  ,3 E  )-3-(2-(2-( tert  -butyldiphenylsilyloxy)-3-(( E  )-2-(6-(diethylamino)benzofuran-2-yl)vinyl)-5,5-dimethylcyclohex-2-enylid-ene)prop-1-enyl)-3-cyano-5-phenyl-5-(trifluoromethyl)furan-2(5 H  )-ylidene)malononitrile( 16 )waspreparedasfollows:Thefinalstepinmaking the ethoxysiloxane-benzofuran dye to heat a solution of 2.69g  15  (4.3mmol) and 1.4g  9  (4.3mmol) in 50mL ethanol to65  C and stir for 5h then cool and concentrate the solution in vac-uum. The residue was chromatographed twice on Silica Gel using30%EtOAc/hexanesand20%EtOAc/hexanestogive0.60gofablueso-lid(15%).MS(ESI):959(M + ).  2.3. Method of film preparation, poling, and r   33  measurements Cyclopentanone and dibromomethane were found to be goodsolvents for all of the dyes and polymers. These solvents have auseful volatility for the spin-casting and baking processes, andgave films of high optical quality. Polymers and dyes were dis-solved in separate solutions. Solutions were stirred with magnetbar until fully dissolved. The total-solids of the polymer solutionswere 5–10wt.%. A noted amount of dye solution was added tothe polymer solution and stirred. Solutions were passed througha 0.2- l m PTFE Teflon  filter and allowed to sit   3h before spin-coating onto an ITO/glass slide (2000rpm, 60s with 500rpmramp). The slides were baked on a hot plate for 2min at 90  C.Then,   100nm thick gold electrode was deposited on the filmsusing a thermal evaporator.Polar orientation of the dye in the guest–host films wasachieved by contact poling. We used an FP90 control processor(Mettler Toledo, Inc.) to communicate with a FP82HT hot stage.The hot plate was enclosed in a nitrogen environment and polingwas performed after the oxygen content decreased to less than  200ppm to avoid oxidation. A high voltage source measurementunit (Keithley, Inc.) was used to apply voltage to the sample. Thedetailsof apolingcycle areshowninFig. 1(thelast of four consec-utive poling cycles on this film). The achievement of an optimumpoling protocol for each type of material and dye loading is anextensive process requiring more material than was available forthis investigation. Fig. 1 displays the temporal profile of the tem-perature (in   C, left axis), poling voltage (in V, left axis), and theresulting current flowing through the film (in amperes, right axis).The temperature was increased close to the  T   g   at a heating rate of   10  C/min and maintained for 5–10min with 300–400V(dependingonthefilmthickness)acrossthesamplefilm,followingby cooling to room temperature with the field on.Simple Teng-Man (T-M) measurements were performed on thefilms to determine the electro-optic coefficients. To improve the OOOOOH 11 Scheme 4.  Preparation of hydroxyethoxy isophorone.1310  A.P. Chafin et al./Optical Materials 33 (2011) 1307–1315
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