功能高分子材料 (14)

功能高分子材料功能高分子材料 14 14 A SupramolecularCross Linked ConjugatedPolymer NetworkforMultiple FluorescentSensingXiaofan Ji Yong Yao Jinying Li Xuzhou Yan and FeiheHuang MOE KeyLaboratory ofMacromolecular Synthesisand Functionalization Department ofChemistry Zhejiang University Hangzhou Zhejiang310027 P R China S Supporting InformationABSTRACT A supramolecular cross linked work wasfabricated anddemonstrated to act as a multiplef l uorescent sensor It wasconstructed froma f l uorescentconjugated polymer and a bisammonium salt cross linkerdriven bydibenzo 24 crown 8 secondary ammoniumsalthost guest interactions Compared withthe conjugatedpolymer the workhas weak f l uorescence due to theaggregation of polymer chains Thanks to the multiplestimuli responsiveness of host guest interactions thef l uorescence intensity of the system can be enhancedbyfour types of signals including potassiumcation chlorideanion pH increase and heating Hence the workcanserve asa cationsensor an anionsensor a pHsensor anda temperature sensor It can be used in bothsolution andthin f i lm Interestingly exposure of a f i lm made from thissupramolecular cross linked work to ammonia leads toanincrease of f l uorescence making ita goodcandidate forgasdetection Supramolecular cross linked polymer works preparedfrom covalentpolymeric backbonestied togetherbynoncovalent interactions have receivedmuch attentioninrecent yearsduetothe mechanicalor photophysicalpropertiesobtained from the polymerihains and also thereversibilityand stimuli responsiveness contributedby noncovalentinter actions usedin cross linking 1The stimuli responsiveness ofcross linking motifscan endowsupramolecular cross linkedworks withplenty ofunique applications such ascontrolledrelease 2self healing 3and f l uorescent sensors 4Nowadays much attentionhas beenpaid to f l uorescentsensors based onsupramolecular cross linked workson aountof theirhighselectivity andsensitivity especially theones whosepolymericbackbones aref l uorescent conjugated polymers 4An importantadvantageof conjugatedpolymers isthe obviouschange off l uorescence intensity in dif f erent states the individualconjugatedpolymers exhibitstrong f l uorescence while theiraggregatesformed bynoncovalent cross linking showweak orquenchedf l uorescence 4b c h makingthem suitablef l uorescentsensors fordetecting signalsthat caninf luence thestate ofaggregation Up tonow considerable eff ortshave beendedicatedto f luorescentsensorsbased on conjugated polymerworks 4For example Swager and co workers reportedthef i rst sensorysystem whichutilized the f l uorescence diff erenceof conjugatedpolymersindiff erentstates and itwas usedfordetecting potassiumion 4b Kakuchiandco workers recentlydevelopeda f luorescentsensory workwhose conjugatedpolymerchains werecross linked throughhydrogen bondingtoprobe anionsthat candisrupt thecross linking 4k Conjugatedpolymer works based on organometalliross links hadalsobeen studied 5However all reportedconjugatedpolymerworksbased onsupramolecular cross links canonly probeoneor twotypes of signals 4Consequently it ischallenging todevelopa conjugatedpolymerworkbased onsupra molecularcross links to detect multiplesignals Noncovalent interactionswith multiresponsivenesshavebeen widelyusedin the constructionof smartor adaptivematerials such as supramolecular gelswith multiplestimuliresponsive properties 6Therefore our strategyis toselect akindof noncovalentinteraction withmultiresponsiveness toserveassupramolecular cross linker Thus the disassemblyofthe conjugatedpolymerwork will betriggered bymultiplestimuli Crown ethers 7the f irstgeneration ofsupramolecularmacrocyclic hosts have beenconsidered asa fascinatingplatformto preparemultiresponsive materials 6a b It is well known thatdibenzo 24 crown 8 DB24C8 and itsple mentary guestdibenzylammonium salt DBA form a1 1threaded structure which isresponsive toquadruple stimuli K Cl pH or temperature change 6b c 8 9b Herein weprepared asupramolecular cross linked polymerwork bymixinga poly phenylene ethynylene PPE polymer withpendentDB24C8groups and a bisammoniumsalt cross linker The workwill formwhen the DB24C8units interactwiththe secondaryammoniumsaltmoieties causing the aggregationof polymermain chainsand leading to asharp decreaseoff l uorescence intensitypared tothat of the PPEpolymer 4bCollapse willhappen tothe workafter treatment with K orCl correspondingly recoveryof the f l uorescence intensitywillour Moreover the workis alsoresponsive topH andtemperaturechanges 3b 7p Hence this system can beutilized asfourtypes ofsensors a cationsensor an anionsensor a pHsensor andatemperaturesensor Scheme1 The systemcanbe usedin bothsolution andthin f i lm Interestingly exposureof a f i lm madefromthis work to ammonialeads to anincrease off l uorescencefrom the f i lm making ita goodcandidatefor gassensing Polymer1 M n 70 6kDa andPDI 1 77 was synthesizedby a Pd catalyzed cross coupling reactionof1 4 diethynylben zene anddiiodo diDB24C8 substituted benzenederivative3 SupportingInformation SI Scheme S1 There wereaboutReceived November4 xxPublished December21 xxCommun icationpubs acs JACS xxAmerican Chemical Society74dx doi 10 1021 ja3108559 J Am Chem Soc xx 135 74 7 7112DB24C8units 56repeat units per singlepolymer chainfor1as calculatedbasedonthe GPCdata The cross linker2isa bisammoniumsalt linkedbyalong f l exiblealkyl chain 7a Asupramolecular cross linked polymerworkwillform uponthe addition of2to1in CHCl3 CH3 1 1 To investigatethe formation of the supramolecular cross linked work NMR spectroscopy f luorescence titrationspectroscopy and scanningelectron micrography SEM were carried out First proton NMR spectra gavedirectevidence for the plexation of polymer1and cross linker2in solution 3b As shown in Figure1 spectra of polymer1 cross linker2 anda mixture of1and2were examined Upf i eld shiftswereobserved foraromatic protons H1 H2 H3 H5 and H6andbenzyloxymethylene protonsH7of2after plexation However the benzylprotonsH4of2shifted downf ieldaftermixing in aordancewith apreviously reportedplexationsystem ofDB24C8 DBA 9Moreover the slowexchangefeature madethe protonsof the DB24C8unit and the DBAmoietysplit intotwo setsofsignals the plexedandunplexed ones These distinctchanges inchemical shiftsindicatedthe ourrenceofhost guest interactions betweenDB24C8and DBA inducing the formation of a supramolecularcross linked polymerwork Fluorescence titrationexperiments were carriedouttoinvestigate the f luorescence responseof theconjugatedpolymer1to cross linker2 Figure2shows the fluorescence spectra ofconjugated polymer1upon additionof cross linker2 As theconcentrationof cross linker2increased the fl uorescenceintensity of polymer1decreased gradually and theinherentblue bandof thePPE shiftedto longerwavelengths from440to447nm in aordancewith aggregation induced planariza tionof the polymerchains 10In addition the photographsinFigure2show that the brightnessof thesolution wasalsoreduced Obviously it isthe plexationof theDB24C8unitsand the DBA moietiesthat resultsin theaggregation ofPPEchains andcauses thereduction of thefluorescence intensity However thefluorescence intensityof polymer1was nottotallyquenched The reasonwas that the longalkyl chainwhichlinks thetwo bisammoniumsalt unitsconf ine thepactnessof theconjuagted polymerchain aggregation These resultsshowed thatthe supramolecular cross linkedpolymer workconstructed byhost guest interactionsbetweentheDB24C8units and theDBAmoieties exhibitsweakfluorescence pared to itsPPE chains To testthe morphologyof the supramolecularcross linkedpolymer work SEM studieswerecarriedout Figure3bshows aninterconnected porous3D structure indicating theformationof thesupramolecularcross linked workowing totheaggregation ofPPE chainsthrough host guest interactions The phenomenonillustrated thatthe presence of cross linkersnot onlyrealized theconversion fromthe linearpolymer tosupramolecularwork but alsobrought aboutthe changeinthe microscopicstructure Figure3a b All theabove resultsconf irmed theformationof thesupramolecular cross linked workfrom1and2 It wasScheme1 Cartoon Representationof theFormation of aSupramolecular Cross Linked ConjugatedPolymer NetworkandIts DisassemblyInduced byDif f erent SignalsFigure1 Partial1H NMRspectra 500MHz 1 1CDCl3 CD3 298K a polymer1 b a mixture of2 00 M polymer1 0 224mM crowher units and20 0 M cross linker2 40 0 Mammonium moieties c cross linker2 Here c and u denoteplexed andunplexed moieties respectively Figure2 Fluorescence spectra of1 2 0 M in CHCl3 CH3 1 1 with differentconcentrations of2 from topto bottom 0 0 20 40 80 100 150 M exc 355nm Journal of the AmericanChemical SocietyCommunicationdx doi 10 1021 ja3108559 J Am Chem Soc xx 135 74 7775also shownthatthefluorescence of thesupramolecularworkis weakerthan thatofconjugatedpolymer1 It iswell knownthat theplexationofDB24C8and DBAcanbecontrolledby potassiumcation K 8b chlorideanion Cl 9b pHchange 3b 7p 8c andtemperaturechange 8a sincetheDB24C8unit forms a morestable1 1plex withK Cl formsatightion pairwith DBA Et3N convertsthe secondaryammonium tothecorresponding secondaryamine and heatingcauses thedisassemblyby reducingthe bindingconstant 3b 6b 7p 9b Hence thefluorescenceofthesystem will be strengthenedby thesedifferenttypesofsignals We usedTBACl KPF6 triethylamine Et3N and heatingto controlthe host guest interactions which resultedin thetransition fromthesupramolecularcross linked workto linearpolymer andthe increaseoffluorescenceintensity Figure4shows thatthefl uorescenceintensityofthe work systemincreased upontheadditionofTBACl KPF6 or Et3N orheating Asshownin Figure3b e the morphologyofthe mixture of1and2changed frominterconnectedporous3D structuretof i berswith parallelarrangementafter treatmentby TBACl KPF6 and Et3N Theparallel arrangementis generatedby the interactionsbetween polymermain chains In theprocess ofsamplepreparation the polymerchains gatheredcloser andcloser withtheevaporation ofsolvents giving suff icient distancefor the interactionsbetweenpolymerchains The1H NMRexperimentalso demonstratedthis disassemblyprocess SI Figures S7 S10 Therefore thisworksystemcanfunctionas amultiple fluorescentsensor In addition inspired byrecentwork aboutmultiresponsive gels 6e thiswork wasdemon strated tobe ableto functionas anXOR gate SI Figures S11and S12 If asingle input K or Cl is set thefl uorescenceincreasesby disassemblyofthework However if bothinputs K and Cl are present KCl precipitatesand theworkreassembles causing decreasedfluorescence Besides insolution thefluorescenceintensitychanges ofpolymer1inthepresenceofcross linker2andtheworksystem underexternal signalscan alsobe observedin thin f i lm Thin f i lms of polymer1andthe mixture of1and2wereprepared byspin casting solutionsin CHCl3 CH3 1 1 onto glassslides Figure5a showsthatthefluorescenceintensityof polymer1in athinfi lmdecreased undertheexistence ofcross linker2 Moreover as showninFigure5b c the thinfi lms displayeda visuallyclear fluorescencecolorchange froma film ofpolymer1toa film ofa mixture of1and2 from brightblue topale blue In addition the thinfilmof thesupramolecular cross linked workcanbeapplied asa gassensortodetectalkaline gasesbecause theplexation ofDB24C8and DBAwillbe destroyed bybase 3b 4a i 7p Whenathin filmoftheworkwasexposed tothe vaporof ammoniavapor Figure5e the ammoniumunit ofcross linker2wasdeprotonated destroying thework structureand givingriseto anincreaseoffluorescenceintensity Figure5d In conclusion we developeda novelsupramolecularcross linked workbasedonthe host guest interactionsbetweenthe pendentDB24C8units ofa conjugatedpolymer andtheDBA moietiesofabisammonium cross linker The workexhibitedweakfluorescenceparedtothe conjugatedpolymerbecause oftheaggregationofpolymermain chains Figure3 SEM images a polymer1 b amixtureof2 00 Mpolymer1 0 224mM crowher units and20 0 M cross linker2 40 0 M ammoniummoieties c after addingTBACl 40 0 M tomixture b d after addingKPF6 40 0 M to mixtureb e afteradding Et3N 40 0 M to mixtureb Figure4 Fluorescence emissionspectra of a themixtureof1 2 0 M and2 100 M and aftertreatmentwith b heating at50 C c KPF6 200 M d TBACl 200 M e Et3N 200 M Fi gure5 a Fluorescence emissionspectraofthin solidfilmsof2 00 M polymer1 0 224mM crowher units andamixtureof2 00 M polymer1and20 0 M cross linker2 40 0 M ammoniummoeties spin cast fromCHCl3 CH3 1 1 solutions b photograph ofa filmofpolymer1 illuminated at365nm c photograph ofafilmofamixtureof1and2with amolar ratioof1 10 illuminated at365nm d fluorescence emissionspectraofthinfi lmsofthemixture before andafter exposureto ammoniafor10min e cartoon representationof exposure ofafilmmadefrom thesupramolecularworktoammonia Journal ofthe AmericanChemical SocietyCommunicationdx doi 10 1021 ja3108559 J Am Chem Soc xx 135 74 7776Owing tothe multiresponsivenessofthehost guestinteractions theworkstruc ture canbedestroyedbymultiple signals leadingtothe enhancementof thefluorescence Therefore thesystemcan serveasamultiplef luorescentsensor Moreover exposureofafilmofthesupramolecula rcross linked worktoammonialeadstoanincrease ofthefluorescencefromthefilm endowing thesystemwith afunction ingas detecting Itisthe binationofsupramolecular chemistryand conjugatedpolymer sciencethatgave birthtothesupramolecularcross linked workwithremarkable features and webelieve thatthe novelworksystem willpave theway fordesigning andpreparing advancedsensormaterials ASSOCIATED CONTENT S SupportingInformationExperimental details synthesis of1 NMRspectra and othermaterials This materialis availablefree ofcharge viatheInter atpubs acs AUTHOR INFORMATIONCorrespondingAuthorfhuang zju NotesThe authorsdeclare nopeting fi nancialinterest ACKNOWLEDGMENTSThis workwas supportedby theNational Natural ScienceFoundation ofChina 20834004 91027006 and21125417 the FundamentalResearch FundsfortheCentral Universities xxQNA3013 Program forNew CenturyExcellent TalentsinUniversity Zhejiang ProvincialNaturalScienceFoundationof China R4100009 and OpenProject ofState KeyLaboratoryof SupramolecularStructure andMaterials REFERENCES 1 a Fleury G Schlatter G Brochon C Travelet C Lapp A Lindner P Hadziioannou G Macromoleculesxx 40 535 543 b L ieleg O Claessens M M A E Bausch A R Soft Matterxx 6 218 225 c Suzuki M Hanabusa K Chem Soc Rev xx 39 455 463 d Steed J W Chem Soc Rev xx 39 3686 3699 e Pie penbrock M O M Lloyd G O Clarke N Steed J W Chem Rev xx 110 1960 xx f Seiffert S Sprakel J Chem Soc Rev xx 41 909 930 2 a Zhu Z Wu C Liu H Zou Y Zhang X Kang H Yang C J Tan W Angew Chem Int Ed xx 49 1052 1056 b Li X M Li J Y Gao Y Kuang Y Shi J F Xu B J Am Chem Soc xx 132 17707 17709 c Li X Kuang Y Shi J Gao Y Lin H C Xu B J Am Ch em Soc xx 133 17513 17518 d Park M H Joo M K Choi B G J eong B A Chem Res xx 45 424 433 3 a Cordier P Tournilhac F Soulie Ziakovic C Leibler L Naturexx 451 977 980 b Zhang M Xu D Yan X Chen J Dong S Zheng B Huang F Angew Chem Int E d xx 51 7011 7015 4 a Chen L McBranch D W Wang H L Helgeson R Wudl F Whitten D G Proc Natl Acad Sci U S A 1999 96 12287 12292 b Kim J McQuade D T McHugh S K Swa ger T M Angew Chem Int Ed 2000 39 3868 3872 c McQuade D T Pullen A E Swager T M Chem Rev 2000 100 2537 2574 d Jia ng H Zhao X Schanze K S Langmuirxx 22 5541 5543 e Nelson T L O Sullivan C Greene N T Maynor M S Lavigne J J J Am Chem Soc xx 128 5640 5641 f Satrijo A Swager T M J Am Chem Soc xx 129 16020 16028 g Kim I B Phillips R Bunz U H F Macromoleculesxx 40 814 817 h Th omas S W Joly G D Swager T M Chem Rev xx 107 1339 1386 i Esser B Swager T M Angew Chem Int Ed xx 49 8872 8875 j Zhao X Schanze K S Chem Commun xx 46 6075 6077 k Sakai R Nagai A Tago Y Sato S Nishimura Y Arai T Satoh T Kak uchi T Macromoleculesxx 45 4122 4127 5 Weder C Chem Commun xx 5378 5389 6 a Yan X Xu D Chi X Chen J Dong S Ding X Yu Y Hua ng F Adv Mater xx 24 362 369 b Dong S Zheng B Xu D Yan X Zhang M Huang F Adv Mater xx 24 3191 3195 c Zheng B W ang F Dong S Huang F Chem Soc Rev xx 41 1621 1636 d Yan X Wang F Zheng B Huang F Chem Soc Rev xx 41 6042 6065 e Qi Z Malo deMolina P Jiang W Wang Q Nowosinski K Schulz A Gradzi elski M Schalley C A Chem Sci xx 3 2073 2082 7 a Yamaguchi N Gibson H W Angew Chem Int Ed 1999 38 14 3 147 b Gibson H W Yamaguchi N Jones J W J Am Chem Soc x x 125 3522 3533 c Huang F Gibson H W J Am Chem Soc xx 126 14738 14739 d Tian H Wang Q Chem Soc Rev xx 35 361 374 e Huang F Nagvekar D S Zhou X Gibson H W Macromoleculesx x 40 3561 3567 f Wang F Han C He C Zhou Q Zhang J Wan g C Ling N Huang F J Am Chem Soc xx 130 11254 11255 g Wa ng F Zheng B Zhu K Zhou Q Zhai C Li S Li N Huang F C hem Commun xx 4375 4377 h Ge Z Hu J Huang F Liu S Angew Chem Int Ed xx 48 1798 1802 i Jiang W Han M Zhang H Z hang Z Liu Y Chem Eur J xx 15 9938 9945 j J