preparation

.2011,2(6),415-418ADVANCEDMATERIALSLetters

.2011,2(6),415-418Copyright©2011VBRIpress.

,,DOI:10.5185/amlett.2011.2227PublishedonlinebytheVBRIpressin2011

ChenMo1,LinLin2,LiXiaoqiang3*

1NorthChinaInstituteofScienceandTechnology,EastYanjiao,Beijing101601,China

2SchoolofFood&BiologicalEngineering,JiangsuUniversity,

3DepartmentsofMechanicalEngineering,IbarakiUniversity(CollegeofEngineering),Hitachi,Ibaraki3168511,Japan

*:(+81)29-438743;E-mail:*****************,*********************.

Received:14Feb2011,Revid:15May2011andAccepted:01June2011

Anewtypeofphotochromichydrogel,spiropyran(SP)-Polyvinylpyrrolidone(PVP)-poly(N-isopropylacrylamide)(PNIPAM)

hydrogelwithfunctionalizedSPchemicallyincorporated,ecularstructureofsynthesizedproducts

wasgivenbynuclearmagneticresonance(NMR)spectraandinfraredspectrum(IR).Thephotochromismofthehydrogelwas

evidencedbyphotographyandcharacterizedbyultraviolet-visible(UV-Vis)tochromicreversibilityof

thehydrogelwastestedthroughoborescence

micrographsshowedthefluorescenteffectaswellasconfirmedthephotochromicpropertiesofthehydrogel,andindicatedthat

thecheght©2011VBRIpress.

Keywords:Photochromism;polymerichydrogel;spiropyran.

MoChenobtainedhisBachelordegreefrom

ent,heis

workinginNorthChinaInstituteofScience

orrearchisfocus

onsynthesizingphotochromiccompound

anddevelopingmultifunctionalproductsfor

biologicalapplications.

fromDonghuaUniversityinMarch,2010.

Currently,heisworkinginIbaraki

University(Japan)asanassistantrearcher.

’smainrearchinterestsinclude

fabricationofbiofunctionalnanofibersfor

TissueEngineeringfromelectrospun

nanofibers,anddevelopmentofdrug-

deliverysystemsbyemulsionorcoaxial

electrospinning.

Introduction

Mostofhydrogelsarewater-swollenpolymericmaterials

thatmaintainadistinctthree-dimensionalstructureandbe

ofhighinterestfortechnicalandmedicalapplications[1].

Theirclassificationbadonthesource,crosslinking

function,

varioushydrogels,poly(N-isopropylacrylamide)

(PNIPAM)isatypicalthermo-nsitivepolymericmaterial

thatdemonstratesalowercriticalsolutiontemperature

(LCST)at32°emperature

andpHarewell-knownsignalsthatinduceresponsin

polymerhydrogels,theuoflightasanothertypeof

rearchershaveinvestigatedvariousfunctionalhydrogels

[2-7].Intheirwork,thephotochromicorthermal-light

doublynsitiveorevenmulti-responsivehydrogelswere

preparedbymodifyingpolymerhydrogelswith

chromophoressuchasazobenzene,spirobenzopyran,etc.

UpontheirradiationofUVorvisiblelight,isomerization

ofthechromophoresinthepolymerhydrogelsgivesrito

phatransitionandthusinducesresponsinthe

hydrogels.

Photochromicmaterialshadabstractedgreatinterest

allyinbiological

applications,theuoflightoffersuniqueopportunities,as

lightfluxesareeasytocontroltemporallyandareless

likelytoperturbdelicatebiologicalstructuresthanmost

otherstimuli[8-10].Asaclassofstructurallydiver

photochromiccompounds,spiropyrans(SP)playaspecial

rolesincetheirphotoinducedandreversiblering-opening

tothecorrespondingmerocyaninesisaccompaniednot

onlybyasignificantstructuralchangefromanon-planarto

aplanarstructurebutalsobyalargepolarityincrea[11].

Thelowwater-solubilityofSPlimitsitspotentialtobe

heyare

Mo,LinandXiaoqiang.

.2011,2(6),415-418Copyright©2011VBRIpress.

oftenconjugatedtobiomaterialssothattoequipthe

materialswithphotochromicproperties[12].However,

incorporationofSPtothewell-studiedPNIPAMhydrogel

hydrogelhasgood

hydrophilicityandbiocompatibility,whichmakeita

promisingmaterialforphotochromicswitchingor

fluorescentlabelinginbiologicalapplicationsifcombined

withsuitablechromophores.

Intheprentstudy,anovelfunctionalizedSPwas

synthesizedandincorporatedintoPNIPAMhydrogelto

produceaphotochromichydrogel,thephotonsitivityof

whichisreflectedincolorchangesandfluorescence

inducedbytheisomerizationofSPratherthanpha

ecularstructureofthefunctionalizedSP

andthesynthesizedhydrogelsweregivenbynuclear

magneticresonance(NMR)andInfrared(IR)spectra.

Variousmethodswereappliedtocharacterizethe

photochromicpropertiesandfluorescenteffectofthe

photochromichydrogels.

Experimental

Materials

AllofthematerialsudforNO

2

SPsynthesisinthisstudy

arechemicallypuredegree.N-isopropylacrylamide

(analyticallypure)wasprovidedbyAcrosCo.,Belgium;

potassiumpersulfate(KPS)andN,N,N’,N’-

tetramethyldiamine(TEMED)wereprovidedbyShanghai

ChemicalReagent,AnalyticReagent;absoluteethanolwas

purchadfromAAPERAlcoholandChemicalCompany;

N,N’-Methylenebis(acrylamide)(BIS),

polyvinylpyrrolidone(PVP)andN-vinylpyrrolidone(NVP)

ctionalizedNO

2

SP

wassynthesizedinourownlab.

SynthesisofSP-P(NIPAM-co-NVP)hydrogel

NVPwasdissolvedinwaterandbondedtoNIPAMusing

KPSandTEMEDasthecatalyststoformcarbonbond.0.5

gNO

2

SPwasdissolvedin5.0gethanol,whichthenwas

addedtoaNIPAMandNVPaqueoussolution(20g,

cNIPAM=cNVP=4wt%).Afterthesolutionbeing

completelymixed,ctionwas

allowedtocontinuefor2hinthedarkatroomtemperature.

TheresultantSP-P(NIPAM-co-NVP)hydrogelwas

immerdinanethanol/water(w/w=20/80)mixturefora

weekandthenindeionizedwaterforanotherweekinthe

ersionprocesswas

carriedoutfourtimesuntilthesupernatantbecame

pectraofhydrogelsamples

(PNIPAM,P(NIPAM-co-NVP)andSP-P(NIPAM-co-

NVP))wereobtainedonaNEXUS670Infrared-Raman

Spectrometer(Nicolet,US).

Characterization

ThehydrogelsampleswerepowderedandmixedwithKBr

pectraofthesampleswere

obtainedonaNEXUS670Infrared-RamanSpectrometer

(Nicolet,US).UVexposureat365nmforthesampleswas

providedbyaUVlamp(Blak-RayModelB,100AP)ata

ightintensityreceivedbythe

sampleswas1.2W/pleswereshapedtofitin

orbanceasafunctionof

wavelengthwasmeasuredusingaLambda35UV-Vis

spectrophotometer(PerkinElmer,US).Thesampleswere

orescenteffectofthe

sampleswasobrvedbyafluorescentmicroscope(UL

100HG,Olympus,Japan).

Resultsanddiscussion

TheIRspectraofdifferentsamplesareshowninFig.1.

Theabsorptionpeakof-C=C-inbenzeneringatabout

1450and1580cm-1andthepeakofC=Oat1680cm-1can

beclearlyenfortheSP-P(NIPAM-co-NVP)sample,

whichdidnotappearinthespectraofthePNIPAMand

P(NIPAM-co-NVP)samples,significantlyindicatedthat

thefunctionalizedSPhadbeenincorporatedintothe

hydrogel.

traofPNIPAM,P(NIPAM-co-NVP),SP-P(NIPAM-co-

NVP)hydrogels.

Fig.2showsthecolorchangeandUV-Visspectraof

PNIPAMandSP-P(NIPAM-co-NVP)hydrogelsunderthe

.2

(a),areprentsthePNIPAMgelafterUVirradiationfor

30s;B,CandDaretheSP-P(NIPAM-co-NVP)gelsafter

irradiationfor0,10and30s,PAM

gelwascolorlessandtransparentasshowninpicture-A

Fig.2(a)rast,theSP-P

(NIPAM-co-NVP)gelexhibitedalightyellowcolorwhen

eincreaof

irradiationtime,thecolorofthegelgettingdarker,andwas

mentionedintheExperimentalction,theSP-P(NIPAM-

co-NVP)gelswerefirstimmerdinanacetone/water

ore,

thecolorshowninthepictureswasascribedtothe

orchangesindicatedthattheSP

wasstillphoto-chemicallyactiveandendowedthe

canbeeninFig.2(b)that,withoutUVirradiation,there

wasnoabsorbanceoverthewholewavelengthrangein

.2011,2(6),415-418ADVANCEDMATERIALSLetters

.2011,2(6),415-418Copyright©2011VBRIpress.417

UV-VisspectrumforthePNIPAMgel,avidencedby

picture-AinFig.2(a).FortheSP-P(NIPAM-co-NVP)

gel,anabsorptionpeakappearedat568nmandincread

withincreadirradiationtime,ingoodaccordancewith

theresultsofFig.2(a).Beforeirradiation,afractionofSP

moleculeswereinthemerocyanineform(openring),

thoughmostoftheSPmoleculeswereinthespiro(clod-

ring)stenceofmeroisomersledtoasmall

rradiation,somespiro

isomersconvertedtothemero(open-ring)form,making

theabsorptionpeakincreawithprolongedirradiation

rogelexhibitedobviousphotochromic

oratingSP

moleculesintothePNIPAMhydrogelcouldenhancethe

applicabilityofphotochromicmaterialsinaqueous

environment.

Fig.2.(a)Colorchangesand(b)UV-Visspectraofhydrogelsirradiated

by365nmUVlightfordifferenttimes.

The568nmlighttransmittanceofSP-P(NIPAM-co-

NVP)gelinrespontoalternatingUVirradiationand

usdabove,SPwasin

thespiroforminthedark,whoabsorptionbandliesin

-P(NIPAM-co-NVP)gelwasthus

nearlycolorlessandtransparentwithatransmittanceof

around82.5%.Whenexpodto365nmUVlight,the

transformationofSPtothemeroformmadethegelturn

intoreddishbrown,leadingtoadramaticdecreaof

er,forveralcyclesinthedata

range,themodulationofthetransmittancewasfully

reversiblewithoutanysignoffatigueeffect,demonstrating

thegreatpotentialofsuchhydrogelsforon-and-off

switchingapplications.

Fig.4showsthefluorescenteffectofhydrogelsunder

omophores(fluorophores)

wereprotectedbythehydrogelfromtheexternal

ore,thequenchingoftheir

cted,thePNIPAM

geldidnotfluoresceuponexcitationbygreenlight(520–

570nm).TheunirradiatedSP-P(NIPAM-co-NVP)gel

ptinthedark,onlya

verysmallamountofSPmoleculeswereinthemeroform.

Thefluorescenceresultedfromelectrontransitionofthe

Virradiation,

however,certainamountsofspiroisomersconvertedto

ectronswereexcitedandtransited

backtothegroundstate,leadingtostrongerfluorescence.

Withtheincreaofirradiationtime,thefluorescencegrew

rmore,thewholehydrogelstripemitted

fluorescenceofthesameintensity(Fig.4E),suggesting

thatSPdistributeduniformlyinthehydrogel.

tionoflighttransmittanceat568nmfortheSP-P(NIPAM-

co-NVP)gelwithalternatingUVanddarkness:Ineachcycle,thesample

wasirradiatedby365nmUVlightfor30s(lowtransmittence)andkept

indarknessfor5min(hightransmittence).

scenteffectofvariousgelsunderdifferentirradiation

conditions:APNIPAMgelirradiatedby365nmUVlightfor10s;BSP-

P(NIPAM-co-NVP)gelbeforeUVirradiation;CSP-P(NIPAM-co-NVP)

gelirradiatedby365nmUVlightfor10s;DSP-P(NIPAM-co-NVP)gel

elengthoftheexciting

lightwasintherangeof520-570nmwhenobrvingfluorescence.

ThefunctionalizedSPmoleculeswereincorporatedinto

thehydrogelviareactionofdoublebonds,makingthem

muchlesslikelytoaggregateandaffectthepropertiesof

fluorescencecouldbeelicitedbygreen

lightafterthehydrogelwasirradiatedbyUVlightfor

Mo,LinandXiaoqiang.

.2011,2(6),415-418Copyright©2011VBRIpress.

veralconds,indicatingthatSP-P(NIPAM-co-NVP)

gelcanbeudinfluorescencelabeling.

Conclusion

AphotochromicSP-P(NIPAM-co-NVP)hydrogelwitha

picturesandtheUV-Visresultssuggestedthatthehydrogel

possdexcellentphotochromicpropertiesandcanbe

undfromthe

rapidresponsofthehydrogeltothealternatingUV

irradiationanddarkcyclesthatithadgreatpotentialfor

orescence

micrographsdemonstratedfluorescenteffectand

photochromismofthehydrogel,whichmakeitpossibleto

distributeduniformlyinthegel,ensuringitsgood

photochromicproperties.

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