Donor-Acceptor-Donor Thienopyrazines via Pd-Catalyzed C-H Activation as NIR Fluorescent Materials

Article abstract of DOI:10.1021/acs.joc.5b01958

A series of thienopyrazine-based donor-acceptor-donor (D-A-D) near-infrared (NIR) fluorescent compounds were synthesized through a rapid, palladium-catalyzed C-H activation route. The dyes were studied through computational analysis, electrochemical prope

Full text of DOI:10.1021/acs.joc.5b01958

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Article
Donor-Acceptor-Donor Thienopyrazines via Pd-
Catalyzed C-H Activation as NIR Fluorescent Materials
Louis Edward McNamara, Nalaka Liyanage, Adithya Peddapuram,
Joseph S Murphy, Jared Heath Delcamp, and Nathan I Hammer
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b01958 • Publication Date (Web): 24 Nov 2015
Downloaded from http://pubs.acs.org on November 25, 2015
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Donor-Acceptor-Donor Thienopyrazines via Pd-Catalyzed C-H Activation as
NIR Fluorescent Materials
†
†
LouisꢀE.ꢀMcNamara, ꢀNalakaꢀLiyanage, ꢀAdithyaꢀPeddapuram,ꢀJ.ꢀScottꢀMurphy,ꢀJaredꢀH.ꢀ
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Delcamp,*ꢀNathanꢀI.ꢀHammer*ꢀ
DepartmentꢀofꢀChemistryꢀandꢀBiochemistry,ꢀUniversityꢀofꢀMississippi,ꢀUniversity,ꢀMSꢀ38677,ꢀUSAꢀ
†
Theseꢀauthorsꢀcontributedꢀequally.ꢀ
KEYWORDS:ꢀThienopyrazine,ꢀDonor-Acceptor-DonorꢀMaterials,ꢀNIRꢀDyes,ꢀNIRꢀEmissionꢀ
ABSTRACT: A series of thienopyrazine-based Donor-Acceptor-Donor (D-A-D) near-infrared (NIR)
fluorescent compounds were synthesized through a rapid, palladium catalyzed C-H activation route. The
dyes were studied through computational analysis, electrochemical properties analysis and
characterization of their photophysical properties. Large Stokes-shifts of approximately 175 nm were
observed which lead to near-infrared emission. Computational evaluation shows the origin of this large
Stokes shift is a significant molecular reorganization particularly about the D-A bond. The series exhibits
quantum yields of up to φ= 5% with emission maxima ranging from 725-820 nm. The emission is strong
in solution, in thin films, and also in isolation at the single molecule level. Their stable emission at the
single molecule level makes these compounds good candidates for single molecule photon sources in the
near-infrared.
ꢀ
Introductionꢀ
ꢀ
ꢀꢀꢀꢀNear-infraredꢀ(NIR)ꢀemissiveꢀorganicꢀmoleculesꢀareꢀanꢀemergingꢀclassꢀofꢀmaterialsꢀwhichꢀhaveꢀ
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attractedꢀmuchꢀinterestꢀdueꢀtoꢀtheirꢀapplicationsꢀinꢀopticalꢀandꢀelectronicꢀareas. ꢀApplicationsꢀofꢀ
theseꢀmaterialsꢀrangeꢀfromꢀuseꢀinꢀnightꢀvisionꢀtechnologies,ꢀsecureꢀcommunications,ꢀfluorescenceꢀ
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imaging,ꢀ transparentꢀ photovoltaics,ꢀ andꢀ heat-blockingꢀ coating. ꢀ Inꢀ particular,ꢀ inꢀ vivoꢀ
fluorescenceꢀ imagingꢀ isꢀ aꢀ rapidlyꢀ growing,ꢀ medicalꢀ diagnosticꢀ techniqueꢀ whichꢀ makesꢀ theꢀ
developmentꢀofꢀstableꢀNIRꢀfluorescentꢀtagsꢀofꢀgreatꢀinterest.ꢀ
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ꢀꢀꢀꢀꢀTheꢀ developmentꢀ ofꢀ stableꢀ NIR-emittingꢀ moleculesꢀ isꢀ complicatedꢀ byꢀ theꢀ energy-gapꢀ lawꢀ
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whichꢀ inherentlyꢀ disfavorsꢀ emissionꢀ fromꢀ systemsꢀ withꢀ lowꢀ energyꢀ bandꢀ gaps. ꢀ Theꢀ mostꢀ
commonꢀ strategyꢀ forꢀ theꢀ developmentꢀ ofꢀ organicꢀ NIRꢀ emittersꢀ isꢀ toꢀ designꢀ largeꢀ π-conjugatedꢀ
1,ꢀ3-4,ꢀ23-33
systemsꢀcontainingꢀelectron-donatingꢀ(D)ꢀandꢀacceptingꢀ(A)ꢀgroups.
ꢀIntramolecularꢀchargeꢀ
transferꢀ(ICT)ꢀbetweenꢀtheꢀconstituentꢀgroupsꢀresultsꢀinꢀNIRꢀabsorptionꢀandꢀemission.ꢀꢀHowever,ꢀ
moleculesꢀ containingꢀ largeꢀ π-systemsꢀ withꢀ theseꢀ featuresꢀ tendꢀ toꢀ aggregate,ꢀ oftenꢀ resultingꢀ inꢀ
aggregationꢀinducedꢀquenchingꢀofꢀemission.ꢀThisꢀaggregationꢀsignificantlyꢀimpairsꢀtheꢀprocessꢀofꢀ
designingꢀefficientꢀNIRꢀemittersꢀinꢀtheꢀcondensedꢀstate.ꢀDespiteꢀtheseꢀintrinsicꢀchallenges,ꢀnarrowꢀ
bandꢀgapꢀorganicꢀcompoundsꢀcontainingꢀdonor-acceptorꢀ(D-A)ꢀtypeꢀchromophoresꢀareꢀofꢀgreatꢀ
interestꢀsinceꢀtheirꢀbandꢀgapꢀenergy,ꢀandꢀotherꢀproperties,ꢀcanꢀeasilyꢀbeꢀtunedꢀthroughꢀvaryingꢀ
theꢀdonorꢀandꢀacceptorꢀsubstituents.ꢀHere,ꢀweꢀreportꢀaꢀnewꢀseriesꢀofꢀ(D-A-D)ꢀthienopyrazinesꢀandꢀ
demonstrateꢀtheirꢀpromiseꢀasꢀNIRꢀemittersꢀinꢀsolution,ꢀwhileꢀdispersedꢀinꢀaꢀpolymerꢀthinꢀfilm,ꢀ
andꢀatꢀtheꢀsingleꢀmoleculeꢀlevel.ꢀ
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ꢀꢀꢀꢀꢀNIRꢀD-A-Dꢀdyeꢀdesignꢀreliesꢀonꢀtheꢀincorporationꢀofꢀsubstantiallyꢀelectronꢀdeficientꢀbuildingꢀ
blocksꢀ toꢀ severꢀ asꢀ aꢀ singleꢀ acceptor.ꢀ ꢀ Thienopyrazinesꢀ (TPzs)ꢀ areꢀ attractive,ꢀ uniqueꢀ acceptorꢀ
buildingꢀblocksꢀasꢀfourꢀsubstitutableꢀpositionsꢀallowꢀforꢀtheꢀinstallationꢀofꢀtwoꢀdonorsꢀandꢀallowꢀ
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accessꢀ toꢀ twoꢀ additionalꢀ tunableꢀ positions.
ꢀ Theꢀ pyrazineꢀ ringꢀ isꢀ electronꢀ deficientꢀ andꢀ theꢀ
relativelyꢀ lowꢀ resonanceꢀ stabilizationꢀ energyꢀ ofꢀ thiopheneꢀ allowsꢀ forꢀ betterꢀ ICTꢀ betweenꢀ theꢀ
donorꢀgroupsꢀandꢀtheꢀacceptingꢀpyrazineꢀthanꢀbenzeneꢀbasedꢀaromatics.ꢀAdditionally,ꢀTPzꢀallowsꢀ
forꢀincreasedꢀplanarityꢀofꢀdonorꢀsubstituentsꢀsubstitutedꢀatꢀtheꢀthiopheneꢀwhenꢀcomparedꢀwithꢀ
benzeneꢀbasedꢀacceptorsꢀdueꢀtoꢀtheꢀuseꢀofꢀaꢀless-stericallyꢀencumberedꢀfiveꢀmemberedꢀringꢀandꢀ
theꢀuseꢀofꢀaꢀring-containedꢀnitrogenꢀatomꢀatꢀtheꢀorthoꢀpositionꢀrelativeꢀtoꢀtheꢀdonorꢀgroup.ꢀThisꢀ
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increasedꢀ planarityꢀ leadsꢀ toꢀ increasedꢀ chargeꢀ transferꢀ bandꢀ strengthꢀ toꢀ accessꢀ lowerꢀ energyꢀ
wavelengthsꢀandꢀincreaseꢀabsorptionꢀstrength.ꢀWeꢀsoughtꢀtoꢀbetterꢀunderstandꢀtheꢀgroundꢀandꢀ
excited-stateꢀenergyꢀlevelꢀinfluenceꢀofꢀsubstituentsꢀonꢀtheꢀpyrazineꢀringꢀthroughꢀtargetingꢀaꢀseriesꢀ
ofꢀdyesꢀwithꢀtheꢀTPzꢀthiopheneꢀsubstituentsꢀheldꢀconstant.ꢀ
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ꢀꢀꢀꢀToꢀ investigateꢀ theꢀ effectsꢀ ofꢀ theꢀ TPzꢀ bridge-basedꢀ dyesꢀ onꢀ NIRꢀ emissiveꢀ andꢀ energeticꢀ
properties,ꢀ weꢀ haveꢀ targetedꢀ fiveꢀ D-A-Dꢀ dyesꢀ basedꢀ onꢀ theꢀ thioenopyrazineꢀ acceptorꢀ withꢀ theꢀ
bis(hexyloxy)triphenylamineꢀ(TPA)ꢀdonorꢀheldꢀconstantꢀthroughoutꢀonꢀtheꢀthiopheneꢀringꢀwhileꢀ
varyingꢀtheꢀsubstituentsꢀonꢀtheꢀpyrazineꢀringꢀtoꢀevaluateꢀtheꢀeffectsꢀonꢀtheꢀemissiveꢀpropertiesꢀofꢀ
theseꢀ materialsꢀ (Figureꢀ 1).ꢀ Theꢀ pyrazineꢀ ringꢀ substituentsꢀ wereꢀ variedꢀ fromꢀ alkylꢀ groups,ꢀ esterꢀ
groups,ꢀ andꢀ aꢀ seriesꢀ ofꢀ phenylꢀ substituentsꢀ baringꢀ electronꢀ donatingꢀ groupsꢀ (OMe),ꢀ electronꢀ
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neutralꢀgroupsꢀ(H)ꢀandꢀelectronꢀwithdrawingꢀgroupsꢀ(CO Me).ꢀꢀꢀ
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Figureꢀ 1:ꢀTPz-basedꢀtargetꢀNIRꢀemissiveꢀmaterialsꢀofꢀTPz-Et,ꢀTPz-CO
TPz-Ph-CO
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Et,ꢀTPz-Ph,ꢀTPz-Ph-OMe,ꢀ
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Meꢀbyꢀvaryingꢀtheꢀ2,3-substituentsꢀofꢀtheꢀTPzꢀringꢀfromꢀelectronꢀdonatingꢀtoꢀelectronꢀ
withdrawingꢀsubstituents.ꢀ
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ResultsꢀandꢀDiscussionꢀ
Synthesis.ꢀ Ideally,ꢀ D-A-Dꢀ dyesꢀ shouldꢀ beꢀ rapidlyꢀ accessibleꢀ forꢀ simplicityꢀ inꢀ evaluatingꢀ
structureꢀfunctionꢀrelationships.ꢀDirectꢀC-HꢀactivationꢀreactionsꢀutilizingꢀtheꢀC-Hꢀbondsꢀofꢀtheꢀ
thiopheneꢀ ringꢀ ofꢀ theꢀ TPzꢀ acceptorꢀ provideꢀ aꢀ direct,ꢀ attractiveꢀ syntheticꢀ route.ꢀ Therefore,ꢀ
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palladiumꢀcatalyzedꢀC-HꢀactivationꢀroutesꢀwereꢀevaluatedꢀforꢀtheꢀsynthesisꢀofꢀtheꢀTPzꢀdyeꢀseries.ꢀ
Theꢀ seriesꢀ ofꢀ TPzꢀ basedꢀ D-A-Dꢀdyesꢀ(Figureꢀ1)ꢀwereꢀ synthesized,ꢀ withꢀ variableꢀ 2,3-substituentsꢀ
basedꢀonꢀaꢀrangeꢀofꢀconjugatedꢀandꢀnon-conjugatedꢀsubstituentsꢀtoꢀidentifyꢀtheꢀelectronicꢀandꢀ
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stericꢀeffectsꢀonꢀperformances. ꢀTheꢀsynthesisꢀofꢀtheꢀTPzꢀbasedꢀD-A-Dꢀdyesꢀwereꢀcarriedꢀoutꢀinꢀ
fourꢀlinearꢀstepsꢀaccordingꢀtoꢀSchemeꢀ1.ꢀꢀ
ꢀ
Schemeꢀ1:ꢀSyntheticꢀschemeꢀforꢀTPz-Et,ꢀTPz-CO
2 2
Et,ꢀTPz-Ph,ꢀTPz-PhOMeꢀandꢀTPz-PhCO Me.ꢀ
(I)ꢀ conc.ꢀ H SO ꢀ (2.4ꢀ M),ꢀ fumingꢀ H SO4ꢀ (1.55ꢀ M),ꢀ conc.ꢀ HNO3ꢀ (2.83ꢀ M),ꢀ 2,5-dibromothiophene,ꢀ
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roomꢀ temperature,ꢀ 3ꢀ hours,ꢀ 52%.ꢀ (II)ꢀ conc.ꢀ HClꢀ (0.16ꢀ M),ꢀ Snꢀ powderꢀ (7.0ꢀ equiv.),ꢀ roomꢀ
temperature,ꢀ2ꢀhours,ꢀ75%.ꢀ(III)ꢀForꢀ4a,ꢀ 4b,ꢀ 4cꢀ andꢀ 4e:ꢀtriethylamineꢀ(0.2ꢀM),ꢀdichloromethaneꢀ
(
0.11ꢀM),ꢀethanolꢀ(0.11ꢀM),ꢀdioneꢀ(1.02ꢀequiv.,ꢀ3,4-hexanedione,ꢀbenzil,ꢀdiethylꢀ2,3-dioxosuccinate,ꢀ
dimethylꢀ4,4'-oxalyldibenzoate),ꢀ50ꢀ°C,ꢀovernight;ꢀ82%ꢀ(4a);ꢀ34%ꢀ(4b);ꢀ45%ꢀ(4c);ꢀ85%ꢀ(4e).ꢀForꢀ4d:ꢀ
,4’-dimethoxybenzilꢀ(1.0ꢀequiv),ꢀmethanolꢀ(0.2ꢀM),ꢀSnCl /SiO ꢀ(5%ꢀw/w),ꢀroomꢀtemperature,ꢀ2.5ꢀ
hours;ꢀ 44%ꢀ (4d).ꢀ (IV)ꢀ Forꢀ TPz-Et:ꢀ 4-bromo-N,N-bis(4-hexyloxyphenyl)anilineꢀ (TPA-Br,ꢀ 2.0ꢀ
equiv),ꢀP(tBu) (5ꢀmol%),ꢀK CO ꢀ(1.5ꢀequiv),ꢀPd(OAc) ꢀ(5%),ꢀpivalicꢀacidꢀ(0.5ꢀequiv.),ꢀtolueneꢀ(0.25ꢀ
M),ꢀ120°C,ꢀovernight,ꢀ50%ꢀ(TPz-Et)ꢀorꢀTPA-Brꢀ(2ꢀequiv),ꢀX-Phosꢀ(0.1ꢀequiv.),ꢀCs CO ꢀ(2ꢀequiv.),ꢀ
Pd(OAc) ꢀ (5ꢀ mol%),ꢀ tolueneꢀ (0.5ꢀ M),ꢀ 120°C,ꢀ 2ꢀ hours,ꢀ 68%ꢀ (TPz-Et).ꢀ ꢀ Forꢀ TPz-CO Et,ꢀ TPz-Ph,ꢀ
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TPz-PhOMeꢀ andꢀ TPz-PhCO
Pd(OAc)
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2 3
Me:ꢀ TPA-Brꢀ (2ꢀ equiv),ꢀ X-Phosꢀ (0.1ꢀ equiv.),ꢀ Cs CO ꢀ (2ꢀ equiv.),ꢀ
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ꢀ (5ꢀ mol%),ꢀ tolueneꢀ (0.5ꢀ M),ꢀ 120°C,ꢀ overnight,ꢀ 34%ꢀ (TPz-CO Et),ꢀ 40%ꢀ (TPz-Ph);ꢀ 50%ꢀ
2
(TPz-PhOMe);ꢀ65%ꢀ(TPz-PhCO Me).ꢀ
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ꢀ
Theꢀ syntheticꢀ routeꢀ toꢀ theꢀ TPzꢀ D-A-Dꢀ dyesꢀ beganꢀ withꢀ theꢀ nitrationꢀ ofꢀ theꢀ commerciallyꢀ
availableꢀ2,5-dibromothiopheneꢀ1ꢀtoꢀgiveꢀ2,5-dibromo-3,4-dinitrothiopheneꢀ2ꢀinꢀpreparativeꢀyieldꢀ
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(
52%). ꢀ Theꢀ reductionꢀ ofꢀ 2ꢀ withꢀ Snꢀ powderꢀ inꢀ acidicꢀ mediumꢀ leadsꢀ toꢀ theꢀ formationꢀ ofꢀ 3,4-
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diaminothiopheneꢀdihydrochlorideꢀ3ꢀ inꢀhighꢀyieldꢀ(75%). ꢀ3ꢀ underwentꢀcondensationꢀreactionsꢀ
withꢀ theꢀ appropriateꢀ diketoneꢀ (3,4-hexanedione,ꢀ diethylꢀ 2,3-dixosuccinate,ꢀ benzil,ꢀ orꢀ 4,4’-
oxalyldibenzoate)ꢀinꢀaꢀbasicꢀenvironmentꢀtoꢀgiveꢀtheꢀdesiredꢀTPzꢀbuildingꢀblocksꢀ4a-4c,ꢀ4eꢀ(85%-
36,ꢀ 41-42
3
4%ꢀ yield).
ꢀ Condensationꢀ withꢀ electronꢀ richꢀ 4,4’-dimethoxybenzilꢀ requiredꢀ alternateꢀ
/SiO ꢀsolidꢀsupportꢀLewisꢀacidꢀcatalystꢀtoꢀgiveꢀappreciableꢀamountsꢀofꢀ
4dꢀ (44%). ꢀFinally,ꢀtheꢀTPzꢀD-A-Dꢀdyesꢀ(TPz-Et,ꢀ TPz-CO Et,ꢀ TPz-Ph,ꢀ TPz-Ph-OMe,ꢀ TPz-Ph-
CO Me)ꢀwereꢀobtainedꢀbyꢀPd-catalyzedꢀdirectꢀC-Hꢀarylationꢀreactionꢀofꢀ4a-4eꢀ inꢀyieldsꢀrangingꢀ
fromꢀ 68%-35%ꢀ withꢀ theꢀ useꢀ ofꢀ X-Phos ꢀ orꢀ PtBu
activationꢀ conditionsꢀ wereꢀ optimizedꢀ withꢀ TPz-Et.ꢀ Theꢀ useꢀ ofꢀ P(tBu)
conditionsꢀinvolvingꢀaꢀSnCl
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ꢀ asꢀ ligand.ꢀ ꢀ Theꢀ palladiumꢀ catalyzedꢀ C-Hꢀ
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ꢀ asꢀ aꢀ ligandꢀ duringꢀ Pd-
o
catalysisꢀledꢀtoꢀreasonableꢀpreparativeꢀyieldsꢀofꢀ50%ꢀwhenꢀtheꢀreactionꢀwasꢀrunꢀovernightꢀatꢀ120 C.ꢀ
o
Pd-catalysisꢀwithꢀX-Phosꢀwasꢀattemptedꢀunderꢀsimilarꢀconditionsꢀ(120 Cꢀovernight),ꢀwhichꢀledꢀtoꢀ
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%ꢀyieldꢀofꢀTPz-Etꢀandꢀcompleteꢀconsumptionꢀofꢀstartingꢀmaterials.ꢀShorteningꢀtheꢀreactionꢀtimeꢀ
toꢀtwoꢀhoursꢀgaveꢀaꢀ68%ꢀyieldꢀwithꢀX-Phos.ꢀLongerꢀreactionꢀtimesꢀseemedꢀtoꢀbeꢀnecessaryꢀwhenꢀ
arylatedꢀ andꢀ esterꢀ groupsꢀ wereꢀ incorporatedꢀ ontoꢀ theꢀ TPzꢀ buildingꢀ blockꢀ potentiallyꢀ dueꢀ toꢀ
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deactivationꢀofꢀtheꢀthiopheneꢀtoꢀnucleophilicꢀattackꢀonꢀaꢀBr-Pd-TPAꢀcatalyticꢀintermediate.
ꢀ
Theꢀwithdrawnꢀnatureꢀofꢀtheseꢀsubstituentsꢀrelativeꢀtoꢀtheꢀethylꢀsubstituentsꢀisꢀoutlinedꢀinꢀtheꢀ
UV-Visꢀsectionꢀbelow.ꢀꢀAllꢀdyesꢀwereꢀavailableꢀjustꢀinꢀ4ꢀsyntheticꢀstepsꢀinꢀupꢀtoꢀ22%ꢀoverallꢀyield.ꢀ
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ꢀ
UV-Vis-NIRꢀ absorbanceꢀ andꢀ electrochemicalꢀ properties.ꢀ Theꢀopticalꢀandꢀelectrochemicalꢀ
propertiesꢀ ofꢀ eachꢀ ofꢀ theꢀ TPzꢀ D-A-Dꢀ dyesꢀ wereꢀ analyzedꢀ toꢀ evaluateꢀ theꢀ effectꢀ ofꢀ R-groupꢀ
substituentsꢀonꢀabsorptionꢀrange,ꢀbandꢀgapꢀsizeꢀandꢀtheꢀpotentialꢀofꢀtheꢀproductsꢀtoꢀfunctionꢀasꢀ
NIRꢀemissiveꢀmaterials.ꢀTheꢀTPzꢀD-A-Dꢀdyeꢀλmaxꢀrangedꢀbroadlyꢀfromꢀ530-665ꢀnmꢀasꢀanꢀapparentꢀ
single,ꢀbroadꢀintramolecularꢀchargeꢀtransferꢀ(ICT)ꢀtransition.ꢀTheꢀsimpleꢀethylꢀalkylꢀchainꢀshowsꢀ
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theꢀhighestꢀenergyꢀabsorptionꢀ(TPz-Et)ꢀandꢀtheꢀdirectꢀesterꢀsubstitutedꢀgroupꢀshowsꢀtheꢀlowestꢀ
ꢀ
energyꢀabsorptionꢀ(TPz-CO
toꢀ830ꢀnmꢀforꢀTPz-CO
2
Et,ꢀFigureꢀ2,ꢀTableꢀ1).ꢀTheꢀλonset valuesꢀrangedꢀfromꢀ650ꢀnmꢀforꢀTPz-Etꢀ
2
EtꢀwithꢀbroadꢀabsorptionsꢀextendingꢀsubstantiallyꢀintoꢀtheꢀNIRꢀrangeꢀforꢀ
D-A-Dꢀdyes.ꢀAꢀclearꢀopticalꢀbandgapꢀresponseꢀcanꢀbeꢀseenꢀasꢀtheꢀabsorptionꢀcurveꢀonsetꢀshiftsꢀ
towardꢀlowerꢀenergyꢀwithꢀincreasedꢀelectronꢀwithdrawingꢀgroupꢀstrengthꢀforꢀtheꢀarylꢀsubstitutedꢀ
2
dyesꢀasꢀTPz-PhOMeꢀ<ꢀTPz-Phꢀ<ꢀTPz-PhCO Et.ꢀꢀAccordingly,ꢀstronglyꢀdonatingꢀsubstituentsꢀonꢀ
theꢀpyrazineꢀringꢀofꢀtheꢀTPzꢀledꢀtoꢀaꢀhypsochromicꢀshiftꢀinꢀabsorptionsꢀwithꢀtheꢀTPz-Etꢀshowingꢀ
theꢀhighestꢀenergyꢀICTꢀband.ꢀTheꢀstrongestꢀelectronꢀwithdrawnꢀsubstitutedꢀpyrazineꢀringꢀ(theꢀtwoꢀ
2
directlyꢀsubstitutedꢀestersꢀofꢀTPz-CO Et,ꢀledꢀtoꢀtheꢀlargestꢀbathochromicꢀshiftꢀinꢀtheꢀseries.ꢀWeꢀ
interpretꢀ theseꢀ resultsꢀ asꢀ increasingꢀ theꢀ electronꢀ withdrawingꢀ natureꢀ onꢀ theꢀ mostꢀ electronꢀ
deficientꢀregionꢀofꢀtheꢀTPzꢀmolecule,ꢀtheꢀpyrazineꢀring,ꢀstrengthensꢀICTꢀthroughꢀmoreꢀcompleteꢀ
chargeꢀ transferꢀ fromꢀ theꢀ mostꢀ electronꢀ richꢀ TPAꢀ region.ꢀ Theꢀ converseꢀ ofꢀ thisꢀ isꢀ empiricallyꢀ
observedꢀasꢀwellꢀinꢀthatꢀifꢀadditionalꢀdonatingꢀgroupsꢀareꢀinstalledꢀdirectlyꢀonꢀtheꢀpyrazineꢀringꢀ
(TPz-Etꢀ orꢀTPz-PhOMe)ꢀtheꢀICTꢀbandꢀshiftsꢀtoꢀhigherꢀenergyꢀbyꢀreducingꢀtheꢀextentꢀofꢀchargeꢀ
transferꢀ throughꢀ aꢀ weakeningꢀ ofꢀ theꢀ acceptorꢀ regionsꢀ strength.ꢀ Allꢀ dyesꢀ hadꢀ relativelyꢀ similarꢀ
-1
-1
molarꢀabsorptivitiesꢀrangingꢀfromꢀ14,000-10,000ꢀM cm ꢀinꢀchlorinatedꢀsolvent.ꢀꢀ
ꢀ
ꢀꢀꢀꢀTheꢀelectrochemicalꢀpropertiesꢀofꢀtheꢀdyesꢀwereꢀevaluatedꢀasꢀtheseꢀareꢀcriticalꢀforꢀaꢀnumberꢀofꢀ
applicationsꢀ involvingꢀ NIRꢀ smallꢀ moleculeꢀ dyesꢀ includingꢀ solarꢀ cells,ꢀ displayꢀ applications,ꢀ
photochemicalꢀ reactionsꢀ andꢀ forꢀ assessingꢀ ofꢀ theꢀ stabilityꢀ ofꢀ theseꢀ materialsꢀ underꢀ ambientꢀ
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atmosphere.ꢀTheꢀdyeꢀground-stateꢀoxidationꢀpotentialsꢀ(E(S+/S))ꢀcloselyꢀrangedꢀfromꢀ0.71ꢀtoꢀ0.78ꢀVꢀ
versusꢀ normalꢀ hydrogenꢀ electrodeꢀ (NHE)ꢀ inꢀ theꢀ followingꢀ orderꢀ forꢀ theꢀ TPzꢀ substituents:ꢀ
2 2
Ph<PhOMe=PhCO Me<Et<CO Etꢀ(TableꢀS1,ꢀFigureꢀ3).ꢀThisꢀorderꢀindicatesꢀtheꢀsubstituentsꢀonꢀtheꢀ
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pyrazineꢀ ringꢀ modestlyꢀ contributeꢀ toꢀ theꢀ ground-stateꢀ potentialꢀ energiesꢀ ofꢀ electronsꢀ inꢀ theꢀ
conjugatedꢀ π-systemꢀ asꢀ theꢀ valuesꢀ areꢀ weaklyꢀ tunableꢀ basedꢀ onꢀ groupꢀ choice.ꢀ ꢀ However,ꢀ theꢀ
opt
excited-stateꢀ oxidationꢀ potentialsꢀ (E(S+/S*)
,
ꢀ
calculatedꢀ fromꢀ theꢀ equationꢀ E(S+/S*)ꢀ =ꢀ E(S+/S)ꢀ –ꢀ E
g
ꢀ
,ꢀ
opt
whereꢀE
g
ꢀ=ꢀ1240/ꢀλonset)ꢀvariedꢀsubstantiallyꢀbasedꢀonꢀTPzꢀsubstituentꢀchoiceꢀfromꢀ-1.17ꢀVꢀtoꢀ-0.71ꢀ
VꢀindicatingꢀtheꢀsubstituentsꢀhaveꢀaꢀstrongꢀcontrolꢀonꢀE(S+/S*)ꢀvaluesꢀandꢀtheꢀopticalꢀbandꢀgapꢀasꢀ
(S+/S)ꢀ valuesꢀ areꢀ relativelyꢀ unchanging.ꢀ Theꢀ oxidationꢀ potentialꢀ measurementsꢀ showꢀ minimalꢀ
E
variationꢀ overꢀ aꢀ 0.71-0.750ꢀ Vꢀ range.ꢀ Itꢀ isꢀ alsoꢀ noteworthyꢀ thatꢀ 4ꢀ reversibleꢀ oxidationꢀ potentialsꢀ
wereꢀobservedꢀforꢀeachꢀofꢀtheꢀdyesꢀexaminedꢀ(SeeꢀTableꢀS1,ꢀFigureꢀ3ꢀtop).ꢀInꢀstarkꢀcontrastꢀtoꢀtheꢀ
oxidationꢀ potentialꢀ measurements,ꢀ theꢀ reductionꢀ potentialsꢀ showꢀ aꢀ moreꢀ dramaticꢀ rangeꢀ ofꢀ
potentialsꢀ(-0.80ꢀtoꢀ-1.30ꢀV)ꢀindicatingꢀaꢀsignificantꢀinfluenceꢀofꢀtheꢀpyrazineꢀringꢀsubstituentsꢀonꢀ
theꢀ energyꢀ atꢀ whichꢀ theꢀ TPz-TPAꢀ dyesꢀ acceptꢀ electronꢀ density.ꢀ Theꢀ lowestꢀ energyꢀ reductionꢀ
potentialꢀwasꢀobservedꢀforꢀTPz-CO2Meꢀdyeꢀwithꢀtheꢀdirectlyꢀsubstitutedꢀestersꢀonꢀtheꢀpyrazineꢀ
ring.ꢀ Theꢀ highestꢀ energyꢀ reductionꢀ potentialꢀ wasꢀ observedꢀ forꢀ TPz-Etꢀ andꢀ theꢀ dyesꢀ generallyꢀ
followedꢀ aꢀ trendꢀ withꢀ theꢀ mostꢀ electronꢀ deficientꢀ substituentsꢀ leadingꢀ toꢀ theꢀ lowestꢀ energyꢀ
2 2
reductionꢀpotentialsꢀ(TPzCO Etꢀ<ꢀTPzPhCO Meꢀ<ꢀTPzPhꢀ<ꢀTPzPhOMeꢀ<ꢀTPzEt).ꢀOnlyꢀaꢀsingleꢀ
reductionꢀpotentialꢀwasꢀobservedꢀforꢀtheseꢀdyes.ꢀTheseꢀmaterialsꢀofferꢀtheꢀattractiveꢀpossibilityꢀofꢀ
tuningꢀ E(S+/S*)ꢀ valuesꢀ whileꢀ holdingꢀ E(S+/S)ꢀ valuesꢀ constantꢀ whichꢀ dramaticallyꢀ simplifiesꢀ theꢀ
controllableꢀmodificationꢀofꢀdyeꢀenergeticsꢀforꢀvariousꢀapplications.ꢀTheꢀalkylꢀsubstitutedꢀTPz-Etꢀ
wasꢀ foundꢀ toꢀ haveꢀ theꢀ highestꢀ energyꢀ E(S+/S*)ꢀ valueꢀ (-1.17).ꢀ Neutralꢀ andꢀ electronꢀ richꢀ arylꢀ
substitutedꢀ TPzꢀ dyes,ꢀ TPz-Phꢀ andꢀ TPz-PhOMeꢀ demonstratedꢀ similarꢀ E(S+/S*)ꢀ valuesꢀ atꢀ -1.00ꢀ V,ꢀ
whichꢀ isꢀ significantlyꢀ stabilizedꢀ (170ꢀ mV)ꢀ whenꢀ comparedꢀ withꢀ theꢀ alkylꢀ substitutedꢀ TPzꢀ dye.ꢀꢀ
AdditionꢀofꢀelectronꢀdeficientꢀarylꢀgroupsꢀandꢀdirectlyꢀsubstitutedꢀestersꢀonꢀtheꢀTPzꢀbridgeꢀgaveꢀ
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substantiallyꢀstabilizedꢀE(S+/S*)ꢀvaluesꢀofꢀ-0.88ꢀVꢀandꢀ-0.71ꢀV.ꢀꢀTheꢀpossibilityꢀofꢀtuningꢀexcited-stateꢀ
potentialsꢀbyꢀ460ꢀmVꢀwithꢀonlyꢀslightꢀmodificationꢀtoꢀtheꢀgroup-stateꢀpotentialsꢀbyꢀ60ꢀmVꢀorꢀlessꢀ
illustratesꢀtheꢀstraightforwardꢀtunabilityꢀofꢀtheseꢀmaterialsꢀforꢀaꢀhostꢀofꢀpotentialꢀapplications.ꢀꢀꢀ
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Figureꢀ2:ꢀꢀAbsorptionꢀcurvesꢀofꢀTPz-Etꢀ(black),ꢀTPz-CO Etꢀ(purple),ꢀTPz-Phꢀ(red),ꢀTPz-PhOMeꢀ
(
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
blue)ꢀandꢀTPz-PhCO Meꢀ(green)ꢀinꢀdichloromethane.ꢀ
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ꢀ
ꢀ
ꢀ
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Tableꢀ1:ꢀUV-Vis-NIRꢀabsorbanceꢀandꢀelectrochemicalꢀdata.ꢀ
opt
Dyeꢀ
TPz-R)ꢀ
Etꢀ
λ
maxꢀ
λ
onsetꢀ
λ
emisꢀꢀ
Stokesꢀ
εꢀ
E
g
ꢀꢀ
E
(0-0)
ꢀ
E
(S+/S*)ꢀꢀ
d
a
b
-1
-1 a
cꢀ
(
(nm) ꢀ
532ꢀ
(nm) ꢀ
650ꢀ
830ꢀ
725ꢀ
(nm)ꢀ
725ꢀ
---ꢀ
shiftꢀ(nm,ꢀeV)ꢀ (M cm ) ꢀ
(eV)
(eV)ꢀ
1.95ꢀ
---ꢀ
(V) ꢀ
-1.17ꢀ
193,ꢀ0.62ꢀ
---ꢀ
13,600ꢀ
12,000ꢀ
14,000ꢀ
11,100ꢀ
1.91ꢀ
1.49ꢀ
1.71ꢀ
1.72ꢀ
1.61ꢀ
CO
Phꢀ
PhOMeꢀ
2
Etꢀ
665ꢀ
600ꢀ
590ꢀ
626ꢀ
-0.71ꢀ
-1.00ꢀ
-0.99ꢀ
-0.88ꢀ
793ꢀ
752ꢀ
820ꢀ
193,ꢀ0.50ꢀ
162,ꢀ0.45ꢀ
194,ꢀ0.47ꢀ
1.78ꢀ
1.81ꢀ
1.70ꢀ
720ꢀ
770ꢀ
PhCO
2
Meꢀ
13,100ꢀ
ꢀ
a
b
Measuredꢀinꢀdichloromethaneꢀ(DCM).ꢀ Theꢀabsorptionꢀonsetꢀ(λonset)ꢀwasꢀtakenꢀatꢀtheꢀinterceptꢀofꢀ
c
opt
aꢀtangentꢀlineꢀonꢀtheꢀlowꢀenergyꢀsideꢀofꢀtheꢀλmaxꢀpeakꢀandꢀtheꢀX-axis.ꢀ E
g
ꢀwasꢀfoundꢀthroughꢀtheꢀ
opt
d
opt 46-48
equationꢀE
g
ꢀ=ꢀ1240/λonset.ꢀ E(S+/S*)ꢀwasꢀcalculatedꢀusingꢀE(S+/S*)ꢀ=ꢀE(S+/S)ꢀ–ꢀE
g
.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
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ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
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Figureꢀ 3:ꢀ Cyclicꢀ voltammetryꢀ curvesꢀ forꢀ oxidationꢀ (top)ꢀ andꢀ reductionꢀ (bottom)ꢀ ofꢀ TPz-Etꢀ
(
black),ꢀTPz-PhOMeꢀ (blue),ꢀTPz-Phꢀ (red),ꢀTPz-PhCO
2
Meꢀ (green)ꢀandꢀ TPz-CO
2
Etꢀ (purple)ꢀ inꢀ
dichloromethane.ꢀꢀ
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Figureꢀ4:ꢀHOMOꢀ(top)ꢀandꢀLUMOꢀ(bottom)ꢀorbitalsꢀofꢀTPz-Et,ꢀTPz-CO Et,ꢀTPz-Ph,ꢀTPz-Ph-
2
OMeꢀandꢀTPz-Ph-CO Me.ꢀꢀIsoꢀvaluesꢀwereꢀsetꢀtoꢀ0.3.ꢀ
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ꢀ
ꢀꢀꢀꢀComputationalꢀ results.ꢀ Densityꢀ functionalꢀ theoryꢀ (DFT)ꢀ andꢀ time-dependentꢀ densityꢀ
functionalꢀ theoryꢀ (TD-DFT)ꢀ computationalꢀ studiesꢀ wereꢀ undertakenꢀ toꢀ evaluateꢀ theꢀ orbitalꢀ
arrangementꢀ(Figureꢀ4)ꢀofꢀtheseꢀdyes,ꢀtoꢀdetermineꢀtheꢀorbitalsꢀinvolvedꢀinꢀtheꢀbroadꢀabsorptionꢀ
spectrum,ꢀ andꢀ toꢀ confirmꢀ theꢀ ICTꢀ natureꢀ ofꢀ theꢀ broadꢀ absorptionꢀ bandꢀ inꢀ theꢀ UV-Vis-NIRꢀ
spectrumꢀ Theꢀ geometriesꢀ ofꢀ theseꢀ dyesꢀ wereꢀ firstꢀ optimizedꢀ withꢀ theꢀ B3LYPꢀ functionalꢀ andꢀ 6-
3
11G(d,p)ꢀbasisꢀsetꢀ(Figureꢀ4,ꢀTableꢀ2).ꢀTheꢀTPz-TPAꢀdihedralꢀbondꢀangleꢀ(Figureꢀ5)ꢀwasꢀfoundꢀtoꢀ
o
beꢀ similarꢀ forꢀ allꢀ theꢀ dyesꢀ nearꢀ 20 .ꢀ Interestingly,ꢀ TPz-CO
2
Et
ꢀ
optimizedꢀ toꢀ aꢀ non-symmetricꢀ
o
structureꢀwithꢀoneꢀTPAꢀgroupꢀgivingꢀaꢀmoreꢀplanarizedꢀTPz-TPAꢀbondꢀofꢀ13 ꢀandꢀtheꢀotherꢀaꢀvalueꢀ
o
nearꢀ 20 .ꢀ Theꢀ dihedralꢀ angleꢀ betweenꢀ theꢀ TPz-Rꢀ substituentsꢀ wasꢀ similarꢀ forꢀ allꢀ theꢀ arylꢀ
o
substituentsꢀatꢀ~40 ꢀregardlessꢀofꢀdonatingꢀorꢀwithdrawingꢀsubstituent.ꢀTPz-CO
2
Et
ꢀ
againꢀgaveꢀaꢀ
dissymmetricꢀstructureꢀwithꢀregardꢀtoꢀbondꢀangleꢀatꢀtheꢀTPz-esterꢀbondꢀwithꢀoneꢀgroupꢀshowingꢀ
o
o
aꢀ29 ꢀangleꢀandꢀtheꢀsecondꢀshowingꢀaꢀ50 ꢀbondꢀangle.ꢀTheꢀlowerꢀbondꢀanglesꢀwereꢀonꢀoppositeꢀ
sidesꢀofꢀtheꢀTPzꢀbridgeꢀindicatingꢀaꢀsignificantꢀelectronicꢀcommunicationꢀfromꢀtheꢀdonorꢀacrossꢀ
theꢀ TPzꢀ bridgeꢀ toꢀ anꢀ oppositeꢀ acceptor.ꢀ Itꢀ isꢀ noteworthy,ꢀ thatꢀ aꢀ simpleꢀ valenceꢀ bondꢀ theoryꢀ
drawingꢀdoesꢀnotꢀallowꢀforꢀchargeꢀseparatedꢀresonanceꢀstructureꢀinvolvingꢀtheseꢀtwoꢀsubstituents.ꢀ
Theꢀ highestꢀ occupiedꢀ molecularꢀ orbitalꢀ (HOMO)ꢀ andꢀ lowestꢀ unoccupiedꢀ molecularꢀ orbitalꢀ
(LUMO)ꢀarrangementsꢀareꢀplottedꢀinꢀFigureꢀ3.ꢀInꢀallꢀcases,ꢀtheꢀHOMOꢀisꢀpredominatelyꢀlocalizedꢀ
onꢀtheꢀTPAꢀdonorꢀgroupꢀwithꢀtheꢀLUMOꢀlocalizedꢀonꢀtheꢀTPzꢀacceptorꢀgroup.ꢀWithꢀaꢀmoderateꢀ
2
isoꢀ valuesꢀ ofꢀ 0.4ꢀ onlyꢀ theꢀ directlyꢀ substitutedꢀ esterꢀ groupꢀ ofꢀ TPz-CO Etꢀ demonstratedꢀ anyꢀ
appreciableꢀLUMOꢀꢀlocalizationꢀontoꢀtheꢀpyrazineꢀsubstituents.ꢀꢀ
ꢀ
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ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
o
o
Dyeꢀ
vert.ꢀtrans.ꢀ(nm,ꢀ
eV)ꢀ
oscillatorꢀ
strengthꢀ
0.59ꢀ
angleꢀ1ꢀ( )ꢀ angleꢀ2ꢀ( )ꢀ
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ꢀ
TPz-Etꢀ
640,ꢀ1.94ꢀ
781,ꢀ1.59ꢀ
706,ꢀ1.76ꢀ
683,ꢀ1.82ꢀ
755,ꢀ1.64ꢀ
19
13,ꢀ18ꢀ
20ꢀ
-ꢀ
29,ꢀ50ꢀ
41ꢀ
TPz-CO
2
Etꢀ
0.43ꢀ
TPz-Phꢀ
TPz-Ph-OMeꢀ
TPz-Ph-
0.41ꢀ
0.42ꢀ
20ꢀ
39ꢀ
0.33ꢀ
21ꢀ
41ꢀ
2
CO Meꢀ
ꢀ
Tableꢀ2:ꢀComputationalꢀresultsꢀfromꢀDFTꢀandꢀTD-DFTꢀanalysis.ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
TD-DFTꢀanalysisꢀwithꢀtheꢀB3LYPꢀfunctionalꢀandꢀ6-311G(d,p)ꢀbasisꢀsetꢀwasꢀpreformedꢀtoꢀanalyzeꢀ
theꢀ predictedꢀ 10ꢀ lowestꢀ verticalꢀ transitionꢀ energiesꢀ inꢀ vacuumꢀ andꢀ toꢀ identifyꢀ theꢀ contributingꢀ
orbitalsꢀtoꢀtheꢀabsorptionꢀbandsꢀobserved.ꢀTheꢀlowestꢀenergyꢀverticalꢀtransitionꢀtrendsꢀareꢀinꢀgoodꢀ
agreementꢀwithꢀtheꢀUV-Vis-NIRꢀexperimentalꢀdataꢀλmaxꢀtrendsꢀgivingꢀtheꢀfollowingꢀorderꢀforꢀdyesꢀ
2 2
fromꢀ highꢀ toꢀ lowꢀ eVꢀ energy:ꢀ TPz-Et>TPz-PhOMe>TPz-Ph>TPz-PhCO Me>TPz-CO Et.ꢀ Theꢀ
oscillatorꢀstrengthꢀpredictionsꢀindicateꢀroughlyꢀsimilarꢀverticalꢀtransitionꢀenergyꢀstrengths,ꢀwhichꢀ
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isꢀinꢀgoodꢀagreementꢀwithꢀtheꢀexperimentalꢀmolarꢀabsorptivityꢀmeasurements.ꢀTheꢀlowestꢀenergyꢀ
verticalꢀtransitionsꢀwereꢀallꢀdominatedꢀbyꢀtheꢀHOMO-LUMOꢀtransitionsꢀ(>99%)ꢀwithꢀtheꢀnextꢀ
nearestꢀtransitionsꢀatꢀ>100ꢀnmꢀhigherꢀinꢀenergy.ꢀTheꢀNIRꢀabsorptionsꢀofꢀtheseꢀdyesꢀareꢀattributedꢀ
toꢀstrongꢀICTꢀeventsꢀbasedꢀonꢀtheꢀfrontierꢀmolecularꢀorbitalꢀarrangementsꢀofꢀtheseꢀdyesꢀandꢀtheꢀ
highꢀpercentꢀcontributionꢀofꢀtheꢀHOMO-LUMOꢀtransitionꢀtoꢀtheꢀlowꢀenergyꢀverticalꢀtransition.ꢀꢀ
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ꢀ
Figureꢀ 5:ꢀ Graphicalꢀ representationꢀ ofꢀ theꢀ TPz-TPAꢀ dihedralꢀ angleꢀ (angleꢀ 1)ꢀ andꢀ ofꢀ theꢀ TPz-Rꢀ
substituentꢀdihedralꢀangleꢀ(angleꢀ2)ꢀforꢀtheꢀTPzꢀD-A-Dꢀdyes.ꢀ
ꢀ
ꢀꢀꢀꢀEmissiveꢀ Properties.ꢀ Theꢀ emissiveꢀ propertiesꢀ ofꢀ theꢀ dyesꢀ wereꢀ evaluatedꢀ inꢀ solution,ꢀ bulk-
solidꢀandꢀinꢀsingleꢀmoleculeꢀfilms.ꢀTheꢀfluorescenceꢀspectraꢀofꢀcompoundsꢀ1-5ꢀwereꢀrecordedꢀinꢀ
3 3
CHCl ,ꢀ DMFꢀ andꢀ MeOH/CHCl ꢀ (Figureꢀ 6).ꢀ Forꢀ applicationsꢀ requiringꢀ significantꢀ separationꢀ ofꢀ
inputꢀ energyꢀ versusꢀ outputꢀ energyꢀ suchꢀ asꢀ liveꢀ fluorescenceꢀ imaging,ꢀ aꢀlargeꢀstokesꢀshiftꢀ(>100ꢀ
nm)ꢀisꢀdesirableꢀtoꢀallowꢀforꢀsignificantꢀenergeticꢀseparationꢀofꢀtheꢀexcitationꢀsourceꢀandꢀemittedꢀ
energyꢀ detectedꢀ toꢀ avoidꢀ backgroundꢀ signalꢀ detection.ꢀ Forꢀ thisꢀ applicationꢀ specifically,ꢀ ideallyꢀ
moleculesꢀ shouldꢀ absorbꢀ andꢀ emitꢀ withinꢀ theꢀ therapeuticꢀ windowꢀ rangingꢀ fromꢀ ~650-1100ꢀ nmꢀ
dependingꢀ onꢀ theꢀ targetedꢀ tissueꢀ region.ꢀ Allꢀ dyesꢀ exceptꢀ TPz-Etꢀ haveꢀ appreciableꢀ absorptionsꢀ
withinꢀtheꢀdesiredꢀregions,ꢀandꢀstokesꢀshiftꢀofꢀ162-194ꢀnmꢀwereꢀobservedꢀthroughoutꢀtheꢀseriesꢀ
(
Tableꢀ1).ꢀTheꢀlargestꢀshiftsꢀwereꢀobservedꢀforꢀTPz-EtꢀandꢀTPz-PhCO
2
MeꢀwithꢀStokesꢀshiftsꢀnearꢀ
2
00ꢀnm.ꢀTheꢀobservedꢀlargeꢀStokesꢀshiftsꢀareꢀlikelyꢀinꢀpartꢀdueꢀtoꢀaꢀgeometricꢀreorganizationꢀinꢀ
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theꢀ excited-stateꢀ toꢀ allowꢀ forꢀ planarizationꢀ ofꢀ theꢀ TPzꢀ substituentsꢀ (discussionꢀ below).ꢀ ꢀ TPz-
2
CO Etꢀ wasꢀ foundꢀ toꢀ beꢀ non-emissiveꢀ whichꢀ mayꢀ beꢀ attributedꢀ toꢀ aꢀ substantiallyꢀ lowerꢀ energyꢀ
absorptionꢀleadingꢀtoꢀthermalꢀenergyꢀlossꢀasꢀtheꢀenergy-gapꢀlawꢀsuggests.ꢀ
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ꢀ
ꢀ
2 3
Figureꢀ6.ꢀFluorescenceꢀspectrumꢀofꢀTPz-Et,ꢀTPz-Ph,ꢀTPz-PhOMeꢀandꢀTPz-PhCO MeꢀinꢀCHCl .ꢀꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢀꢀꢀAꢀ solvatochromismꢀ studyꢀ wasꢀ performedꢀ onꢀ TPz-Phꢀ inꢀ orderꢀ toꢀ elucidateꢀ theꢀ natureꢀ ofꢀ theꢀ
intramolecularꢀchargeꢀtransferꢀstate.ꢀꢀTheꢀresultsꢀrevealꢀclearꢀtrendꢀofꢀanꢀincreasedꢀstokesꢀshiftꢀasꢀ
solventꢀpolarityꢀincreases,ꢀFigureꢀS1.ꢀTheꢀAbsorptionꢀmaximumꢀisꢀrelativelyꢀunaffectedꢀbyꢀsolventꢀ
polarityꢀwhileꢀtheꢀemissionꢀmaximumꢀrangesꢀfromꢀ748-806ꢀnmꢀsuggestingꢀthatꢀtheꢀgeometryꢀofꢀ
theꢀ excitedꢀ stateꢀ isꢀ sensitiveꢀ toꢀ solventꢀ effects.ꢀ ꢀ Theꢀ resultsꢀ canꢀ beꢀ seenꢀ inꢀ Figureꢀ 7ꢀ andꢀ areꢀ
summarizedꢀinꢀTableꢀ3.ꢀꢀ
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ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Solventꢀ
Tolueneꢀ
Etherꢀ
AbsorptionꢀMax.ꢀ
nm)ꢀ
EmissionꢀMax.ꢀ
(nm)ꢀ
StokesꢀShiftꢀ
(nm,ꢀeV)ꢀ
(
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ꢀ
600ꢀ
600ꢀ
601ꢀ
594ꢀ
601ꢀ
598ꢀ
592ꢀ
748ꢀ
148,ꢀ0.41
751ꢀ
770ꢀ
768ꢀ
777ꢀ
793ꢀ
793ꢀ
151,ꢀ0.42ꢀ
169,ꢀ0.45ꢀ
174,ꢀ0.47ꢀ
176,ꢀ0.47ꢀ
195,ꢀ0.51ꢀ
201,ꢀ0.53ꢀ
THFꢀ
EAꢀ
Chloroformꢀ
DCMꢀ
Acetoneꢀ
DMFꢀ
598ꢀ
806ꢀ
208,ꢀ0.54ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Tableꢀ3.ꢀResultsꢀofꢀSolvatochromismꢀStudyꢀonꢀTPz-Ph.ꢀ
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ꢀ
Figureꢀ7.ꢀAbsorptionꢀ(left)ꢀandꢀemissionꢀ(right)ꢀspectraꢀofꢀTPz-Phꢀinꢀdifferentꢀsolvents.ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Figureꢀ 8.ꢀComputationalꢀanalysisꢀofꢀtheꢀground-stateꢀ(left)ꢀandꢀexcited-stateꢀ(right)ꢀgeometriesꢀ
forꢀTPz-PhꢀthroughꢀDFTꢀanalysisꢀatꢀtheꢀB3LYP/6-311G(d,p)ꢀlevel.ꢀAnꢀenergeticꢀdiagramꢀillustratingꢀ
1
resultsꢀfromꢀTD-DFTꢀ(B3LYP/6-311G(d,p))ꢀanalysisꢀofꢀbothꢀtheꢀS0ꢀandꢀS ꢀgeometriesꢀisꢀprovidedꢀasꢀ
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theꢀ centerꢀ figure.ꢀ Theꢀ energeticꢀ differenceꢀ inꢀ theꢀ twoꢀ verticalꢀ excitationsꢀ (absorptionꢀ andꢀ
0 1
emission)ꢀisꢀshownꢀasꢀtheꢀreorganizationꢀenergyꢀandꢀisꢀtheꢀsumꢀofꢀtheꢀ∆S ꢀgeometryꢀandꢀtheꢀ∆S ꢀ
geometries.ꢀ
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ToꢀbetterꢀunderstandꢀtheꢀoriginꢀofꢀtheseꢀlargeꢀStokesꢀshiftsꢀcomputationalꢀanalysisꢀofꢀtheꢀ
ground-stateꢀgeometry,ꢀexcited-stateꢀgeometryꢀandꢀverticalꢀtransitionsꢀwereꢀundertakenꢀthroughꢀ
DFTꢀ andꢀ TD-DFTꢀ (B3LYP/6-311G(d,p))ꢀ methodsꢀ (Figureꢀ 8).ꢀ Sinceꢀ theꢀ Franck-Condonꢀ principleꢀ
teachesꢀelectronsꢀmoveꢀfasterꢀthanꢀatomicꢀnuclei,ꢀtheꢀfirstꢀverticalꢀexcitationsꢀshouldꢀoccurꢀinꢀtheꢀ
absenceꢀofꢀatomꢀnucleiꢀmovementsꢀ(Figureꢀ8).ꢀAfterꢀexcitation,ꢀatomicꢀnucleousꢀreorganizationꢀ
mayꢀ occurꢀ toꢀ giveꢀ aꢀ lowerꢀ energyꢀ excited-stateꢀ geometryꢀ (∆S1ꢀ geometry)ꢀ priorꢀ toꢀ energyꢀ lossꢀ
throughꢀ emissionꢀ whereꢀ againꢀ atomicꢀ nucleusꢀ reorganizationꢀ isꢀ slowerꢀ thanꢀ electronicꢀ stateꢀ
changes.ꢀAfterꢀemission,ꢀtheꢀexcited-stateꢀgeometryꢀisꢀaccessedꢀinꢀtheꢀS
toꢀ theꢀ ground-stateꢀ geometryꢀ (∆S0ꢀ geometry).ꢀ Theꢀ differenceꢀ inꢀ theꢀ twoꢀ electronicꢀ transitionsꢀ
yieldsꢀtheꢀsumꢀofꢀtheꢀ∆S1ꢀꢀandꢀ∆S ꢀgeometries.ꢀThisꢀenergyꢀrepresentsꢀtheꢀreorganizationꢀenergyꢀofꢀ
0
ꢀstate,ꢀwhichꢀthenꢀrelaxesꢀ
0
theꢀmoleculeꢀorꢀtheꢀStokesꢀshift.ꢀWeꢀemployedꢀtheꢀfollowingꢀoperationsꢀtoꢀbetterꢀunderstandꢀtheꢀ
observedꢀ Stokesꢀ shifts:ꢀ (1)ꢀ optimizationꢀ ofꢀ theꢀ ground-stateꢀ geometry,ꢀ (2)ꢀ verticalꢀ excitationꢀ ofꢀ
electronsꢀinꢀthisꢀgeometryꢀ(absorption),ꢀ(3)ꢀoptimizationꢀofꢀtheꢀexcited-stateꢀgeometry,ꢀandꢀ(4)ꢀ
verticalꢀexcitationꢀofꢀelectronsꢀinꢀtheꢀexcited-stateꢀgeometryꢀ(emission).ꢀComputationalꢀanalysisꢀ
ofꢀTPz-Phꢀshowsꢀaꢀverticalꢀexcitationꢀofꢀtheꢀground-stateꢀgeometryꢀatꢀ706ꢀnmꢀ(1.76ꢀeV)ꢀandꢀaꢀ
verticalꢀexcitationꢀofꢀtheꢀexcited-stateꢀgeometryꢀatꢀ913ꢀnmꢀ(1.36ꢀeV)ꢀforꢀaꢀdifferenceꢀofꢀ0.40ꢀeV.ꢀ
Thisꢀvalueꢀisꢀinꢀgoodꢀagreementꢀwithꢀtheꢀexperimentalꢀvalueꢀforꢀtheꢀdifferenceꢀinꢀabsorptionꢀandꢀ
emissionꢀmaximumsꢀ(0.46ꢀeV).ꢀꢀHavingꢀfoundꢀaꢀreasonableꢀagreementꢀbetweenꢀexperimentalꢀandꢀ
computationalꢀ valuesꢀ forꢀ theꢀ magnitudeꢀ ofꢀ energyꢀ ofꢀ theꢀ Stokes-shifts,ꢀ weꢀ thenꢀ analyzedꢀ theꢀ
geometryꢀ toꢀ betterꢀ understandꢀ whereꢀ theꢀ atomicꢀ nucleiꢀ geometriesꢀ wereꢀ changing.ꢀ Thoughꢀ
dihedralꢀbondꢀangleꢀanalysisꢀweꢀfoundꢀthatꢀinꢀtheꢀground-stateꢀgeometryꢀtheꢀTPz-Phꢀbondꢀangleꢀ
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oꢀ
o
isꢀ 20 whereasꢀ inꢀ theꢀ excited-stateꢀ geometryꢀ theꢀ TPz-Phꢀ bondꢀ angleꢀ isꢀ onlyꢀ 3 .ꢀ Thisꢀ resultꢀ isꢀ
supportedꢀbyꢀtheꢀsolvachromaticꢀstudies,ꢀwhereꢀhighlyꢀpolarꢀsolventsꢀpromotingꢀchargeꢀtransferꢀ
ledꢀtoꢀlargerꢀStokesꢀshiftsꢀandꢀpresumablyꢀmoreꢀplanarꢀexcited-stateꢀgeometriesꢀ(Figureꢀ7).ꢀThisꢀ
significantꢀchangeꢀinꢀbondꢀangleꢀgeometryꢀbetweenꢀtheꢀTPAꢀdonorꢀandꢀTPzꢀacceptorꢀwasꢀfoundꢀ
toꢀbeꢀtheꢀlargestꢀcontributorꢀtoꢀtheꢀreorganizationꢀenergy.ꢀTheꢀremainingꢀbondꢀanglesꢀareꢀnearlyꢀ
unchanged.ꢀ Thisꢀ analysisꢀ providesꢀ aꢀ methodꢀ forꢀ rationallyꢀ controllingꢀ Stokes-shiftꢀ magnitudeꢀ
throughꢀstericꢀmodificationsꢀnearꢀtheꢀTPA-TPzꢀbond.ꢀꢀ
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ꢀ
ꢀꢀꢀꢀTheꢀfluorescenceꢀquantumꢀyieldꢀ(QY)ꢀisꢀanꢀimportantꢀparameterꢀinꢀtheꢀevaluationꢀofꢀemissiveꢀ
materialsꢀasꢀaꢀhighꢀQYꢀisꢀdesirableꢀforꢀaccurateꢀdetectionꢀdyesꢀinꢀlowꢀconcentrationꢀandꢀforꢀlowꢀ
powerꢀconsumptionꢀdevices.ꢀAllꢀdyesꢀwereꢀtestedꢀinꢀthreeꢀsolventsꢀsystemsꢀincludingꢀDMF,ꢀCHCl3ꢀ
andꢀ aꢀ MeOH-CHCl
DMFꢀwasꢀselectedꢀtoꢀevaluateꢀtheꢀeffectsꢀofꢀaꢀpolarꢀaproticꢀsolvent,ꢀCHCl
theꢀeffectsꢀofꢀaꢀrelativelyꢀlowꢀpolarityꢀsolvent,ꢀandꢀMeOH-CHCl ꢀwasꢀselectedꢀasꢀaꢀpolarꢀproticꢀ
3
ꢀ mixtureꢀ bothꢀ underꢀ aꢀ nitrogenꢀ atmosphereꢀ anꢀ underꢀ ambientꢀ conditions.ꢀ
3
ꢀwasꢀselectedꢀtoꢀevaluateꢀ
3
solventꢀsystemꢀasꢀtheꢀdyesꢀwereꢀnotꢀhighlyꢀsolubleꢀinꢀpureꢀMeOH.ꢀIdeally,ꢀforꢀbiologicallyꢀrelatedꢀ
imagingꢀtheꢀdyesꢀshouldꢀemitꢀstronglyꢀinꢀproticꢀenvironments.ꢀTheꢀQYsꢀofꢀtheꢀTPz-PhꢀandꢀTPz-
PhOMeꢀdyesꢀareꢀcomparableꢀtoꢀwidelyꢀusedꢀNIRꢀdyesꢀwithꢀemissionꢀpeaksꢀinꢀtheꢀ700-800ꢀnmꢀ
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regionꢀ suchꢀ asꢀ cyanines ,ꢀ ꢀ benzothiadiazoles ꢀ andꢀ benzothiophenes. ꢀ TPz-Et,ꢀ TPz-Ph,ꢀ TPz-
PhOMeꢀ andꢀ TPz-PhCO Meꢀ wereꢀ foundꢀ toꢀ giveꢀ QYsꢀ rangingꢀ fromꢀ 0.3%ꢀ toꢀ 4.3%ꢀ inꢀ variousꢀ
2
environments.ꢀ Allꢀ dyesꢀ wereꢀ foundꢀ toꢀ haveꢀ higherꢀ quantumꢀ yieldsꢀ underꢀ nitrogenꢀ ratherꢀ thanꢀ
underꢀambientꢀconditions;ꢀhowever,ꢀtheꢀpercentꢀdecreaseꢀinꢀquantumꢀyieldꢀvariedꢀdramaticallyꢀ
fromꢀaꢀ4%ꢀdecreaseꢀforꢀTPz-EtꢀinꢀCHCl
Phꢀ gaveꢀ theꢀ highestꢀ QYꢀ ofꢀ 4.3%ꢀ inꢀ CHCl
MeOH-CHCl ꢀmixturesꢀwereꢀminimallyꢀaffectedꢀbyꢀambientꢀatmosphericꢀconditions,ꢀwhileꢀDMFꢀ
3
ꢀtoꢀanꢀ80%ꢀdecreaseꢀforꢀTPz-PhOMeꢀwhenꢀinꢀDMF.ꢀTPz-
3
ꢀ underꢀ aꢀ nitrogenꢀ atmosphere.ꢀ Inꢀ generalꢀ CHCl ꢀ andꢀ
3
3
solutionsꢀ wereꢀ muchꢀ moreꢀ stronglyꢀ affected.ꢀ Underꢀ theꢀ bestꢀ conditionsꢀ tested,ꢀ theꢀ trendꢀ inꢀ
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maximumꢀQYꢀproceededꢀfromꢀTPz-PhCO
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Meꢀ(0.26%)ꢀ<ꢀTPz-Etꢀ(2.3%)ꢀ<ꢀTPz-PhOMeꢀ(2.9%)ꢀ<ꢀ
TPz-Phꢀ (4.3%).ꢀ Itꢀ isꢀ noteworthyꢀ thatꢀ despiteꢀ aꢀ ~75ꢀ nmꢀ lowerꢀ energyꢀ absorptionꢀ TPz-Phꢀ
demonstratedꢀaꢀnearlyꢀ2ꢀfoldꢀincreaseꢀinꢀQYꢀwhenꢀcomparedꢀwithꢀTPz-Et.ꢀThisꢀisꢀlikelyꢀinꢀpartꢀ
dueꢀtoꢀaꢀreducedꢀStokes-shiftꢀasꢀaꢀlowerꢀreorganizationꢀenergyꢀisꢀneededꢀtoꢀaccessꢀtheꢀexcited-
stateꢀresultingꢀinꢀaꢀhigherꢀemissionꢀenergyꢀandꢀbetterꢀintermolecularꢀspacingꢀofꢀtheꢀconjugatedꢀ
electronsꢀthroughꢀoutꢀofꢀplaneꢀphenylꢀspacersꢀversusꢀethylꢀgroups.ꢀTPz-Phꢀalsoꢀdemonstratedꢀtheꢀ
higherꢀ QYꢀ inꢀ aꢀ proticꢀ environmentꢀ ofꢀ 3.7%,ꢀ whichꢀ isꢀ nearlyꢀ anꢀ orderꢀ ofꢀ magnitudeꢀ (8ꢀ times)ꢀ
higherꢀ thanꢀ forꢀ theꢀ nextꢀ highestꢀ performingꢀ dyeꢀ inꢀ thisꢀ environment.ꢀ Theꢀ fullꢀ solventꢀ andꢀ
atmosphericꢀdependenceꢀofꢀtheꢀQYꢀisꢀshownꢀinꢀTableꢀ4.ꢀꢀ
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ꢀ
ꢀꢀꢀꢀFluorescenceꢀ lifetimesꢀ (τ)ꢀ ofꢀ compoundsꢀ 1-3ꢀ wereꢀ alsoꢀ measuredꢀ asꢀ theꢀ QYꢀ isꢀ relatedꢀ toꢀ
fluorescenceꢀlifetimesꢀbyꢀtheꢀequationsꢀφꢀ=ꢀk /(k ꢀ+ꢀknr),ꢀwhereꢀk ꢀisꢀtheꢀradiativeꢀrateꢀandꢀknrꢀisꢀtheꢀ
non-radiativeꢀrateꢀandꢀτꢀ=ꢀ1/(ꢀk ꢀ+ꢀknr)ꢀwhichꢀgivesꢀφꢀ=ꢀ(τ)(k ).ꢀꢀWhileꢀaꢀlargeꢀτꢀdoesꢀnotꢀnecessitateꢀ
aꢀ higherꢀ φꢀ asꢀ k ꢀ isꢀ independant,ꢀ increasingꢀ τꢀ oftenꢀ correlatesꢀ toꢀ higherꢀ φ ꢀ TPz-Phꢀ showedꢀ aꢀ
r
r
r
r
r
r
.
significantlyꢀ longerꢀ lifetimeꢀ thanꢀ theꢀ otherꢀ dyes.ꢀ Interestingly,ꢀ TPz-Phꢀ wasꢀ observedꢀ toꢀ haveꢀ aꢀ
two-componentꢀ decayꢀ curveꢀ withꢀ fastꢀ componentꢀ atꢀ ~1ꢀ nsꢀ forꢀ eachꢀ solvent/atmosphereꢀ andꢀ
substantiallyꢀlongerꢀexcitedꢀstateꢀdecayꢀcomponentꢀlastingꢀapproximatelyꢀanꢀorderꢀofꢀmagnitudeꢀ
longerꢀthanꢀtheꢀfastꢀcomponent.ꢀOnlyꢀtheꢀpyrazine-arylatedꢀTPzꢀacceptorsꢀgaveꢀsignificantꢀtwoꢀ
1
componentꢀ fluorescenceꢀ lifetimes.ꢀ Forꢀ allꢀ dyesꢀ theꢀ initialꢀ τ ꢀ rangedꢀ betweenꢀ ~0.5-1.0ꢀ nsꢀ inꢀ allꢀ
solventsꢀandꢀatmospheresꢀanalyzed.ꢀTheꢀsolventꢀdependenceꢀofꢀtheꢀfluorescentꢀlifetimesꢀisꢀshownꢀ
inꢀTableꢀ4ꢀforꢀtheꢀfullꢀdyeꢀseries.ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
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ꢀ
ꢀꢀꢀꢀꢀꢀꢀTableꢀ4:ꢀEmissiveꢀpropertiesꢀ
dyeꢀ
solventꢀ
QY(φ)ꢀ
%)ꢀ
τ
1
ꢀꢀ(ns)ꢀ
2
τ ꢀ(ns)ꢀ
(
a
TPz-Etꢀ
DMF ꢀ
1.63ꢀ
2.05ꢀ
2.16ꢀ
2.25ꢀ
0.36ꢀ
0.45ꢀ
2.13ꢀ
0.85ꢀ
0.92ꢀ
1.12ꢀ
N/Aꢀ
N/Aꢀ
N/Aꢀ
N/Aꢀ
0.41ꢀ
0.52ꢀ
10
11
12
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14
15
16
17
18
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20
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22
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29
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31
32
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35
36
37
38
39
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b
ꢀ
DMF ꢀ
a
ꢀ
CHCl3ꢀ
CHCl3ꢀ
ꢀ
b
ꢀ
ꢀ
1.09ꢀ
0.41ꢀ
0.52ꢀ
0.44ꢀ
0.65ꢀ
1.22ꢀ
a
ꢀ
MeOH/CHCl3ꢀ
MeOH/CHCl3ꢀ
ꢀ
b
ꢀ
ꢀ
a
TPz-Phꢀ
DMF ꢀ
14.58ꢀ
13.68ꢀ
11.42ꢀ
13.04ꢀ
4.46ꢀ
7.11ꢀ
b
ꢀ
DMF ꢀ
3.29ꢀ
3.51ꢀ
a
ꢀ
CHCl3ꢀ
CHCl3ꢀ
ꢀ
b
ꢀ
ꢀ
4.29ꢀ
2.62ꢀ
3.74ꢀ
0.56ꢀ
2.87ꢀ
0.86ꢀ
1.40ꢀ
0.34ꢀ
0.41ꢀ
0.15ꢀ
0.21ꢀ
0.21ꢀ
0.26ꢀ
0.08ꢀ
0.12ꢀ
1.23ꢀ
a
ꢀ
MeOH/CHCl3ꢀ
MeOH/CHCl3ꢀ
ꢀ
0.85ꢀ
1.02ꢀ
0.50ꢀ
0.57ꢀ
0.68ꢀ
0.75ꢀ
0.55ꢀ
0.55ꢀ
0.54ꢀ
0.61ꢀ
0.51ꢀ
0.58ꢀ
0.60ꢀ
0.63ꢀ
b
ꢀ
ꢀ
a
TPz-PhOMeꢀ
DMF ꢀ
N/Aꢀ
N/Aꢀ
3.34ꢀ
4.06ꢀ
N/Aꢀ
N/Aꢀ
N/Aꢀ
N/Aꢀ
N/Aꢀ
N/Aꢀ
N/Aꢀ
N/Aꢀ
b
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
DMF ꢀ
a
CHCl3ꢀ
CHCl3ꢀ
ꢀ
b
ꢀ
a
MeOH/CHCl3ꢀ
ꢀ
b
MeOH/CHCl3ꢀ
ꢀ
a
TPz-PhCO
2
Meꢀ DMF ꢀ
b
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
DMF ꢀ
a
CHCl3ꢀ
CHCl3ꢀ
ꢀ
b
ꢀ
a
MeOH/CHCl3ꢀ
MeOH/CHCl3ꢀ
ꢀ
b
ꢀ
ꢀ
a
b
Readingsꢀ wereꢀ takenꢀ inꢀ solventsꢀ underꢀ ambientꢀ conditions.ꢀ Readingsꢀ wereꢀ takenꢀ inꢀ N
2
ꢀ
degassedꢀsolvents.ꢀꢀ
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ꢀ
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ꢀ
Figureꢀ9.ꢀFluorescenceꢀspectrumꢀofꢀTPz-PhꢀinꢀDMFꢀ(upperꢀleft),ꢀasꢀaꢀneatꢀthinꢀfilmꢀonꢀaꢀglassꢀ
slideꢀ(upperꢀright),ꢀandꢀdispersedꢀinꢀaꢀZeonex®ꢀthinꢀfilmꢀ(middle),ꢀandꢀtheꢀaccumulatedꢀspectrumꢀ
ofꢀapproximatelyꢀ20ꢀsingleꢀmoleculesꢀdispersedꢀinꢀaꢀsolidꢀZeonex®ꢀfilmꢀ(bottom).ꢀ
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ꢀ
ꢀꢀꢀꢀSinceꢀTPz-PhꢀwasꢀfoundꢀtoꢀhaveꢀtheꢀhighestꢀQYꢀwithꢀemissionꢀintoꢀtheꢀNIRꢀregion,ꢀsolid-stateꢀ
measurementsꢀwithꢀthinꢀfilmꢀfluorescenceꢀmeasurementsꢀwereꢀtakenꢀ(Figureꢀ9).ꢀꢀStandardꢀthinꢀ
filmsꢀ ofꢀ TPz-Phꢀ displayꢀ emissionꢀ spectraꢀ comparableꢀ toꢀ solutionꢀ phaseꢀ samplesꢀ suggestingꢀ aꢀ
limitedꢀaggregativeꢀinteractionꢀbetweenꢀtheꢀdyeꢀmoleculesꢀinꢀtheꢀsolidꢀstate.ꢀꢀHowever,ꢀtheꢀthinꢀ
filmꢀ emissionꢀ spectrumꢀ ofꢀ TPz-Phꢀ doesꢀ notꢀ showꢀ theꢀ sameꢀ degreeꢀ ofꢀ redꢀ shiftingꢀ observedꢀ inꢀ
solutionꢀ phase.ꢀ Thisꢀ indicatesꢀ thatꢀ theꢀ moleculesꢀ areꢀ moreꢀ tightlyꢀ packedꢀ inꢀ theꢀ filmsꢀ thanꢀ inꢀ
solution,ꢀ inhibitingꢀ reorganization.ꢀ Zeonex®ꢀ filmsꢀ allowꢀ forꢀ theꢀ directꢀ observationꢀ ofꢀ singleꢀ
moleculeꢀemissionꢀinꢀtheꢀsolid-stateꢀthroughꢀdissolvingꢀofꢀtheꢀemissiveꢀmaterialꢀinꢀaꢀsolutionꢀofꢀ
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Zeonexꢀ andꢀ castingꢀ films. ꢀ Theseꢀ studiesꢀ allowꢀ forꢀ theꢀ directꢀ observationꢀ ofꢀ theꢀ stabilityꢀ ofꢀ aꢀ
singleꢀmoleculeꢀtoꢀcontinuousꢀirradiationꢀandꢀemission.ꢀꢀUltraꢀdispersedꢀsingleꢀmoleculeꢀspectraꢀ
inꢀaꢀsolidꢀZeonex®ꢀfilmꢀdisplayꢀaꢀsimilarꢀλmaxꢀasꢀtheꢀmoreꢀconcentratedꢀthinꢀfilmꢀandꢀtheꢀsolutionꢀ
butꢀdoesꢀnotꢀtailꢀasꢀfarꢀintoꢀtheꢀlongerꢀwavelengthꢀregion.ꢀAꢀfluorescenceꢀtimeꢀtraceꢀofꢀaꢀsingleꢀ
moleculeꢀofꢀTPz-PhꢀisꢀshownꢀinꢀFigureꢀ9,ꢀdemonstratingꢀthatꢀtheꢀemissionꢀofꢀaꢀsingleꢀmoleculeꢀinꢀ
theꢀZeonex®ꢀfilmꢀisꢀstableꢀwithꢀcontinuousꢀfluorescence.ꢀꢀꢀ
Conclusionꢀ
Aꢀ seriesꢀ ofꢀ fourꢀ NIRꢀ fluorescentꢀ compounds,ꢀ withꢀ emissionꢀ rangingꢀ fromꢀ 600-900ꢀ nm,ꢀ wereꢀ
synthesizedꢀandꢀtheꢀopticalꢀpropertiesꢀstudied.ꢀꢀꢀTheꢀfacileꢀ4-stepꢀsynthesisꢀwasꢀmadeꢀpossibleꢀ
throughꢀ directꢀ C-Hꢀ bondꢀ arylationꢀ withꢀ catalyticꢀ palladium.ꢀ Theꢀ NIRꢀ dyesꢀ wereꢀ analyzedꢀ withꢀ
electrochemicalꢀstudies,ꢀUV-Visꢀspectroscopy,ꢀandꢀfluorometryꢀinꢀaꢀvarietyꢀofꢀsolutions,ꢀasꢀaꢀthinꢀ
filmꢀandꢀinꢀatꢀtheꢀsolid-stateꢀsingleꢀmoleculeꢀlevelꢀinꢀZeonex®ꢀfilms.ꢀTheseꢀmaterialsꢀwereꢀshownꢀ
toꢀ haveꢀ nearꢀ independentlyꢀ tunableꢀ ground-stateꢀ andꢀ excited-stateꢀ oxidationꢀ potentialsꢀ whichꢀ
givesꢀ riseꢀ toꢀ theꢀ opportunityꢀ toꢀ controlꢀ andꢀ tuneꢀ energyꢀ valuesꢀ inꢀ aꢀ straightforwardꢀ manner.ꢀ
SolutionꢀabsorptionꢀandꢀemissionꢀcurvesꢀshowꢀStokesꢀshiftsꢀnearꢀ200ꢀnmꢀtheꢀTPA-Pz-TPAꢀ(D-A-
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D)ꢀ dyes.ꢀ Theꢀ Stokesꢀ shiftꢀ originꢀ wasꢀ examinedꢀ throughꢀ computationalꢀ analysisꢀ andꢀ foundꢀ toꢀ
correlateꢀ withꢀ aꢀ substantialꢀ bondꢀ angleꢀ changeꢀ betweenꢀ theꢀ donorꢀ andꢀ acceptorꢀ rings.ꢀ Goodꢀ
quantumꢀ yieldsꢀ nearꢀ thatꢀ ofꢀ commonlyꢀ usedꢀ biologicalꢀ imagingꢀ dyesꢀ suchꢀ asꢀ cyanineꢀ dyesꢀ areꢀ
observedꢀatꢀ>4%ꢀinꢀtheꢀNIRꢀregionꢀ(775ꢀnmꢀpeakꢀemission)ꢀdespiteꢀaꢀconsiderableꢀenhancementꢀ
inꢀStokesꢀshiftꢀvaluesꢀ(200ꢀnmꢀvs.ꢀ~5ꢀnm).ꢀLargeꢀStokesꢀshiftsꢀareꢀdesirableꢀforꢀlivingꢀbiologicalꢀ
imagingꢀapplicationsꢀtoꢀavoidꢀbackgroundꢀsignalsꢀfromꢀtheꢀexcitationꢀsource,ꢀandꢀtheꢀTPz-basedꢀ
dyesꢀexaminedꢀhaveꢀdemonstratedꢀaꢀlargeꢀshiftꢀandꢀgoodꢀemissionꢀquantumꢀyield.ꢀTheꢀemissionꢀ
ofꢀtheseꢀmaterialsꢀwasꢀshownꢀtoꢀbeꢀstableꢀinꢀaꢀsolidꢀfilmꢀduringꢀirradiation,ꢀwhichꢀsuggestsꢀtheꢀ
moleculesꢀareꢀpartꢀofꢀaꢀrobustꢀdesignꢀwithꢀpotentialꢀapplicationsꢀinꢀaꢀrangeꢀofꢀdevices.ꢀꢀ
ꢀ
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ExperimentalꢀSectionꢀ
Materials. Allꢀ commerciallyꢀ obtainedꢀ reagentsꢀ andꢀ solventsꢀ wereꢀ usedꢀ asꢀ receivedꢀ withoutꢀ
furtherꢀpurification.ꢀ2,5-dibromothiophene,ꢀbenzil,ꢀ4,ꢀ4’-dimethozybenzil,ꢀ3,4-hexanedioneꢀꢀandꢀ
methylꢀ 4-formylbenzoateꢀ wereꢀ purchasedꢀ commercially.ꢀ Bis(hexyloxy)triphenylamineꢀ bromideꢀ
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wasꢀ preparedꢀ accordingꢀ toꢀ literatureꢀ procedures. ꢀ Diethylꢀ 2,3-dioxosuccinateꢀ wasꢀ preparedꢀ
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5
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literatureꢀprocedure. ꢀTheꢀSnCl /SiO ꢀsolidꢀsupportꢀcatalystꢀwasꢀpreparedꢀaccordingꢀtoꢀliteratureꢀ
43
procedure. ꢀ Thin-layerꢀ chromatographyꢀ (TLC)ꢀ wasꢀ visualizedwithꢀ UV.ꢀ Flashꢀ columnꢀ
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chromatographyꢀ wasꢀ performedꢀ asꢀ describedꢀ byꢀ Still. ꢀ Hꢀ andꢀ Cꢀ NMRꢀ spectraꢀ wereꢀ recordedꢀ
on300MHzꢀ andꢀ 500MHzspectrometersꢀ andꢀ areꢀ reportedꢀ inꢀ ppmꢀ usingꢀ solventꢀ asꢀ anꢀ internalꢀ
standardꢀ(CDCl
3
ꢀatꢀ7.26ꢀppm).ꢀDataꢀreportedꢀas:ꢀsꢀ=ꢀsinglet,ꢀdꢀ=ꢀdoublet,ꢀtꢀ=ꢀtriplet,ꢀqꢀ=ꢀquartet,ꢀpꢀ
=
ꢀpentet,ꢀmꢀ=ꢀmultiplet,ꢀbꢀ=ꢀbroad,ꢀapꢀ=ꢀapparent,ꢀddꢀ=ꢀdoubletꢀofꢀdoublets;ꢀcouplingꢀconstant(s)ꢀ
inꢀ Hz;ꢀ integration.ꢀ UV-Visꢀ Spectraꢀ wereꢀ measuredꢀ withꢀ aꢀ UV-Vis-NIRꢀ spectrometer.ꢀ Cyclicꢀ
voltammetryꢀ wasꢀ measuredꢀ withꢀ aꢀ electrochemicalꢀ analyzer.ꢀ Compoundsꢀ 2-4cꢀ areꢀ knownꢀ
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compoundsꢀ referencedꢀ belowꢀ withꢀ aꢀ briefꢀ descriptionꢀ ofꢀ theꢀ preparativeꢀ methodsꢀ usedꢀ andꢀ
1
matchingꢀ Hꢀ NMRꢀ dataꢀ reported.ꢀ Duringꢀ NMRꢀ sampleꢀ preparation,ꢀ weꢀ foundꢀ extractionꢀ withꢀ
dichloromethaneꢀ andꢀ aqueousꢀ NaHCO3ꢀ wasꢀ necessaryꢀ forꢀ resolvedꢀ signalsꢀ afterꢀ silicaꢀ gelꢀ
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purificiation.ꢀPresumablyꢀtheseꢀcompoundsꢀtightlyꢀclingꢀtoꢀtraceꢀSiO ꢀparticlesꢀleadingꢀtoꢀpoorlyꢀ
resolvedꢀNMRꢀpeaksꢀandꢀaqueousꢀextractionꢀallowsꢀforꢀseparationꢀofꢀtheseꢀparticles.ꢀHRMSꢀwereꢀ
obtainedꢀwithꢀaꢀQTOFꢀHRMSꢀutilizingꢀnano-sprayꢀionization.ꢀꢀTheꢀmassꢀanalyzerꢀwasꢀsetꢀtoꢀ100-
2
000ꢀDaltonꢀrangeꢀbutꢀisꢀcapableꢀofꢀaꢀrangeꢀbetweenꢀ0-24000ꢀDaltons.ꢀꢀ
40
Synthesisꢀ ofꢀ 2,5-dibromo-3,4-dinitrothiopheneꢀ (2): ꢀ Toꢀ aꢀ flameꢀ dried,ꢀ roundꢀ bottomꢀ flaskꢀ wasꢀ
addedꢀconcentratedꢀH
SO ꢀ (40ꢀ mL,ꢀ 1.55ꢀ M).ꢀ Theꢀ flaskꢀ wasꢀ thenꢀ cooledꢀ toꢀ 0ꢀ °Cꢀ followedꢀ byꢀ additionꢀ ofꢀ 2,5-
dibromothiopheneꢀ(6.98ꢀmL,ꢀ62.0ꢀmmol)ꢀdropwiseꢀatꢀaꢀrateꢀwhichꢀkeptꢀtheꢀtemperatureꢀbelowꢀ15ꢀ
C.ꢀ Afterꢀ completeꢀ additionꢀ theꢀ reactionꢀ mixtureꢀ wasꢀ thenꢀ stirredꢀ forꢀ 3ꢀ hoursꢀ atꢀ roomꢀ
2 4 3
SO ꢀ(25.00ꢀmL,ꢀ2.40ꢀM),ꢀconcentratedꢀHNO ꢀ(22ꢀmL,ꢀ2.83ꢀM)ꢀandꢀfumingꢀ
H
2
4
°
temperature.ꢀ Theꢀ reactionꢀ mixtureꢀ wasꢀ pouredꢀ intoꢀ aꢀ 300ꢀ gꢀ ofꢀ crushedꢀ ice,ꢀ whileꢀ theꢀ iceꢀ wasꢀ
meltingꢀ theꢀ yellowꢀ precipitateꢀ wasꢀ collectedꢀ byꢀ vacuumꢀ filtration.ꢀ Theꢀ productꢀ wasꢀ purifiedꢀ
throughꢀrecrystallizationꢀwithꢀmethanolꢀtoꢀgiveꢀaꢀyellowꢀcolorꢀcrystallineꢀsolidꢀ(10.70ꢀg,ꢀ52.0ꢀ%).ꢀ
1
3
CꢀNMRꢀ(500ꢀMHz,ꢀDMSO)ꢀδꢀ140.2,ꢀ117.1ꢀppm.ꢀ
Synthesisꢀ ofꢀ 3,4-diaminothiopheneꢀ dihydrochlorideꢀ (3): ꢀ Toꢀ aꢀ flameꢀ driedꢀ flaskꢀ wasꢀ addedꢀ
4
0
concentratedꢀHClꢀ(146ꢀmL,ꢀ37%)ꢀandꢀ2ꢀ(8.00ꢀg,ꢀ24.10ꢀmmol).ꢀTheꢀflaskꢀwasꢀthenꢀcooledꢀtoꢀ0°Cꢀ
followedꢀbyꢀadditionꢀofꢀSnꢀpowderꢀ(20.15ꢀg,ꢀ169.90ꢀmmol)ꢀwithinꢀaꢀoneꢀhourꢀinꢀsmallꢀportionsꢀtoꢀ
keepꢀ theꢀ temperatureꢀ belowꢀ 25°C.ꢀ Afterꢀ completeꢀ additionꢀ theꢀ mixtureꢀ wasꢀ stirredꢀ atꢀ roomꢀ
o
temperatureꢀuntilꢀallꢀtheꢀSnꢀwasꢀconsumedꢀ(2hr).ꢀAfterꢀcoolingꢀ1ꢀhourꢀinꢀaꢀ-18 Cꢀrefrigerator,ꢀtheꢀ
productꢀwasꢀcollectedꢀbyꢀvacuumꢀfiltrationꢀandꢀwashedꢀwithꢀdiethylꢀetherꢀandꢀacetonitrileꢀtoꢀgiveꢀ
aꢀwhiteꢀpowderꢀ(3.39ꢀg,ꢀ75%).ꢀTheꢀproductꢀwasꢀusedꢀasꢀisolatedꢀwithoutꢀfurtherꢀcharacterization.ꢀ
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42
Synthesisꢀ ofꢀ 2,3-diethylthieno[3,4-b]pyrazineꢀ (4a): ꢀ Aꢀ mixtureꢀ ofꢀ 3,4-diaminothiopheneꢀ
dihydrochlorideꢀ(3)ꢀ(ꢀ1.00ꢀg,ꢀ5.35ꢀmmol),ꢀ3,4-hexanedioneꢀ(0.67ꢀmL,ꢀ5.46ꢀmmol),ꢀtriethylamineꢀ(27ꢀ
mL),ꢀ ethanolꢀ (49ꢀ mL),ꢀ andꢀ dichloromethaneꢀ (49ꢀ mL)ꢀ wereꢀ stirredꢀ atꢀ 50°Cꢀ overnightꢀ underꢀ
ambientꢀatmosphere.ꢀTheꢀreactionꢀmixtureꢀwasꢀextractedꢀwithꢀdichloromethaneꢀandꢀdriedꢀoverꢀ
0
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1
2
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7
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2
3
4
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4
MgSO .ꢀ Theꢀ crudeꢀ productꢀ wasꢀ purifiedꢀ withꢀ flashꢀ silicaꢀ gelꢀ chromatographyꢀ withꢀ 10%ꢀ ethylꢀ
acetate:ꢀdichloromethaneꢀàꢀ30%ꢀethylꢀacetate:ꢀdichloromethaneꢀasꢀtheꢀeluentꢀtoꢀgiveꢀtanꢀcolorꢀ
1
crystallineꢀsolidꢀ(0.85ꢀg,ꢀ82.4%).ꢀ HꢀNMRꢀ(300ꢀMHz,ꢀCDCl
3
)ꢀδꢀ2.95ꢀ(q,ꢀJꢀ=ꢀ7.4ꢀHz,ꢀ4H),ꢀ1.38ꢀ(t,ꢀJꢀ=ꢀ
7
.4ꢀꢀHz,ꢀ6H).ꢀ
Synthesisꢀ ofꢀ diethylꢀ thieno[3,4-b]pyrazine-2,3-dicarboxylateꢀ (4b): ꢀ Theꢀ syntheticꢀ procedureꢀ isꢀ
4
1
similarꢀ toꢀ theꢀ conditionsꢀ forꢀ 4a,ꢀ exceptꢀ diethylꢀ 2,3-dioxosuccinateꢀ (excess,ꢀ estimatedꢀ 4ꢀ
equivalents)ꢀwasꢀuseꢀinsteadꢀofꢀ3,4-hexanedione.ꢀTheꢀcrudeꢀproductꢀwasꢀpurifiedꢀthroughꢀaꢀsilicaꢀ
gelꢀ plugꢀ usingꢀ 100%ꢀ dichloromethaneà10%ꢀ ethylꢀ acetate:ꢀ dichloromethaneꢀ toꢀ giveꢀ aꢀ tanꢀ colorꢀ
1
solidꢀ(155ꢀmg,ꢀ34%).ꢀ HꢀNMRꢀ(300ꢀMHz,ꢀCDCl
3
)ꢀδꢀ8.29ꢀ(s,ꢀ2H),ꢀ4.54ꢀ(q,ꢀJꢀ=ꢀ7.1ꢀHz,ꢀ4H),ꢀ1.47ꢀ(t,ꢀJꢀ=ꢀ7.1ꢀ
Hz,ꢀ6H).ꢀ
3
6
Synthesisꢀ ofꢀ 2,3-diphenylthieno[3,4-b]pyrazineꢀ (4c): ꢀ Theꢀsyntheticꢀprocedureꢀisꢀsimilarꢀtoꢀtheꢀ
conditionsꢀforꢀ4a,ꢀexceptꢀbenzilꢀ(1.15ꢀg,ꢀ5.45ꢀmmol)ꢀwasꢀuseꢀinsteadꢀofꢀ3,4-hexanedione.ꢀTheꢀcrudeꢀ
productꢀwasꢀpurifiedꢀthroughꢀsilicaꢀgelꢀchromatographyꢀwithꢀ100%ꢀdichloromethaneà5%ꢀethylꢀ
1
acetate:dichloromethaneꢀ asꢀ theꢀ eluentꢀ toꢀ giveꢀ tanꢀ colorꢀ crystallineꢀ solidꢀ (0.69ꢀ g,ꢀ 45%). Hꢀ NMRꢀ
(
300ꢀMHz,ꢀCDCl
Synthesisꢀ ofꢀ 2,3-bis(4-methoxyphenyl)thieno[3,4-b]pyrazineꢀ (4d):ꢀ Toꢀ aꢀ flameꢀ dried,ꢀ N
roundꢀbottomꢀflackꢀwasꢀaddedꢀ3,4-diaminothiopheneꢀdihydrochlorideꢀ(3)ꢀ (ꢀ0.50ꢀg,ꢀ2.67ꢀmmol),ꢀ
,4’-dimethoxybenzilꢀ(0.66ꢀg,ꢀ2.43ꢀmmol),ꢀSnCl /SiO ꢀ(0.72ꢀg,ꢀ0.12ꢀmmol)ꢀandꢀmethanolꢀ(14ꢀmL).ꢀ
3
)ꢀδꢀ8.05ꢀ(s,ꢀ1H),ꢀ7.44ꢀ(dd,ꢀ,ꢀJꢀ=ꢀ2.2,ꢀ7.7ꢀHz,ꢀ4H),ꢀ7.36-7.30ꢀ(m,ꢀ6H).ꢀ
2
ꢀ filledꢀ
4
2
2
Theꢀ mixtureꢀ wasꢀ stirredꢀ atꢀ roomꢀ temperatureꢀ forꢀ 3ꢀ hours.ꢀ Theꢀ reactionꢀ mixtureꢀ wasꢀ filteredꢀ
throughꢀ aꢀ thinꢀ padꢀ ofꢀ SiO2ꢀ withꢀ 20%ꢀ ethylꢀ acetate:ꢀ dichloromethane.ꢀ Theꢀ filtrateꢀ wasꢀ thenꢀ
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concentratedꢀ andꢀ purifiedꢀ throughꢀ flashꢀ silicaꢀ gelꢀ chromatographyꢀ withꢀ 5%ꢀ ethylꢀ
acetate:dichloromethaneꢀàꢀ10%ꢀethylꢀacetate:ꢀdichloromethaneꢀtoꢀgiveꢀaꢀpaleꢀgreenꢀcolorꢀsolidꢀ(ꢀ
1
0.37ꢀg,ꢀ43.5ꢀ%).ꢀ HꢀNMRꢀ(300ꢀMHz,ꢀCDCl
3
)ꢀδꢀ7.97ꢀ(s,ꢀ2H),ꢀ7.40ꢀ(d,ꢀJꢀ=ꢀ8.6ꢀHz,ꢀ4H),ꢀ6.85ꢀ(d,ꢀJꢀ=ꢀ8.7ꢀ
)ꢀδꢀ160.2,ꢀ153.0,ꢀ142.6,ꢀ131.8,ꢀ131.3,ꢀ117.0,ꢀ113.6,ꢀ55.3.ꢀIRꢀ
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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52
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54
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58
59
60
13
Hz,ꢀ4H),ꢀ3.83ꢀ(s,ꢀ6H).ꢀ CꢀNMRꢀ(75ꢀMHz,ꢀCDCl
3
-
1
(
16 2 2
neat,ꢀ cm )ꢀ 3435.1,ꢀ 3066.4,ꢀ 1635.6,ꢀ 1606.2,ꢀ 1248.7,ꢀ 1173.4.ꢀ HRMSꢀ (ESI)ꢀ m/zꢀ calcdꢀ forꢀ C20H N O Sꢀ
+
(MHꢀ )ꢀ349.1011,ꢀfoundꢀ349.0984.ꢀ
Synthesisꢀ ofꢀ dimethylꢀ 4,4'-(thieno[3,4-b]pyrazine-2,3-diyl)dibenzoateꢀ (4e):ꢀ Theꢀ syntheticꢀ
procedureꢀisꢀsimilarꢀtoꢀtheꢀconditionsꢀforꢀ4a,ꢀexceptꢀdimethylꢀ4,4'-oxalyldibenzoateꢀ(0.43ꢀg,ꢀ1.31ꢀ
mmol)ꢀwasꢀuseꢀinsteadꢀofꢀ3,4-hexanedione.ꢀTheꢀcrudeꢀreactionꢀmixtureꢀwasꢀpurifiedꢀthroughꢀaꢀ
1
silicaꢀgelꢀcolumnꢀ40%ꢀethylꢀacetate:hexaneꢀàꢀ100%ꢀmethanolꢀ(0.40ꢀg,ꢀ85%).ꢀ HꢀNMRꢀ(500ꢀMHz,ꢀ
ꢀ13
CDCl
MHz,ꢀCDCl
1435.5,ꢀ1280.5,ꢀ1109.8.ꢀHRMSꢀ(ESI)ꢀm/zꢀcalcdꢀforꢀC22
Synthesisꢀ ofꢀ 4,4'-(2,3-diethylthieno[3,4-b]pyrazine-5,7-diyl)bis(N,N-bis(4-
hexyloxy)phenyl)aniline)ꢀ(TPz-Et):ꢀToꢀaꢀhighꢀvacuum-N ꢀ3xꢀcycledꢀvialꢀcontainingꢀ4aꢀ(40ꢀmg,ꢀ0.21ꢀ
mmol)ꢀwasꢀaddedꢀ4-bromo-N,N-bis(4-hexyloxyphenyl)anilineꢀ(TPA-Br)ꢀ(220ꢀmg,ꢀ0.42ꢀmmol),ꢀP(t-
Bu)3ꢀ(1Mꢀ inꢀ tolueneꢀ )ꢀ (11ꢀ μL,ꢀ 0.012ꢀ mmol),ꢀ K CO ꢀ (43ꢀ mg,ꢀ 0.31ꢀ mmol),ꢀ Pd(OAc) ꢀ (2.4ꢀ mg,ꢀ 0.012ꢀ
ꢀatmosphere.ꢀ
3
)ꢀδꢀ8.11ꢀ(s,ꢀ2H),ꢀ7.98ꢀ(d,ꢀJꢀ=ꢀ7.9ꢀHz,ꢀ4H),ꢀ7.49ꢀ(d,ꢀJꢀ=ꢀ7.8ꢀHz,ꢀ4H),ꢀ3.92ꢀ(s,ꢀ6H). CꢀNMRꢀ(75ꢀ
-
1
3
)ꢀδꢀ167.1,ꢀ152.4,ꢀ143.6,ꢀ142.0,ꢀ131.1,ꢀ129.8,ꢀ129.7,ꢀ118.5,ꢀ52.4.ꢀIRꢀ(neat,ꢀcm )ꢀ3114.6,ꢀ1709.2,ꢀ
16 2 4
H N O
Sꢀ(M+H)ꢀ405.0909,ꢀfoundꢀ405.0934.ꢀ
(
2
2
3
2
mmol),ꢀPivalicꢀacidꢀ(11ꢀmg,ꢀ0.10ꢀmmol)ꢀandꢀSTSꢀdriedꢀtolueneꢀ(1.5ꢀmL)ꢀunderꢀanꢀN
2
0
Thenꢀtheꢀvialꢀwasꢀsealedꢀandꢀreactionꢀmixtureꢀwasꢀstirredꢀatꢀ120ꢀ Cꢀforꢀthreeꢀhours.ꢀTheꢀreactionꢀ
mixtureꢀ wasꢀ filteredꢀ throughꢀ thinꢀ padꢀ ofꢀ celiteꢀ withꢀ dichloromethane.ꢀ Theꢀ filtrateꢀ wasꢀ
concentratedꢀandꢀpurifiedꢀbyꢀflashꢀsilicaꢀgelꢀchromatographyꢀusingꢀ30%ꢀethylꢀacetate:hexanesꢀtoꢀ
1
giveꢀaꢀpurpleꢀcolorꢀsolidꢀ(165ꢀmg,ꢀ68%).ꢀ HꢀNMRꢀ(500ꢀMHz,ꢀCDCl
3
)ꢀδꢀ8.10ꢀ(d,ꢀJꢀ=ꢀ8.7ꢀHz,ꢀ4H),ꢀ7.08ꢀ
(d,ꢀJꢀ=ꢀ8.9ꢀHz,ꢀ8H),ꢀ6.98ꢀ(d,ꢀJꢀ=ꢀ8.8ꢀHz,ꢀ4H),ꢀ6.83ꢀ(d,ꢀJꢀ=ꢀ9.0ꢀHz,ꢀ8H),ꢀ3.94ꢀ(t,ꢀJꢀ=ꢀ7.2ꢀHz,ꢀ8H),ꢀ2.90ꢀ(q,ꢀ
Jꢀ=ꢀ7.2ꢀHz,ꢀ4H),ꢀ1.81-1.75ꢀ(m,ꢀ8H),ꢀ1.40-1.36ꢀ(m,ꢀ8H),ꢀ1.39ꢀ(t,ꢀJꢀ=ꢀ7.3ꢀHz,ꢀ6H),ꢀ1.35-1.26(m,ꢀ16H),ꢀ0.93-
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13
0
.90ꢀ(m,ꢀ12H).ꢀ CꢀNMRꢀ(125ꢀMHz,ꢀCDCl
3
)ꢀδꢀ155.6,ꢀ155.5,ꢀ147.9,ꢀ140.6,ꢀ138.3,ꢀ128.6,ꢀ128.0,ꢀ126.7,ꢀ126.1,ꢀ
-
1
1
20.4,ꢀ115.3,ꢀ68.3,ꢀ31.6,ꢀ29.4,ꢀ28.2,ꢀ25.8,ꢀ22.7,ꢀ14.1,ꢀ11.3.ꢀIRꢀ(neat,ꢀcm )ꢀ3849.5,ꢀ3746.4,ꢀ2921.7,ꢀ2859.8,ꢀ
1503.1,ꢀ1235.0.ꢀElementalꢀanalysisꢀforꢀC70
H
86
N
4
O
4
S:ꢀCalc.:ꢀC,ꢀ77.88%;ꢀH,ꢀ8.03%;ꢀN,ꢀ5.19%,ꢀfound:ꢀC,ꢀ
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+
7
8.15%;ꢀ H,ꢀ 8.03%;ꢀ N,ꢀ 5.02%.ꢀ HRMSꢀ (ESI)ꢀ m/zꢀ calcdꢀ forꢀ C70
H
86
N
4
O
4
Sꢀ (Mꢀ )ꢀ 1078.6370,ꢀ foundꢀ
0
1
078.6378.ꢀMeltingꢀpointꢀ91.1ꢀ C.ꢀ
Synthesisꢀ ofꢀ diethylꢀ 5,7-bis(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thieno[3,4-b]pyrazine-2,3-
dicarboxylateꢀ(TPz-CO Et):ꢀToꢀaꢀhighꢀvacuum-N ꢀ3xꢀcycledꢀvialꢀcontainingꢀ4bꢀ(50ꢀmg,ꢀ0.18ꢀmmol)ꢀ
wasꢀ addedꢀ (TPA-Br)ꢀ (190ꢀ mg,ꢀ 0.37ꢀ mmol),ꢀ X-Phosꢀ (17ꢀ mg,ꢀ 0.035ꢀ mmol),ꢀ Cs CO ꢀ (230ꢀ mg,ꢀ 0.70ꢀ
mmol),ꢀPd(OAc) ꢀ(3.9ꢀmg,ꢀ0.018ꢀmmol),ꢀandꢀSTSꢀdriedꢀtolueneꢀ(0.5ꢀmL)ꢀunderꢀanꢀN2ꢀatmosphere.ꢀ
2
2
2
3
2
0
Theꢀvialꢀwasꢀsealedꢀandꢀreactionꢀmixtureꢀwasꢀstirredꢀatꢀ120ꢀ Cꢀforꢀovernight.ꢀThenꢀtheꢀreactionꢀ
mixtureꢀ wasꢀ filteredꢀ throughꢀ thinꢀ padꢀ ofꢀ celiteꢀ withꢀ dichloromethane.ꢀ Theꢀ filtrateꢀ wasꢀ
concentratedꢀandꢀpurifiedꢀbyꢀsilicaꢀgelꢀchromatographyꢀusingꢀ100%ꢀchloroformꢀasꢀtheꢀeluentꢀtoꢀ
1
giveꢀaꢀgreenꢀcolorꢀsolidꢀ(68ꢀmg,ꢀ35%).ꢀ HꢀNMRꢀ(300ꢀMHz,ꢀCDCl
3
)ꢀδꢀ7.98ꢀ(d,ꢀJꢀ=ꢀ8.9ꢀHz,ꢀ4H),ꢀꢀ7.12ꢀ
(
d,ꢀJꢀ=ꢀ8.9ꢀHz,ꢀ8H),ꢀ6.99ꢀ(d,ꢀJꢀ=ꢀ8.9ꢀHz,ꢀ4H),ꢀ6.87ꢀ(d,ꢀJꢀ=ꢀ8.4,ꢀ8H),ꢀ4.48(q,ꢀJꢀ=ꢀ7.1ꢀHz,ꢀ4H),ꢀ3.97ꢀ(t,ꢀJꢀ=ꢀ
6
.5ꢀHz,ꢀ8H),ꢀ1.60-1.58ꢀ(m,ꢀ8H),ꢀ1.43-1.37ꢀ(m,ꢀ8H),ꢀ1.36-1.30ꢀ(m,ꢀ6H),ꢀ1.27-1.24ꢀ(m,ꢀ16H),ꢀ0.93-0.90ꢀ(m,ꢀ
1
3
3
12H).ꢀ CꢀNMRꢀ(300ꢀMHz,ꢀCDCl )ꢀδꢀ165.2,ꢀ156.1,ꢀ149.2,ꢀ142.4,ꢀ140.2,ꢀ136.8,ꢀ133.4,ꢀ128.7,ꢀ127.2,ꢀ124.4,ꢀ
-
1
1
1
19.9,ꢀ115.5,ꢀ68.4,ꢀ62.4,ꢀ31.7,ꢀ29.5,ꢀ25.9,ꢀ22.8,ꢀ14.3,ꢀ14.2.ꢀIRꢀ(neat,ꢀcm )ꢀ2927.4,ꢀ1720.7,ꢀ1597.4,ꢀ1502.3,ꢀ
468.4,1234.8,ꢀ 1150.0.ꢀ Elementalꢀ analysisꢀ forꢀ C72
H
86
N
4
O
8
S:ꢀ Calc.:ꢀ C,ꢀ 74.07%;ꢀ H,ꢀ 7.42%;ꢀ N,ꢀ 4.80%,ꢀ
+
found:ꢀ C,ꢀ 73.07%;ꢀ H,ꢀ 7.58%;ꢀ N,ꢀ 4.45%.ꢀ HRMSꢀ (ESI)ꢀ m/zꢀ calcdꢀ forꢀ C72
H
86
N
4
O
8
Sꢀ (Mꢀ )ꢀ 1166.6166,ꢀ
0
foundꢀ1166.6169.ꢀMeltingꢀpointꢀ139.2ꢀ C.ꢀ
Synthesisꢀ
hexyloxy)phenyl)aniline)ꢀ (TPz-Ph):ꢀToꢀaꢀhighꢀvacuum-N
0.17ꢀmmol)ꢀwasꢀaddedꢀ(TPA-Br)ꢀ(180ꢀmg,ꢀ0.35ꢀmmol),ꢀX-Phosꢀ(8.3ꢀmg,ꢀ0.017ꢀmmol),ꢀCs
2
mg,ꢀ0.35ꢀmmol),ꢀPd(OAc) ꢀ(2.0ꢀmg,ꢀ0.0087ꢀmmol),ꢀandꢀSTSꢀdriedꢀtolueneꢀ(1.5ꢀmL)ꢀunderꢀanꢀN ꢀ
ofꢀ
4,4'-(2,3-diphenylthieno[3,4-b]pyrazine-5,7-diyl)bis(N,N-bis(4-
ꢀ3xꢀcycledꢀvialꢀcontainingꢀ4cꢀ(50ꢀmg,ꢀ
CO ꢀ(110ꢀ
(
2
2
3
2
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Page 29 of 35
The Journal of Organic Chemistry
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2
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8
9
0
atmosphere.ꢀ Theꢀ vialꢀ wasꢀ sealedꢀ andꢀ reactionꢀ mixtureꢀ wasꢀ stirredꢀ atꢀ 120ꢀ Cꢀ forꢀ overnight.ꢀ Theꢀ
reactionꢀmixtureꢀwasꢀfilteredꢀthroughꢀthinꢀpadꢀofꢀceliteꢀwithꢀdichloromethane.ꢀTheꢀfiltrateꢀwasꢀ
concentratedꢀandꢀpurifiedꢀbyꢀflashꢀsilicaꢀgelꢀchromatographyꢀusingꢀ50%ꢀdichloromethane:hexanesꢀ
10
11
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60
1
toꢀgiveꢀaꢀpurpleꢀcolorꢀsolidꢀ(52ꢀmg,ꢀꢀ40.0%).ꢀ HꢀNMRꢀ(500ꢀMHz,ꢀCDCl
3
)ꢀδꢀ8.10ꢀ(d,ꢀJꢀ=ꢀ8.8ꢀHz,ꢀ4H),ꢀꢀ
7
.51ꢀ(d,ꢀJꢀ=ꢀ8.4ꢀHz,ꢀ4H),ꢀ7.33-7.26ꢀ(m,ꢀ6H),ꢀ7.11(d,ꢀJꢀ=ꢀ8.9ꢀHz,ꢀ8H),ꢀ7.01(d,ꢀJꢀ=ꢀ8.9ꢀHz,ꢀ4H),ꢀ6.85ꢀ(d,ꢀJꢀ=ꢀ
9.0ꢀHz,ꢀ8H),ꢀ3.95ꢀ(t,ꢀJꢀ=ꢀ6.5ꢀHz,ꢀ8H),ꢀ1.82-1.77ꢀ(m,ꢀ8H),ꢀ1.55-1.51ꢀ(m,ꢀ8H)ꢀ1.38-1.28ꢀ(m,ꢀ16H)ꢀ0.94-0.85ꢀ
1
3
(
m,ꢀ12H).ꢀ CꢀNMRꢀ(75ꢀMHz,ꢀCDCl
3
)ꢀδꢀ155.8,ꢀ151.9,ꢀ148.3,ꢀ140.5,ꢀ139.7,ꢀ138.1,ꢀ130.2,ꢀ130.0,ꢀ128.7,ꢀ128.4,ꢀ
S:ꢀ
1
28.1,ꢀ127.1,ꢀ125.8,ꢀ120.4,ꢀ115.4,ꢀ68.4,ꢀ31.8,ꢀ29.5,ꢀ25.9,ꢀ22.8,ꢀ14.2.ꢀElementalꢀanalysisꢀforꢀC78H N O
86 4 4
-
1
Calc.:ꢀC,ꢀ79.69%;ꢀH,ꢀ7.37%;ꢀN,ꢀ4.77%,ꢀfound:ꢀC,ꢀ78.84%;ꢀH,ꢀ7.46%;ꢀN,ꢀ4.71%.ꢀIRꢀ(neat,ꢀcm )ꢀ2925.8,ꢀ
+
2855.7,ꢀ 1499.0,ꢀ 1235.0.ꢀ HRMSꢀ (ESI)ꢀ m/zꢀ calcdꢀ forꢀ C78
H
86
N
4
O
4
Sꢀ (Mꢀ )ꢀ 1174.6370,ꢀ foundꢀ 1174.6376.ꢀ
0
Meltingꢀpointꢀ128.3ꢀ C.ꢀ
Synthesisꢀ
(hexyloxy)phenyl)aniline)ꢀꢀ (TPz-PhOMe):ꢀToꢀaꢀhighꢀvacuum-N
mg,ꢀ0.14ꢀmmol)ꢀwasꢀaddedꢀ(TPA-Br)ꢀ(150ꢀmg,ꢀ0.30ꢀmmol),ꢀX-Phosꢀ(6.8ꢀmg,ꢀ0.014ꢀmmol),ꢀCs
93ꢀmg,ꢀ0.29ꢀmmol),ꢀPd(OAc) ꢀ(1.6ꢀmg,ꢀ0.0072ꢀmmol),ꢀandꢀSTSꢀdriedꢀtolueneꢀ(1.5ꢀmL)ꢀunderꢀanꢀN
ofꢀ
4,4'-(2,3-bis(4-methoxyphenyl)thieno[3,4-b]pyrazine-5,7-diyl)bis(N,N-bis(4-
2
ꢀ3xꢀcycledꢀvialꢀcontainingꢀ4dꢀ(50ꢀ
2
CO
3
ꢀ
ꢀ
(
2
2
0
atmosphere.ꢀThenꢀtheꢀvialꢀwasꢀsealedꢀandꢀreactionꢀmixtureꢀwasꢀstirredꢀatꢀ120ꢀ Cꢀovernight.ꢀThenꢀ
theꢀreactionꢀmixtureꢀwasꢀfilteredꢀthroughꢀaꢀthinꢀpadꢀofꢀceliteꢀwithꢀdichloromethane.ꢀTheꢀfiltrateꢀ
wasꢀconcentratedꢀandꢀpurifiedꢀbyꢀsilicaꢀgelꢀchromatographyꢀusingꢀ50%ꢀdichloromethane:hexanesꢀ
1
wasꢀ theꢀ eluentꢀ toꢀ giveꢀ aꢀ blueꢀ colorꢀ solidꢀ (51ꢀ mg,ꢀ 50.0ꢀ %).ꢀ Forꢀ aꢀ resolvedꢀ Hꢀ NMRꢀ spectrum,ꢀ
additionꢀofꢀanꢀaqueousꢀbaseꢀwasꢀnecessaryꢀduringꢀdataꢀaquistion,ꢀpotentiallyꢀdueꢀtoꢀthisꢀmoleculeꢀ
uniquelyꢀstronglyꢀbindingꢀtraceꢀSiO
2
ꢀparticlesꢀafterꢀcolumꢀpurificationꢀtightly.ꢀSimpleꢀexctractionꢀ
withꢀ aꢀ baseꢀ afterꢀ silicaꢀ gelꢀ purificationꢀ didꢀ notꢀ leadꢀ toꢀ resolvedꢀ peaks.ꢀ Dueꢀ toꢀ theꢀ necessaryꢀ
1
3
additionꢀofꢀaꢀbaseꢀduringꢀNMRꢀsampleꢀaquisition,ꢀanꢀadiquateꢀ CꢀNMRꢀspectrumꢀcouldꢀnotꢀbeꢀ
obtainedꢀ dueꢀ toꢀ theꢀ presenceꢀ ofꢀ aꢀ largeꢀ baseꢀ signalꢀ inꢀ theꢀ spectrum.ꢀ Elementalꢀ analysisꢀ wasꢀ
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