Fluorogenic Ubiquinone Analogue for Monitoring Chemical and Biological Redox Processes

Article abstract of DOI:10.1021/jacs.6b06899

We report herein the synthesis and characterization of a fluorogenic analogue of ubiquinone designed to reversibly report on redox reactions in biological systems. The analogue, H₂B-Q, consists of the redox-active quinone segment found in ubiquinone, 2,3-dimethoxy-1,4-benzoquinone, coupled to a boron-dipyrromethene (BODIPY) fluorophore segment that both imparts lipophilicity in lieu of the isoprenyl tail of ubiquinone, and reports on redox changes at the quinone/quinol segment. Redox sensing is mediated by a photoinduced electron transfer intramolecular switch. In its reduced dihydroquinone form, H₂B-QH₂ is highly emissive in nonpolar media (quantum yields 55-66%), while once oxidized, the resulting quinone H₂B-Q emission is suppressed. Cyclic voltammetry of H₂B-Q shows two reversible, 1-electron reduction peaks at -1.05 V and -1.37 V (vs ferrocene) on par with those of ubiquinone. Chemical reduction of H₂B-Q by NaBH₄ resulted in >200 fold emission enhancement. H₂B-QH₂ is shown to react with peroxyl radicals, a form of reactive oxygen species (ROS) as well as to cooperatively interact with chromanol (the active segment of α-tocopherol). Kinetic analysis further shows the antioxidant reactivity of the nonfluorescent intermediate semiquinone. We anticipate that the H₂B-Q/H₂B-QH₂ off/on reversible couple may serve as a tool to monitor chemical redox processes in real-time and in a noninvasive manner.

Full text of DOI:10.1021/jacs.6b06899

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Article
Fluorogenic Ubiquinone Analogue for Monitoring
Chemical and Biological Redox Processes
Lana E. Greene, Robert Godin, and Gonzalo Cosa
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b06899 • Publication Date (Web): 10 Aug 2016
Downloaded from http://pubs.acs.org on August 14, 2016
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Journal of the American Chemical Society
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FluorogenicꢀUbiquinoneꢀAnalogueꢀforꢀMonitoringꢀChemicalꢀandꢀBio-
logicalꢀRedoxꢀProcessesꢀ
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LanaꢀE.ꢀGreene,ꢀRobertꢀGodin,ꢀandꢀGonzaloꢀCosa*.ꢀ
DepartmentꢀofꢀChemistryꢀandꢀCenterꢀforꢀSelfꢀAssembledꢀChemicalꢀStructuresꢀ(CSACS/CRMAA),ꢀMcGillꢀUniversity,ꢀ
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01ꢀSherbrookeꢀStreetꢀWest,ꢀMontreal,ꢀQuebecꢀH3Gꢀ0B8,ꢀCanada.ꢀꢀ
ABSTRACT:ꢀWeꢀreportꢀhereinꢀtheꢀsynthesisꢀandꢀcharacterizationꢀofꢀaꢀfluorogenicꢀanalogueꢀofꢀubiquinoneꢀdesignedꢀtoꢀ
reversiblyꢀreportꢀonꢀredoxꢀreactionsꢀinꢀbiologicalꢀsystems.ꢀTheꢀanalogue,ꢀH B-Q,ꢀconsistsꢀofꢀtheꢀredox-activeꢀquinoneꢀ
2
segmentꢀfoundꢀinꢀubiquinoneꢀ-2,3-dimethoxy-1,4-benzoquinone-,ꢀcoupledꢀtoꢀaꢀboron-dipyrrometheneꢀ(BODIPY)ꢀfluoro-
phoreꢀsegmentꢀthatꢀbothꢀimpartsꢀlipophilicityꢀinꢀlieuꢀofꢀtheꢀisoprenylꢀtailꢀofꢀubiquinone,ꢀandꢀreportsꢀonꢀredoxꢀchangesꢀatꢀ
theꢀquinone/quinolꢀsegment.ꢀRedoxꢀsensingꢀisꢀmediatedꢀbyꢀaꢀphotoinducedꢀelectronꢀtransferꢀintramolecularꢀswitch.ꢀInꢀitsꢀ
reducedꢀdihydroquinoneꢀform,ꢀH
dized,ꢀtheꢀresultingꢀquinoneꢀH B-Qꢀemissionꢀisꢀsupressed.ꢀCyclicꢀvoltammetryꢀofꢀH
reductionꢀpeaksꢀatꢀ-1.05ꢀVꢀandꢀ-1.37ꢀVꢀ(vsꢀferrocene)ꢀonꢀparꢀwithꢀthoseꢀofꢀubiquinone.ꢀChemicalꢀreductionꢀofꢀH
NaBH ꢀresultedꢀinꢀ>200ꢀfoldꢀemissionꢀenhancement.ꢀH B-QH2,ꢀisꢀshownꢀtoꢀreactꢀwithꢀperoxylꢀradicals,ꢀaꢀformꢀofꢀreactiveꢀ
2
B-QH
2
ꢀisꢀhighlyꢀemissiveꢀinꢀnon-polarꢀmediaꢀ(quantumꢀyieldsꢀ55-66%),ꢀwhileꢀonceꢀoxi-
B-Qꢀshowsꢀtwoꢀreversible,ꢀ1-electronꢀ
B-Qꢀbyꢀ
2
2
2
4
2
oxygenꢀspeciesꢀ(ROS)ꢀasꢀwellꢀasꢀtoꢀcooperativelyꢀinteractꢀwithꢀchromanolꢀ(theꢀactiveꢀsegmentꢀofꢀα-tocopherol).ꢀKineticꢀ
analysisꢀfurtherꢀshowsꢀtheꢀantioxidantꢀreactivityꢀofꢀtheꢀnon-fluorescentꢀintermediateꢀsemiquinone.ꢀWeꢀanticipateꢀthatꢀtheꢀ
H B-Q/ꢀH B-QH2ꢀoff/onꢀreversibleꢀcoupleꢀmayꢀserveꢀasꢀaꢀtoolꢀtoꢀmonitorꢀchemicalꢀredoxꢀprocessesꢀinꢀreal-timeꢀandꢀinꢀaꢀ
2 2
non-invasiveꢀmanner.ꢀ
INTRODUCTIONꢀ
eitherꢀbyꢀitselfꢀorꢀviaꢀregeneratingꢀotherꢀantioxidantsꢀsuchꢀ
7
,8
asꢀα-tocopherolꢀ(vitaminꢀE). ꢀTheꢀintermediateꢀubisem-
iquinoneꢀ radicalꢀ formedꢀ inꢀ theseꢀ processesꢀ isꢀ howeverꢀ
consideredꢀtoꢀpromoteꢀoxidationꢀthroughꢀdirectꢀreactionꢀ
withꢀ molecularꢀ oxygenꢀ toꢀ generateꢀ superoxideꢀ radicalꢀ
Theꢀmitochondrionꢀisꢀtheꢀmajorꢀproductionꢀsiteꢀofꢀcel-
lularꢀ energyꢀ duringꢀ aerobicꢀ respiration.ꢀ Followingꢀ elec-
tronꢀtransportꢀinꢀtheꢀelectronꢀtransportꢀchainꢀofꢀtheꢀinnerꢀ
mitochondrialꢀ membraneꢀ throughꢀ aꢀ seriesꢀ ofꢀ relayꢀ sys-
tems,ꢀelectronsꢀfromꢀe.g.ꢀNADH,ꢀandꢀsuccinateꢀareꢀtrans-
ferredꢀtoꢀoxygen,ꢀreducingꢀitꢀtoꢀwater,ꢀandꢀreleasingꢀener-
gy.ꢀ Thisꢀ energyꢀ isꢀ nextꢀ storedꢀ asꢀ aꢀ protonꢀ gradientꢀ andꢀ
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anion. ꢀ
Regularꢀ cellꢀ homeostasisꢀ isꢀ intrinsicallyꢀ associatedꢀ toꢀ
theꢀchemicalꢀactivityꢀofꢀubiquinoneꢀinꢀitsꢀtripleꢀroleꢀasꢀanꢀ
electronꢀandꢀprotonꢀcoupleꢀtransporter,ꢀandꢀasꢀanꢀantiox-
idant.ꢀNotꢀsurprisingly,ꢀaꢀnumberꢀofꢀpathologiesꢀareꢀasso-
1
ultimatelyꢀinꢀtheꢀformꢀofꢀadenosineꢀtriphosphateꢀ(ATP). ꢀꢀ
Theꢀ essentialꢀ co-factorꢀ ubiquinoneꢀ (coenzymeꢀ Q10),ꢀ
situatedꢀinꢀtheꢀhydrophobicꢀcoreꢀofꢀtheꢀinnerꢀmitochon-
drialꢀ membraneꢀ lipidꢀ bilayerꢀ isꢀ activelyꢀ involvedꢀ inꢀ theꢀ
transportꢀofꢀtheꢀelectronsꢀthroughꢀtheꢀmembrane.ꢀDueꢀtoꢀ
itsꢀ lipophilicityꢀ andꢀ itsꢀ redoxꢀ reversibility,ꢀ ubiquinoneꢀ
mayꢀserveꢀasꢀbothꢀaꢀmobileꢀtransporterꢀofꢀelectronsꢀinꢀtheꢀ
redoxꢀreactionsꢀofꢀtheꢀelectronꢀtransportꢀchain,ꢀandꢀasꢀaꢀ
hydrogenꢀcarrierꢀtoꢀcreateꢀaꢀprotonꢀgradientꢀbetweenꢀtheꢀ
mitochondrialꢀ matrixꢀ andꢀ theꢀ mitochondrialꢀ intermem-
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ciatedꢀwithꢀubiquinoneꢀdeficiency. ꢀKeyꢀtoꢀunderstand-
ingꢀtheꢀcomplexꢀroleꢀofꢀubiquinoneꢀandꢀitsꢀassociationꢀtoꢀ
disease,ꢀasꢀwellꢀasꢀtheꢀpalliativeꢀeffectꢀofꢀnewꢀdrugs,ꢀisꢀtheꢀ
availabilityꢀofꢀprobesꢀwithꢀtheꢀproperꢀchemicalꢀselectivityꢀ
andꢀenhancedꢀsensitivityꢀtowardꢀmonitoringꢀtheꢀcomplexꢀ
redoxꢀ pathwaysꢀ ofꢀ quinonesꢀ inꢀ biologicalꢀ systemsꢀ real-
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time,ꢀinꢀsituꢀandꢀinꢀaꢀnon-perturbingꢀmanner. ꢀꢀ
Hereꢀweꢀdescribeꢀtheꢀdesign,ꢀpreparation,ꢀandꢀcharac-
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braneꢀ space. ꢀ Importantly,ꢀ ubiquinoneꢀ hasꢀ threeꢀ redoxꢀ
states:ꢀubiquinoneꢀ(oxidized),ꢀubisemiquinoneꢀ(1ꢀelectronꢀ
reductionꢀfromꢀubiquinoneꢀtoꢀyieldꢀaꢀsemiquinoneꢀradi-
cal),ꢀ andꢀ ubiquinolꢀ (2ꢀ electronꢀ reducedꢀ form).ꢀ Variousꢀ
protonationꢀstatesꢀareꢀalsoꢀpossibleꢀforꢀtheꢀreducedꢀspe-
cies,ꢀleadingꢀtoꢀcomplexꢀproton-coupledꢀelectronꢀtransferꢀ
terizationꢀ ofꢀ aꢀ two-segmentꢀ -receptor-reporter- ꢀ fluoro-
genicꢀanalogueꢀofꢀubiquinoneꢀconceivedꢀtoꢀreportꢀonꢀtheꢀ
redoxꢀstatusꢀofꢀcellularꢀenvironments.ꢀTheꢀnewꢀprobeꢀwasꢀ
obtainedꢀ uponꢀ covalentlyꢀ bindingꢀ 2,3-dimethoxy-1-4-
benzoquinone,ꢀ theꢀ redox-activeꢀ quinoneꢀ segmentꢀ foundꢀ
inꢀubiquinoneꢀ(receptorꢀsegment),ꢀtoꢀaꢀlipophilicꢀboron-
dipyrrometheneꢀ (BODIPY)ꢀ fluorophoreꢀ (reporterꢀ seg-
ment).ꢀ Theꢀ newꢀ compoundꢀ exploitsꢀ activa-
tion/deactivationꢀ ofꢀ photoinducedꢀ electronꢀ transferꢀ
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processes. ꢀ Besidesꢀ actingꢀ asꢀ aꢀ transporterꢀ ofꢀ electronsꢀ
andꢀprotonsꢀinꢀtheꢀelectronꢀtransportꢀchain,ꢀubiquinolꢀisꢀ
alsoꢀinvolvedꢀinꢀpreventingꢀlipidꢀperoxidationꢀwithinꢀtheꢀ
mitochondrialꢀ membraneꢀ viaꢀ trappingꢀ peroxylꢀ radicalsꢀ
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(PeT) ꢀbetweenꢀtheꢀtrapꢀandꢀreporterꢀsegmentsꢀtoꢀswitchꢀ
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Journal of the American Chemical Society
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off/onꢀ theꢀ emissionꢀ fromꢀ theꢀ BODIPYꢀ coreꢀ yieldingꢀ aꢀ
Schemeꢀ 1:ꢀ A)ꢀ Structureꢀ ofꢀ Ubiquinoneꢀ B)ꢀ Proposedꢀ
off/onꢀsensingꢀmechanismꢀforꢀH B-QꢀrelyingꢀonꢀPeT.ꢀꢀ
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highlyꢀsensitiveꢀprobeꢀofꢀredoxꢀstatus.ꢀCyclicꢀvoltammo-
gramꢀ experimentsꢀ conductedꢀ inꢀ organicꢀ solutionsꢀ con-
firmedꢀthatꢀtheꢀredoxꢀpotentialsꢀforꢀtheꢀquinoneꢀsegmentꢀ
ofꢀtheꢀnewꢀprobeꢀareꢀonꢀparꢀwithꢀthoseꢀreportedꢀforꢀubiq-
uinone.ꢀ Redoxꢀ chemicalꢀ reactionsꢀ conductedꢀ inꢀ bulkꢀ inꢀ
theꢀ presenceꢀ ofꢀ reducingꢀ andꢀ oxidizingꢀ agentsꢀ validatedꢀ
theꢀ fluorogenicꢀ characterꢀ ofꢀ theꢀ probe,ꢀ itsꢀ sensitivityꢀ toꢀ
redoxꢀ processesꢀ andꢀ itsꢀ reversibleꢀ nature.ꢀ Experimentsꢀ
withꢀbothꢀperoxylꢀradicalsꢀandꢀaꢀfluorogenicꢀanalogueꢀofꢀ
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α-tocopherolꢀ previouslyꢀ reportedꢀ byꢀ usꢀ (H B-PMHC) ꢀ
confirmedꢀ thatꢀ theꢀ quinolꢀ segmentꢀ regeneratesꢀ chroma-
nolꢀ asꢀ wellꢀ asꢀ competitivelyꢀ scavengesꢀ freeꢀ radicals.ꢀ Theꢀ
newꢀ probe,ꢀ forꢀ whichꢀ weꢀ haveꢀ coinedꢀ theꢀ nameꢀ H B-Q,ꢀ
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appropriatelyꢀ emulatesꢀ theꢀ partitioningꢀ andꢀ reactivityꢀ ofꢀ
ubiquinoneꢀandꢀdisplaysꢀdesirableꢀfluorescenceꢀsensitivi-
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ty.ꢀWeꢀanticipateꢀthatꢀH B-Qꢀmayꢀserveꢀasꢀaꢀtoolꢀtoꢀimageꢀ
redoxꢀprocesses,ꢀpotentiallyꢀincludingꢀtheꢀcellularꢀlevel,ꢀinꢀ
real-timeꢀandꢀinꢀaꢀnon-invasiveꢀmanner.ꢀ
RESULTSꢀANDꢀDISCUSSIONꢀ
Designꢀ
Ourꢀ
designꢀ
incorporatedꢀ
2,3-Dimethoxy-1,4-
benzoquinone,ꢀ theꢀ activeꢀ partꢀ ofꢀ ubiquinone,ꢀ asꢀ theꢀ re-
dox-sensitiveꢀreceptorꢀsegmentꢀtoꢀemulateꢀbothꢀtheꢀredoxꢀ
propertiesꢀ andꢀ theꢀ antioxidantꢀ activityꢀ ofꢀ theꢀ ubiqui-
none/ubiquinolꢀ redoxꢀ couple.ꢀ Ourꢀ designꢀ furtherꢀ envi-
sionedꢀ aꢀ BODIPYꢀ lipophilicꢀ fluorophoreꢀ asꢀ aꢀ reporterꢀ
segmentꢀ inꢀ lieuꢀ ofꢀ theꢀ isoprenoidꢀ tailꢀ ofꢀ ubiquinone,ꢀ toꢀ
preserveꢀinꢀtheꢀnewꢀprobeꢀtheꢀpreferentialꢀpartitioningꢀofꢀ
ꢀ
Synthesisꢀꢀ
Ourꢀpreparationꢀinvolvedꢀaꢀconvergentꢀsynthesisꢀwhereꢀ
theꢀBODIPYꢀdyeꢀandꢀaꢀprecursorꢀofꢀtheꢀredoxꢀactiveꢀqui-
noneꢀsegmentꢀwereꢀpreparedꢀseparatelyꢀandꢀnextꢀcoupledꢀ
viaꢀKnoevenagelꢀcondensation.ꢀAꢀBODIPY-phenolꢀconju-
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ubiquinoneꢀwithinꢀlipidꢀmembranes. ꢀInꢀadditionꢀtoꢀtheꢀ
2
gateꢀ(H B-phenol)ꢀwasꢀthusꢀinitiallyꢀpreparedꢀwhereꢀtheꢀ
desirableꢀlipophilicꢀcharacter,ꢀBODIPYꢀfluorophoresꢀhaveꢀ
phenolꢀ segmentꢀ carriedꢀ aꢀ freeꢀ paraꢀ positionꢀ thatꢀ wouldꢀ
nextꢀ beꢀ oxidizedꢀ toꢀ theꢀ desiredꢀ quinone.ꢀ Thisꢀ strategyꢀ
circumventedꢀtheꢀchallengesꢀassociatedꢀwithꢀtheꢀsynthesisꢀ
andꢀ purificationꢀ ofꢀ dihydroquinonesꢀ (proneꢀ toꢀ auto-
oxidation)ꢀandꢀquinonesꢀ(Michaelꢀacceptorsꢀproneꢀtoꢀnu-
cleophilicꢀattack).ꢀꢀ
optimalꢀspectroscopicꢀpropertiesꢀandꢀareꢀeasilyꢀmodifiedꢀ
23-25
syntheticallyꢀtoꢀaccommodateꢀgroupsꢀofꢀinterest.
Fur-
thermore,ꢀ theꢀ redoxꢀ propertiesꢀ ofꢀ BODIPYꢀ dyesꢀ canꢀ beꢀ
tunedꢀtoꢀfacilitateꢀexergonicꢀPeTꢀinꢀorderꢀtoꢀimpartꢀaꢀfluo-
rescenceꢀ‘off-on’ꢀswitchingꢀmechanismꢀinꢀtheꢀredoxꢀprobeꢀ
andꢀensureꢀaꢀhighꢀcontrastꢀbetweenꢀoffꢀ(oxidized)ꢀandꢀonꢀ
21,26
(
reduced)ꢀstates. ꢀꢀ
Compoundꢀ1ꢀwasꢀchosenꢀasꢀourꢀstartingꢀmaterialꢀforꢀtheꢀ
synthesisꢀ ofꢀ theꢀ precursorꢀ ofꢀ theꢀ redoxꢀ activeꢀ quinoneꢀ
segment,ꢀ whereꢀ aꢀ formylꢀ moietyꢀ wasꢀ installedꢀ usingꢀ theꢀ
Vilsmeier-Haackꢀ reactionꢀ accordingꢀ toꢀ literatureꢀ proce-
ToꢀcalculateꢀandꢀvisualizeꢀtheꢀHOMO,ꢀLUMO,ꢀHOMO-
1
ꢀ andꢀ LUMO+1ꢀ ofꢀ theꢀ optimizedꢀ geometriesꢀ ofꢀ H
2
B-Qꢀ
(
oxidized)ꢀ andꢀ H B-QH2ꢀ (reduced),ꢀ andꢀ toꢀ predictꢀ theꢀ
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duresꢀ (Schemeꢀ 2). ꢀ Theꢀ methoxyꢀ groupꢀ orthoꢀ toꢀ theꢀ
potentialꢀforꢀPeT,ꢀweꢀemployedꢀdensityꢀfunctionalꢀtheoryꢀ
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formylꢀmoietyꢀwasꢀselectivelyꢀde-methylatedꢀusingꢀboronꢀ
(
DFT)ꢀcalculationsꢀatꢀtheꢀB3LYPꢀ6-31G(d)ꢀlevel ꢀ(Figuresꢀ
S1,ꢀS2).ꢀOurꢀresultsꢀsuggestꢀanꢀoperatingꢀPeTꢀmechanismꢀ
forꢀH B-QꢀbutꢀnotꢀforꢀH B-QH ꢀandꢀwasꢀexperimentallyꢀ
validatedꢀ (seeꢀ Spectroscopicꢀ Properties).ꢀ Hereꢀ theꢀ oxi-
dizedꢀ formꢀ (H B-Q)ꢀ isꢀ quenchedꢀ dueꢀ toꢀ PeTꢀ fromꢀ theꢀ
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tribromide. ꢀ Removalꢀ ofꢀ thisꢀ methoxyꢀ groupꢀ yieldedꢀ
compoundꢀ 2ꢀ withꢀ theꢀ desiredꢀ freeꢀ phenolꢀ bearingꢀ aꢀ
formylꢀ moietyꢀ neededꢀ forꢀ couplingꢀ toꢀ BODIPYꢀ 5ꢀ viaꢀ
Knoevenagelꢀcondensationꢀ(videꢀinfra).ꢀTheꢀBODIPYꢀdyeꢀ5ꢀ
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2
2
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wasꢀsynthesisedꢀfromꢀ3ꢀandꢀ4ꢀfollowingꢀtheꢀliterature. ꢀꢀ
photoexcitedꢀBODIPYꢀtoꢀtheꢀLUMOꢀofꢀtheꢀquinoneꢀmoie-
tyꢀ (BODIPYꢀ photoinducedꢀ oxidation,ꢀ Schemeꢀ 1).ꢀ Reduc-
Inꢀ orderꢀ toꢀ coupleꢀ phenolꢀ 2ꢀ andꢀ BODIPYꢀ 5ꢀ weꢀ em-
32
tionꢀ ofꢀ theꢀ quinoneꢀ toꢀ theꢀ dihydroquinoneꢀ (H
2
B-QH
2
)ꢀ
ployedꢀ aꢀ Knoevenagelꢀ condensation ꢀ inꢀ theꢀ presenceꢀ ofꢀ
deactivatesꢀ PeTꢀ andꢀ restoresꢀ emissionꢀ byꢀ raisingꢀ theꢀ
HOMOꢀandꢀLUMOꢀofꢀtheꢀubiquinolꢀsegmentꢀpreventingꢀ
efficientꢀelectronꢀtransferꢀfromꢀtheꢀBODIPYꢀdye.ꢀ
4-methyl-piperidineꢀ andꢀ glacialꢀ aceticꢀ acidꢀ toꢀ giveꢀ H
phenolꢀ asꢀ aꢀ fluorescentꢀ dye.ꢀ Subsequentꢀ oxidationꢀ ofꢀ
B-phenolꢀ toꢀ giveꢀ theꢀ correspondingꢀ non-fluorescentꢀ
quinoneꢀ(H B-Q)ꢀwasꢀperformedꢀusingꢀcatalyticꢀamountsꢀ
ofꢀ theꢀ cobaltꢀ catalystꢀ salcomine.ꢀ H B-Qꢀ wasꢀ finallyꢀ re-
ducedꢀ toꢀ theꢀ correspondingꢀ dihydroquinone,ꢀ H B-QH
2
B-
H
2
2
ꢀ
ꢀ
ꢀ
2
2
2
ꢀ
throughꢀ inꢀ situꢀ productionꢀ ofꢀ hydrogenꢀ gasꢀ fromꢀ cyclo-
hexeneꢀinꢀtheꢀpresenceꢀofꢀpalladiumꢀcatalyst.ꢀꢀ
ACS Paragon Plus Environment

Page 3 of 10
Schemeꢀ2:ꢀSynthesisꢀofꢀH
Journal of the American Chemical Society
2
B-phenol,ꢀH
2
B-Q,ꢀandꢀH
2
2
B-QH .ꢀ
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
H
O
1
) POCl3 DMF 99%
2) 0.9 eq BBr3 DCM 96%
MeO
OMe
MeO
OH
OMe
2
Methyl-Piperidine
AcOH
Toluene, reflux
Dean-Stark apparatus
OMe
N
N
B
1
F
F
5
h 35%
OH
OMe
OMe
TFA
1) 2,4-dimethylpyrrole
POCl3, DCM
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
TMOF
5%
O
8
H2B-phenol
2) DIPEA, Toluene
3) BF3(OEt2) 96%
N
N
N
H
N
H
B
H
F
F
3
4
5
N
N
N
N
N
N
B
B
B
0
1
.2 eq Salcomine
atm O2
Pd/C Cyclohexene
MeOH/THF, 50%
F
F
F
F
F
F
OH
O
OH
OMe
OMe
2.5 h 45%
OMe
OMe
OMe
OMe
H B-phenol
H B-Q
H B-QH2
2
2
2
O
HO
ꢀ
ꢀ
ꢀ
SpectroscopicꢀPropertiesꢀ
Theꢀ absorptionꢀ andꢀ fluorescenceꢀ maxima,ꢀ fluores-
cenceꢀquantumꢀyieldsꢀ(ɸ ),ꢀabsorptionꢀextinctionꢀcoeffi-
cientsꢀ andꢀ fluorescenceꢀ decayꢀ lifetimesꢀ (τdec)ꢀ ofꢀ H B-
phenol,ꢀH B-Q,ꢀandꢀH B-QH2ꢀareꢀlistedꢀinꢀTableꢀ1.ꢀTheꢀ
dyesꢀpreparedꢀhereꢀareꢀcharacterizedꢀbyꢀredꢀshiftedꢀab-
2 2
Tableꢀ1:ꢀSpectroscopicꢀpropertiesꢀofꢀH B-phenol,ꢀH B-
QꢀandꢀH
2
B-QH
2
ꢀinꢀvariousꢀsolventsꢀ
f
3
Dyeꢀ
Solventꢀ Absꢀ Emꢀ εꢀxꢀ10 ꢀ
ɸ
fꢀ
dec
τ ꢀ
(ns)ꢀ
2
-
λ
maxꢀ
λ
max
ꢀ
(M
2
2
1
-1
cm )ꢀ
31
sorptionꢀ (ca.ꢀ 580ꢀ nm)ꢀ comparedꢀ toꢀ precursorꢀ 5 ꢀ (505ꢀ
nm)ꢀ dueꢀ toꢀ theꢀ extendedꢀ conjugationꢀ ofꢀ theꢀ BODIPYꢀ
resultingꢀ uponꢀ theꢀ Knoevenagelꢀ condensationꢀ whichꢀ
H B-
MeCNꢀ
574ꢀ 602ꢀ
91ꢀ
0.65ꢀ 3.84ꢀ
2
phenolꢀ
ꢀ
ꢀ
Tolueneꢀ 584ꢀ 597ꢀ
95ꢀ
89ꢀ
35ꢀ
37ꢀ
34ꢀ
45ꢀ
51ꢀ
0.88ꢀ 3.67ꢀ
0.80ꢀ 3.83ꢀ
<0.01ꢀ N/Aꢀ
0.02ꢀ 0.37ꢀ
<ꢀ0.01ꢀ N/Aꢀ
0.01ꢀ N/Aꢀ
0.66ꢀ 3.62ꢀ
0.55ꢀ 3.16ꢀ
installsꢀanꢀarylvinylꢀmoietyꢀbond.ꢀH
QH2ꢀ bothꢀ exhibitꢀ aꢀ weakꢀ absorptionꢀ bandꢀ aroundꢀ 330ꢀ
nmꢀ correspondingꢀ toꢀ theꢀ arylꢀ group,ꢀ whileꢀ H B-Qꢀ ex-
2 2
B-phenolꢀandꢀH B-
DCMꢀ
582ꢀ 595ꢀ
H
2
B-Qꢀ
MeCNꢀ
573ꢀ N/Aꢀ
2
hibitsꢀaꢀstrongꢀabsorptionꢀbandꢀatꢀ287ꢀnmꢀcorrespond-
ingꢀtoꢀtheꢀquinoneꢀmoietyꢀ(FigureꢀS3),ꢀinꢀlineꢀwithꢀpre-
aꢀ
ꢀ
ꢀ
Tolueneꢀ 583ꢀ 740
3
3
DCMꢀ
582ꢀ N/Aꢀ
572ꢀ 592ꢀ
viousꢀopticalꢀinvestigationꢀofꢀubiquinones. ꢀꢀ
AsꢀpredictedꢀbyꢀtheꢀDFTꢀcalculations,ꢀH B-Qꢀisꢀnon-
emissiveꢀ inꢀ polarꢀ (acetonitrile)ꢀ andꢀ non-polarꢀ (di-
cholormethane)ꢀ solvents.ꢀ H B-phenolꢀ isꢀ veryꢀ fluores-
centꢀinꢀallꢀsolventsꢀstudied,ꢀH B-QH ꢀisꢀhighlyꢀfluores-
centꢀinꢀnon-polarꢀsolvents,ꢀwithꢀquantumꢀyieldsꢀrangingꢀ
fromꢀ 55%-66%.ꢀ Inꢀ polarꢀ solventsꢀ suchꢀ asꢀ acetonitrileꢀ
2 2
however,ꢀtheꢀemissionꢀofꢀH B-QH ꢀisꢀreducedꢀ(quantumꢀ
yieldꢀ~ꢀ1%).ꢀWeꢀpostulateꢀthatꢀPeTꢀfromꢀtheꢀHOMOꢀofꢀ
theꢀ dihydroquinoneꢀ moietyꢀ toꢀ theꢀ photo-excitedꢀ
BODIPYꢀ segmentꢀ (BODIPYꢀ photoinducedꢀ reduction)ꢀ
readilyꢀ occursꢀ inꢀ polarꢀ solventsꢀ whereꢀ chargeꢀ transferꢀ
andꢀformationꢀofꢀradicalꢀionsꢀisꢀstabilizedꢀInꢀsummary,ꢀ
B-Qꢀisꢀnonꢀemissiveꢀwhile,ꢀasꢀperꢀ
B-QH ꢀ displaysꢀ desirableꢀ
emission.ꢀTheꢀsoughtꢀafterꢀredox-mediatedꢀoff/onꢀfluo-
rescenceꢀswitchingꢀisꢀobservedꢀinꢀdichloromethaneꢀandꢀ
tolueneꢀsolvents.ꢀ
H
2
B-QH
2
ꢀ
MeCNꢀ
2
ꢀ
ꢀ
Tolueneꢀ 582ꢀ 595ꢀ
DCMꢀ 579ꢀ 595ꢀ
2
41ꢀ
2
2
a
Theꢀsignificantꢀdifferencesꢀinꢀemissionꢀpropertiesꢀinꢀtol-
uene,ꢀnamelyꢀaꢀlargeꢀStoke’sꢀshift,ꢀshortꢀlifetime,ꢀandꢀsol-
ventꢀ dependence,ꢀ indicateꢀ aꢀ probableꢀ changeꢀ inꢀ emissionꢀ
mechanismꢀ whichꢀ weꢀ tentativelyꢀ proposeꢀ toꢀ beꢀ intramo-
34
lecularꢀchargeꢀtransferꢀemission. ꢀ
ElectrochemicalꢀPropertiesꢀ
Inꢀorderꢀtoꢀverifyꢀtheꢀelectrochemicalꢀreversibilityꢀofꢀ
H
2
B-Q,ꢀ cyclicꢀ voltammetryꢀ wasꢀ employedꢀ toꢀ measureꢀ
theꢀ redoxꢀ characteristicsꢀ ofꢀ H B-Q.ꢀ H B-Qꢀ (0.7ꢀ mM)ꢀ
theꢀoxidizedꢀform,ꢀH
design,ꢀ theꢀ reducedꢀ form,ꢀ H
2
2
2
2
2
wasꢀ dissolvedꢀ inꢀ argon-spargedꢀ 10%ꢀ v/vꢀ acetonitrileꢀ inꢀ
tolueneꢀ solutionꢀ withꢀ 0.1ꢀ Mꢀ tetrabutylammoniumꢀ hex-
afluorophosphateꢀ asꢀ theꢀ supportingꢀ electrolyte.ꢀ Theꢀ
Ferrocenium/Ferroceneꢀ(Fc /Fc)ꢀredoxꢀcoupleꢀwasꢀusedꢀ
toꢀcalibrateꢀtheꢀsilver/silverꢀchlorideꢀreferenceꢀelectrodeꢀ
+
ꢀ
2
used.ꢀTheꢀcyclicꢀvoltammogramꢀofꢀH B-Qꢀoverꢀ6ꢀscansꢀ
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 10
isꢀ shownꢀ inꢀ Figureꢀ 1.ꢀ Twoꢀ separateꢀ andꢀ reversibleꢀ oneꢀ
electronꢀredoxꢀprocessesꢀwereꢀobserved,ꢀinꢀlineꢀwithꢀtheꢀ
electrochemicalꢀbehaviorꢀofꢀquinonesꢀinꢀaproticꢀmedia. ꢀ
Theꢀfirstꢀredoxꢀprocessꢀcorrespondsꢀtoꢀtheꢀreductionꢀofꢀ
Schemeꢀ 3:ꢀ Oneꢀ potꢀ reductionꢀ andꢀ subsequentꢀ oxi-
dationꢀofꢀH BQꢀꢀ
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
35
1 mg/mL NaBH4
.1 µL/mL H O
0
2
H
1
2
B-Qꢀtoꢀitsꢀsemiquinoneꢀradicalꢀformꢀandꢀoccursꢀatꢀ-
.05ꢀVꢀ(vs.ꢀferrocene),ꢀinꢀaccordanceꢀwithꢀreportedꢀval-
1
h
H B-Q
2
H B-QH2
36
2
uesꢀforꢀubiquinoneꢀ(-1.1ꢀVꢀvs.ꢀferroceneꢀinꢀDMF). ꢀTheꢀ
secondꢀprocessꢀisꢀtheꢀsubsequentꢀreductionꢀofꢀtheꢀsem-
1 mM TEMPO
o
2-
40 C
iquinoneꢀradicalꢀtoꢀH
1.37ꢀVꢀ(vs.ꢀferrocene),ꢀatꢀmoreꢀpositiveꢀbiasꢀthanꢀwhatꢀ
hasꢀbeenꢀreportedꢀforꢀubiquinoneꢀ(-1.8ꢀVꢀvs.ꢀferroceneꢀinꢀ
2 ꢀ 2 2
B-Q (deprotonatedꢀH B-QH )ꢀatꢀ
2
h
ꢀ
-
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
Theꢀ fluorescenceꢀ spectraꢀ ofꢀ theꢀ startingꢀ solutionꢀ ofꢀ
B-Q,ꢀ1.3ꢀμMꢀinꢀtoluene,ꢀandꢀthoseꢀfollowingꢀchemicalꢀ
reductionꢀandꢀoxidationꢀareꢀshownꢀinꢀFigureꢀ2.ꢀInꢀaꢀcu-
vette,ꢀ H B-Qꢀ wasꢀ reducedꢀ atꢀ roomꢀ temperatureꢀ overꢀ
NaBH ꢀ(1ꢀmg/mL)ꢀwithꢀtheꢀadditionꢀofꢀaꢀsmallꢀamountꢀ
36
H
2
DMF,ꢀnoꢀisoprenoidꢀtail). ꢀWeꢀattributeꢀanꢀeasierꢀ(lessꢀ
negative)ꢀ secondꢀ reductionꢀ toꢀ theꢀ conjugationꢀ ofꢀ theꢀ
quinoneꢀ moietyꢀ toꢀ theꢀ BODIPYꢀ core.ꢀ Theꢀ radicalꢀ di-
anionꢀformedꢀafterꢀtwoꢀsubsequentꢀreductionsꢀisꢀstabi-
lizedꢀviaꢀresonanceꢀthroughꢀtheꢀBODIPYꢀcore,ꢀeffective-
lyꢀfacilitatingꢀtheꢀsecondꢀreductionꢀofꢀtheꢀquinoneꢀmoi-
ety.ꢀ Theꢀ peakꢀ currentꢀ ratiosꢀ (ipa/ipc)ꢀ wereꢀ estimatedꢀ toꢀ
beꢀ aroundꢀ 0.93ꢀ each,ꢀ approximatelyꢀ unity,ꢀ indicatingꢀ
thatꢀtheꢀradicalꢀanionꢀandꢀdi-anionꢀwereꢀstableꢀandꢀthatꢀ
noꢀ additionalꢀ reactionsꢀ tookꢀ place.ꢀ Sequentialꢀ reduc-
tion/oxidationꢀoverꢀ6ꢀscansꢀwereꢀperformedꢀtoꢀshowꢀtheꢀ
2
4
ofꢀwaterꢀ(1ꢀμL/mL),ꢀactingꢀasꢀaꢀsourceꢀofꢀprotons,ꢀtoꢀac-
celerateꢀtheꢀreaction.ꢀTheꢀincreasingꢀfluorescenceꢀinten-
sityꢀ wasꢀ periodicallyꢀ monitoredꢀ toꢀ determineꢀ reactionꢀ
completion.ꢀ Maximalꢀ fluorescenceꢀ wasꢀ observedꢀ afterꢀ
8
0ꢀminutesꢀ(Figureꢀ2,ꢀredꢀtrace),ꢀatꢀwhichꢀpointꢀtheꢀin-
solubleꢀNaBH4ꢀwasꢀfilteredꢀout.ꢀTheꢀspectroscopicꢀprop-
ertiesꢀofꢀtheꢀreductionꢀproductꢀmatchedꢀthoseꢀofꢀisolat-
edꢀH B-QH ,ꢀconfirmingꢀtheꢀproductꢀofꢀhydrideꢀreduc-
2 2
tion.ꢀSignificantly,ꢀaꢀ200-foldꢀfluorescenceꢀenhancementꢀ
wasꢀ measuredꢀ followingꢀ completionꢀ ofꢀ theꢀ reductionꢀ
reaction,ꢀdemonstratingꢀtheꢀremarkableꢀon/offꢀfluores-
cenceꢀratioꢀofꢀtheꢀprobe.ꢀ
highꢀ electrochemicalꢀ reversibilityꢀ ofꢀ H
2
B-Qꢀ andꢀ henceꢀ
itsꢀpotentialꢀutilityꢀasꢀaꢀredox-reversibleꢀprobe.ꢀꢀ
-6
4.0x10
-6
2.0x10
Followingꢀconfirmationꢀofꢀtheꢀreductionꢀproduct,ꢀtheꢀ
resultingꢀ H
2 2
B-QH ꢀ wasꢀ nextꢀ oxidizedꢀ byꢀ addingꢀ 1ꢀ mMꢀ
0.0
TEMPOꢀ toꢀ theꢀ sameꢀ cuvette.ꢀ TEMPOꢀ aerobicꢀ
-
6
6
6
37
oxidation ꢀwasꢀusedꢀtoꢀreconvertꢀH
darkꢀH B-Qꢀstate.ꢀTheꢀminimumꢀfluorescenceꢀintensityꢀ
wasꢀobservedꢀafterꢀ2.5ꢀhoursꢀatꢀ40ꢀ°C.ꢀTheꢀabsorptionꢀofꢀ
theꢀsolutionꢀatꢀthisꢀpointꢀmatchedꢀthatꢀofꢀpristineꢀH B-
2 2
B-QH ꢀtoꢀtheꢀinitialꢀ
-
-
-
2.0x10
2
-
4.0x10
-
2
6.0x10
Qꢀconfirmingꢀtheꢀsuccessꢀofꢀtheꢀoxidation.ꢀWeꢀestimateꢀ
anꢀ overallꢀ yieldꢀ ofꢀ 52%ꢀ forꢀ theꢀ fullꢀ chemicalꢀ reduc-
tion/oxidationꢀ cycleꢀ byꢀ comparingꢀ theꢀ initialꢀ andꢀ finalꢀ
-2.0
-1.5
-1.0
-0.5
Potential (V) vs Ferrocence
absorbancesꢀatꢀ640ꢀnm,ꢀwhereꢀtheꢀcontributionꢀofꢀH
2
B-
ꢀ
QH ꢀandꢀTEMPOꢀisꢀnegligibleꢀ(FigureꢀS4).ꢀAtꢀtheꢀendꢀofꢀ
2
Figureꢀ 1:ꢀ Cyclicꢀ Voltammogramꢀ ofꢀ H
solvedꢀ inꢀ 10%ꢀ v/vꢀ MeCNꢀ inꢀ Tolueneꢀ (0.1ꢀ Mꢀ tetrabu-
tylammoniumꢀhexafluorophosphate)ꢀunderꢀargonꢀrecordedꢀ
2
B-Qꢀ (0.7ꢀ mM)ꢀ dis-
theꢀoxidation,ꢀaꢀresidualꢀfluorescenceꢀwasꢀobservedꢀwithꢀ
aꢀ peakꢀ atꢀ 606ꢀ nmꢀ (opposedꢀ toꢀ 595ꢀ nmꢀ forꢀ H B-QH ),ꢀ
2
2
whichꢀ weꢀ attributeꢀ toꢀ sideꢀ productsꢀ fromꢀ theꢀ TEMPOꢀ
oxidationꢀreaction.ꢀ
-1
atꢀ 100ꢀ mVs .ꢀ Potentialsꢀ wereꢀ normalizedꢀ toꢀ theꢀ ferroceneꢀ
oxidationꢀinꢀtheseꢀconditions.ꢀ
ꢀ
RedoxꢀReversibilityꢀ
6
3
2
1
x10
Afterꢀdemonstratingꢀtheꢀelectrochemicalꢀreversibilityꢀ
H B-Q
2
ofꢀH
bilityꢀ ofꢀ theꢀ H
2
B-Q,ꢀweꢀnextꢀsoughtꢀtoꢀtestꢀtheꢀchemicalꢀreversi-
H B-Q + NaBH4
6
2
2
B-Q/H B-QH ꢀ redoxꢀ coupleꢀ byꢀ takingꢀ
2
2
x10
H B-Q + NaBH + TEMPO
advantageꢀ ofꢀ theꢀ differentialꢀ fluorescenceꢀ ofꢀ theꢀ twoꢀ
redoxꢀ states.ꢀ Theꢀ chemicalꢀ reversibilityꢀ ofꢀ theꢀ redoxꢀ
coupleꢀwasꢀevaluatedꢀbyꢀtheꢀoneꢀpotꢀsequentialꢀreduc-
2
4
6
x10
tionꢀ ofꢀ H
2
B-Qꢀ byꢀ sodiumꢀ borohydrideꢀ (NaBH
4
),ꢀ fol-
lowedꢀ byꢀ oxidationꢀ ofꢀ theꢀ resultingꢀ H
2
B-QH2ꢀ byꢀ theꢀ
0
stableꢀfreeꢀradicalꢀTEMPOꢀ(Schemeꢀ3).ꢀ
ꢀ
600
700
Wavelength (nm)
800
ꢀ
ꢀ
ACS Paragon Plus Environment

Page 5 of 10
Journal of the American Chemical Society
Figureꢀ 2:ꢀ Emissionꢀ spectraꢀ ofꢀ H
2
B-Qꢀ (1.3ꢀ μMꢀ inꢀ toluene)ꢀ
rangementꢀofꢀEquationꢀ4.ꢀInhibitionꢀtimesꢀ(τ,ꢀFigureꢀ3)ꢀ
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
beforeꢀtheꢀredoxꢀcycleꢀ(black,ꢀ■),ꢀafterꢀreductionꢀbyꢀsodiumꢀ
borohydrideꢀ(red,ꢀ●),ꢀandꢀafterꢀsubsequentꢀTEMPOꢀoxida-
tionꢀ(blue,ꢀ▲).ꢀ
wereꢀdeterminedꢀfromꢀtheꢀinterceptꢀofꢀtangentialꢀlinesꢀ
fromꢀtheꢀincreaseꢀ(orꢀdecrease)ꢀinꢀfluorescenceꢀintensityꢀ
andꢀtheꢀsubsequentꢀlinearꢀchangeꢀarisingꢀfromꢀBODIPYꢀ
2
1
degradation. ꢀTheꢀrateꢀofꢀgenerationꢀofꢀfreeꢀradicalsꢀ(R
wasꢀ inꢀ turnꢀ estimatedꢀ fromꢀ theꢀ thermolysisꢀ rateꢀ con-
stantꢀofꢀtheꢀradicalꢀinitiatorꢀ(k )ꢀandꢀtheꢀescapeꢀfractionꢀ
e)ꢀfromꢀgeminateꢀrecombinationꢀ(Equationꢀ5). ꢀUnderꢀ
g
)ꢀ
ROSꢀScavengingꢀandꢀSynergyꢀwithꢀα-Tocopherolꢀꢀꢀ
Toꢀ investigateꢀ theꢀ antioxidantꢀ activityꢀ ofꢀ H
weꢀ nextꢀ determinedꢀ theꢀ stoichiometricꢀ coefficientꢀ “n”ꢀ
forꢀperoxylꢀradicalꢀscavengingꢀbyꢀH B-QH ,ꢀthatꢀisꢀtheꢀ
2 2
B-QH ,ꢀ
i
39
(
2
2
theꢀconditionsꢀusedꢀherein,ꢀ0.5ꢀmMꢀMeO-AMVNꢀatꢀ37ꢀ
numberꢀofꢀequivalentsꢀofꢀROSꢀeachꢀequivalentꢀofꢀanti-
oxidantꢀmayꢀreactꢀwith.ꢀLipophilicꢀperoxylꢀradicalsꢀwereꢀ
generatedꢀ viaꢀ thermolysisꢀ ofꢀ theꢀ azoꢀ initiator,ꢀ 2,2′-
azobis(4-methoxy-2,4-dimethylꢀ valeronitrile)ꢀ (MeO-
AMVN),ꢀinꢀair-equilibratedꢀdichloromethaneꢀ(Equationꢀ
o
Cꢀinꢀair,ꢀperoxylꢀradicalsꢀwereꢀgeneratedꢀatꢀaꢀconstantꢀ
-8ꢀ
-1ꢀ
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
rateꢀofꢀR
chloroform. ꢀꢀ
B-QH ꢀ mayꢀ reactꢀ withꢀ atꢀ mostꢀ 2ꢀ equivalentsꢀ ofꢀ
g
ꢀ=ꢀ4.3ꢀxꢀ10 Ms assumingꢀeꢀ=ꢀ0.8ꢀasꢀreportedꢀinꢀ
40,41
H
2
2
ROSꢀasꢀshownꢀinꢀEquationsꢀ2ꢀandꢀ3,ꢀhoweverꢀhydroqui-
nonesꢀmayꢀhaveꢀnꢀvaluesꢀrangingꢀfromꢀ0ꢀtoꢀ2ꢀdependingꢀ
onꢀtheꢀreactionꢀconditions,ꢀdueꢀtoꢀtheirꢀsusceptibilityꢀtoꢀ
auto-oxidation.ꢀUnderꢀtheꢀconditionsꢀweꢀused,ꢀweꢀesti-
1
).ꢀIntensity-timeꢀtrajectoriesꢀwereꢀrecordedꢀandꢀshowedꢀ
theꢀ oxidationꢀ ofꢀ H B-QH2ꢀ (asꢀ indicatedꢀ byꢀ aꢀ dropꢀ inꢀ
2
fluorescence)ꢀ overꢀ timeꢀ viaꢀ reactionꢀ withꢀ radicalsꢀ pro-
ducedꢀ uponꢀ MeO-AMVNꢀ thermolysisꢀ (Figureꢀ 3,ꢀ solidꢀ
redꢀtrace).ꢀTheꢀfluorescenceꢀquenchingꢀobservedꢀisꢀcon-
sistentꢀ withꢀ theꢀ activationꢀ ofꢀ theꢀ intramolecularꢀ PeTꢀ
processꢀ uponꢀ theꢀ scavengingꢀ ofꢀ peroxylꢀ radicalsꢀ andꢀ
concomitantꢀ oxidationꢀ ofꢀ theꢀ dihydroquinoneꢀ moietyꢀ
matedꢀ nꢀ forꢀ H
2
B-QH
2 c
ꢀ toꢀ beꢀ 0.7ꢀ basedꢀ onꢀ τ ꢀ ofꢀ 1560ꢀ s.ꢀ
SinceꢀH B-QH
2
2
ꢀrequiresꢀonlyꢀ1ꢀreactionꢀwithꢀROSꢀbeforeꢀ
becomingꢀnon-fluorescentꢀtheꢀvalueꢀofꢀnꢀ=ꢀ0.7ꢀobtained
ꢀ
thusꢀ correspondsꢀ toꢀ theꢀ firstꢀ oxidationꢀ processꢀ (for-
mationꢀofꢀtheꢀquenchedꢀsemiquinone,ꢀEquationꢀ2).ꢀThisꢀ
valueꢀthusꢀreportsꢀpartialꢀoxidationꢀandꢀdoesꢀnotꢀreflectꢀ
theꢀ potentialꢀ reactivityꢀ ofꢀ theꢀ semiquinoneꢀ productꢀ orꢀ
(
2 2 2
H B-QH )ꢀtoꢀtheꢀquinoneꢀformꢀ(H B-Q)ꢀ(Equationsꢀ2ꢀ
andꢀ3).ꢀWeꢀalsoꢀnoteꢀthatꢀpartialꢀoxidationꢀtoꢀtheꢀsem-
iquinoneꢀ radicalꢀ (Equationꢀ 2)ꢀ wouldꢀ leadꢀ toꢀ theꢀ for-
mationꢀofꢀaꢀnon-emissiveꢀproductꢀdueꢀtoꢀparamagneticꢀ
2 2
H B-QH ꢀasꢀaꢀwhole.ꢀꢀ
38
! [!"#$%&$'("#]
quenchingꢀbyꢀtheꢀunpairedꢀelectron. ꢀ
ꢀ
=
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(4)ꢀ
!
!
∆
!!
•
R-N=N-R
2ꢀꢁꢀ + ꢀ ꢀꢀꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ(1)ꢀ
ꢀ(2)ꢀ
ꢀ(3)ꢀ
!
ꢀ = 2ꢀꢀ [azoꢀinitiaor]ꢀ ꢀ
(5)ꢀ
!
!
•
•
ꢀꢀ
ꢀꢁꢀ + ꢀꢁꢀ → ꢀ ꢀꢁꢀ + ꢀꢁꢁꢂ ꢀ
ꢀ
ꢀ
ꢀ
•
•
ꢀꢀ
ꢀꢁꢀ + ꢀꢁꢀ → ꢀꢁꢂꢃ + ꢀꢁꢁꢀꢀ
Ubiquinoneꢀhasꢀbeenꢀnotedꢀtoꢀparticipateꢀsynergisti-
callyꢀwithꢀα-tocopherolꢀinꢀtheꢀinhibitionꢀofꢀlipidꢀperoxi-
8,42
6
H B-PMHC
2
dation. ꢀSpecificallyꢀitꢀhasꢀbeenꢀshownꢀthatꢀuponꢀtheꢀ
scavengingꢀofꢀROSꢀinꢀlipidꢀmembranesꢀbyꢀα-tocopherolꢀ
toꢀyieldꢀtocopheroxylꢀradical,ꢀubiquinolꢀcanꢀ(inꢀadditionꢀ
toꢀ directlyꢀ scavengingꢀ ROS)ꢀ regenerateꢀ α-tocopherolꢀ
thusꢀ prolongingꢀ theꢀ lifeꢀ ofꢀ α-tocopherolꢀ toꢀ actꢀ asꢀ anꢀ
antioxidantꢀ (Schemeꢀ 4).ꢀ Indeed,ꢀ inꢀ organicꢀ solution,ꢀ
ubiquinolꢀ reactsꢀ withꢀ tocopheroxylꢀ radicalsꢀ veryꢀ effi-
7
6
5
x10
H B-QH2
6
2
x10
H B-QH with H B-PMHCλem= 520 nm
2
2
2
6
x10
H B-QH with H B-PMHCλem= 600 nm
2 2 2
6
4x10
6
τa
3
2
1
x10
6
x10
6
-1 -1
cientlyꢀ withꢀ aꢀ rateꢀ constantꢀ ofꢀ aboutꢀ 10 ꢀ M s ,ꢀ whileꢀ
reactionꢀwithꢀperoxylꢀradicalsꢀproceedsꢀwithꢀaꢀrateꢀcon-
6
τc
τb
x10
5
ꢀ
-1 -1ꢀ
0
stantꢀofꢀaboutꢀ10 ꢀM s (aboutꢀoneꢀorderꢀofꢀmagnitudeꢀ
slowerꢀthatꢀthatꢀreportedꢀforꢀα-tocopherolꢀscavengingꢀofꢀ
0
2000 4000 6000 8000
4
3
Time (s)
peroxylꢀ radicals). ꢀ Theꢀ synergisticꢀ regenerationꢀ ofꢀ α-
tocopherolꢀbyꢀubiquinolꢀmayꢀbeꢀunderstoodꢀthermody-
namicallyꢀsinceꢀtheꢀone-electronꢀredoxꢀpotentialꢀofꢀtheꢀ
semiquinoneꢀ radical/ubiquinolꢀ coupleꢀ isꢀ 0.200ꢀ Vꢀ (vs.ꢀ
SHE)ꢀ whileꢀ thatꢀ ofꢀ tocopheroxylꢀ radical/α-tocopherolꢀ
coupleꢀisꢀmoreꢀpositiveꢀatꢀ0.50ꢀVꢀ(vs.ꢀSHE),ꢀsuggestingꢀ
thatꢀubiquinolꢀwillꢀspontaneouslyꢀreduceꢀtheꢀtocopher-
ꢀ
Figureꢀ 3:ꢀ Fluorescence-timeꢀ trajectoriesꢀ ofꢀ 100ꢀ μMꢀ H
PMHCꢀ (blackꢀ traces)ꢀ orꢀ 100ꢀ μMꢀ H B-QH2ꢀ (redꢀ traces)ꢀ inꢀ
theꢀpresenceꢀofꢀ0.5ꢀmMꢀMeO-AMVN.ꢀDashedꢀlinesꢀindicateꢀ
theꢀsolutionꢀwhereꢀH B-PMHCꢀandꢀH B-QH2ꢀ wereꢀmixedꢀ
together.ꢀH B-PMHCꢀwasꢀexcitedꢀatꢀ480ꢀnmꢀandꢀemissionꢀ
wasꢀmonitoredꢀatꢀ520ꢀnm.ꢀInꢀturnꢀH B-QH2ꢀwasꢀexcitedꢀatꢀ
2
B-
2
2
2
2
4
4
oxylꢀradical. ꢀMoreover,ꢀα-tocopherolꢀhasꢀbeenꢀshownꢀ
2
8
toꢀsuppressꢀtheꢀrateꢀofꢀauto-oxidationꢀofꢀubiquinol. ꢀꢀ
550ꢀnmꢀandꢀemissionꢀwasꢀmonitoredꢀatꢀ600ꢀnm.ꢀτꢀindicatesꢀ
theꢀ timeꢀ ofꢀ consumptionꢀ ofꢀ antioxidantꢀ inꢀ solution.ꢀ τaꢀ =ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3670ꢀ sꢀ (consumptionꢀ ofꢀ H
sumptionꢀofꢀH B-PMHCꢀinꢀtheꢀpresenceꢀofꢀH
cꢀ=ꢀ1560ꢀsꢀ(consumptionꢀofꢀH B-QH ).ꢀ
2
B-PMHC),ꢀ τbꢀ =ꢀ 6290ꢀ sꢀ (con-
2
2
B-QH ),ꢀandꢀ
2
τ
2
2
Theꢀvalueꢀofꢀnꢀwasꢀestimatedꢀfromꢀtheꢀconsumptionꢀ
timeꢀ(orꢀinhibitionꢀtime,ꢀτ)ꢀobservedꢀforꢀH B-QH2ꢀ andꢀ
fromꢀtheꢀrateꢀofꢀgenerationꢀofꢀradicalsꢀ(R )ꢀuponꢀrear-
2
g
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 10
Schemeꢀ 4:ꢀ Regenerationꢀ ofꢀ α-tocopherolꢀ fromꢀ theꢀ
tocopheroxylꢀradicalꢀbyꢀH B-QH .ꢀ
rateꢀ ofꢀ consumptionꢀ ofꢀ H
chromanone)ꢀwasꢀ14ꢀfoldꢀslowerꢀinꢀtheꢀpresenceꢀofꢀH B-
2
B-PMHCꢀ (formationꢀ ofꢀ
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
2
2
QH
uponꢀ consumptionꢀ ofꢀ H
enhancementꢀuponꢀformationꢀofꢀoxidizedꢀH
halfꢀthatꢀrecordedꢀwhenꢀnoꢀH B-QH ꢀisꢀpresentꢀinꢀsolu-
tionꢀThisꢀwouldꢀbeꢀconsistentꢀwithꢀtheꢀnewlyꢀgeneratedꢀ
2
.ꢀ Closeꢀ inspectionꢀ ofꢀ Figureꢀ 3ꢀ furtherꢀ revealsꢀ thatꢀ
B-QH ꢀ theꢀ rateꢀ ofꢀ intensityꢀ
B-PMHCꢀisꢀ
2
2
2
2
2
•
ubiquinolꢀ semiquinoneꢀ radical,ꢀ H
QH ꢀ effectivelyꢀ competingꢀ withꢀ theꢀ α-tocopherolꢀ ana-
logueꢀforꢀperoxylꢀradicalsꢀ(compareꢀτ ꢀvsꢀtheꢀtimeꢀspanꢀ
betweenꢀτ ꢀandꢀτ ).ꢀAꢀkineticꢀanalysisꢀbasedꢀonꢀEquationꢀ
,ꢀwhereꢀI ,ꢀI ,ꢀandꢀI ꢀareꢀtheꢀintensityꢀofꢀH B-PMHCꢀatꢀ
2 2
B-QH ꢀ fromꢀ H B-
2
a
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
c
b
6
∞
t
0
2
2
1
theꢀ maximum,ꢀ timeꢀ t,ꢀ andꢀ atꢀ t=0ꢀ s,ꢀ respectively ꢀ pro-
videsꢀtheꢀrelativeꢀperoxylꢀradicalꢀscavengingꢀactivityꢀofꢀ
•
H
2
B-QH ꢀ toꢀ H
2
B-PMHC.ꢀ Weꢀ obtainedꢀ aꢀ relativeꢀ rateꢀ
B-
constantꢀforꢀreactionꢀwithꢀperoxylꢀradicalsꢀofꢀ1ꢀforꢀH
QH ꢀcomparedꢀtoꢀH B-PMHCꢀ(FigureꢀS5)ꢀꢀ
2
2
•
!!!!!"#$
!
!!!!
!!
!
ꢀꢁ 1 − ꢀꢀ
!
"!
−
ꢀꢁ
= −
ꢀ
(6)ꢀ
!"#
!!!!!
!
!"!
Takenꢀ together,ꢀ H
2 2
B-QH ꢀ reactivityꢀ towardsꢀ α-
2 2
ToꢀtestꢀtheꢀcooperativeꢀrelationshipꢀofꢀH B-QH ꢀandꢀ
α-tocopherol,ꢀweꢀdeterminedꢀtheꢀinhibitionꢀtimeꢀforꢀtheꢀ
oxidationꢀofꢀanꢀα-tocopherolꢀanalogueꢀinꢀtheꢀpresenceꢀ
tocopheroxylꢀradicalꢀisꢀanalogousꢀtoꢀthatꢀreportedꢀinꢀtheꢀ
8
2 2
literatureꢀforꢀubiquinol. ꢀH B-QH ꢀcanꢀscavengeꢀROS,ꢀasꢀ
wellꢀ asꢀ inhibitꢀ theꢀ oxidationꢀ ofꢀ andꢀ regenerateꢀ α-
tocopherolꢀ fromꢀ theꢀ tocopheroxylꢀ radical.ꢀ Weꢀ haveꢀ
shownꢀthisꢀbehaviourꢀviaꢀaꢀdropꢀinꢀfluorescenceꢀofꢀH
ofꢀ H
enceꢀ H
followingꢀ reactionꢀ ofꢀ twoꢀ peroxylꢀ radicalsꢀ withꢀ theꢀ
chromanolꢀ moiety.ꢀ Toꢀ thatꢀ effectꢀ weꢀ utilizedꢀ H B-
PMHC,ꢀaꢀfluorogenicꢀα-tocopherolꢀanalogueꢀpreviouslyꢀ
2
B-QH
2
.ꢀ Specifically,ꢀ weꢀ measuredꢀ howꢀ theꢀ pres-
2
B-QH
2
ꢀ delaysꢀ theꢀ formationꢀ ofꢀ chromanoneꢀ
2
B-
QH ꢀinꢀtheꢀpresenceꢀofꢀH B-PMHC,ꢀasꢀwellꢀasꢀviaꢀaꢀde-
2
2
2
2
layedꢀfluorescenceꢀenhancementꢀofꢀH B-PMHC.ꢀꢀ
2
1
reportedꢀbyꢀus. ꢀH
segmentꢀ andꢀ aꢀ chromanolꢀ (theꢀ activeꢀ partꢀ ofꢀ α-
tocopherol)ꢀ trapꢀ segment.ꢀ Inꢀ itsꢀ reducedꢀ form,ꢀ H B-
2
B-PMHCꢀbearsꢀaꢀBODIPYꢀreporterꢀ
CONCLUSIONꢀ
Hereꢀweꢀprovideꢀguidingꢀrulesꢀforꢀtheꢀsynthesisꢀofꢀaꢀ
fluorogenicꢀ ubiquinoneꢀ analogueꢀ whichꢀ mayꢀ provideꢀ
usefulꢀinꢀpreparingꢀrelatedꢀanaloguesꢀinꢀtheꢀfuture.ꢀUp-
onꢀexploitingꢀPeTꢀfromꢀBODIPYꢀtoꢀtheꢀquinoneꢀmoietyꢀ
(BODIPYꢀphotoinducedꢀoxidation),ꢀweꢀhaveꢀsuccessfullyꢀ
achievedꢀaꢀsensitiveꢀprobeꢀthatꢀisꢀnon-emissiveꢀwhenꢀinꢀ
itsꢀoxidizedꢀform,ꢀyetꢀemissiveꢀonceꢀtheꢀquinoneꢀmoietyꢀ
becomesꢀaꢀdihydroquinone.ꢀWhileꢀaꢀcurrentꢀlimitationꢀ
ofꢀourꢀnewlyꢀpreparedꢀcompoundꢀliesꢀinꢀitsꢀlowerꢀsensi-
tivityꢀinꢀhighꢀpolarityꢀsolvents,ꢀanꢀoutcomeꢀthatꢀisꢀrelat-
edꢀtoꢀtheꢀextentꢀthatꢀPeTꢀmayꢀoccurꢀfromꢀtheꢀubiquinolꢀ
moietyꢀ toꢀ theꢀ BODIPYꢀ dye,ꢀ weꢀ anticipateꢀ thatꢀ futureꢀ
evolutionsꢀ mayꢀ drasticallyꢀ enhanceꢀ theꢀ sensitivityꢀ atꢀ
thisꢀendꢀofꢀtheꢀsolventꢀspectrum.ꢀInꢀthisꢀregardꢀweꢀfur-
therꢀ noteꢀ thatꢀ aꢀ judiciousꢀ choiceꢀ ofꢀ theꢀ BODIPYꢀ dyeꢀ
utilizedꢀ mayꢀ renderꢀ theꢀ oxidizedꢀ formꢀ emissiveꢀ whileꢀ
theꢀ reducedꢀ formꢀ mayꢀ inꢀ turnꢀ beꢀ renderedꢀ non-
emissive.ꢀꢀ
2
PMHCꢀisꢀquenchedꢀthroughꢀintramolecularꢀPeT.ꢀOxida-
tionꢀofꢀtheꢀnon-emissiveꢀchromanolꢀbyꢀ2ꢀequivalentsꢀofꢀ
ROS,ꢀ viaꢀ theꢀ alsoꢀ non-emissiveꢀ chromanoxylꢀ radicalꢀ
intermediateꢀyieldsꢀanꢀemissiveꢀchromanoneꢀwithꢀaꢀdis-
tinctꢀspectralꢀwindowꢀcomparedꢀtoꢀH
ingꢀ theꢀ onsetꢀ ofꢀ enhancementꢀ ofꢀ oxidizedꢀ H
establishꢀtheꢀinhibitionꢀtime)ꢀinꢀtheꢀabsenceꢀandꢀpres-
enceꢀofꢀH B-QH ꢀweꢀwereꢀableꢀtoꢀconfirmꢀtheꢀregenera-
tionꢀofꢀtheꢀchromanolꢀformꢀfromꢀtheꢀchromanoxylꢀradi-
calꢀbyꢀH B-QH .ꢀ
Consistentꢀ withꢀ aꢀ cooperativeꢀ behaviourꢀ betweenꢀ
B-QH ꢀ andꢀ α-tocopherol,ꢀ additionꢀ ofꢀ H B-QH ꢀ leadꢀ
toꢀanꢀinductionꢀinꢀtheꢀonsetꢀofꢀemissionꢀfromꢀoxidizedꢀ
B-PMHCꢀ (compareꢀ solidꢀ vs.ꢀ dashedꢀ blackꢀ tracesꢀ inꢀ
Figureꢀ3).ꢀOnlyꢀafterꢀfullꢀconsumptionꢀofꢀH B-QH ꢀ(lossꢀ
ofꢀemissionꢀfromꢀthisꢀsubstrate)ꢀdidꢀtheꢀonsetꢀofꢀemis-
sionꢀfromꢀoxidizedꢀH B-PMHCꢀtakeꢀplaceꢀ(compareꢀredꢀ
andꢀ blackꢀ dashedꢀ tracesꢀ inꢀ Figureꢀ 3).ꢀ Theꢀ rateꢀ ofꢀ con-
sumptionꢀ ofꢀ H B-QH ꢀ inꢀ turnꢀ wasꢀ notꢀ affectedꢀ byꢀ theꢀ
2
B-QH
2
.ꢀByꢀfollow-
2
B-PMHCꢀ
(
2
2
2
2
H
2
2
2
2
H
2
2
2
2
Importantꢀtoꢀourꢀworkꢀisꢀtheꢀpreparationꢀrouteꢀforꢀtheꢀ
ubiquinoneꢀ analogueꢀ thatꢀ circumventsꢀ theꢀ syntheticꢀ
challengesꢀ ofꢀ workingꢀ withꢀ eitherꢀ dihydroquinoneꢀ orꢀ
quinoneꢀ moietiesꢀ byꢀ introducingꢀ thisꢀ functionalityꢀ
throughꢀ aꢀ selectiveꢀ oxidationꢀ ofꢀ aꢀ phenolꢀ precursorꢀ inꢀ
theꢀ lastꢀ reactionꢀ step.ꢀ Suchꢀ aꢀ protocolꢀ shouldꢀ becomeꢀ
importantꢀinꢀplanningꢀrelatedꢀprobesꢀwithꢀsensitiveꢀre-
ceptorꢀsegmentsꢀinꢀtheꢀfuture.ꢀ
2
2
presenceꢀofꢀtheꢀα-tocopherolꢀanalogue.ꢀAltogetherꢀtheseꢀ
resultsꢀ areꢀ inꢀ accordanceꢀ withꢀ theꢀ regenerationꢀ ofꢀ theꢀ
non-emissiveꢀ H
copheroxylꢀradicalꢀbyꢀH
edꢀsynergyꢀbetweenꢀα-tocopherolꢀandꢀubiquinol.
Importantly,ꢀevaluationꢀofꢀtheꢀinitialꢀratesꢀofꢀintensityꢀ
enhancementꢀforꢀH B-PMHCꢀrecordedꢀwithoutꢀvsꢀwithꢀ
B-QH ꢀinꢀotherwiseꢀidenticalꢀconditionsꢀenabledꢀde-
terminingꢀ theꢀ effectꢀ ofꢀ H B-QH ꢀ onꢀ theꢀ rateꢀ ofꢀ con-
sumptionꢀ ofꢀ H B-PMHC.ꢀ ꢀ Basedꢀ onꢀ initialꢀ slopes,ꢀ theꢀ
2
B-PMHCꢀ fromꢀ theꢀ non-emissiveꢀ to-
2
B-QH ,ꢀonꢀparꢀwithꢀtheꢀreport-
2
4
5,46
ꢀꢀ
Theꢀ newlyꢀ developedꢀ probeꢀ exhibitsꢀ bothꢀ chemicalꢀ
andꢀelectrochemicalꢀreversibility,ꢀcrucialꢀforꢀmonitoringꢀ
bothꢀreductionꢀandꢀoxidationꢀreactions.ꢀInꢀadditionꢀweꢀ
showꢀtheꢀantioxidantꢀbehaviorꢀofꢀH2B-QH2,ꢀasꢀwellꢀasꢀ
2
H
2
2
2
2
2
ACS Paragon Plus Environment

Page 7 of 10
Journal of the American Chemical Society
solventꢀrefractiveꢀindexꢀforꢀtheꢀunknownꢀ(x)ꢀorꢀstandardꢀ
itsꢀ synergisticꢀ activityꢀ withꢀ chromanolꢀ (theꢀ activeꢀ seg-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
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1
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6
mentꢀofꢀVitaminꢀE)ꢀtowardsꢀperoxylꢀradicalꢀscavenging.ꢀ
Theseꢀ areꢀ well-establishedꢀ behaviorsꢀ forꢀ ubiquinoneꢀ
whichꢀfurtherꢀvalidatesꢀH2B-Qꢀasꢀaꢀsuitableꢀfluorogenicꢀ
analogueꢀofꢀubiquinone.ꢀTheꢀnewlyꢀpreparedꢀfluorogen-
icꢀubiquinoneꢀanalogueꢀH2B-Qꢀshouldꢀprovideꢀaꢀcrucialꢀ
toolꢀtowardsꢀunderstandingꢀtheꢀcomplexꢀroleꢀofꢀubiqui-
noneꢀ inꢀ itsꢀ tripleꢀ characterꢀ asꢀ anꢀ electronꢀ andꢀ protonꢀ
coupleꢀtransporter,ꢀandꢀasꢀanꢀantioxidant.ꢀWeꢀanticipateꢀ
thatꢀH2B-Q/H2B-QH2ꢀmayꢀserveꢀasꢀaꢀcandidateꢀforꢀun-
derstandingꢀcomplexꢀredoxꢀreactionsꢀinꢀnon-polarꢀme-
dia,ꢀ andꢀ asꢀ aꢀ modelꢀ forꢀ developingꢀ secondꢀ generationꢀ
probesꢀwithꢀtheꢀrequiredꢀsensitivityꢀtoꢀmonitoringꢀelec-
tronꢀtransferꢀprocessesꢀinꢀmitochondria.ꢀ
(st).ꢀꢀ
!!
∆!
!
ꢀ!
=
×
ꢀꢀ
ꢀ
ꢀ
ꢀ
(7)ꢀ
!
∆!"
!
!"
FluorescenceꢀLifetimeꢀStudiesꢀꢀ
Theꢀfluorescenceꢀlifetimeꢀmeasurementsꢀwereꢀcarriedꢀ
outꢀ usingꢀ aꢀ Picoquantꢀ Fluotimeꢀ 200ꢀ Timeꢀ Correlatedꢀ
Singleꢀ Photonꢀ Countingꢀ (TCSPC)ꢀ setupꢀ employingꢀ anꢀ
LDHꢀ 470ꢀ diodeꢀ laserꢀ fromꢀ Picoquantꢀ asꢀ theꢀ excitationꢀ
source.ꢀ Theꢀ laserꢀ outputꢀ wasꢀ 466ꢀ nm.ꢀ Theꢀ excitationꢀ
rateꢀwasꢀ10ꢀMHz,ꢀandꢀtheꢀlaserꢀpowerꢀwasꢀadjustedꢀtoꢀ
ensureꢀ thatꢀ theꢀ detectionꢀ frequencyꢀ wasꢀ lessꢀ thanꢀ 100ꢀ
kHz.ꢀTheꢀlaserꢀwasꢀcontrolledꢀbyꢀaꢀPDLꢀ800ꢀBꢀpicose-
condꢀlaserꢀdriverꢀfromꢀPicoquant.ꢀPhotonsꢀwereꢀcollect-
edꢀatꢀtheꢀmagicꢀangleꢀtoꢀmitigateꢀpolarizationꢀeffects.ꢀꢀ
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
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0
ꢀ
ElectrochemicalꢀStudiesꢀꢀ
EXPERIMENTALꢀSECTIONꢀ
Materialsꢀ
Electrochemicalꢀmeasurementsꢀwereꢀperformedꢀusingꢀ
aꢀthree-electrodeꢀsystem.ꢀTheꢀworkingꢀelectrodeꢀwasꢀaꢀ
Ptꢀwire.ꢀAꢀtwistedꢀPtꢀwireꢀwasꢀusedꢀasꢀtheꢀcounterꢀelec-
trode,ꢀandꢀaꢀAg/AgClꢀelectrodeꢀ(solutionꢀofꢀ1ꢀMꢀKClꢀinꢀaꢀ
separateꢀ frittedꢀ compartment)ꢀ wasꢀ usedꢀ asꢀ theꢀ refer-
ence.ꢀ Aꢀ 0.1ꢀ Mꢀ solutionꢀ ofꢀ tetrabutylammoniumꢀ hex-
afluorophosphateꢀ inꢀ dryꢀ acetonitrile/tolueneꢀ wasꢀ usedꢀ
8
-Acetoxymethyl-2,6-diethyl-1,3,5,7-tetramethyl-
pyrrometheneꢀ fluoroborateꢀ (PM605)ꢀ wasꢀ purchasedꢀ
fromꢀExciton,ꢀInc.ꢀ(Dayton,ꢀOH).ꢀHPLCꢀgradeꢀsolventsꢀ
forꢀ spectroscopyꢀ andꢀ columnꢀ chromatographyꢀ wereꢀ
purchasedꢀthroughꢀFisherꢀScientific.ꢀAllꢀotherꢀchemicalsꢀ
wereꢀsuppliedꢀbyꢀSigma-Aldrich,ꢀCo.ꢀandꢀusedꢀwithoutꢀ
furtherꢀpurificationꢀꢀ
asꢀtheꢀelectrolyteꢀsolventꢀinꢀwhichꢀ0.7ꢀmMꢀH
dissolved.ꢀH B-Qꢀconcentrationsꢀwereꢀdeterminedꢀfromꢀ
2
B-Qꢀwasꢀ
2
Instrumentationꢀ
theꢀ absorptionꢀ andꢀ calculatedꢀ extinctionꢀ coefficient.ꢀ
Solutionsꢀalsoꢀcontainedꢀ1ꢀmMꢀferroceneꢀasꢀanꢀinternalꢀ
standard.ꢀTheꢀsolutionꢀwasꢀequilibratedꢀwithꢀargon,ꢀandꢀ
measuredꢀ underꢀ inertꢀ atmosphere,ꢀ withꢀ aꢀ minimumꢀ
scanꢀrateꢀofꢀ0.1ꢀVꢀs .ꢀFormalꢀredoxꢀpotentialsꢀwereꢀcal-
culatedꢀasꢀtheꢀaverageꢀofꢀtheꢀcathodicꢀandꢀanodicꢀpeakꢀ
potentialsꢀ observedꢀ inꢀ theꢀ cyclicꢀ voltammograms.ꢀ Allꢀ
valuesꢀwereꢀreportedꢀvs.ꢀferrocene.ꢀ
AbsorptionꢀspectraꢀwereꢀrecordedꢀusingꢀaꢀHitachiꢀU-
2800ꢀ Uv−Vis−NIRꢀ spectrophotometer.ꢀ Luminescenceꢀ
spectraꢀwereꢀrecordedꢀusingꢀaꢀPTIꢀQuantaMasterꢀspec-
trofluorimeterꢀusingꢀ1ꢀcmꢀ×ꢀ1ꢀcmꢀquartzꢀcuvettes.ꢀSpec-
−
1
1
traꢀwereꢀcorrectedꢀforꢀdetectorꢀsensitivity.ꢀ HꢀNMRꢀandꢀ
1
3
CꢀNMRꢀspectraꢀwereꢀrecorderꢀonꢀaꢀVarianꢀVNMRSꢀ500ꢀ
instrumentꢀ atꢀ 500ꢀ andꢀ 125ꢀ MHz,ꢀ respectively.ꢀ Elec-
trosprayꢀ ionizationꢀ (ESI)ꢀ massꢀ spectraꢀ wereꢀ measuredꢀ
onꢀ aꢀ Brukerꢀ maXisꢀ impact.ꢀ Voltammetryꢀ experimentsꢀ
wereꢀ conductedꢀ withꢀ aꢀ computer-controlledꢀ CHI760Cꢀ
potentiostat.ꢀ
Kineticꢀ Studiesꢀ inꢀ theꢀ Presenceꢀ ofꢀ ROSꢀ andꢀ H
PMHCꢀ
2
B-
Oxidationꢀ ofꢀ H
2 2
B-QH2ꢀ (100ꢀ µM)ꢀ and/orꢀ H B-PMHCꢀ
(
100ꢀµM)ꢀinꢀtheꢀpresenceꢀofꢀperoxylꢀradicalsꢀgeneratedꢀ
ComputationalꢀMethodsꢀ
uponꢀMeO-AMVNꢀ(0.5ꢀmM)ꢀthermolysisꢀwasꢀmonitoredꢀ
viaꢀfluorescenceꢀatꢀ37 Cꢀinꢀdichloromethane.ꢀIntensity-
o
Quantumꢀ mechanicalꢀ calculationsꢀ wereꢀ performedꢀ
2
7
usingꢀtheꢀGaussianꢀ09Mꢀpackage. ꢀHOMOꢀandꢀLUMOꢀ
orbitalꢀenergiesꢀwereꢀdeterminedꢀfromꢀmolecularꢀgeom-
etriesꢀ optimizedꢀ atꢀ theꢀ B3LYPꢀ 6-31G(d)ꢀ levelꢀ withꢀ anꢀ
appliedꢀpolarizableꢀcontinuumꢀmodelꢀsolvationꢀofꢀtolu-
ene.ꢀ Orbitalsꢀ wereꢀ visualizedꢀ usingꢀ theꢀ Gaussviewꢀ 5ꢀ
package.ꢀꢀ
timeꢀ trajectoriesꢀ wereꢀ recordedꢀ usingꢀ aꢀ PTIꢀ Quan-
taMasterꢀ spectrofluorimeterꢀ equippedꢀ withꢀ aꢀ four-
positionꢀPeltierꢀwithꢀmotorizedꢀturret.ꢀThreeꢀsamplesꢀinꢀ
totalꢀ wereꢀ measured:ꢀ 1)ꢀ H
PMHCꢀ(100ꢀµM),ꢀandꢀ3)ꢀH B-QH2ꢀ(100ꢀµM)ꢀinꢀtheꢀpres-
enceꢀ ofꢀ H B-PMHCꢀ (100ꢀ µM).ꢀ Samplesꢀ (1.5ꢀ mL)ꢀ wereꢀ
2 2
B-QH2ꢀ (100ꢀ µM),ꢀ 2)ꢀ H B-
2
2
measuredꢀinꢀtriangularꢀquartzꢀcuvettesꢀ(1cmꢀxꢀ1cm)ꢀwithꢀ
Teflonꢀ stoppers.ꢀ Eachꢀ sampleꢀ wasꢀ excitedꢀ atꢀ 480ꢀ nmꢀ
FluorescenceꢀQuantumꢀYieldꢀ
Fluorescenceꢀ quantumꢀ yieldsꢀ wereꢀ measuredꢀ usingꢀ
PM605ꢀinꢀacetonitrileꢀasꢀaꢀreferenceꢀ(Φꢀ=ꢀ0.72).ꢀAbsorp-
tionꢀandꢀemissionꢀspectraꢀofꢀPM605ꢀandꢀtheꢀdyeꢀofꢀin-
terestꢀwereꢀmeasuredꢀ-atꢀtheꢀsameꢀwavelengthꢀinꢀeachꢀ
case-ꢀinꢀacetonitrileꢀatꢀfiveꢀdifferentꢀconcentrations.ꢀTheꢀ
integratedꢀ intensityꢀ versusꢀ absorbanceꢀ wereꢀ thenꢀ plot-
tedꢀandꢀfittedꢀlinearly.ꢀRelativeꢀquantumꢀyieldsꢀofꢀfluo-
rescenceꢀforꢀtheꢀunknownꢀwithꢀrespectꢀtoꢀtheꢀstandardꢀ
wereꢀobtainedꢀfromꢀEquationꢀ7,ꢀwhereꢀΦ,ꢀΔ,ꢀandꢀnꢀrefer,ꢀ
respectively,ꢀ toꢀ theꢀ fluorescenceꢀ quantumꢀ yield,ꢀ theꢀ
slopeꢀobtainedꢀfromꢀtheꢀabove-mentionedꢀplot,ꢀandꢀtheꢀ
(
H
2
B-PMHC)ꢀ andꢀ 550ꢀ nmꢀ (H
wasꢀcollectedꢀatꢀ520ꢀnm,ꢀandꢀ600ꢀnmꢀrespectivelyꢀoverꢀ
000ꢀs.ꢀSlitsꢀwereꢀsetꢀtoꢀ1ꢀnmꢀspectralꢀresolution.ꢀꢀ
Synthesisꢀ
6-methyl-2,3,4-trimethoxy-benzaldehyde ꢀ andꢀ ,3,5,7-
2 2
B-QH ),ꢀ andꢀ emissionꢀ
8
2
8
31
tetramethyl-8-H-pyrrometheneꢀ fluoroborateꢀ (5) ꢀ wereꢀ
preparedꢀaccordingꢀtoꢀliteratureꢀproceduresꢀwhereꢀspec-
troscopicꢀdataꢀmatchedꢀthatꢀofꢀtheꢀreportedꢀmaterial.ꢀꢀ
3
,4-dimethoxy-2-hydroxy-6-methylbenzaldehydeꢀ
(
2)ꢀ 6-methyl-2,3,4-trimethoxy-benzaldehydeꢀ (1.15ꢀ g,ꢀ 5.5ꢀ
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 10
):ꢀδꢀꢀ7.69ꢀ(d,ꢀJꢀ=ꢀ16.8ꢀ
1
mmol,ꢀ 1ꢀ equiv)ꢀ wasꢀ dissolvedꢀ inꢀ dryꢀ dichloromethaneꢀ
mg,ꢀ45%).ꢀ H-NMRꢀ(500ꢀMHz;ꢀCDCl
3
o
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
36ꢀ mL)ꢀ underꢀ argonꢀ andꢀ cooledꢀ toꢀ -78 Cꢀ usingꢀ aꢀ dryꢀ
Hz,ꢀ1H),ꢀ7.24ꢀ(d,ꢀJꢀ=ꢀ16.8ꢀHz,ꢀ1H),ꢀ7.07ꢀ(s,ꢀ1H),ꢀ6.71ꢀ(s,ꢀ1H),ꢀ
ice-acetoneꢀ bath.ꢀ Borontribromideꢀ 1ꢀ Mꢀ inꢀ dichloro-
methaneꢀ solutionꢀ (4.7ꢀ mL,ꢀ 4.7ꢀ mmol,ꢀ 0.85ꢀ equiv)ꢀ wasꢀ
addedꢀ dropwiseꢀ toꢀ theꢀ reactionꢀ mixture.ꢀ Theꢀ reactionꢀ
mixtureꢀwasꢀgraduallyꢀwarmedꢀupꢀtoꢀroomꢀtemperature.ꢀ
Theꢀ reactionꢀ wasꢀ monitoredꢀ byꢀ TLC,ꢀ andꢀ itꢀ wasꢀ com-
pleteꢀafterꢀ2ꢀh.ꢀTheꢀreactionꢀwasꢀquenchedꢀwithꢀwaterꢀ
6.12ꢀ(s,ꢀ1H),ꢀ4.03ꢀ(s,ꢀ3H),ꢀ4.01ꢀ(s,ꢀ3H),ꢀ2.57ꢀ(s,ꢀ3H),ꢀ2.30ꢀ(s,ꢀ
1
3
3H),ꢀ 2.28ꢀ (s,ꢀ 3H),ꢀ 2.28ꢀ (s,ꢀ 3H).ꢀ Cꢀ NMRꢀ (126ꢀ MHz;ꢀ
CDCl ):ꢀδꢀ184.0,ꢀ183.6,ꢀ160.2,ꢀ151.3,ꢀ145.1,ꢀ144.0,ꢀ143.1,ꢀ139.4,ꢀ
3
138.4,ꢀ 136.4,ꢀ 135.3,ꢀ 134.8,ꢀ 129.9,ꢀ 125.6,ꢀ 120.4,ꢀ 119.6,ꢀ 115.6,ꢀ
61.28,ꢀ 61.13,ꢀ 15.1,ꢀ 13.4,ꢀ 11.40,ꢀ 11.30.ꢀ HRMSꢀ (ESI)ꢀ forꢀ
+
C
23
H
24
N
2
O
4
BF
2
ꢀ
(M )ꢀ calculated:ꢀ 441.17917,ꢀ found:ꢀ
(
30ꢀ mL)ꢀ andꢀ extractedꢀ 3ꢀ timesꢀ withꢀ dichloromethane.ꢀ
Theꢀ organicꢀ phaseꢀ wasꢀ washedꢀ withꢀ brineꢀ andꢀ driedꢀ
overꢀanhydrousꢀMgSO .ꢀTheꢀsolventꢀwasꢀremovedꢀunderꢀ
441.17960;ꢀ
-(2-(E)-vinyl-5,6-dimethoxy-3-methyl-1,4-quinol)-
,5,7-tetramethyl-8-H-pyrrometheneꢀ fluoroborateꢀ
B-QH )ꢀ B-Qꢀ (3-(2-(E)-vinyl-5,6-dimethoxy-3-
3
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
4
1
(
reducedꢀpressureꢀleavingꢀaꢀpaleꢀbrownꢀsolid.ꢀTheꢀsolidꢀ
residueꢀ wasꢀ loadedꢀ ontoꢀ aꢀ silicaꢀ gelꢀ flashꢀ columnꢀ andꢀ
elutedꢀwithꢀhexanes/ethylꢀacetateꢀ4/1ꢀtoꢀgiveꢀtheꢀprod-
H
2
2
H
2
methyl-1,4-quinone)-1,5,7-tetramethyl-8-H-
pyrrometheneꢀfluoroborate)ꢀ(22ꢀmg,ꢀ0.05ꢀmmol,ꢀ1ꢀequiv)ꢀ
wasꢀ dissolvedꢀ inꢀ tetrahydrofuranꢀ (1ꢀ mL)ꢀ andꢀ methanolꢀ
1
uctꢀ asꢀ aꢀ paleꢀ yellowꢀ solidꢀ (1.02ꢀ g,ꢀ 5.2ꢀ mmol,ꢀ 96%).ꢀ H-
NMRꢀ (300ꢀ MHz;ꢀ CDCl
6.25ꢀ(s,ꢀ1H),ꢀ3.86ꢀ(s,ꢀ3H),ꢀ3.79ꢀ(s,ꢀ3H),ꢀ2.48ꢀ(s,ꢀ3H).ꢀ C-
NMRꢀ(75ꢀMHz,ꢀCDCl ):ꢀδꢀꢀ193.7,ꢀ159.0,ꢀ157.5,ꢀ139.0,ꢀ134.4,ꢀ
3
):ꢀ δꢀ ꢀ 12.14ꢀ (s,ꢀ 1H),ꢀ 10.03ꢀ (s,ꢀ 1H),ꢀ
(
2ꢀmL)ꢀunderꢀargon.ꢀPalladiumꢀonꢀcarbonꢀ(2ꢀmg,ꢀ10%ꢀbyꢀ
1
3
weight)ꢀ wasꢀ addedꢀ followedꢀ byꢀ theꢀ additionꢀ ofꢀ cyclo-
o
3
hexeneꢀ(1ꢀmL).ꢀTheꢀreactionꢀmixtureꢀwasꢀheatedꢀtoꢀ45 Cꢀ
114.1,ꢀ106.1,ꢀ60.7,ꢀ56.1,ꢀ18.2.ꢀHRMSꢀ(APCI)ꢀforꢀC10
11 4
H O ꢀ(M-
andꢀstirredꢀforꢀ18ꢀh.ꢀItꢀwasꢀsubsequentlyꢀfilteredꢀthroughꢀ
celiteꢀandꢀtheꢀsolventꢀwasꢀremovedꢀunderꢀreducedꢀpres-
sure.ꢀTheꢀresultingꢀcrudeꢀpurpleꢀresidueꢀwasꢀloadedꢀonꢀ
toꢀ aꢀ silicaꢀ gelꢀ flashꢀ columnꢀ andꢀ elutedꢀ withꢀ hex-
H)ꢀcalculated:ꢀ195.06628,ꢀfoundꢀ195.06583ꢀ
3
-(2-(E)-vinyl-5,6-dimethoxy-3-methylphenol)-
,5,7-tetramethyl-8-H-pyrrometheneꢀ fluoroborateꢀ
B-phenol)ꢀ 5ꢀ (1,3,5,7-tetramethyl-8-H-pyrrometheneꢀ
1
(
H
2
anes/ethylꢀacetateꢀ3/2ꢀtoꢀaffordꢀtheꢀproductꢀasꢀaꢀpurpleꢀ
1
fluoroborate)ꢀ(390ꢀmg,ꢀ16ꢀmmol,ꢀ1ꢀequiv)ꢀandꢀ2(280ꢀmg,ꢀ
4ꢀ mmol,ꢀ 0.9ꢀ equiv)ꢀ wereꢀ dissolvedꢀ inꢀ 15ꢀ mLꢀ tolueneꢀ
residue.ꢀ H-NMRꢀ(500ꢀMHz;ꢀCDCl
3
):ꢀδꢀꢀ7.94ꢀ(d,ꢀJꢀ=ꢀ16.5ꢀ
1
Hz,ꢀ1H),ꢀ7.41ꢀ(d,ꢀJꢀ=ꢀ16.5ꢀHz,ꢀ1H),ꢀ7.01ꢀ(s,ꢀ1H),ꢀ6.70ꢀ(s,ꢀ1H),ꢀ
6.05ꢀ(s,ꢀ1H),ꢀ6.03ꢀ(s,ꢀ1H),ꢀ5.40ꢀ(s,ꢀ1H),ꢀ3.95ꢀ(s,ꢀ3H),ꢀ3.89ꢀ(s,ꢀ
underꢀ argon.ꢀ 4-methyl-piperidineꢀ (0.8ꢀ mL)ꢀ andꢀ glacialꢀ
aceticꢀacidꢀ(0.8ꢀmL)ꢀwereꢀaddedꢀdropwiseꢀtoꢀtheꢀsolu-
tionꢀ atꢀ roomꢀ temperature.ꢀ Theꢀ reactionꢀ mixtureꢀ wasꢀ
stirredꢀforꢀ5ꢀhoursꢀatꢀ110ꢀ°CꢀusingꢀaꢀDean-Starkꢀtrap.ꢀTheꢀ
reactionꢀmixtureꢀwasꢀdilutedꢀwithꢀethylꢀacetate,ꢀwashedꢀ
3H),ꢀ2.55ꢀ(s,ꢀ3H),ꢀ2.33ꢀ(s,ꢀ3H),ꢀ2.30ꢀ(s,ꢀ3H),ꢀ2.25ꢀ(s,ꢀ3H).ꢀ
13
3
Cꢀ NMRꢀ (126ꢀ MHz;ꢀ CDCl ):ꢀ δꢀ 156.0,ꢀ 155.4,ꢀ 142.3,ꢀ 140.5,ꢀ
140.18,ꢀ140.08,ꢀ139.2,ꢀ136.8,ꢀ135.0,ꢀ133.6,ꢀ130.6,ꢀ123.4,ꢀ118.8,ꢀ
118.36,ꢀ118.19,ꢀ117.9,ꢀ115.1,ꢀ60.92,ꢀ60.81,ꢀ14.8,ꢀ12.1,ꢀ11.36,ꢀ11.31.ꢀ
-
onceꢀwithꢀsaturatedꢀaqueousꢀNaHCO
ratedꢀ aqueousꢀ NH Cl,ꢀ andꢀ theꢀ organicꢀ layerꢀ wasꢀ driedꢀ
overꢀanhydrousꢀMgSO .ꢀTheꢀsolventꢀwasꢀremovedꢀunderꢀ
3
,ꢀonceꢀwithꢀsatu-
HRMSꢀ (ESI)ꢀ forꢀ C23
H
24
N
2
O
4
BF
2
ꢀ (M )ꢀ calculated:ꢀ
441.18027,ꢀfound:ꢀ441.18103;ꢀ
4
4
ASSOCIATEDꢀCONTENTꢀꢀ
SupportingꢀInformationꢀ
reducedꢀ pressureꢀ leavingꢀ aꢀ darkꢀ purpleꢀ residue.ꢀ Theꢀ
crudeꢀproductꢀwasꢀloadedꢀontoꢀaꢀsilicaꢀgelꢀflashꢀcolumnꢀ
andꢀelutedꢀwithꢀhexanes/ethylꢀacetateꢀ3/2ꢀaffordingꢀtheꢀ
1
13
1
Hꢀ NMRꢀ andꢀ Cꢀ NMRꢀ spectraꢀ forꢀ compoundsꢀ 2,ꢀ H
phenol,ꢀ H B-Q,ꢀ andꢀ H B-QH .ꢀ Alsoꢀ ꢀ UV-Visꢀ absorptionꢀ
spectraꢀ forꢀ compoundsꢀ H B-phenol,ꢀ H B-Q,ꢀ andꢀ H B-
2
B-
productꢀasꢀaꢀpurpleꢀsolidꢀ(165ꢀmg,ꢀ24%).ꢀ H-NMRꢀ(500ꢀ
2
2
2
MHz;ꢀCDCl
3
):ꢀδꢀꢀ7.94ꢀ(d,ꢀJꢀ=ꢀ16.5ꢀHz,ꢀ1H),ꢀ7.43ꢀ(d,ꢀJꢀ=ꢀ16.4ꢀ
2
2
2
Hz,ꢀ1H),ꢀ6.99ꢀ(s,ꢀ1H),ꢀ6.69ꢀ(s,ꢀ1H),ꢀ6.54ꢀ(s,ꢀ1H),ꢀ6.34ꢀ(s,ꢀ
QH2.ꢀ Calculatedꢀ energiesꢀ ofꢀ orbitalsꢀ forꢀ H2B-Qꢀ andꢀ H2B-
QH2.Visualizationꢀ ofꢀ calculatedꢀ orbitalsꢀ forꢀ H2B-Qꢀ andꢀ
H2B-QH2ꢀAbsorbanceꢀspectraꢀofꢀH B-Qꢀbeforeꢀreduction,ꢀ
2
afterꢀreduction,ꢀandꢀafter-re-oxidation.ꢀꢀ
TheꢀSupportingꢀInformationꢀisꢀavailableꢀfreeꢀofꢀchargeꢀonꢀ
theꢀACSꢀPublicationsꢀwebsite.ꢀ
ꢀ
1
2
H),ꢀ6.04ꢀ(s,ꢀ1H),ꢀ3.88ꢀ(s,ꢀ3H),ꢀ3.88ꢀ(s,ꢀ3H),ꢀ2.56ꢀ(s,ꢀ3H),ꢀ
1
3
.44ꢀ (s,ꢀ 3H),ꢀ 2.29ꢀ (s,ꢀ 3H),ꢀ 2.25ꢀ (s,ꢀ 3H).ꢀ C-NMRꢀ (126ꢀ
):ꢀ δꢀ ꢀ 156.1,ꢀ 155.4,ꢀ 151.7,ꢀ 149.2,ꢀ 140.6,ꢀ 139.7,ꢀ
35.1,ꢀ133.9,ꢀ133.6,ꢀ133.4,ꢀ131.0,ꢀ121.6,ꢀ118.6,ꢀ118.0,ꢀ115.7,ꢀ115.0,ꢀ
15.0,ꢀ106.2,ꢀ61.1,ꢀ55.7,ꢀ21.3,ꢀ14.8,ꢀ11.4,ꢀ11.3.ꢀHRMSꢀ(ESI)ꢀforꢀ
MHz,ꢀ CDCl
1
1
3
-
23 24 2 3 2
C H N O BF ꢀ (M )ꢀ calculated:ꢀ 425.18535,ꢀ found:ꢀ
4
25.18524;ꢀ
-(2-(E)-vinyl-5,6-dimethoxy-3-methyl-1,4-
quinone)-1,5,7-tetramethyl-8-H-pyrrometheneꢀ
fluoroborateꢀ(H B-Q)ꢀH B-phenol ꢀ(3-(2-(E)-vinyl-5,6-
AUTHORꢀINFORMATIONꢀ
CorrespondingꢀAuthorꢀ
3
2
2
ꢀ
*ꢀEmail:ꢀgonzalo.cosa@mcgill.ca.ꢀ
ꢀ
dimethoxy-3-methylphenol)-1,5,7-tetramethyl-8-H-
pyrrometheneꢀfluoroborate)ꢀ(48ꢀmg,ꢀ0.11ꢀmmol,ꢀ1ꢀequiv)ꢀ
wasꢀ dissolvedꢀ inꢀ dryꢀ acetonitrileꢀ (8ꢀ mL).ꢀ Salcomineꢀ (7ꢀ
mg,ꢀ0.02ꢀmmol,ꢀ0.2ꢀequiv)ꢀwasꢀaddedꢀandꢀtheꢀreactionꢀ
mixtureꢀwasꢀstirredꢀunderꢀanꢀoxygenꢀatmosphereꢀforꢀ3ꢀ
h.ꢀTheꢀreactionꢀmixtureꢀwasꢀfilteredꢀthroughꢀcelite,ꢀandꢀ
theꢀ solventꢀ wasꢀ removedꢀ underꢀ reducedꢀ pressure.ꢀ Theꢀ
resultingꢀ darkꢀ purpleꢀ residueꢀ wasꢀ loadedꢀ ontoꢀ aꢀ silicaꢀ
gelꢀflashꢀcolumnꢀandꢀelutedꢀwithꢀhexanes/ethylꢀacetateꢀ
ACKNOWLEDGMENTꢀꢀ
G.C.ꢀ isꢀ gratefulꢀ toꢀ theꢀ Naturalꢀ Sciencesꢀ andꢀ Engineeringꢀ
Researchꢀ Councilꢀ ofꢀ Canadaꢀ (NSERC)ꢀ andꢀ theꢀ Canadianꢀ
Foundationꢀ forꢀ Innovationꢀ (CFI)ꢀ forꢀ funding;ꢀ L.E.G.ꢀ isꢀ
thankfulꢀtoꢀVanierꢀCanadaꢀforꢀaꢀpostgraduateꢀscholarship;ꢀ
R.G.ꢀisꢀthankfulꢀtoꢀNSERCꢀforꢀaꢀpostgraduateꢀscholarship.ꢀ
WeꢀareꢀgratefulꢀtoꢀRichardꢀLincolnꢀforꢀhisꢀhelpꢀrunningꢀtheꢀ
DFTꢀcalculationsꢀpresentedꢀinꢀtheꢀSIꢀofꢀthisꢀwork.ꢀꢀ
3
/2ꢀ toꢀ affordꢀ theꢀ productꢀ asꢀ aꢀ darkꢀ purpleꢀ residueꢀ (22ꢀ
ACS Paragon Plus Environment

Page 9 of 10
Journal of the American Chemical Society
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