Treść książki
Przejdź do opcji czytnikaPrzejdź do nawigacjiPrzejdź do informacjiPrzejdź do stopki
frozenorrelativelyslowstructuraldynamics–fromvitrifiedandhighlyvis-
coussolutionstopolymermatrices.Theywererecognizedasdemonstrations
ofageneralphenomenonthatgotacommonnameoftheRed-Edgeeffects
(REE).Toexplainthemaphysicaltheoryandmodelingstartedtoplayanin-
creasinglyimportantrole.Theanalysisofopticallineshapeshasbeenper-
formedwiththesuggestiontoseparatethehomogeneous(duetoelectronic-
vibrationalinteractions)andinhomogeneous(arisingfromdistributionsin
solute-solventinteractions)broadeningcomponents(Rubinov&Tomin1983,
Nemkovichetal.1991).TheRed-Edgeeffectsappearwhentheensemble
ofexcitedmoleculesisdistributedoninteractionenergywithmolecules
intheirsurroundings.Tomodelinhomogeneousbroadening,G.Weber
(Macgregor&Weber1981)consideredasimplemodelbasedoninteraction
ofphysicaldipole(thedipolewithdistributedcharge)withsolventdipoles
whentheseinteractionsconformtoLangevindistribution.Yu.Mazurenko
(Mazurenko1983)developedaquasi-thermodynamicmethodforthede-
scriptionofstochasticsolvationofmoleculesinsolutions.S.Gorbatsevichet
al.(Gorbatsevichetal.1982)calculatedthedistributionfunctiononthefre-
quencyofelectronictransitioninpolarsolventbyMonte-Carlotechnique.
Asaresultofbothexperimentalandtheoreticalstudiestheconceptwasde-
velopedontheexclusiveroleinallthesephenomenaofinhomogeneousbroad-
eningofspectrathatarisesfromsolute-solventdistributioninexcitationen-
ergy.Thisbroadeningallowsprovidingthesite-photoselectionbyexcitation
andemissionquantawithwell-definedenergiesdeviatingfromtheiraver-
agevalues.Theobserveddeviatingpropertiescanbecomparedwiththeir
meanvalues.
Inthemostclearwaythenewconceptwasformulatedinthereviewof
Nemkovichetal.(Nemkovichetal.1991).Incondensedmediumthedistri-
butiononsolute-solventinteractionenergyformingensembleofsub-states
shouldalwaysexistatthetimeofexcitation.Butitsdisplayinavarietyof
spectroscopicphenomenadependsonhowfastarethetransitionswithin
thisensemblewithinthetimewindowofemission.Dependentonthecondi-
tionsthebroadeningofspectracanbestaticordynamic(Fig.1).Thesigna-
turesofstaticbroadeningareobservedinrigidenvironments,whenthedy-
namicsisslowerthantherateofemission.Itisdynamicifthemotionsinthe
fluorophoreenvironmentoccursimultaneouslyorfasterthantheemission.
Thus,theRed-Edgeeffectsareessentiallythesite-selectiveeffects,whichal-
lowprobingthedynamicsofredistributionoffluorophoresbetweendiffer-
entmolecularenvironments.Probingtheinhomogeneousbroadeningallows
obtainingtheinformationaboutthedynamicpropertiesofcondensedsys-
23
