Treść książki
Przejdź do opcji czytnikaPrzejdź do nawigacjiPrzejdź do informacjiPrzejdź do stopki
1.2.THEHISTORYOFTHERED-EDGEEFFECTS
Aparadigmdominatedinphotophysicsupto1970wasbasedontwo
empiricalprinciplesthatwereconsideredfundamental(Birks1970,Terenin
1967).OneofthemistheVavilov’slawstatinganindependenceofemission
energyonexcitationenergywithintheabsorptionbandor,inotherwords,
anindependenceoffluorescencequantumyieldonexcitationwavelength
(Turro1991,Turroetal.2009).TheothercalledtheKasha’srule(Kasha1950)
statesthattheemissionspectrumoccupiesthesamepositiononenergyscale
irrespectiveofthewavelengthofexcitationsothattheemissionalwayspro-
ceedsfromthelowestelectronicandvibrationalstateofthesamemultiplici-
ty.Allobservationsdemonstratingdeviationsfromtheseprincipleswere
consideredasoriginatingnotfromviolationofthesefundamentalprinciples
butfromtheiroperationinspecificconditions.Particularly,thiscouldbethe
ground-stateheterogeneityandphotoselectionofminorcomponentsin
studiedsamples(impurities,conformers,differentlyionizedspecies,etc.).
InthiswaywereinterpretedtheresultsofinitiatedbyWeber(Weber&Teale
1958)measurementsofexcitationwavelengthdependenceoffluorescence
quantumyieldfordifferentdyesinsolutions.Fluorescencefromhigherex-
citedstatesviolatingtheKasha’srulewasfoundforseveraltypesoforganic
dyes(e.g.fromtheS2stateofazulene)andwasinterpretedintermsoflarge
energygapsandpoorFranck-CondonfactorsbetweenS1andhigherelec-
tronicstates(Turroetal.1978).
Fordecadesthereafter,thefindinganddescriptionofanti-Kashafluores-
cencebecameinfocusofmanyresearchers.Theyrequiredthemeasure-
mentsofexcitationspectraatmuchhigherexcitationenergiesthantheemis-
sion,buttheresearchersdidnotdisplayanyinterestinthelow-energyside
ofemissionbands.ThissituationchangedwiththediscoveryofRubinov
andTominworkinginMinsk,Belarus(Rubinov&Tomin1970)ofunusual
effectofbathochromicspectralshiftswiththegradualincreaseofexcitation
wavelength(decreaseinenergyofexcitationquanta)onthelong-
wavelengthslope(red-edge)ofS1excitationband.Theseresultswereob-
tainedandconfirmedinfurtherstudiesonseveraltypesoflaserdyes.The
21
