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FU Berlin
Digitale Dissertation

Christian Spitz :
Excitons in Cylindrical J-Aggregates of Organic Dyes
Exzitonische Anregungen in zylindrischen J-Aggregaten von organischen Farbstoffen

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Abstract

Structure an exciton dynamics of TDBC/C8 J-aggregates which represent those members of the TDBC derivates (5,5´, 6,6´-tetrachlorobenzimidacarbocyanines with different 1,1´- and 3,3´-substituents) that have a split aggregat spectrum were investigated.

After it was shown that both absorption bands belong to the same species of aggregates and to a common excitonic system the shift of the absorption and fluorescence bands under very high hydrostatic pressure as well as the fluorescence anisotropy and the polarization dependent absorption of aligned aggregates indicated that those aggregates probably have a cylindical structure. A concrete model for this structure that was developed on the basis of the spectroscopic characteristics shows the micellar character of these aggregates.

In contrast to the so far assumed incoherent energy migration in the aggregates of TDBC/C8 the coherent exciton dynamics could be proved by three laserspectroscopic measurement techniques in ps time resolution (APE, TCPP, and TCSPC). Wavelength- and temperature- dependence of the dephasing was attributed to the phonon coupled intraband relaxation. In addition the number of molecules over which one exciton is delocalized on the cylindric aggregates of TDBC/C8 was found to be comparable to that on the linear J-aggregates of PIC and of TDBC.

Based on the exceptional loss of fluorescence-anisotropy at low temperature a very efficient energy conduction was concluded that could be technically used by applying cylindrical dye aggregates as artficial light harvesting systems in dye sensitised solar cells.

Table of Contents

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0.Inhaltsverzeichnis 2
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1.Einleitung4
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2.Theorie der Frenkel-Exzitonen in Farbstoffagregaten
2.1 Kollektive Anregungen 11
2.2 Exzitonentheorie für lineare Aggregate 12
2.3 Exzitonische Aufspaltung in zirkularen Aggregaten 17
2.4 Temperaturunabhängige Exzitonendynamik 23
2.5 Temperaturabhängigkeit der Exzitonendynamik 27
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3.Untersuchungen zur Struktur
3.1 Vorbemerkung 30
3.2 Umlagerung zwischen Aggregat und Monomer 33
3.3 Das Fluoreszenz-Anregungsspektrum36
3.4 Das Spektrum der nichtlinearen Polarisation 39
3.5 Spektroskopie unter hohem Druck 42
3.6 Fluoreszenzanisotropie 53
3.7 Messungen im gestreckten Polymerfilm 61
3.8 Zirkularer Dichroismus 67
3.9 Modell der Aggregatgeometrie aus den
spektroskopischen Daten 80
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4.Exzitonendynamik
4.1 Temperaturabhängige statische Spektren 87
4.2 Akkumulierte Photonen-Echo Messung 93
4.3 Dephasierung bei Tieftemperatur 97
4.4 Zwei-Farben-Pump-Probe Spektroskopie 99
4.5 Besetzungslebensdauer bei Tieftemperatur 102
4.6 Zeitaufgelöste Einzelphotonenzählung 105
4.7 Fluoreszenzlebensdauer bei Tieftemperatur 108
4.8 Temperaturabhängigkeit der Fluoreszenzlebensdauer 111
4.9 Temperaturabhängigkeit der Besetzungslebensdauer 118
4.10 Temperaturabhängigkeit der Dephasierungszeit 120
4.11 Fluoreszenzlebensdauer bei hohem Druck 123
4.12 Absorption des Angeregten Zustands 127
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5.Ausblick
5.1 Übertragung der Ergebnisse auf biologische Systeme 131
5.2 Anwendung zylindrischer Aggregate bei
der Nutzung der Solarenergie 134
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6.Zusammenfassung 138
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7.Anhang
7.1 Abkürzungen 141
7.2 Symbole 142
7.3 Literaturverzeichnis 143
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8.Danksagung 148
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9.Lebenslauf 150

More Information:

Online available: http://www.diss.fu-berlin.de/1999/15/indexe.html
Language of PhDThesis: german
Keywords: J-aggregates; Exciton; Dynamics; Spectroscopy
DNB-Sachgruppe: 29 Physik, Astronomie
Classification PACS: 36.40.MR; 71.35.Aa
Date of disputation: 11-Feb-99
PhDThesis from: Department Physik, Freie Universität Berlin
First Referee: Prof. Dr. Dietmar Stehlik
Second Referee: Prof. Dr. Siegfried Dähne
Contact (Author): c.spitz@gmx.de
Contact (Advisor): Siegfried.Daehne@BAM-Berlin.de
Date created:27-Feb-99
Date available:30-Jun-99

 

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