Cet ouvrage fait partie de la bibliothèque YouScribe
Obtenez un accès à la bibliothèque pour le lire en ligne
En savoir plus

Testing molecular wires [Elektronische Ressource] : a photophysical and quantum chemical assay / vorgelegt von Mateusz Wielopolski

258 pages
TESTING MOLECULAR WIRESA Photophysical and QuantumChemical AssayDer Naturwissenschaftlichen Fakultät derFriedrich-Alexander-Universität Erlangen-NürnbergzurErlangung des Doktorgradesvorgelegt vonMateusz WielopolskiErlangen, Deutschland2008Als Dissertation genehmigt von der Naturwissenschaftlichen Fakultät der UniversitätErlangen-Nürnberg.Tag der mündlichen Prüfung: 10. Februar 2009Vorsitzender derPromotionskommission: Professor Dr. Eberhard BänschErstberichterstatter: Professor Dr. Dirk M. GuldiZweitberichterstatter: Professor Dr. Andreas HirschDas geilste Zitat habe ich schon für meine Diplomarbeit verbraten.Fabian Spänig, (*1981),deutscher Lebenskünstler, Naturwissenschaftler und Staatsmannaus “Das Büro”, 2008.Für MaximusAcknowledgmentsIn the first place, I would like to dedicate a great THANK YOU to Prof. Dr. Dirk M. Guldiand Prof. Dr. Timothy Clark for giving me the opportunity to accomplish the presentPhD thesis as an interdisciplinary project between the two institutes of Physical ChemistryI and the Computer Chemie Centrum. With their continual interest and assistance fromboth ends - the experimental and theoretical - I was able to gather a very detailed scientificbackground for the investigated processes and their various characterization methods. Byfar more important is the fact that, whenever we had the chance to leave the scientific fields,our conversations turned out to be even more motivating and fruitful.
Voir plus Voir moins

TESTING MOLECULAR WIRES
A Photophysical and Quantum
Chemical Assay
Der Naturwissenschaftlichen Fakultät der
Friedrich-Alexander-Universität Erlangen-Nürnberg
zur
Erlangung des Doktorgrades
vorgelegt von
Mateusz Wielopolski
Erlangen, Deutschland
2008Als Dissertation genehmigt von der Naturwissenschaftlichen Fakultät der Universität
Erlangen-Nürnberg.
Tag der mündlichen Prüfung: 10. Februar 2009
Vorsitzender der
Promotionskommission: Professor Dr. Eberhard Bänsch
Erstberichterstatter: Professor Dr. Dirk M. Guldi
Zweitberichterstatter: Professor Dr. Andreas HirschDas geilste Zitat habe ich schon für meine Diplomarbeit verbraten.
Fabian Spänig, (*1981),
deutscher Lebenskünstler, Naturwissenschaftler und Staatsmann
aus “Das Büro”, 2008.Für MaximusAcknowledgments
In the first place, I would like to dedicate a great THANK YOU to Prof. Dr. Dirk M. Guldi
and Prof. Dr. Timothy Clark for giving me the opportunity to accomplish the present
PhD thesis as an interdisciplinary project between the two institutes of Physical Chemistry
I and the Computer Chemie Centrum. With their continual interest and assistance from
both ends - the experimental and theoretical - I was able to gather a very detailed scientific
background for the investigated processes and their various characterization methods. By
far more important is the fact that, whenever we had the chance to leave the scientific fields,
our conversations turned out to be even more motivating and fruitful.
Additionally, I would like to thank Prof. Dr. Andreas Hirsch for taking the chair during
the exam and his commitment to the musical side of science.
Another giant THANK YOU is addressed to Anna Wielopolski for dismissing me from
extended fatherhood duties and her support in everyday life. Without her the combination
"daddy and scientist" would not be possible. In the same way, my son, Maximus, deserves
special thanks for being such an insightful little boy whenever he had to amuse himself at
www.lego.com during the time he had to spend at the office. Furthermore, I appreciate his
interest in fullerene-like architectures on various playgrounds.
Moreover, I want to say thank you to my Parents and Family for their steady support
in any circumstances of life. Especially, I would like to thank my Mom, who advised me
to finish university first and then become a rockstar. Now, I will be a rockstar with a clear
conscience.
Thanks also to Dr. Carmen Atienza-Castellanos for the perfect instructions regarding
various measurement techniques and scientific problems. Her preliminary works provided
a solid basis for the obtained results in this thesis. Her steady support - even from the far
Madrid - renders her not only a reliable colleague but also a good friend.
Similarly, I would like to set Fabian Spänig apart who turned out to be the perfect room
mate. Not only his immense knowledge, but also his qualities in drinking, smoking and
partying make him a very special person and friend to me.
Thank you, Freddy and Kramer, for the good times at university and, in particular, out-side.
The synthetic groups in Madrid and in Durham deserve great thanks for their efforts in
very reliable chemical synthesis of the investigated compounds. In this regard, it should
be stressed that without the grandiose work of Prof. Dr. Nazario Martin, Prof. Dr. Martin
Bryce, Dr. Cornelia van der Pol and Dr. Salvatore Filippone, none of the published and
herein presented results would even be imaginable.
Thanks also to Dr. Harald Lanig and Dr. Nico van Eikema Hommes for their support re-
garding any molecular modeling issues in praxis and theory, especially hard- and software
problems.
Great thanks are dedicated to Dr. Guido Sauer, Dr. Axel Kahnt, Christian Ehli and
Dr. Georg Brehm for providing me a perfect working environment regarding femto- and
nanosecond spectroscopy.
All my colleagues from the Guldi group deserve a huge THANK YOU for so much fun and
such an enjoyable working atmosphere. In that sense, thank you Bruno, Fabian W., Daniel,
Droste (for coffee-control), Vito, Shankara (for the good conscience in science), Wolfgang,
Christina, Anita, Jürgen, Gustavo, Silke, Esther, Andres, Christian Ö., Daniela, Renata,
Sebastian, Gerd and Dirk. Needless to say, thank you Anna for all the enrichments.
Equally important, the group members of Professor Clark earn great thanks for all the
fun and fruitful discussions. Thus, thank you Christof, Florian and Volker (for the nec-
essary motivation to do it fast), Angela, Matthias Schwofi, Rene Weller, Tatyana, Hakan,
Sebastian, Frank and Jr-Hung.
Finally, I would like to thank L&M, Gauloises, Mr van Nelle from Javansen, the coffee
machine companies and the Catwoman.Zusammenfassung
Der Einsatz molekularer Elektronik bedarf unter anderem der Untersuchung von Ladungs-
transfer-Eigenschaften maßgeschneiderter Moleküle aus dem Nanobereich. Oft entste-
hen dadurch neuartige molekulare Materialien mit einer Vielzahl unterschiedlicher Funk-
tionalitäten (z.B. Redoxfunktionen, Elektronentransfereigenschaften oder photo-sensiblen
Schalter). Um den Ladungstransport durch einzelne Moleküle steuern zu können, haben
wir konventionelle Elektroden durch Donor- und Akzeptorstrukturen ersetzt. In den da-
raus resultierenden DONOR-”wire”-AKZEPTOR Konjugaten ist es uns gelungen, den Trans-
port von Elektronen durch photochemische (für Ladungsseparation) bzw. thermische (für
Ladungsrekombination) Impulse zu kontrollieren. Durch den Einsatz vielfältiger spek-
troskopischer Charakterisierungsmethoden, ergänzt durch eine Reihe quantenchemischer
Rechnungen, konnten diese Prozesse genau analysiert werden. Die Erforschung von Energie-
transfer-Reaktionen an z.B. korrespondierenden C -”wire”-C Systemen ebneten den Weg60 60
für ein vollständiges Verständnis der zugrundenliegenden Vorgänge im angeregten Zus-
tand.
Hinsichtlich der Verbindung zwischen Donor und Akzeptor, kristallisierten sich…-kon-
jugierte Oligomere als vielversprechende Kandidaten heraus. Eingehende photophysikalis-
che Messungen - u.a. Transientenabsorptionsspektroskopie auf Femto- und Nanosekun-
den Zeitskala - gewährten detaillierte Einblicke in den den Ladungstransfer zwischen ver-
schiedenen Elektronendonoren (exTTF, H P/ZnP und Ferocen) und C als Elektronen-2 60
akzeptor.ƒ-konjugierte Brückensysteme, wie oPPV,oPPE bzw. oFL, vermittelten den Ladungs-
†¯ †¡transport und garantierten die Bildung stabiler DONOR / C Radikalionenpaarzustände.60
In allen Systemen wurde die Ladungstrennung und Ladungsrekombination untersucht und
als Funktion des Donor-Akzeptor Abstands analysiert. Der Transport von Ladungsträgern
über Distanzen von bis zu 40 Å wird durch besonders niedrige Attenuationsfaktoren (fl)
¡1 ¡1begünstigt. Diese bewegen sich in Größenordnungen von 0.01 Å für oPPVs, bis 0.21 Å
¡1für oPPEs und 0.09 Å für oFLs. Hierbei, wurde ebenfalls der Einfluss der chemischen
Struktur der Donoreinheiten evaluiert.Im Rahmen quantenchemischer Untersuchungen auf der Basis von Dichtefunktionalthe-
orie und semi-empirischen Methoden konnten die Konzepte für effizienten Elektronen-
transfer abgerundet werden. So wurden Systemeigenschaften - sowohl im Grundzustand
als auch im angeregten Zustand - berechnet und trugen zum Verständnis der experimentellen
Trends bei. Durch die Kombination der verschiedenen quantenmechanischen Ansätze ist
eine systematische Kategorisierung organischer Moleküle in Hinblick auf ihre Elektronen-
transfereigenschaften möglich gewesen. Es konnte auch festgestellt werden, dass außer der
…-Konjugation, die die absolute Voraussetzung für effizienten Ladungstransfer darstellt,
die relativen Energien von DONOR, ”wire” und AKZEPTOR die Elektronentransfer-Eigen-
schaften maßgeblich beeinflussen.Abstract
The investigation of charge-transfer properties of tailored nanoscale molecules for molecu-
lar electronics affords novel molecular materials with the systematic variation of function-
ality (e.g. redox, electron-transfer or photo-switching behavior). To address charge trans-
port through single molecules, we have replaced conventional electrode leads with elec-
tron donors and electron acceptors. In the resulting DONOR-wire-ACCEPTOR conjugates,
the transport of electrons was triggered either photochemically (i.e., charge separation) or
thermally (i.e., charge recombination) and examined by various spectroscopic character-
ization techniques. The latter were further supplemented by quantum chemical calcula-
tions. A comprehensive study of energy transfer reactions in, for instance, corresponding
C -wire-C conjugates paved the way for a thorough understanding of the underlying ex-60 60
cited state processes.
With respect to the connecting wires,…-conjugated oligomers emerged as the most pro-
mising prototypes. Detailed measurements - including femtosecond and nanosecond tran-
sient absorption spectroscopy - provided insight into the nature of charge transfer pro-
cesses between different electron donors (i.e., exTTF, H P/ZnP and ferrocenes) and elec-2
tron acceptors (i.e. C ). Charge transfer was mediated by…-conjugated bridges, i.e. oPPV,60
†¯ †¡oPPE or oFL, and ascertained the formation of DONOR / C radical ion pair states.60
Charge-separation and charge-recombination dynamics were determined in all systems
and analyzed as a function of distance. Particularly small attenuation factors (fl), which
¡1 ¡1 ¡1range from 0.01 Å for oPPVs and 0.09 Å for oFLs to 0.21 Å for oPPEs guarantee charge
transfer processes over distances up to 40 Å. Thereby, the impact of the DONOR structure
was examined.
Quantum chemical investigation by density functional theory and semi-empirical meth-
ods rounds off the concepts of efficient electron transfer. Both ground- and excited-state
properties have been computed in order to yield a comprehensive description of the exper-
imental trends. Further, a practical methodology was developed to describe the electron-transfer pathway in such systems, which provides a fast and efficient way for the systematic
acquisition of potential organic structures capable of photo-induced electron-transfer re-
actions. It was found that besides…-conjugation, which is undoubtedly the sine qua non
for efficient charge-transfer processes, the relative energies of DONOR, wire and ACCEP-
TOR play a decisive role in governing these electron-transfer features.