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Tailor made organic molecules for electronic applications

Hellstern, Manuel. Tailor made organic molecules for electronic applications. 2017, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_13093

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Abstract

Within this thesis, the synthesis of functional molecules with specific characteristics and a wide
application spectrum was of major interest. Due to the nature of their applications, it is rather
difficult to categorize all the designed molecules within one general topic. For the purpose of a
clearly represented structure, this work is divided in three individual chapters, each treating
one independent topic by its own introduction, synthetic strategy, results and conclusion.
Chapter 1 - Surface Functionalization
Protection groups for alkynes, representing structural building blocks in various chemical
applications, are sensitive to a fluoride source or basic conditions. The synthetic
accessibility and efficient functionalization by click chemistry of the alkyne moiety makes
them interesting target structures in surface functionalization approaches. A main
challenge is the site-selective functionalization of a surface. To address this challenge, an
electrochemically cleavable protecting group for alkynes was developed. The
immobilization of the designed molecules on TiO2 surfaces was achieved with an EDTA
based anchoring group, linked by a phenyl ethylene moiety to the protected alkyne. Upon
reduction of the naphthoquinone based protecting group, an intramolecular ring formation
forces the release of the alkyne moiety, which remains immobilized on the TiO2 surface.
The site-selectivity was achieved by dividing a wafer into electronically separated sections.
By applying a potential of -0.9 V vs. SCE on individual areas of the wafer, selective
deprotection was achieved. The received free alkyne moieties were further functionalized
with naphthalene diimide based azide dyes by copper catalyzed 1,3-dipolar Huisgen
cycloaddition reactions. To confirm the individual steps of the procedure, solid-state UVVis
measurements were performed.
Chapter 2 - Molecular Wires
The scientific challenge to build electronic circuits by bottom-up approaches in a nanometer
scale appealed generation of chemists. With organic synthetic techniques, an atomic precision
in the structural design is achievable and enables the creation of identical molecules in large
quantities. The understanding of structural and electronical characteristics and their influences
on the behavior of molecules in electronic circuits has risen during the last decade. As
consequence, molecules acting as molecular wires, rectifiers, switches or memory elements
have been developed.
Most of the conformation effects contributing to the conductivity of molecular wires were
investigated with rather short molecules. By elongate the molecular wires, a change in the
transport mechanism was reported in literature from a tunneling to a hopping process.
Therefore, new molecules were designed with a length within the determined mechanism
changing range. The molecular design was based on already investigated biphenyl structures
with defined inter-plane angles, to determine if the same conformation effects were observable
in the elongated analogues.
The second part of this chapter is based on an earlier study with a bipyridyl derivative[1], which
has shown a switch between an “on” state of higher conductance and “off” state with lower
conductance in break junction measurements. The switching was achieved by applying a
positive or negative voltage in the range of ± 0.9 V. The state of the molecule was readable by
the conductance difference of both states at an applied potential, lower than the required
switching potential. To further investigate this phenomenon, biphenyl derivatives with electron
withdrawing and electron donating moieties were synthesized. The resulting intrinsic dipole
moment of the molecules is considered crucial for the switching behavior.
Chapter 3 - High-Triplet State Energy Materials
Used as building blocks for organic light emitting diodes (OLED), 4,4’-dicarbazole-1,1’-biphenyl
(CBP) derivatives are of major interest in the field of electrophosphorescence.[2] Carbazole
moieties in CBP provide a high triplet energy state and thereby enable the use as matrix
materials with an efficient energy transfer to a phosphorescence light emitting dye.[3] For an
efficient triplet energy transfer, especially for deep blue light emitting dyes, the triplet energy
state of the matrix material should be higher than 2.7 eV.
Five new CBP derivatives were synthesized by introducing sterically demanding substituents
to the carbazole subunit in 1,8-position or to the biphenyl backbone. With these modifications,
a perpendicular alignment between the carbazole subunit and the biphenyl backbone was
achieved, resulting in a decreased π-conjugation through the molecule and therefore an
increased triplet state energy. Furthermore, by introducing electron withdrawing and electron
donating groups at the carbazole subunit, a shift of the HOMO / LUMO level was achieved.[4]
Advisors:Mayor, Marcel and Wenger, Oliver S.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Molecular Devices and Materials (Mayor)
UniBasel Contributors:Mayor, Marcel
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:13093
Thesis status:Complete
Bibsysno:Link to catalogue
Number of Pages:1 Online-Ressource (v, 162 Seiten)
Language:English
Identification Number:
Last Modified:07 Jun 2019 04:30
Deposited On:06 Jun 2019 08:36

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