טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentCohen Irit
SubjectSequence Independent Preparation and Characterization of
Oligophenylenevinylenes
DepartmentDepartment of Chemistry
Supervisor Professor Yoav Eichen
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Over the past decade p-conjugated organic metariels have generated considerable attention because of their possible applications in organic electronics, such as in light-emitting diodes, field-effect transistors (FET), sensors and photovoltaic cells. Despite the many possible structures of these materials, most of the research is limited to very simple sequences, mostly homo-oligomers and homo-polymers. This stems mainly from the increasing complexity of synthesis and purification as one moves to more complex sequences of large building blocks. Because of this reason, it is widely accepted that synthesis is still a major obstacle for the full realization of the potential embedded in organic optoelectronics and molecular nanoelectronics. Assembling by design complex structures with molecular, electronic grade, precision is expected to open new frontiers in organic electronics by offering new families of materials to the organic electronics world.

Sequence-independent or “Click”chemistry is applied for the preparation of a series of novel and structurally similar π-conjugated oligomers. The new oligomers are made using Wittig-Horner chemistry using bi-functional building blocks that can be interconnected to one another at any desired sequence. The bi-functional building blocks are aromatic skeletones bearing acetal protected aldehyde groups on their one side and a phosphonic acid diethyl ester group on their other side. A stepwise protection - deprotection process is applied for the preparation of structurally similar π-conjugated oligo-phenylene vinylenes.

The first step in the arylenevinylene formation is a Wittig-Horner condensation of a functionalized aldehyde with the methyl phosphonate ester ylide of a bi-functional monomer. After the first coupling step and formation of the new double bond, the product is deprotected to release the aldehyde group of the diarylenevinylene for a subsequent step. This sequence may be repeated with the product of the proceeding step as the starting material of the next step, using any bi-functional monomer to construct an oligophenylenevinylene of any desired sequence. Additionally, at any stage, the deprotected oligomer can be coupled with a bifunctional aromatic/non aromatic system bearing two diethoxy phosphoryl methyl groups, producing symmetrical oligopheneylenevinylenes.

The new optical and electrochemical properties of the new oligomers were characterized, demonstrating the ability to fine-tune and optimize the optical properties as well as the HOMO and LUMO band positions. The potential embedded in using such a sequence-independent approach is also demonstrated in applying selected penta-arylenevinylenes as the semiconductor channel in organic field-effect transistors.