Date of Award
Doctor of Philosophy (PhD)
MOLECULAR TWEEZERS: STUDIES DIRECTED TOWARDS THE PREPARATION OF EFFECTIVE CHARGE TRANSPORT MATERIALS
Khushabu Thakur, B.Sc, M.Sc.
Marquette University, 2013
An important focus of the modern areas of photovoltaics and molecular electronics is to identify molecules or molecular assemblies that can promote effective charge/exciton transport over long distances. In order to be able to exert control and establish necessary structural parameters for reproducible production of self-assembled structures for long-distance charge transport, our laboratory has been actively engaged towards the preparation of a variety of well-defined, cofacially-arrayed polybenzenoid nanostructures in which aromatic donors are cofacially stacked.
Herein, we undertake the design and synthesis of tweezer-like molecules for their usage for the preparation of long-range charge transport assemblies. We have successfully developed an efficient synthesis of molecular tweezers with different pincers using a common doubly-annulated m-terphenyl platform. The ready availability of these tweezers with different pincers allows us to demonstrate that they bind a variety of electron acceptors as guests via electron donor-acceptor or charge-transfer interactions. Moreover, the tweezers with electron-rich pincers [e.g. trimethylpyrene (TMP) pincers] undergo a ready self-assembly into cofacially-arrayed polybenzenoid nanostructures when prompted by 1-electron oxidation. The effectiveness of the functionality of various tweezers and the rigidity of the tweezer platforms was evaluated by comparison of the EDA complexation binding constants with the tweezers derived from completely rigid (CRP) and non-annulated platforms (NAP) and that of doubly-annulated platform (DAP). These studies established that rigidification of the tweezer platform does not contribute, in any significant way, to the functionality of the tweezers. Moreover, a comparative study of electron transfer prompted self-assembly of the NAP-TMP and DAP-TMP tweezers established that they both undergo ready self-association with comparable efficiency.
We have also synthesized a triptycene scaffold and carefully evaluated its optoelectronic properties. This triptycene scaffold and its derivatives are expected to form two-dimensional self-assemblies which are potentially useful as long-range charge-transport materials in modern photovoltaic devices.