Study of new functional molecular materials based on π-conjugated oligomers, dithiafulvene, and tetrathiafulvalene vinylogues

Abstract

This thesis is primarily aimed at the development of new functional organic materials based on two classes of important π-conjugated molecular building blocks, namely conjugated oligomers and tetrathiafulvalene analogues (TTFVs). While rational molecular design has been the overarching theme of my synthetic and characterization work, the ultimate objective of this research is locked on exploring applications in nanoscale molecular and supramolecular materials and devices. The detailed thesis work consists of three major projects as summarized below. The first project investigates a series of boronic acid functionalized π-conjugated oligomers as efficient fluorescence chemosensors for some biologically important analytes (e.g., monosaccharides and fluoride ion). The novelty of this project lies in the design of diverse shapes and -conjugation patterns of the oligomer fluorophores. In particular, structurally-defined co-oligomers made of phenylene ethynylene and phenylene vinylene repeat units (simply referred to as OPE/OPV hybrids), which were constructed in linear, cruciform, and H-shapes. Synthetic access to these unprecedented -oligomers has allowed systematic characterizations and comparative studies to be conducted, leading to in-depth understanding of the fundamental structure-property relationships. The second project deals with the synthesis of dithiafulvalene (DTF) endcapped OPE/OPV co-oligomers and the characterization of their supramolecular interactions with carbon nanomaterials (fullerenes and carbon nanotubes). These studies indicate that the DTF functionality plays a key role in enhancing the non-covalent binding of the DTF-derived oligomers with fullerenes and carbon nanotubes, owing to the excellent electron-donating properties of DTF. The third project embarked on the design of a group of novel TTFV-arene hybrids as synthetic receptors for fullerenes and transition metal ions. The chemical synthesis of these functional materials has been implemented on the basis of various classical and modern organic synthetic methodologies, such as the Arbuzov reaction, the Horner-Wittig reaction, the Sonogashira coupling and the Cu-catalyzed alkyne azide coupling (one of the flagship click reactions). The use of such high-yielding reactions paved the way for modular preparation of TTFVbased chemosensors and other functional molecular systems. While a major portion of this thesis work is dedicated to advanced organic synthesis, material characterizations using state-of-the-art instrumental techniques constitutes an indispensible part as well. It is worth highlighting that the characterization work done in this thesis encompasses a broad range of analytical methods, including UVVis absorption and fluorescence spectroscopy, electrochemical (cyclic voltammetry and differential pulse voltammetry) analyses, atomic force microscopy (AFM), and singlecrystal X-ray structure analysis. Moreover, the acquired UV-Vis and fluorescence data in the studies of chemosensors and receptors were subjected to a comprehensive global spectral fitting analysis to elicit equilibrium constants and binding stoichiometry in an accurate and reliable manner.