Surface engineered quantum dots in photoelectrochemistry and supramolecular assembly

Abstract

This thesis demonstrates the power of chemical surface engineering in the design and fabrication of functional hybrid materials made of Quantum Dots. The small size of the QDs, in the range of 1 to 10 nm, and related stability in solution, require a careful consideration of a proper surface chemistry for the ligand shell. By a judicious choice of the coating one can remarkably influence the physicochemical and photophysical properties of the semiconductor nanocrystals as well as design and engineer new generations of advanced nanoscale materials. This work describes in detail the synthetic approaches to chemical surface functionalization of QDs with electroactive ligands, including ferrocenyl thiols and poly(ferrocenylsilanes), and with β-cyclodextrin (β-CD) ligands suitable for supramolecular host-guest assembly. These functional ligands are shown to be important components in the engineering of new types of QD hybrid materials. The influence of the electroactive ligands on the optical properties of QDs was investigated by spectroscopic and electrochemical methods. These investigations gave an important insight into the quenching mechanisms of QDs by ferrocene and to the fundamental electron transfer processes in hybrid materials composed of QDs and electro-active ligands. Additionally, ferrocene groups located on the QD surface were shown to be able to take part in host-guest complexation reactions with β-cyclodextrin in solution. This ability was useful in the phase transfer of hydrophobic nanoparticles between solvents of markedly different polarities. The complexation ability of β-CD-functionalized QDs and adamantyl dendrimers was exploited for the preparation of supramolecular multilayer structures on surfaces. Surface bound QDs were shown to be able to transduce optically the binding events to the β-CD cavity, a proof-of-principle for a sensor design. This thesis demonstrates that both FRET and ET can be used as the transduction mechanisms. Thus, proper surface design and engineering of QDs gives unique opportunities to obtain the new class of hybrid materials using numerous functionalization approaches and surface chemistries.