"The main goal of this project comprised the development of multi-stimuli responsive supramolecular systems based on nanocrystals (NCs) and their subsequent use in the controlled assembly of complex organic-inorganic architectures and reversible modulation of their properties. This was accomplished by employing one of the most promising self-assembly motifs based on the barrel-shaped cyclic oligomers of cucurbit[n]urils (CB[n]s) that can bind within their cavity external stimuli (ES) responsive molecules, i.e. derivatives of viologen (MV) and/or photochromic guest molecules displaying light-control binding affinity for CB[n] molecular cavity. Particular attention was paid to the novel concept of self-assembly of inorganic building blocks and modulation of their interfaces triggered by photo-induced reduction of electron-accepting derivatives localized on the NC' surfaces.
The research strategy has been carefully designed to proceed in a stepwise manner and divided into four Work Packages (WP1-WP4). The first WP involved the synthesis, purification and characterization of a variety of metal and metal chalcogenide NCs. Within this part of the project a variety of selected NCs were synthesized, functionalized and structurally characterized. These NCs served further as nanostructured building blocks for investigation of assembly processes in colloids (WP2 and WP3) as well as nanofabrication of devices (WP4).
Within WP2, these well-characterized NCs where combined with monotopic ligands, i.e. short organic ligands or homopolymers both terminated by a variety of MV derivatives and/or second guest molecules, to achieve ES-controlled supramolecular discrete nanoparticulate assemblies in water. Research carried out in this part of the project allowed for the incorporation of semiconducting NCs into host–guest chemistry of cucurbit[n]urils (CB[n]s), as one of the most promising self-assembly motifs that can act as molecular ""handcuffs"" able to bind two various chemical entities leading in this way to more complex systems. The reversibility of these complex CB[n]–based organic–inorganic nanoarchitectures formation processes was achieved through classical chemical factors as well as by light and dioxygen (Figure 1).
The self-assembly of inorganic NCs into ES-responsive organic-inorganic hybrid networks was further evaluated in WP3. We demonstrated that semiconducting and metallic NCs can be brought together into hybrid homo- and heterogeneous nanosystems by simple aprotic and rigid binding motifs, cucurbit[n]urils (CB[n]). The CB[n]-mediated assembly provided an efficient way to well-defined nano-, micro- and macro-sized constructs.
Furthermore, the assembly processes developed within WP1, 2, and 3 provided the unique opportunity to study photo-induced electron transfer processes within the hybrid organic-inorganic nanosystems both in colloidal systems as well as in the solid state. The presented synthetic approach provided prototipical hybrid constructs for in situ tracking of redox processes at nanoscale in a water environment."
