Energy and electron transfer dynamics on different metal nanoclusters in homogeneous and biomimicking heterogeneous environments

Bhunia, Soumyadip (2021) Energy and electron transfer dynamics on different metal nanoclusters in homogeneous and biomimicking heterogeneous environments. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Soumyadip Bhunia (17RS037)) 17RS037.pdf - Submitted Version Restricted to Repository staff only Download (9MB)

Abstract

The present thesis, “Energy and electron transfer dynamics on different metal nanoclusters in homogeneous and bio-mimicking heterogeneous environments”, comprises synthesis and characterisation of ligand-protected fluorescent gold (Au) and copper (Cu) nanoclusters (NCs) aimed to be applied as electron injecting candidates to investigate the ultrafast dynamics in various systems and exploring their further applications. In the process, luminescent and hydrophobic surfactant-bound Au NCs were encaged by cyclodextrins (CDs) of various sizes to develop engineered suprastructures of different shapes in aqueous medium. These suprastructures are porous and promising to be applied as carriers and microreactors. Such surfactant-bound Au NCs could also be incorporated into the crystalline brightly luminescent cubic CsPbBr3 perovskites that tactically produced 2D Au-embedded large nanoplatelets. These composites are promising towards applications in solar cells since the embedded Au NCs would modulate electron transfer in the perovskite systems. Further endeavour to enhance the photoluminescence quantum yield (PLQY) of Au NCs was undertaken through surface ligand rigidification using proteins by physisorption. Enhancement in the PLQY could quantitatively control the resonance energy transfer (RET) to non-luminescent silver nanoparticles (Ag NPs) that acted as dark quenchers. A bio-friendly energy harvesting antenna was designed with the ligand-modified highly fluorescent Au NCs and a newly synthesised hemicyanine dye (a neuro-responsive drug). The outcome of the studies unravelled the formation an efficient FRET pair with potential to act as biomarker. Along with the development of prospective Au NCs, studies on the less expensive Cu NCs were undertaken to develop a new strategy for photoinduced electron transfer (PET) to look into the characteristic differences of protein pockets. Various hydrophilic/hydrophobic methyl viologen (MV) derivatives were used to selectively identify the protein pockets and PET served as a reporter to note the inherent properties. Along with the above processes, the present dissertation incorporates studies on the excited state properties of the Cu NCs on interaction with oppositely charged various organic/inorganic cyclometalated complexes of Ir(III) and Rh(III). The objective was to explore possibilities of finding various efficient systems to modulate PET for vivid applications. However, the instability of fluorescent Cu NCs due to aerial oxidation was a perennial problem. A part of the thesis explains an interesting way to stabilise the Cu NCs by synthesizing them inside the aqueous pools of reverse micelles (RMs). Further, these protected Cu NCs were found to be promising candidates for PET modulation by changing the aqueous pool size of the RMs. The photosensitizing capability of the Cu NCs decreased with reduction in the aqueous pool size. The principal aim of the works summarised above, is to explore various conditions to precisely tune the energy and electron transfer processes using fluorescent metal NCs so that the concepts can be used in number of applications for the benefit of science, society and mankind.

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