Photophysical Dynamics of Fluorescent Nanomaterials and Small Molecules at the Interfaces of Bio-Mimicking Molecular Self-Assemblies: Implication towards Energy/Electron Transfer

Chatterjee, Arunavo (2025) Photophysical Dynamics of Fluorescent Nanomaterials and Small Molecules at the Interfaces of Bio-Mimicking Molecular Self-Assemblies: Implication towards Energy/Electron Transfer. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Arunavo Chatterjee (20RS005)) 20RS005.pdf - Submitted Version Restricted to Repository staff only Download (12MB)

Abstract

This thesis explores the modulation of photophysics, quantum yields and fluorescence intensity of carbon quantum dots (CQDs), metal nanoclusters (MNCs), and small fluorescent molecules within bio-mimicking self-assemblies, focusing on energy and electron transfer applications. Glutathione-coated gold nanoclusters (GSH-AuNCs) interact with giant unilamellar lipid vesicles (GUVs) composed of DMTAP (positive) and DPPC (zwitterionic) lipids, inducing photophysical changes. Methyl viologen (MV²⁺) triggers photoinduced electron transfer (PET) at neutral pH. The attachment of GSH-AuNCs to GUVs with different head groups influences PET efficiency, with DMTAP GUVs promoting that more effectively than DPPC GUVs. A stepwise surface ligand engineering by arranging L-arginine and cationic surfactants, such as, DTAB and CTAB, layer by layer over the green emitting 6-azo-thiothymine (ATT) protected AuNCs (ATT-AuNCs), which modulates the photoluminescence quantum yield (PLQY), solvation dynamics, PET behaviour and reactive oxygen (ROS) generation propensity. Niosomes effectively incorporate BSA-coated silver nanoclusters (BSA-AgNCs) and reduce aggregation-caused quenching of a model dye, Coumarin 6 (C6). The composite responds to temperature and UV radiation, enabling analysis of Förster resonance energy transfer (FRET) between BSA-AgNCs and C6, creating a "FRET on-off" system and an energy antenna. Biocompatible carbon quantum dots (CQDs) were used to distinguish lipid rafts in model membranes via fluorescence lifetime imaging (FLIM) and confocal microscopy. The photophysical properties of CQDs changed on incorporating into lipid rafts, revealing membrane heterogeneity. This was further investigated with lyotropic liquid crystals (LLCs) to monitor the change in the microviscosity and tested on controlled ROS generation via FRET. Niosome-trapped CQDs and methylene blue formed a FLIM-FRET pair, generating ROS controllably and exhibiting an unprecedented 300 nm Stokes shift. Modulations in the photophysical dynamics of CQDs and MNCs, in different bio-mimicking self-assemblies and further implication on their energy/electron transfer behaviour, as analysed in the thesis, can be utilized in various avenues of nanotechnology.

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