Sameeksha Agrawal

Thermally activated delayed fluorescence (TADF) in metal nanoclusters (MNCs) is an effective strategy to harvest the emission from the excited-triplet states. However, the applications of these TADF-active MNCs are limited by the use of hydrophobic ligands, which generally make these MNCs insoluble. Herein, we report the NIR-TADF emitting CuNCs that are highly water-soluble and display intense-red emission in the solid state. The atomic connectivity of the CuNCs was determined by SC-XRD technique. The delayed fluorescence phenomenon is validated by temperature-dependent photoluminescence studies, and the excited singlet–triplet energy gap (ΔE_ST) was experimentally estimated to be ∼98 meV, thereby substantiating the TADF mechanism. DFT calculations performed on the crystal geometry of the CuNCs further attested to the TADF mechanism along with the associated charge-transfer dynamics. Additionally, the CuNCs demonstrate excellent catalytic activity involving the reduction of ferricyanide and Methylene Blue, highlighting their multifunctional applications in the aqueous phase.

Reported herein are long-lived, red-luminescent silver nanoclusters (AgNCs) protected by the small-molecule ligand thiolactic acid, which exhibit exceptional stability (shelf life exceeding three years, photostability ∼100%), water-solubility, and high biocompatibility, making them suitable for diverse applications such as sensing and live-cell imaging. The AgNCs display extremely sensitive (>2% K^-1) temperature-dependent luminescence, monitored by a dual approach of changes in photoluminescence intensity and excited-state lifetime, enabling precise local thermal environment monitoring with a very high-resolution temperature sensing down to subdegree levels (<0.5 K). MTT assay, confocal fluorescence imaging, and fluorescence lifetime imaging microscopy (FLIM) analysis of mammalian cells suggest that the non-cytotoxic AgNCs specifically stain lysosomes in live cells, functioning as an organelle-specific biomarker and providing critical insights into lysosomal dynamics and intracellular temperature fluctuations. The unique properties of these AgNCs, corroborated by detailed mechanistic studies, open new avenues for studying nanoscale subcellular physiology and developing temperature-sensitive diagnostics and preservation strategies.

Assembling metal nanoclusters (MNCs) to form superstructures generates exciting photophysical properties distinct from those of their discrete precursors. Controlling the assembly process of MNCs and understanding the assembly-disassembly dynamics can have implications in achieving the reversible self-assembly of MNCs. The formation of self-assembled copper nanoclusters (CuNCs) as homogeneous superstructures and the underlying mechanisms governing such a process remain unexplored. Smart molecular imprinting of surface ligands can establish the forces necessary for the formation of such superstructures. Herein, we report highly luminescent, ordered superstructures of 4-phenylimidazole-2-thiol (4-PIT)-protected CuNCs with the help of l-ascorbic acid as a secondary ligand. Through a comprehensive spectroscopic analysis, we deciphered the mechanism of the self-assembly process, where the role of interligand H-bonding and C-H-π interactions was established. Notably, efficient reversibility of assembly-disassembly was demonstrated by re-establishing the interligand interactions and regenerating their photophysical and morphological signatures.

The real-time monitoring of the stepwise growth process of the molecular crystal reveals a conclusive understanding of the morphological evolution, which otherwise remains elusive during the conventional crystallization processes. Herein, we report the in situ crystallization of silver nanoclusters (AgNCs) with special emphasis on their differential growth and multicolor emissive properties. A subtle variation of the methanol (MeOH) proportion in the reaction mixture induces the differential growth of these AgNCs, and thereby, a dramatic modulation in their optical properties was observed. Additionally, by increasing the temperature of the reaction (from a low temperature ice bath to 25 degrees C), an uncontrolled formation of AgNCs along with metallic silver nanoparticles (AgNPs) was observed, which was primarily induced by accelerating the reaction kinetics. We hope that this investigation comprehensively uncovers the serious bottlenecks of the conventional crystallization processes by showcasing systematic monitoring of structural evolution to the higher-ordered crystalline state.

The understanding of interactions between organic chromophores and biocompatible luminescent noble metal nanoclusters (NCs) leading to an energy transfer process that has applications in light-harvesting materials is still in its nascent stage. This work describes a photoluminescent supramolecular assembly, made in two stages, employing an energy transfer process between silver (Ag) NCs as the donor and a host-guest system as the acceptor that can find potential applications in diverse fields. Initially, we explored the host-guest chemistry between a cationic guest ethidium bromide and cucurbit[8]uril host to modulate the fluorescence property of the acceptor. The host-guest interactions were characterized by using UV-vis absorption, steady-state and time-resolved spectroscopy, molecular docking, proton ¹H nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and isothermal calorimetry studies. Next, we prepared a series of blue-emitting AgNCs using different templates such as proteins and peptides. We have found that these AgNCs can be employed as a donor in the energy transfer process upon mixing with the above acceptor for emission color tuning. Our in-depth studies also revealed that surface ligands could play a key role in modulating the energy transfer efficiency. Overall, by employing a noncovalent strategy, we have tried to develop Förster resonance energy transfer (FRET) pairs using blue-emitting NCs and a host-guest complex that could find potential applications in constructing advanced sustainable light-harvesting, white light-emitting, and anti-counterfeiting materials.