Ultrafast Photoinduced Electron Transfer from Cyclometalated Rhodium and Iridium Complexes to Cyan Emitting Copper Nanoclusters: Footsteps toward Light Harvesting

Fluorescent metal nanoclusters: prospects for photoinduced electron transfer and energy harvesting

Research on noble metal nanoclusters (MNCs) (elements with filled electron d-bands) is progressing forward because of the extensive and extraordinary chemical, optical, and physical properties of these materials. Because of the ultrasmall size of the MNCs (typically within 1-3 nm), they can be applied in areas of nearly all possible scientific domains. The greatest advantage of MNCs is the tunability that can be imposed, not only on their structures, but also on their chemical, physical, and biological properties. Nowadays, MNCs are very effectively used as energy donors and acceptors under suitable conditions and hence act as energy harvesters in solar cells, semiconductors, and biomarkers. In addition, ultrafast photoinduced electron transfer (PET) can be practised using MNCs under various circumstances. Herein, we have focused on the energy harvesting phenomena of Au-, Ag-, and Cu-based MNCs and elaborated on different ways to apply them.

Mechanistic elucidation of the catalytic activity of silver nanoclusters: exploring the predominant role of electrostatic surface

The core and the ligand shell of metal nanoclusters (MNCs) have an influential role in modulating their spectroscopic signatures and catalytic properties. The aspect of electrostatic interactions to regulate the catalytic properties of MNCs has not been comprehensively addressed to date. Our present work conclusively delineates the role of the metal core and the electrostatic surface of MNCs involved in the reduction of nitroarenes. A facile surface modification of mercaptosuccinic acid (MSA)-templated AgNCs has been selectively achieved through Mg2+ ions (Mg-AgNCs). Microscopic studies suggest that the size of Mg-AgNCs is ∼3.3 nm, which is considerably higher than that of MSA-templated AgNCs (∼1.75 nm), confirming the formation of a nano-assembled structure. Our spectroscopic and microscopic experiments revealed that the negatively charged AgNCs efficiently catalyze the reduction of 4-nitrophenol (4-NP) with a rate constant of 0.23 ± 0.01 min-1. However, upon surface modification, the catalytic efficiency almost doubles due to the formation of Mg-AgNCs. Catalysis through AgNCs and Mg-AgNCs collectively portrays the role of the core and electrostatic surfaces. Furthermore, the role of electrostatic interaction has been substantiated by varying the ionic strength of the medium, as well as employing different molecular systems. A quantitative assessment of the Debye screening length asserts the correlation between the ionic strength of the medium and the role of electrostatic interactions involved herein. This highly enhanced catalytic aspect has been utilized for the real sample analysis, wherein AgNCs unexpectedly outperform Mg-AgNCs. This approach of real sample analysis also emanates the role of electrostatics involved. This comprehensive investigation represents the influential role of the core and ligand shell of MNCs as well as the role of electrostatics on its catalytic activities, which is relevant for the rational design of highly efficient catalysts.

Photosensitization Dynamics of Stable Copper Nanoclusters inside the Aqueous Core of Reverse Micelles with Different Pool Sizes

The perennial problem of instability of fluorescent copper nanoclusters (Cu NCs), stemming principally from aerial oxidation, has prevented their vivid usage in energy harvesting compared to the other metal NCs. However, replacement of the much expensive metal NCs with the cheaper Cu NCs is desirable if the functions are met with. Although thiolate protection of Cu NCs could bring some stability to them, appreciably decentlystable Cu NCs were produced inside the aqueous core of reverse micelles (RMs). However, this recent development has not been further explored on the photosensitization of the Cu NCs inside the RMs and their controlled modulation as energy antenna. Here we have synthesized stable Cu NCs inside the aqueous core of RMs with three different pool sizes and established photoinduced electron transfer (PET) to an electron acceptor. Considering the bulk quencher concentration, it appears that the extent of PET increases with decrease in the size of the aqueous core of RMs. However, calculating the effective concentration of the electron acceptor inside the RMs and considering the polarity of the microheterogeneous systems, it becomes clear that the extent of PET actually decreases with decrease in the size of the aqueous pool (w₀, i.e., [H₂O]/[AOT]) = 5-20) in the RMs. This proof of concept and the results are promising toward applications in PET-driven phenomena such as solar cells or batteries.