Photophysics of atomically precise metal nanoclusters (MNCs) is an emerging area of research due to their potential applications in optoelectronics, photovoltaics, sensing, bio-imaging and catalysis.

Controlled synthesis of atomically precise metal nanoclusters (MNCs) and fundamental understanding of their physical properties have emerged as an active area of research because of their potential applications in healthcare and energy-related materials. In the present study, atomically precise copper nanoclusters (Cu NCs) have been synthesized from nonluminescent plasmonic copper nanoparticles (Cu NPs) by core etching with excess reduced glutathione (GSH). Electrospray ionization (ESI) mass spectrometry confirms the formation of kinetically controlled, polydisperse Cu34–32(SG)16–13 NCs at room temperature and monodisperse Cu25(SG)20 NCs at elevated temperature (70 °C). Cu34–32(SG)16–13 NCs exhibit weak red emission (625 nm), while Cu25(SG)20 NCs emit intense blue luminescence at 442 nm with 9.7% quantum yield. Rational tuning of reaction temperature, pH, GSH concentration, and reaction time are crucial for the composition and emission band tuning of atomically precise Cu NCs. Interestingly, Cu34–32(SG)16–13 NCs exhibit an aggregation induced emission (AIE) with addition of a less polar solvent, ethanol (EtOH), and the enhancement in the luminescence is attributed to the alteration in the excited state dynamics with the change in solvent polarity. The unique and low cost synthetic methodology of Cu NCs with interesting AIE property may open up new possibilities for their applications in the field of bioimaging, photocatalysis, photosensors, and light emitting devices.

Luminescent copper nanoclusters (Cu NCs) have emerged as fascinating nanomaterials for potential applications in optoelectronics, catalysis, and sensing. Here, we demonstrate the synthesis of L-cysteinecapped Cu NCs in aqueous medium having a bright cyan emission (489 nm) with a quantum yield of 6.2%. The structure of the Cu NCs (Cu 7 L 3 ) is investigated by using density functional theory (DFT) calculation and mass spectrometric study. Further, time-dependent density functional theory (TD-DFT) calculations provide the insights of electronic transitions, and it is correlated with experimental data. With near-HOMO−LUMO gap excitation, Cu NCs are excited to the S 4 state and subsequently relaxed to the S 1 state through an internal conversion process with a time scale in the ultrafast region (326.8 ± 6.5 fs). Furthermore, the structural relaxation in S 1 takes place at a picosecond time scale, and the radiative relaxation occurs from S 1 to S 0 . Finally, Cu NCs are attached with imidazole-functionalized partially reduced graphene oxide (ImRGO) via electrostatic attraction. A dramatic photoluminescence (PL) quenching and shortening of the decay time of the Cu cluster in the presence of ImRGO indicate the photoinduced electron transfer process, which is confirmed from ultrafast spectroscopic study. The photoinduced electron transfer in a Cu NC−ImRGO nanocomposite should pave the way for potential applications in light harvesting.

Gold nanoclusters (Au NCs) are new class of fluorescent nanomaterials with widespread applications in energy, water and healthcare. Here, we report a green synthesis of Au NCs with tunable emission wavelength from 590 to 510 nm in aqueous medium by core etching and ligand exchange method. Investigation reveals that the number of Au atoms present in the core of nanoclusters controls the emission wavelength. The quantum yield (QY) of nanoclusters increases from 0.57 to 3.15% with changing core from Au 12 to Au 6 . Time resolved spectroscopic study reveals that the emission with higher lifetime (>100 ns) originates from ligand to metal charge transfer (LMCT; S to gold core of NCs). It is demonstrated that the highly green emitting NCs (Au-510) are more sensitive than orange emitting NCs (Au-590) toward Pb 2+ . The detection limit of Pb 2+ is found to be 10 nM which is much lower than allowed concentration of Pb 2+ in drinking water. Thus, Au NCs based optical sensor is promising for the selective detection of Pb 2+ in drinking water.

The electronic interactions between colloidal two-dimensional (2D) semiconductor nanoplatelets (NPLs) and Au nanoclusters (NCs) remain unexplored, which are decisive for optoelectronic applications. Here, we report the synthesis of heterostructures based on colloidal 2D CdSe NPLs and Au 25 NCs and investigate their electronic interactions using density functional theory (DFT) calculations. The steady state, time-resolved photoluminescence, and transient absorption (TA) spectroscopic studies are carried out to understand the charge-transfer dynamics. The replacement of CdSe bands by Au bands in the valence band edge in CdSe NPLs−Au NCs heterostructures attests the charge transfer from the conduction band of CdSe to Au. Ultrafast TA spectroscopy further confirms the electron transfer in the heterostructures, and the faster bleach recovery kinetics is also observed in CdSe NPLs−Au NCs heterostructures. The observed charge transfer from the conduction band of CdSe NPLs to Au NCs has been corroborated by the difference in the orbital composition of the valence band edges between CdSe and Au NCs, as calculated by DFT. Photodetectors fabricated with these heterostructures feature high enhancement in photocurrent (∼350-fold), fast photoresponse (∼200 ms), and high detectivity (∼2.5 × 10 11 Jones), which hold promise for the future design of 2D NPL-based materials for optoelectronic applications.