Ultrafast Relaxation Dynamics of Luminescent Copper Nanoclusters (Cu₇L₃) and Efficient Electron Transfer to Functionalized Reduced Graphene Oxide

Abstract

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.

Highly Luminescent Copper Nanoclusters Stabilized by Ascorbic Acid for the Quantitative Detection of 4-Aminoazobenzene

“…Mass spectrometric analysis showed that the Cu NCs@AA core was composed of 5–7 copper atoms, and the outside of the copper core was protected by 4 AA ligands. This structure was similar to the green fluorescent Cu NCs protected by L-cysteine prepared by the Amitava team [ 31 ], which proved the rationality of the Cu NCs@AA structure. At the same time, it reflected the size-dependent fluorescence properties of the metal nanoclusters.…”

Electrical transport properties and ultrafast optical nonlinearity of rGO–metal chalcogenide ensembles

“…The fast decaying component (s 1 ) corresponds to electron transfer from the conduction band of the nanoparticle to rGO and the second term (s 2 ) is due to electron transition from an intermediate defect state to the valence band of the nanoparticle. 56,57 Interestingly, from Table 1 it is observed that the fast component for C1 is twice as much as that for C2 (0.50 ns vs. 0.26 ns) whereas the slow time scale is comparable for both. The decrease in the fast component signies a better transfer rate of photogenerated electrons to rGO in C2.…”

Application of Photoinduced Electron Transfer with Copper Nanoclusters toward Finding Characteristics of Protein Pockets

“…Fluorescent Cu NCs were synthesized following an earlier reported protocol with some modifications. 26 In brief, 0.2 mL of 100 mM Cu(NO 3 ) 2 ·3H 2 O solution was diluted with 19 mL of HPLC water in a round-bottom flask under vigorous stirring. The mixture turned faint green immediately on adding 4.8 mg of l -cysteine thereafter under nitrogen atmosphere.…”