Thalappil Pradeep’s research while affiliated with Indian Institute of Technology Madras and other places

Self‐emissive atomically precise metal nanoclusters (NCs) are emerging as promising emissive layer material for next‐generation light‐emitting diodes (LEDs), thanks to their solid‐state luminescence, well‐defined structures, photo/thermal stability, low toxicity, and unique excited‐state properties. However, achieving high external quantum efficiency (EQE) in solid‐state NCs remains a formidable challenge. In this study, a highly stable bimetallic gold‐copper NC forming [Au2Cu6(Sadm)6(DPPEO)2] stabilized with 1‐adamantanethiol (HSadm) and 1,2‐bis(diphenylphosphino)ethane (DPPE) as the primary and secondary ligands, respectively is reported. Single‐crystal X‐ray diffraction and spectroscopic analyses suggest that the as‐synthesized NC contains one phosphine bound to gold and the second phosphine has oxidized to phosphine oxide (P═O). The presence of such P═O moieties in the NC facilitated C─H···O interactions along with C─H···π and H···H interactions between ligands, promoting rapid crystallization. Due to the exceptional photo/thermal stability and enhanced solid‐state photoluminescence quantum yield (PLQY), [Au2Cu6(Sadm)6(DPPEO)2] NC is utilized to fabricate the NC‐based LED (NC‐LED) via the solution‐processed technique, without using any additional host materials. The fabricated NC‐LED shows a maximum brightness of 1246 cd m⁻² and an EQE of 12.60% with a pure red emission ≈668 nm. This EQE value coupled with saturated pure red emission is the best among solution‐processed and non‐doped NC‐LEDs, suggesting the enormous potential of the NCs for electro‐optical devices.

Photolysis of mixed ices, such as H2O–CO2, is a key driver of chemical evolution in planetary, cometary, and interstellar environments. Despite their ubiquitous presence, the photolysis of H2O–CO2 ices remains underexplored experimentally, largely due to the significant attenuation of vacuum ultraviolet light caused by the intermixing of H2O and CO2, which restricts the formation of new species. Here, we demonstrate two previously unknown photolysis pathways for H2O–CO2 ices at 10 K under ultrahigh vacuum (∼10−10 mbar), revealing differences between bulk and surface photochemistry. In bulk, first, we trapped CO2 within clathrate hydrate (CH) cages to prevent intermixing with H2O, then subjected it to photolysis and analyzed it via reflection absorption infrared spectroscopy. Our results demonstrate that photon-induced destruction of the clathrate cages prompts the free CO2 to migrate into the ice matrix without producing any new photoproducts. In contrast, a mixed solid formed by the simultaneous deposition of residual H2O on CO2 ice produces a variety of photoproducts on the surface, which were detected using Cs+-based secondary ion mass spectrometry. Photoproducts such as CO, H2CO3, and CH3OH, along with elusive intermediates such as HCO, H2CO, and HCO3 were seen on the surface but were not observed in the bulk. These results present a better understanding of the synthesis and chemical evolution of H2O–CO2-rich astrophysical environments.

Noble metal nanoparticles (NPs) exhibit superior plasmonic, catalytic, electronic, and magnetic properties upon alloying with a second metal. However, the synthesis of bimetallic alloy NPs of non‐spherical morphologies presents a challenge due to the necessity of concurrently modulating the nucleation and growth kinetics of various metallic constituents. In this study, a simple solution‐phase reaction between a phosphine‐protected copper nanocluster (NC), namely [Cu18(DPPE)6H16]²⁺ [DPPE = 1,2‐bis(diphenylphosphino)ethane] (abbreviated as Cu18) and gold nanotriangles (AuNTs) is reported as a straightforward strategy to obtain gold‐copper alloy nanotriangles (AuCuNTs) while keeping their sizes and sharp edges intact. Extending this protocol to gold nanorods (AuNRs) and nanocubes (AuNCbs) demonstrates its generality for creating anisotropic AuCu alloy NPs. Auger spectroscopic analyses confirm that Cu(0) is the predominant Cu species in the AuCuNTs, indicating that oxidation of Cu in the resulting nanostructures is prevented. A further interaction of AuCuNTs with [Ag25(DMBT)18]− [DMBT = 2,‐dimethylbenzenethiol] (abbreviated as Ag25) has yielded AuCuAgNTs, offering a facile synthetic route to trimetallic anisotropic NPs. Thus, the current study corroborates atomically precise metal NCs as versatile precursors for tuning the composition of plasmonic anisotropic NPs to meet diverse technological and industrial needs.

Many ligand‐protected metal clusters exhibit phosphorescence at room temperature. However, strategies for improving their phosphorescence quantum yield, a critical parameter of performance, remain poorly developed. In contrast, fluorescent dyes are commonly modified by introducing heavy atoms, such as iodine (I), to enhance intersystem crossing in the excited state, thereby harnessing the heavy atom effect to increase phosphorescence efficiency. In this study, a pair of ligand‐protected silver (Ag) clusters is successfully synthesized with internal cavities encapsulating anions (Xz⁻), namely sulfide ions (S²⁻) or iodide ions (I⁻), which significantly differ in atomic number each other. Single‐crystal X‐ray diffraction and nuclear magnetic resonance spectroscopy revealed that the resulting Ag clusters are composed of X@Ag54S20(thiolate)20(sulfonate)m, where (X, m) = (S, 12) or (I, 11). X‐ray photoelectron spectroscopy revealed that the Ag atoms in these compounds exhibit a mixed‐valence state. Furthermore, experiments on their photoluminescence revealed that a heavy central anion induced an internal heavy‐atom effect similar to that observed in organic fluorescent dyes. As a result, the phosphorescence quantum yield became 16 times higher when S²⁻ is replaced by I⁻ as the central atom.

Electrospray-driven transformation of 2D materials to 0D structures within the reactive environment of charged water microdroplets.

We report the synthesis of [Ag17(o1-CBT)12]³⁻ abbreviated as Ag17, a stable 8e⁻ anionic cluster with a unique Ag@Ag12@Ag4 core-shell structure, where o1-CBT is ortho-carborane-1-thiol. By substituting Ag atoms with Au and/or Cu at specific sites we created isostructural clusters [AuAg16(o1-CBT)12]³⁻ (AuAg16), [Ag13Cu4(o1-CBT)12]³⁻ (Ag13Cu4) and [AuAg12Cu4(o1-CBT)12]³⁻ (AuAg12Cu4). These substitutions make systematic modulation of their structural and electronic properties. We show that Au preferentially occupies the core, while Cu localizes in the tetrahedral shell, influencing stability and structural diversity of the clusters. The band gap expands systematically (2.09 eV for Ag17 to 2.28 eV for AuAg12Cu4), altering optical absorption and emission. Ultrafast optical measurements reveal longer excited-state lifetimes for Cu-containing clusters, highlighting the effect of heteroatom incorporation. These results demonstrate a tunable platform for designing nanoclusters with tailored electronic properties, with implications for optoelectronics and catalysis.