Interplay of kernel shape and surface structure for NIR luminescence in atomically precise gold nanorods

Unprecedented stacking-dependent piezoluminescence enhancement in atomically precise superatomic gold nanoclusters

Deciphering the structure-property relationship between cluster stacking and high-efficiency luminescence of metal nanoclusters is crucial for designing and synthesizing high-performance light-emitting materials and devices. Here, we successfully synthesized two polymorphic gold nanoclusters (Au8-C and Au8-P) and investigated their stacking-dependent piezoluminescence based on hydrostatic pressure. Under compression, Au8-C exhibits notable piezoluminescence enhancement. However, Au8-P presents monotonic piezoluminescence quenching. High-pressure structural characterizations confirm the existence of stacking-dependent anisotropic compression in Au8-C and Au8-P. Under high pressure, the columnar-stacked Au8-C shrinks faster along the a axis, increasing the aspect ratio (AR) of the fusiform Au8 core. However, the layered Au8-P is compressed faster along the c axis, reducing the AR and leading to a flatter Au8 core. High-pressure femtosecond transient absorption, time-resolved photoluminescence, and Raman spectra collaboratively confirm that differentiated anisotropic compression notably suppresses nonradiative loss caused by low-frequency vibrations of the Au8 core, which is responsible for the piezoluminescence enhancement in Au8-C.

Anti-Heavy-Atom Effect Observed in Near-Infrared Emissive Bimetallic Nanoclusters Au28Cu12X4Cl4 (X = Cl, Br, and I)

Metal nanoclusters with high photoluminescence quantum yield (PLQY) in the near-infrared region (NIR) have attracted considerable interest, and the elucidation of their structure-property relationships and luminescence mechanisms facilitates rational synthesis and practical applications. The direct reduction of alkynyl-gold precursors and copper salts leads to the formation of a series of face-centered cubic bimetallic nanoclusters Au28Cu12X4Cl4 (X = Cl, Br, and I), which exhibits strong NIR emission (∼850 nm) with PLQY being 14, 10, and 8% in the solution at room temperature, respectively. In contrast to the well-known heavy-atom effect, when the four chlorides in the Au24Cu4 core are replaced with bromides or iodides, the luminescence of Au28Cu12X4Cl4 is not enhanced but diminished instead. Excited-state dynamics studies reveal that heavier halogen atoms have a negligible effect on the intersystem crossing rate. Instead, their larger atomic sizes lead to an expansion of the cluster cores, which increases nonradiative transition rates and reduces PLQY. This is the first observation of an anti-heavy-atom effect in luminescent nanoclusters.

Enhancement of NIR II Emission of Au12Ag32 Clusters by Tuning the Au Positions

Precise alloying at the preferred location to enhance the optical properties of metal nanoclusters is challenging as often the most stable isomer is produced. To alter the location of Au atoms on the [Au12Ag32(SR)30]4- cluster, a new approach by changing the reacting Au precursor following an inter-cluster reaction is reported. A Au(I) containing cluster, [Au18Se8(DPPE)6]2+ as the Au source, while reacting with [Ag44(SR)30]4-, is used, and the 12 Au atoms occupy the surface position instead of the core. The whole reaction is monitored in-line using high-resolution trapped ion mobility spectrometry (TIMS), and the change in collision cross section (CCS) of the intermediates and the final product reveal that Au atoms can dynamically migrate within the cluster and in the final product is an all Au out isomer of [Au12Ag32(SR)30]4-. Changing the location of the Au atoms shows an impact on the NIR II emission at ≈1340 nm of parent [Ag44(SR)30]4-. The emission of the synthesized alloy is enhanced tenfold compared to [Ag44(SR)30]4- and is ≈20 nm blueshifted. Density functional theory calculations reveal that the Au/Ag atoms on the staple are slightly positively charged, making it convenient for the reacting Au(I)18Se8 cluster to be exchanged on the surface.

Low Optical Loss and Bent Waveguides: Crystals of a One-Dimensional Pt1Ag14 Nanocluster

Photoluminescent nanoclusters are promising materials for optical waveguides. However, their photon transmission under mechanical stress is very challenging. Here, we report an low-loss metallic nanocluster crystal, [Pt1Ag14(DPPP)6Cl4](SbF6)2 (DPPP = 1,3-bis(diphenylphosphino) propane), which exhibits stable optical performance with an optical loss coefficient of 7.15 × 10-4 dB·μm-1─lower than most reported inorganic, organic, and hybrid materials. The Pt1Ag14 crystals maintain excellent optical stability under mechanical deformation, with an optical loss difference of only 0.15 × 10-3 dB·μm-1 before and after mechanical stress. Reasonable molecular design endows Pt1Ag14 crystals with robust mechanical flexibility, resulting in their bending radius being smaller than that of nanocluster crystals with similar structures. Structural analysis has shown that multiple π···π, C-H···π, and C-H···F intra- and intermolecular interactions originating from the ligands and between the ligands and counterions ensure molecular and crystal stability under mechanical stress. Metallic nanocluster crystals with low loss and mechanical flexibility generated by rational molecular design offer promising candidates in the fields of active waveguides and flexible electronic materials.

Thermally Activated Delayed Fluorescence-Based Near-Infrared-II Luminescence and Controlled Size Growth of Silver Nanoclusters

Due to the significant relationships between structure and properties, the controlled construction of atomically precise metal clusters presents both a formidable challenge and great importance. The innovative synthesis of well-defined silver nanoclusters with near-infrared II (NIR-II) luminescent properties may inspire further exploration of functional metal nanoclusters for bioimaging applications. In this study, we employed the multidentate chelating nitrogen ligand 3,5-di(2-pyridyl)pyrazole (Hbpypz) to construct three unprecedented silver nanoclusters: [Ag27(bpypz)14]3+ (Ag27), [Ag62(bpypz)18]6+ (Ag62), and [Ag91(bpypz)24]5+ (Ag91). Single-crystal X-ray analysis indicated that these cluster structures stem from Ag13 units, exhibiting cluster-of-cluster configurations. By modulating the stoichiometry of the chelating ligand and silver centers, we achieved controlled size growth and reversible cluster-to-cluster conversions among these silver nanoclusters. Notably, the Ag27 nanocluster exhibits an interesting thermally activated delayed fluorescence (TADF) based luminescence in the second near-infrared (NIR-II) region and demonstrates high catalytic efficiency in the oxidative coupling of benzylamines via a singlet oxygen (1O2) oxidation mechanism.

Suppression of Photoexcited Small Polarons-Mediated Energy Transfer to Boost Photoluminescence of Lanthanide-Titanium Nanoclusters

Lanthanide (Ln3+)-titanium-based molecular nanoclusters (NCs) have attracted much attention due to their atomically precise total structure and promising optical behavior, while there is still minimal cognition of structure-dictated electron relaxation dynamics in such an NCs regime with unsatisfied photoluminescence quantum yield (PLQY, in general below 20%). Herein, the photoexcited small polarons (i.e., local electron-phonon coupling) are identified and emphasized in modulating the emission of Ln3+ NCs. Taking 4-tert-butylbenzoate coordinated Eu2Ti4 NCs as a model, the excited electron is capable of being captured by the Ti4+ to form the Ti3+-dominated small polarons, which allows influencing the ligands-sensitive antenna effect for Eu3+ emission. Most importantly, by chelating the Eu2Ti4 NCs with Eu3Ti3 units bilaterally, the evolved Eu8Ti10 NCs perform suppressed lattice vibration and therefore eliminate the photoexcited small polaron-mediated energy transfer, giving a remarkable enhancement in PLQY, from 17.6% to 73.1%.

Observing high dependence of red luminescence on localized symmetry in Mn4+ activated inverse spinel phosphors

Localized symmetry has been shown to significantly impact the luminescence behavior of Mn4+ ions through the electron-phonon coupling process. Building on this characteristic, three types of inverse spinel structure oxides (Mg2XO4, where X = Ti, Ti/Ge, Ge) doped with Mn4+ were developed, exhibiting strong red emission when exposed to UV and blue light. A thorough examination reveals that the symmetric improvement of the Mn4+ sites within the octahedral environment leads to significant changes in their luminescence behavior, including a suppression of zero-phonon-line (ZPL) emission, a blueshift, and an extension of the luminescence lifetime. Moreover, variable-temperature PL spectra of phosphors are carefully measured. Low-temperature PL spectra demonstrate three distinct sharp emission peaks for Mg2GeO4:Mn4+, while Mg2TiO4:Mn4+ exhibits a broad emission band. The average primary phonon energies involved in the vibronic processes are determined through theoretical fitting of temperature-dependent PL intensities. Lastly, the luminescence dynamics associated with anti-Stokes, ZPL, and Stokes emissions are analyzed. The observed increase in luminescence lifetime indicates a significant impact of the localized environment on luminescence properties.

Synergistic coordination of diphosphine with primary and tertiary phosphorus centers: Ultrastable icosidodecahedral Ag30 nanoclusters with metallic aromaticity

As versatile ligands with extraordinary coordination capabilities, RPH2 (R = alkyl or aryl) are rarely used in constructing metal nanoclusters due to their volatility, toxicity, spontaneous flammability, and susceptibility to oxidation. In this work, we designed a primary and tertiary phosphorus-bound diphosphine chelator (2-Ph2PC6H4PH2) to create ultrastable silver nanoclusters with metallic aromaticity. By controlling the deprotonation rate of 2-Ph2PC6H4PH2 and adjusting the templates, we successfully synthesized two near-infrared emissive nanoclusters, Ag30 and Ag32, which have analogous icosidodecahedral Ag30 shells with an Ih symmetry. Deprotonated ligand (2-Ph2PαC6H4Pβ2-) exhibits a coordination mode of μ5-η1(Pβ),η2(Pα,Pβ), which endows a unique metallic aromaticity to Ag30 and Ag32. The solution-processed organic light-emitting diodes based on Ag30 achieve an external quantum efficiency of 15.1%, representing the breakthrough in application of silver nanoclusters to near-infrared-emitting devices. This work represents a special ligand system for synthesizing ligand-protected coinage metal nanoclusters and opens up horizons of creating nanoclusters with distinct geometries and metal aromaticity.

Raising Near-Infrared Photoluminescence Quantum Yield of Au42 Quantum Rod to 50% in Solutions and 75% in Films

Highly emissive gold nanoclusters (NCs) in the near-infrared (NIR) region are of wide interest, but challenges arise from the excessive nonradiative dissipation. Here, we demonstrate an effective suppression of the motions of surface motifs on the Au42(PET)32 rod (PET = 2-phenylethanethiolate) by noncoordinative interactions with amide molecules and accordingly raise the NIR emission (875/1045 nm peaks) quantum yield (QY) from 18% to 50% in deaerated solution at room temperature, which is rare in Au NCs. Cryogenic photoluminescence measurements indicate that amide molecules effectively suppress the vibrations associated with the Au-S staple motifs on Au42 and also enhance the radiative relaxation, both of which lead to stronger emission. When Au42 NCs are embedded in a polystyrene film containing amide molecules, the PLQY is further boosted to 75%. This research not only produces a highly emissive material but also provides crucial insights for the rational design of NIR emitters and advances the potential of atomically precise Au NCs for diverse applications.