Diverse structural reactivity patterns of a POCOP ligand with coinage metals.

We have utilised the 4,6-di-tert-butyl resorcinol bis(diphenylphosphinite) (POCOP) ligand for exploring its coordination ability towards group 11 metal centres. The treatment of the bidentate ligand 1 with various coinage metal precursors afforded a wide range of structurally diverse complexes 2-12, depending upon the metal precursors used. This furnishes several multinuclear Cu(I) complexes with dimeric (2) and tetrameric cores (3, 4, and 5). The tetrameric stairstep complex 4 shows thermochromic behaviour, whereas the dimeric complex 2 and tetrameric complex 3 show luminescence properties at cryogenic temperatures. Interestingly, the halide substitution reaction of the dimeric complex 2 with KPPh2 produces a unique mixed phosphine-based tetrameric Cu(I) complex, 5. Treatment of the POCOP ligand with [CuBF4(CH3CN)4] in the presence of 2,2'-bipyridine afforded heteroleptic complex 6, consisting of tri- and tetra-coordinated cationic Cu(I) centres. Furthermore, we could also isolate cubane (8) and stairstep (9) complexes of Ag(I). The cationic Au(I) complex (12) was obtained from the dinuclear Au(I) complex of POCOP, 11. Complex 12 revealed the presence of a strong intramolecular aurophilic interaction with an Au⋯Au bond distance of 3.1143(9) Å. Subsequently, the photophysical properties of these complexes have been studied. All the complexes were characterised by single-crystal X-ray diffraction studies, routine NMR techniques, and mass spectroscopy.

Tunable near-infrared emission and three-photon absorption in lanthanide-doped double perovskite nanocrystals.

Cs2AgInCl6 double perovskite (DP) nanocrystals (NCs) are an emerging class of materials with promising application potential in photonics/optoelectronics owing to their nontoxicity, direct bandgap, and high thermal and moisture stability. These NCs are, however, rarely explored for nonlinear optical (NLO) applications. Herein, we present a comprehensive investigation of the photophysical and nonlinear optical properties of erbium- (Er) and ytterbium (Yb)-doped Cs2AgInCl6 nanocrystals (denoted as Er-DP and Yb-DP, respectively). Temperature-dependent photoluminescence of these NCs was analyzed to estimate their exciton binding energy, Huang-Rhys parameter (S), and electron-phonon coupling strength, which are of fundamental interest to gain an in-depth understanding of the material systems. Femtosecond Z-scan experiments with 800 nm excitation revealed the reverse saturable absorption (RSA) behavior owing to three-photon absorption (3PA). The obtained values of the 3PA coefficients were 1.35 × 10-4 and 1.64 × 10-4 cm3 GW-2, respectively, and the nonlinear refractive indices were estimated to be 1.02 × 10-15 and 1.15 × 10-15 cm2 W-1, respectively, for Er-DP and Yb-DP. These values are superior to those obtained in undoped Cs2AgInCl6 NCs. The physical parameter, Kane energy, which is closely related to the magnitude of the oscillator strength, was estimated to be 25 eV and 26 eV for Er-DP and Yb-DP, respectively. As a proof-of-concept application, we further obtained the optical limiting onset and figure of merit to reveal their prospect as an optical limiter and in photonic switching application. With such emission and nonlinear optical properties, we anticipate that lanthanide-doped Cs2AgInCl6 NCs can be used for designing eco-friendly nonlinear optoelectronic/photonic devices.

Strong Dopant-Dopant Electronic Coupling in Emissive Codoped Two Dimensional Metal Halide Hybrid.

Multimetallic halide hybrids are attractive for the fundamental understanding of interacting excitons. However, realizing halide hybrids that incorporate multiple heterometal centers has been synthetically challenging. This further limits access to gaining physical insight into the electronic coupling mechanism between the constituent metal halide units. Reported herein is an emissive heterometallic halide hybrid, synthesized by codoping (with Mn2+, Sb3+) a 2D host (C6H22N4CdCl6) hybrid, that shows strong dopant-dopant interaction. Here, C6H22N4Sb0.003Mn0.128Cd0.868Cl6 codoped hybrid shows weak green emission (Sb3+ dopant based) and strong orange emission (Mn2+ dopant based). The observed dominance of the Mn2+ dopant emission, arising due to efficient energy transfer between the distant dopants (Sb3+ → Mn2+), highlights strong dopant-dopant electronic coupling. DFT calculations, supporting the observed dopant-dopant interaction, suggest that the electronic coupling between the dopant units (Mn-Cl; Sb-Cl) is mediated by the 2D networked host structure. This work reports physical insight into the coupling mechanism of interacting excitons in multimetallic halide hybrids synthesized through a codoping strategy.

Controlled Modulation of the Structure and Luminescence Properties of Zero-Dimensional Manganese Halide Hybrids through Structure-Directing Metal-Ion (Cd2+ and Zn2+) Centers.

Zero-dimensional (0D) metal halide hybrids with high exciton binding energy are excellent materials for lighting applications. Controlling/modulating the structure of the constituent metal halide units allows tunability of their photoluminescence properties. 0D manganese halide hybrids are currently attracting research efforts in lighting applications due to their eco-friendly and strong emission. However, structural transformation-induced tunability of their photophysical properties has rarely been reported. Herein, we demonstrate a rational synthetic strategy to modulate the structure and luminescence properties of 0D Mn(II) halide hybrids utilizing the structure-directing d10 metal ions (Cd2+/Zn2+). 0D metal halide hybrids of Cd2+/Zn2+, which act as hosts with tunable structures, accept Mn2+ ions as substitutional dopants. This structural flexibility of the host d10 metal ions is realized by optimizing the metal-to-ligand ratio (Cd/AEPip). This reaction parameter allows structural transformation from an octahedral (AEPipCdMnBrOh) to a tetrahedral (AEPipCdMnBrTd) 0D Mn halide hybrid with tunable luminescence (orange → green) with high photoluminescence quantum yield. Interestingly, when Zn2+ is utilized, a tetrahedral AEPipZnMnBr structure forms exclusively with strong green emission. Optical and single-crystal X-ray diffraction structural analysis of the host and the doped system supports our experimental data and confirms the structure-directing role played by Cd2+/Zn2+ centers. This work demonstrates a rational strategy to modulate the structure/luminescence properties of 0D Mn(II) halide hybrids, which can further be implemented for other 0D metal halide hybrids.

Synthetic Control on Structure/Dimensionality and Photophysical Properties of Low Dimensional Organic Lead Bromide Perovskite.

Low dimensional lead halide perovskites have attracted huge research interest due to their structural diversity and remarkable photophysical properties. The ability to controllably change dimensionality/structure of perovskites remains highly challenging. Here, we report synthetic control on structure/dimensionality of ethylenediammonium (ED) lead bromide perovskite from a two dimensionally networked (2DN) sheet to a one dimensionally networked (1DN) chain structure. Intercalation of solvent molecules into the perovskite plays a crucial role in directing the final dimensionality/structure. This change in dimensionality reflects strongly in the observed differences in photophysical properties. Upon UV excitation, the 1DN structure emits white light due to easily formed " self-trapped" excitons. 2DN perovskites show band edge blue emission (∼410 nm). Interestingly, Mn2+ incorporated 2DN perovskites show a highly red-shifted Mn2+ emission peak at ∼670 nm. Such a long wavelength Mn2+ emission peak is unprecedented in the perovskite family. This report highlights the synthetic ability to control the dimensionality/structure of perovskite and consequently its photophysical properties.