"Two-in-one" organic-inorganic hybrid MnII complexes exhibiting dual-emissive phosphorescence

Direct Evidence of the Effect of Water Molecules Position in the Spectroscopy, Dynamics, and Lighting Performance of an Eco-Friendly Mn-Based Organic-Inorganic Metal Halide Material for High-Performance LEDs and Solvent Vapor Sensing

Luminescent Mn(II)-based organic-inorganic hybrid halides have drawn attention as potential materials for sensing and photonics applications. Here, the synthesis and characterization of methylammonium (MA) manganese bromide ((MA)nBrxMn(H2O)2, (n = 1, 4 and x = 3, 6)) with different stoichiometries of the organic cation and inorganic counterpart, are reported. While the Mn2+ centers have an octahedral conformation, the two coordinating water molecules are found either in cis (1) or in trans (2) positions. The photophysical behavior of 1 reflects the luminescence of Mn2+ in an octahedral environment. Although Mn2+ in 2 also has octahedral coordination, at room temperature dual emission bands at ≈530 and ≈660 nm are observed, explained in terms of emission from Mn2+ in tetragonally compressed octahedra and self-trapped excitons (STEs), respectively. Above the room temperature, 2 shows quasi-tetrahedral behavior with intense green emission, while at temperatures below 140 K, another STE band emerges at 570 nm. Time-resolved experiments (77-360 K) provide a clear picture of the excited dynamics. 2 shows rising components due to STEs formation equilibrated at room temperature with their precursors. Finally, the potential of these materials for the fabrication of color-tunable down-converted light-emitting diode (LED) and for detecting polar solvent vapors is shown.

Satellite Red Emission from a Single Green-Emissive MnBr42- Tetrahedron in Soft Hybrid Single Crystals

Photoinduced self-trapped exciton emission is common in soft matter metal halide semiconductors, whereas analogous phenomena in metal halide insulators with localized emitting centers and delayed satellite emission have rarely been identified. In this study, a new zero-dimensional Mn(II) hybrid of [3DPTPP]MnBr4 (3DPTPP = (3-(dimethylamino)propyl)(triphenyl)phosphonium) with only one crystallographic Mn2+ site but dual emission is reported. The delayed red emission (∼630 nm) is successfully assigned to a satellite of the green-emissive (∼530 nm) MnBr42- tetrahedron shifted by N-H vibration (∼2500 cm-1), directly evidenced by the Raman spectra and further supported by density functional theory calculation. The photoluminescence decay curves demonstrate their same origin, but the red emission exhibits a delayed process. The temperature- and pressure-dependent PL spectra, temperature-dependent distortion of the MnBr42- tetrahedron, and light polarization spectra confirmed the consistency and distinctness of the dual emission. This study will inspire further research on self-trapped optoelectronic processes in soft metal halides.

Long-lived spin-triplet excitons in manganese complexes for room-temperature phosphorescence

Low-dimensional metal halide perovskites have become emerging candidates for applications in light emitting diodes due to the quantum confinement effect by tuning their composition and structure. However, they suffer from longstanding issues of environmental stability and lead toxicity. Herein, we report phosphorescent manganese halides, (TEM)₂MnBr₄ (TEM = HN(CH₂CH₃)₃, triethylammonium) and (IM)₆[MnBr₄][MnBr₆] (IM = C₃H₆N₂, imidazolium) with a photoluminescence quantum yield (PLQY) of 50% and 7%, respectively. (TEM)₂MnBr₄ with a tetrahedral configuration exhibits brilliant green light emission centered at 528 nm, while the (IM)₆[MnBr₄][MnBr₆] compound, in which octahedral and tetrahedral units coexist, exhibits red colored emission at 615 nm. The excited state of (TEM)₂MnBr₄ and (IM)₆[MnBr₄][MnBr₆] is found to exhibit distinct photophysical emission characteristics consistent with triplet state phosphorescence. Efficient phosphorescence was achieved with a long lifetime of several milliseconds, 0.38 ms for (TEM)₂MnBr₄ and 5.54 ms for (IM)₆[MnBr₄][MnBr₆], at room temperature. By studying the temperature dependent PL and single-crystal X-ray diffraction measurements and comparing our results with those of previously reported analogues, we have found a direct correlation between Mn⋯Mn distances and PL emission. Our study reveals that the long distance between the Mn centers has made a significant contribution to the long-lived phosphorescence with a highly emissive triplet state.

The Effects of Mono- and Bivalent Linear Alkyl Interlayer Spacers on the Photobehavior of Mn(II)-Based Perovskites

Mn(II)-based perovskite materials are being intensively explored for lighting applications; understanding the role of ligands regarding their photobehavior is fundamental for their development. Herein, we report on two Mn (II) bromide perovskites using monovalent (perovskite 1, P1) and bivalent (perovskite 2, P2) alkyl interlayer spacers. The perovskites were characterized with powder X-ray diffraction (PXRD), electron spin paramagnetic resonance (EPR), steady-state, and time-resolved emission spectroscopy. The EPR experiments suggest octahedral coordination in P1 and tetrahedral coordination for P2, while the PXRD results demonstrate the presence of a hydrated phase in P2 when exposed to ambient conditions. P1 exhibits an orange-red emission, while P2 shows a green photoluminescence, as a result of the different types of coordination of Mn(II) ions. Furthermore, the P2 photoluminescence quantum yield (26%) is significantly higher than that of P1 (3.6 %), which we explain in terms of different electron-phonon couplings and Mn-Mn interactions. The encapsulation of both perovskites into a PMMA film largely increases their stability against moisture, being more than 1000 h for P2. Upon increasing the temperature, the emission intensity of both perovskites decreases without a significant shift in the emission spectrum, which is explained in terms of an increase in the electron-phonon interactions. The photoluminescence decays fit two components in the microsecond regime-the shortest lifetime for hydrated phases and the longest one for non-hydrated phases. Our findings provide insights into the effects of linear mono- and bivalent organic interlayer spacer cations on the photophysics of these kinds of Mn (II)-based perovskites. The results will help in better designs of Mn(II)-perovskites, to increase their lighting performance.

Highly Luminescent Earth-Benign Organometallic Manganese Halide Crystals with Ultrahigh Thermal Stability of Emission from 4 to 623 K

The phosphor-converted light-emitting diode (PC-LED) has become an indispensable solid-state lighting and display technologies in the modern society. Nevertheless, the use of scarce rare-earth elements and the thermal quenching (TQ) behavior are still two most crucial issues yet to be solved. Here, this work successfully demonstrates a highly efficient and thermally stable green emissive MnI₂ (XanPO) crystals showing a notable photoluminescence quantum yield (PLQY) of 94% and a super TQ resistance from 4 to 623 K. This unprecedented superior thermal stability is attributed to the low electron-phonon coupling and the unique rigid crystal structure of MnI₂ (XanPO) over the whole temperature range based on the temperature-dependent photoluminescence (PL) and single crystal X-ray diffraction (SCXRD) analyses. Considering these appealing properties, green PC-LEDs with a power efficacy of 102.5 lm W^-1 , an external quantum efficiency (EQE) of 22.7% and a peak luminance up to 7750 000 cd m^-2 are fabricated by integrating MnI₂ (XanPO) with commercial blue LEDs. Moreover, the applicability of MnI₂ (XanPO) in both micro-LEDs and organic light-emitting diodes (OLEDs) is also demonstrated. In a nutshell, this study uncovers a candidate of highly luminescent and TQ resistant manganese halide suitable for a variety of emission applications.

Manganese(II) Bromide Compound with Diprotonated 1-Hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole: Dual Emission and the Effect of Proton Transfers

An organic–inorganic cation–anion manganese(II) tetrabromide compound with diprotonated 1-hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole, [H3L][MnBr4][H2O], has been synthesized and investigated. The compound has a few possible pathways for proton transfers, which play an important role in the observed luminescence, optical, and magnetic properties. The proton transfers result in the appearance of two-band luminescence. One band is caused by the Mn(II) d-d transitions. The other band is caused by the transition from the triplet state of organic cation and the d-d transition of manganese(II) coupled through {[H3L]}-{[MnBr4]}-{[H2O]} vibrations. The optical absorption spectra of [H3L][MnBr4][H2O] indicate the presence of two direct and one indirect band transitions. The reason for the two-band luminescence and complex optical absorption in [H3L][MnBr4][H2O] were additionally considered using the DFT calculations.

A theory-driven synthesis of symmetric and unsymmetric 1,2-bis(diphenylphosphino)ethane analogues via radical difunctionalization of ethylene

1,2-Bis(diphenylphosphino)ethane (DPPE) and its synthetic analogues are important structural motifs in organic synthesis, particularly as diphosphine ligands with a C₂-alkyl-linker chain. Since DPPE is known to bind to many metal centers in a bidentate fashion to stabilize the corresponding metal complex via the chelation effect originating from its entropic advantage over monodentate ligands, it is often used in transition-metal-catalyzed transformations. Symmetric DPPE derivatives (Ar¹₂P-CH₂-CH₂-PAr¹₂) are well-known and readily prepared, but electronically and sterically unsymmetric DPPE (Ar¹₂P-CH₂-CH₂-PAr²₂; Ar¹≠Ar²) ligands have been less explored, mostly due to the difficulties associated with their preparation. Here we report a synthetic method for both symmetric and unsymmetric DPPEs via radical difunctionalization of ethylene, a fundamental C₂ unit, with two phosphine-centered radicals, which is guided by the computational analysis with the artificial force induced reaction (AFIR) method, a quantum chemical calculation-based automated reaction path search tool. The obtained unsymmetric DPPE ligands can coordinate to several transition-metal salts to form the corresponding complexes, one of which exhibits distinctly different characteristics than the corresponding symmetric DPPE-metal complex.

New Approach toward Dual-Emissive Organic-Inorganic Hybrids by Integrating Mn(II) and Cu(I) Emission Centers in Ionic Crystals

Inorganic-organic hybrid luminescent materials have received great attention for their potential applications in a wide range of clean/renewable energy-related areas, including photovoltaics and solid-state lighting. Herein, we present a unique and general "Mn + Cu" approach by blending two earth-abundant luminogenic metals, manganese and copper, within a single ionic structure to construct a remarkable family of low-cost and multifunctional hybrid materials featuring dual emission, as well as triboluminescence and second-harmonic generation response. The novel hybrid materials are made of diphosphine dioxide-chelated [Mn(O∧O)₃]²⁺ cations and various anionic [Cu_xI_y]^(y-x)- clusters, ensuring manifestation of dual phosphorescence streamed from octahedral Mn²⁺ ions (605-648 nm) and iodocuprate anions (480-728 nm). Noteworthily, the relative ratio of the emission bands, and hence a resulting emission chromaticity, can be tuned in a wide range through modification of cluster [Cu_xI_y]^(y-x)- modules. The structural diversity, enhanced robustness, and up to 100% luminescence quantum yield make the designed materials promising phosphors for lighting and sensing applications.

Functionalized triphenylphosphine oxide-based manganese(II) complexes for luminescent printing

Three novel neutral manganese(ii) complexes (TPhPONMe2)2MnBr2, (TPhPOOMe)2MnBr2, and (TPhPOCF3)2MnBr2 have been designed and synthesized based on a functionalized Ph3PO ligand. These structures are clarified by single crystal X-ray diffraction analysis, which reveals that they crystallize in centrosymmetric space groups and feature an isolated mononuclear structure with Mn2+ in a tetrahedral environment. The photoluminescence spectra and emission lifetime decay curves of three manganese(ii) complexes show distinct green emission (λem = 498-512 nm) and phosphorescence lifetime (τ = 362.0-663.0 μs). The results of DFT calculations indicate that the energy levels of (TPhPONMe2)2MnBr2 and (TPhPOOMe)2MnBr2 are higher than that of (TPhPOCF3)2MnBr2 due to the electron-donating effect of the NMe2 or OMe group, which explains the blue-shift of the emission wavelength and the increase of emission lifetime. Furthermore, the prepared neutral manganese(ii) complexes can be used for high-resolution luminescent printing.

Synthesis and photoluminescence of manganese(II) naphtylphosphonic diamide complexes

Manganese(ii) halide complexes with N,N,N',N'-tetramethyl-P-naphtalen-2-ylphosphonic diamide were synthesized from anhydrous MnX2 salts (X = Cl, Br, I) and characterized. Single-crystal X-ray diffraction revealed in all the cases slightly distorted tetrahedral geometry of the coordination sphere. The photoluminescence spectra showed the superimposition of a green emission, related to the 4T1(4G) → 6A1(6S) transition of Mn(ii), with a band in the red range. Different possible attributions to the lowest-energy emission were taken into account. The emission spectra of the isolated products are dependent upon the nature of the halide and, in the case of X = Br, also upon the excitation wavelength.

Manganese(ii) bromo- and iodo-complexes with phosphoramidate and phosphonate ligands: synthesis, characterization and photoluminescence

Phosphoramidates and phosphonates are suitable ligands for the preparation of tetrahedral mono- and polynuclear Mn(ii) complexes characterized by green luminescence, influenced by the symmetry of the compounds and by the P-bonded substituents.

Photo- and triboluminescent robust 1D polymers made of Mn(ii) halides and meta-carborane based bis(phosphine oxide)

The 1D CPs of [Mn(L)X₂]_n type (X = Cl, Br, I), designed on 1,7-bis(diphenylphosphinyl)-m-carborane (L), show bright phosphorescence and triboluminescence, as well as exhibit thermo- and solvatochromic luminescence.

A family of Mn(ii) complexes exhibiting strong photo- and triboluminescence as well as polymorphic luminescence

New Mn(ii) complexes supported by diphosphine dioxides exhibit strong room-temperature phosphorescence as well as bright triboluminescence and polymorphic luminescence.

Light harvesting indolyl-substituted phosphoramide ligand for the enhancement of Mn(ii) luminescence

Excitation of the coordinated ligands in tetrahedral complexes having the general formula [MnX₂L₂] (X = Cl, Br, I; L = N,N′,N′-tetramethyl-P-indol-1-ylphosphonic diamide) causes bright green luminescence from the Mn(ii) centre.

Thermo-responsive light-emitting metal complexes and related materials

This review discusses the fundamentals and design strategies for the development of thermo-responsive metal–ligand coordination materials and the applications of these materials in temperature sensing, bioimaging, information security, etc.

Copper(II), Zinc(II), and Cadmium(II) Formylbenzoate Complexes: Reactivity and Emission Properties

Synthesis, characterization, reactivity, and sensing properties of 4-formylbenzoate complexes of copper(II), zinc(II), and cadmium(II) possessing the 1,10-phenanthroline ancillary ligand are studied. The crystal structures of the (1,10-phenanthroline)bis(4-formylbenzoate)(aqua)copper(II) and (1,10-phenanthroline)bis(4-formylbenzo-ate)zinc(II) and a novel molecular complex comprising an assembly of mononuclear and dinuclear species of (1,10-phenanthroline)bis(4-formylbenzoate)cadmium(II) are reported. These zinc and cadmium complexes are fluorescent; they show differentiable sensitivity to detect three positional isomers of nitroaniline. The mechanism of sensing of nitroanilines by 1,10-phenanthroline and the complexes are studied by fluorescence titrations, photoluminescence decay, and dynamic light scattering. A plausible mechanism showing that 1,10-phenanthroline ligand-based emission quenched by electron transfer from the excited state of 1,10-phenanthroline to nitroaniline is supported by density functional theory calculations. In an anticipation to generate a fluorescent d¹⁰-copper(I) formylbenzoate complex by a mild reducing agent such as hydroxylamine hydrochloride for similar sensing of nitroaromatics as that of the d¹⁰-zinc and cadmium 4-formylbenzoate complexes, reactivity of d⁹-copper(II) with hydroxylamine hydrochloride in the presence of 4-formylbenzoic acid and 1,10-phenanthroline is studied. It did not provide the expected copper(I) complex but resulted in stoichiometry-dependent reactions of 4-formylbenzoic acid with hydroxylamine hydrochloride in the presence of copper(II) acetate and 1,10-phenanthroline. Depending on the stoichiometry of reactants, an inclusion complex of bis(1,10-phenanthroline)(chloro)copper(II) chloride with in situ-formed 4-((hydroxyimino)methyl)benzoic acid or copper(II) 4-(hydroxycarbamoyl)benzoate complex was formed. The self-assembly of the inclusion complex has the bis(1,10-phenanthroline)(chloro)copper(II) cation encapsulated in hydrogen-bonded chloride-hydrate assembly with 4-((hydroxyimino)methyl)benzoic acid.

Thermoinduced structural-transformation and thermochromic luminescence in organic manganese chloride crystals

The [Mn2Cl9]5- mode of red emissive (C4NOH10)5Mn2Cl9·C2H5OH under thermal treatment will be cleaved into [MnCl4]2- in the green emissive (C4NOH10)2MnCl4 with the departure of ethanol. The rapid conversion of luminescence from red to green provides new insight into the luminescence origin and thermal stability of organic-inorganic metal halide hybrids.

Luminescence of the Mn2+ ion in non-Oh and Td coordination environments: the missing case of square pyramid

The luminescence of Mn²⁺ ion in a square-pyramidal (C_4v) ligand field was discovered. The molecular complexes with such coordination geometry exhibit red emission with enhanced Stokes shift and millisecond lifetimes.

Achievement of ligand-field induced thermochromic luminescence via two-step single-crystal to single-crystal transformations

We report here a new approach to achieve thermochromic luminescence through thermally induced ligand-field transformations. A one-dimensional chain manganese(ii) complex exhibits thermochromic luminescence from blue-green (502 nm) to red (617 nm) emission in a wide range of temperatures (480-80 K), ascribed to the conversion of a tetrahedronal to trigonal bipyramidal ligand-field via two-step single-crystal to single-crystal transformations.