Luminescent Behavior of Zn(II) and Mn(II) Halide Derivatives of 4-Phenyldinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine 4-Oxide and Single-Crystal X-ray Structure Determination of the Ligand

The two enantiomers of chiral phosphonate 4-phenyldinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine 4-oxide, O=PPh(BINOL), were synthesized from the proper 1,1'-bi-2-naphtol (BINOL) enantiomer and characterized. The structure of the (S)-enantiomer was elucidated by means of single-crystal X-ray diffraction. The reaction with anhydrous ZnBr2 afforded complexes having the general formula [ZnBr2{O=PPh(BINOL)}2] that showed intense fluorescence centered in the near-UV region rationalized on the basis of TD-DFT calculations. The corresponding Mn(II) complexes with the general formula [MnX2{O=PPh(BINOL)}2] (X = Cl, Br) exhibited dual emission upon excitation with UV light, with the relative intensity of the bands dependent upon the choice of the halide. The highest energy transition is comparable with that of the Zn(II) complex, while the lowest energy emission falls in the red region of the spectrum and is characterized by lifetimes in the hundreds of microseconds range. Although the emission at lower energy can also be achieved by direct excitation of the metal center, the luminescence decay curves suggest that the band in the red range is possibly derived from BINOL-centered excited states populated by intersystem crossing.

E- or Z-Isomers Arising from the Geometries of Ligands in the Mercury Complex of 2-(Anthracen-9-ylmethylene)-N-phenylhydrazine Carbothioamide

An anionic mercury(II) complex of 2-(anthracen-9-ylmethylene)-N-phenylhydrazine carbothioamide (HATU) and two isomers of a neutral mercury(II) complex of the anion of the same ligand (ATU) were reported. The anionic complex [Hg(HATU)2Cl2]·CH2Cl2 had a monodentate HATU ligand (a neutral form of the ligand) and chloride ligands. The two conformational isomers were of the neutral mercury(II) complex Hg(ATU)2·2DMF. The two isomers were from the E or Z geometry of the ligands across the conjugated C=N-N=C-N scaffold of the coordinated ligand. The two isomers of the complex were independently prepared and characterized. The spectroscopic properties of the isomers in solution were studied by 1H NMR as well as fluorescence spectroscopy. Facile conversion of the E-isomer to the Z-isomer in solution was observed. Density functional theory (DFT) calculations revealed that the Z-isomer of the complex was stable compared to the E-isomer by an energy of 14.35 kJ/mol; whereas, E isomer of the ligand was more stable than Z isomer by 8.37 KJ/mol. The activation barrier for the conversion of the E-isomer to the Z-isomer of the ligand was 167.37 kJ/mol. The role of the mercury ion in the conversion of the E-form to the Z-form was discussed. The mercury complex [Hg(HATU)2Cl2]·CH2Cl2 had the E-form of the ligand. Distinct photophysical features of these mercury complexes were presented.

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.

Competitive Dual-Emission-Induced Thermochromic Luminescence in Organic-Metal Halides

Lead-free Halides, especially Mn-based ones, are preferred as hotspots in the exploration of photoluminescent materials. However, there are few reports on sensitive reversible thermochromism and switchable dual emission originating from self-trapped exciton emission in pure Mn-Based materials. Here, we report a new Mn-based hybrid material [TMPA]₂MnI₄ (TMPA = trimethylphenylammonium), which shows two emission peaks at 545 and 660 nm benefitting from the d-d orbital transition of Mn²⁺ and the generation of self-trapped excitons, respectively. Due to the different sensitivity to temperature, the stages of thermal activation and thermal quenching of the two emission types are also inconsistent, showing a certain competition relationship and dominating the emission colors in different temperature ranges, resulting in adjustable green-orange-green thermochromic luminescence from 100 to 403 K (both high and low temperatures correspond to green, and orange is displayed at near room temperature). Therefore, thermochromic luminescence can be easily achieved by controlling the temperature under the guidance of excited states. This work provides new insights into the synthesis and application of thermochromic materials. Therefore, it is certain that regulating temperature while being guided by excited states will achieve thermochromic luminescence. This research offers fresh perspectives on the development and potential of thermochromic materials.

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.

Controlled Synthesis of Luminescent Xanthene Dyes and Use of Ionic Liquid in Thermochromic Reaction

In this study, we demonstrate six novel xanthene derivatives and their spectroscopic and chemical properties. The presented synthesis examination allowed us to obtain two different compounds during one step, with open and closed lactone rings substituted with different length alkyl chains. Increasing the reaction efficiency to 77% was obtained using the microwave-assisted method. Moreover, the modification of O-alkylation synthesis in an ecofriendly way using a ball mill led to achieving exclusively one opened ring product. All of the synthesized compounds showed different spectroscopic behaviors in comparison with the different organic dyes; the typical concentration quenching of luminescence was not observed. The relationship between the length of the alkyl chain and the time of luminescence decay is presented. Synthetized closed forms of dyes turned out to be promising leuco dyes. For the first time, an ionic liquid was used as a developer of synthesized xanthene derivatives (as leuco dyes), which led to obtaining an irreversible thermochromic marker.

Metal ion modulation triggers dielectric double switching and green fluorescence in A2MX4-type compounds

Multifunctional switching materials show great potential for applications in sensors, smart switches, and other fields due to their ability to integrate different physical channels in one single device. However, multifunctional responsive materials with multiple switching and luminescence properties have rarely been reported. Here, we report three organic-inorganic hybrids: [TMAA]₂[CoCl₄] (compound 1), [TMAA]₂[CdBr₄] (compound 2) and [TMAA]₂[MnCl₄] (compound 3). Compound 1 and compound 2 undergo two reversible phase transitions at high temperature (328.95/359.25 K and 350.45/393.15 K, respectively). Since the inorganic skeleton has a strong influence on the luminescence properties of such structured substances, Cd and Co were replaced with Mn, after which compound 3 was obtained as expected. The above strategy triggered bright green luminescence with a quantum yield of 35.19%, and significantly increased the phase transition temperature of compound 3 to above 400 K. The above results show that the regulation of the inorganic skeleton provides a new strategy for researchers to develop dual phase change/luminous materials.

Sawtooth chains self-assembled from clusters of MnO6 octahedra within the silicate framework of K3Mn4Si10O24.33(H2O,OH)3/V,B

A disordered mineralogically probable silicate hydrate K3Mn4Si10O24.33(H2O,OH)3/V,B, obtained hydrothermally, demonstrates low-dimensional magnetic behavior.