Vibration-Dependent Dual-Phosphorescent Cu4 Nanocluster with Remarkable Piezochromic Behavior.

The dual emission (DE) characteristics of atomically precise copper nanoclusters (Cu NCs) are of significant theoretical and practical interest. Despite this, the underlying mechanism driving DE in Cu NCs remains elusive, primarily due to the complexities of excited state processes. Herein, a novel [Cu4(PPh3)4(C≡C-p-NH2C6H4)3]PF6 (Cu4) NC, shielded by alkynyl and exhibiting DE, was synthesized. Hydrostatic pressure was applied to Cu4, for the first time, to investigate the mechanism of DE. With increasing pressure, the higher-energy emission peak of Cu4 gradually disappeared, leaving the lower-energy emission peak as the dominant emission. Additionally, the Cu4 crystal exhibited notable piezochromism transitioning from cyan to orange. Angle-dispersive synchrotron X-ray diffraction results revealed that the reduced inter-cluster distances under pressure brought the peripheral ligands closer, leading to the formation of new C-H⋅⋅⋅N and N-H⋅⋅⋅N hydrogen bonds in Cu4. It is proposed that these strengthened hydrogen bond interactions limit the ligands' vibration, resulting in the vanishing of the higher-energy peak. In situ high-pressure Raman and vibrationally resolved emission spectra demonstrated that the benzene ring C=C stretching vibration is the structural source of the DE in Cu4.

Chirality-Dependent Structural Transformation in Chiral 2D Perovskites under High Pressure.

Chiral perovskites have attracted considerable attention owing to their potential applications in spintronic- and polarization-based optoelectronic devices. However, the structural chirality/asymmetry transfer mechanism between chiral organic ammoniums and achiral inorganic frameworks is still equivocal, especially under extreme conditions, as the systematic structural differences between chiral and achiral perovskites have been rarely explored. Herein, we successfully synthesized a pair of new enantiomeric chiral perovskite (S/R-3PYEA)PbI4 (3PYEA2+ = C5NH5C2H4NH32+) and an achiral perovskite (rac-3PYEA)PbI4. Hydrostatic pressure was used, for the first time, to systematically investigate the differences in the structural evolution and optical behavior between (S/R-3PYEA)PbI4 and (rac-3PYEA)PbI4. At approximately 7.0 GPa, (S/R-3PYEA)PbI4 exhibits a chirality-dependent structural transformation with a bandgap "red jump" and dramatic piezochromism from translucent red to opaque black. Upon further compression, a previously unreported chirality-induced negative linear compressibility (NLC) is achieved in (S/R-3PYEA)PbI4. High-pressure structural characterizations and first-principles calculations demonstrate that pressure-driven homodirectional tilting of homochiral ammonium cations strengthens the interactions between S/R-3PYEA2+ and Pb-I frameworks, inducing the formation of new asymmetric hydrogen bonds N-H···I-Pb in (S/R-3PYEA)PbI4. The enhanced asymmetric H-bonding interactions further break the symmetry of (S/R-3PYEA)PbI4 and trigger a greater degree of in-plane and out-of-plane distortion of [PbI6]4- octahedra, which are responsible for chirality-dependent structural phase transition and NLC, respectively. Nevertheless, the balanced H-bonds incurred by equal proportions of S-3PYEA2+ and R-3PYEA2+ counteract the tilting force, leading to the absence of chirality-dependent structural transition, spectral "red jump", and NLC in (rac-3PYEA)PbI4.

Enantiomorphic Single Crystals of Linear Lead(II) Bromide Perovskitoids with White Circularly Polarized Emission.

Chiroptical hybrid organic-inorganic perovskites are emerging as a new class of promising materials with mirror optical signal responses for optoelectronic applications. However, chiroptical white-emission materials have been scarcely unearthed. Herein, four pairs of hybrid lead(II) bromide perovskitoids were obtained, namely, (R)- and (S)-(H2 MPz)PbBr4 (R/S-MPz=(R)-(-)/(S)-(+)-2-methylpiperazine) (1 and 2), (R)- and (S)-(H2 MPz)3 Pb2 Br10 ⋅2 DMAc (3 and 4), (R)- and (S)-(H2 MPz)PbBr4 ⋅0.5 MeCN (5 and 6) and (R)- and (S)-(H2 MPz)2 Pb2 Br8 ⋅DCM (7 and 8). Notably, they all exhibit ultrabroadband emission and chiroptical signals. Perovskitoids 3-6 even achieve white circularly polarized emission with a high dissymmetric factor (glum ) (±3×10-3 for 3 and 4; ±8×10-3 for 5 and 6). This new type of hybrid perovskitoids will attract attention and find applications in chiroptical fields because of the extensively and easily tunable photophysical properties.

A multi-responsive indium-viologen hybrid with ultrafast-response photochromism and electrochromism.

A novel 0D organic-inorganic metal halide hybrid (C13H16N2O2)2InCl6·Cl (1) has been obtained by integrating the mono-viologen derivative with InCl3. Compound 1 exhibits reversible and ultrafast UV/sunlight/X-ray induced photochromic properties, as well as excellent electrochromic performance, which is the first example of an indium-based organic-inorganic chromic hybrid.

Pressure-Triggered Blue Emission of Zero-Dimensional Organic Bismuth Bromide Perovskite.

Understanding the structure-property relationships in Zero-dimensional (0D) organic-inorganic metal halide perovskites (OMHPs) is essential for their use in optoelectronic applications. Moreover, increasing the emission intensity, particularly for blue emission, is considerably a challenge. Here, intriguing pressure-induced emission (PIE) is successfully achieved from an initially nonluminous 0D OMHP [(C6H11NH3)4BiBr6]Br·CH3CN (Cy4BiBr7 ) upon compression. The emission intensity increases significantly, even reaching high-efficiency blue luminescence, as the external pressure is increased to 4.9 GPa. Analyses of the in situ high-pressure experiments and first-principle calculations indicate that the observed PIE can be attributed to the enhanced exciton binding energy associated with [BiBr6]3- octahedron distortion under pressure. This study of Cy4BiBr7 sheds light on the relationship between the structure and optical properties of OMHPs. The results may improve potential applications of such materials in the fields of pressure sensing and trademark security.

Thermochromism and piezochromism of an atomically precise high-nuclearity silver sulfide nanocluster.

A novel high-nuclearity silver sulfide nanocluster [Ag50S7(SC6H4F)36(dppp)6]·4DMI, (hereafter abbreviated as 1⋅4DMI) was synthesised. Solvent-free crystals of 1 displayed a completely reversible narrowing and broadening of the optical band gap that was accompanied by visual thermochromism and piezochromism changeovers, when stimulated by varying temperatures between 113 and 413 K or by changing the pressure from 1 atm to 7.5 GPa.

Circularly Polarized Luminescence from Achiral Single Crystals of Hybrid Manganese Halides.

[K(dibenzo-18-crown-6)]+ (KC) cations are used for cocrystallization with manganese halides, producing isostructural single crystals of organic-inorganic hybrid complexes, [K(dibenzo-18-crown-6)]2MnX4 (abbreviated (KC)2MnX4) (X = Cl, Br), which feature one-dimensional morphology and green phosphorescence with considerable photoluminescence quantum yields accompanied by excellent optical waveguide behavior with a low loss coefficient. More interestingly, (KC)2MnX4 crystallizes in the monoclinic space group Cc belonging to the achiral point group m (Cs), where the non-centrosymmetric arrangement of racemic units, with right- and left-handed rotating optical axes, endows these achiral single crystals with circularly polarized luminescence, observed for the first time.

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.