The pressure effects on the optical and structural properties of NiWO4 have been studied experimentally and theoretically. The fundamental bandgap decreases with a pressure coefficient of −12.0 ± 0.2 meV/GPa. Meanwhile, the Ni2+ d–d transition energies increase at a rate of 7.4–14.8 meV/GPa. Therefore, the energy differences between the fundamental band and the Ni2+ d–d transition bands gradually decrease under pressure, which is beneficial to improve its optical performance. These optical phenomena are associated with structural variations. The shrinkage of the WO6 octahedron enhances the hybridization between the W 5d and O 2p orbitals, resulting in bandgap reduction. The pressure-induced enhancement of the NiO6 octahedral symmetry increases the crystal field splitting, thereby yielding increases in the Ni2+ d–d intraband transition energies. Besides, a pressure-induced structural phase transition is also observed around 20.0 GPa by both angle-dispersive synchrotron X-ray diffraction (ADXRD) and Raman experiments. This study provides valuable insight into the electron–lattice coupling of NiWO4 under compression and an effective way to modulate the electronic structure and optical properties of isomorphic wolframite materials.

Supramolecular coordination complexes with solidstate stimuli-responsive characteristics are highly desirable but are rarely reported. Herein, we describe two coordination-driven selfassembled monoanthracene or dianthracene-based hexagonal metallacycles by subtle structure modification. Notably, the dianthracenecontaining hexagon 1 exhibits tricolor mechanochromic and vapochromic characteristics, while the monoanthracene-containing hexagon 4 does not show obvious changes toward mechanical force. Further studies have indicated that changes in hexagon 1, especially the ulterior anthracene of hexagon 1 in the molecular stacking through intermolecular interactions toward external stimuli, are responsible for the above behavioral differences. Furthermore, the present work also demonstrates a novel light-harvesting strategy for achieving high-contrast mechanochromic fluorescence involving solidstate energy transfer from hexagon 1 to an organic carbazole derivant 6 without mechanofluorochromism or tetraphenylethylene derivant 7 exhibiting inconspicuous mechanofluorochromism.

Mechanochromic polymers exhibit potential applications in damage reporting and stress sensing. Despite the rapid progress achieved in recent years, mechanochromic structural polymers, such as epoxy thermosets, remain difficult to develop, let alone structural materials that can distinguish different levels of stress by a visual color change. This work presents a new class of multicolor mechanochromic epoxy thermosets that can discriminate between low and high compressive stresses via the incorporation of two distinct mechanophores. Amino-functionalized rhodamine (Rh) moieties serve as efficient curing agents and ratiometric stress sensors for epoxy thermosets. The Rh mechanophore in the epoxy network can be activated either by scratch or uniaxial compression, showing a reversible color change and a red fluorescence turn-on response. A stress-dependent multicolor response under uniaxial compression and hydrostatic pressure is achieved by the combination of Rh mechanophores with a commercial epoxy resin containing a 4,4′-diaminodiphenylmethane (DDM) framework. The Rh zwitterion formed at a low compressive stress turns the sample red, while a high compressive stress turns the sample green via the formation of the quinoidal methine form of DDM. Differential activation under varying degrees of compressive stress is demonstrated by UV–vis spectroscopy. The facile preparation and ability to recognize stress intensity by the naked eye make this strategy suitable for practical applications.

The pressure induced emission (PIE) behavior of halide perovskites has attracted extensive interest due to its potential application in pressure sensors and trademark security. However, the PIE phenomenon of white-light-emitting hybrid perovskites (WHPs) is rare, and that at pressures above 10.0 GPa has never been reported. Here, we effectively adjusted the perovskite to emit high-quality “cold” or “warm” white light and successfully realized pressure-induced emission (PIE) upon even higher pressure up to 35.1 GPa in one-dimensional halide perovskite C 4 N 2 H 14 PbCl 4 . We reveal that the degree of structural distortion and the rearrangement of the multiple self-trapped states position are consistent with the intriguing photoluminescence variation, which is further supported by in situ high-pressure synchrotron X-ray diffraction experiments and time-resolved photoluminescence decay dynamics data. The underlying relationship between octahedron behavior and emission plays a key role to obtain high-quality white emission perovskites. We anticipate that this work enhances our understanding of structure-dependent self-trapped exciton (STE) emission characteristics and stimulates the design of high-performance WHPs for next generation white LED lighting devices.

All lead-free inorganic halide perovskites, as efficient solid-state light emission materials, have become ideal green optoelectronic materials to replace lead halide perovskites for diversified lighting and display applications with their excellent stability. Here, we investigated the pressure-derived optical and structural response of a zero-dimensional lead-free perovskite Rb7Sb3Cl16 through applying controllable pressure. A pressure-induced blue shift of the broadband emission was achieved, and it was followed by the emission color transformation from yellow to green, which was ascribed to the electron–phonon coupling weakening and the suppression of structural deformation upon lattice contraction. In parallel, the band gap was narrowed by about 0.5 eV as a result of enhanced metal halide orbital overlap under high pressure. This work provides a fundamental understanding for modulating the optical properties of the low-dimensional metal halide perovskites.

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