Most organic piezochromic materials exhibit red-shifted and quenched emission as pressure increases. However, an abnormal phenomenon of pressure-induced blue-shifted and enhanced emission is observed in a 9-(3-(1,2,2-triphenylvinyl)phenyl)anthracene crystal, which is based on discrete π−π anthracene (AN) dimers stacking with tetraphenylethylene (TPE) as spacer. A blue-shifted emission appears and strengthens when the pressure is more than 1.23 GPa, and it reaches the maximum when the pressure is 4.28 GPa. This phenomenon is ascribed to the cooperative effect between the aggregation-induced emission of TPE units and energy-transfer suppression from TPE to an AN excimer. This work reports a new concept in the piezochromic field and provides a novel strategy to achieve luminescence from a high-lying excited state.

Pressure-induced emission enhancement (PIEE), a novel phenomenon in the enhancement of the solid-state emission efficiency of fluorophores, has been arousing wide attention in recent years. However, research on PIEE is still in the early stage. To further pursue more enhanced efficiency, discovering and designing more PIEE systems would be urgently desirable and of great importance. In this Letter, we found that carbazole presented a conspicuous emission enhancement under high pressure up to 1.0 GPa. In situ high-pressure infrared spectroscopy and angle-dispersive X-ray diffraction analysis combined with Hirshfeld surface theory calculation indicated that the PIEE of carbazole was attributed to the decrease of the nonradiation vibration process. This phenomenon mainly resulted from restriction of the N-H stretching vibration by increased N-H···π interactions under high pressure. Our study puts forward a mechanism of PIEE related to the restriction of intramolecular vibration, which provided deep insight into the essential role of intermolecular interaction in fluorescence emission properties.

Although some bright, organic mechanoluminescence (ML) luminogens with aggregation‐induced emission properties and twisted molecular structures are recently reported, those with planar structures and bright ML and their related effective design strategies are not yet explored, partially due to aggregation‐caused quenching in luminogens with planar structures. Herein, using the unique solid‐state packing style of pyrene, bright dual monomer‐excimer‐ML and excimer‐ML from two pyrene derivatives (Py‐Bpin and Py‐Br) with a simple, planar molecular structure are reported for the first time, and two analogs of pyrene and Py‐H are used for comparison. These four luminogens display similar optical properties in dilute solution but different luminescent properties in the solid state, mainly due to their different molecular packing. Interestingly, pyrene is mechanochromism (MC)‐ and ML‐inactive, while Py‐H is MC‐active, Py‐Bpin is MC‐ and ML‐active, and Py‐Br is ML‐active. The relationship between molecular packing and ML/MC properties is confirmed by analyzing single‐crystal structures and related experimental results, providing important information to further understand the mysterious ML process and opening a new way to design efficient luminogens with both MC and ML.

Mechanoresponsive luminescent (MRL) materials have attracted considerable attention because of their potential applications in mechanical sensors, memory chips, and security inks; MRL materials possessing high efficiency and multicolor emission qualities are especially interesting. In this Letter, we found 1,2,3,4-tetraphenyl-1,3-cyclopentadiene (TPC) crystal exhibited both pressure-induced emission enhancement (PIEE) and multicolor behavior. In addition, infrared spectroscopy analysis indicated that the ring-opening reaction of the phenyl ring occurred when pressure was beyond 24.7 GPa. The reaction was promoted from 24.7 to 35.9 GPa, which resulted in the redder irreversible color change for the sample released from 35.9 GPa than from 24.7 GPa. The results regarding the mechanoresponsive behavior of TPC offered a deep insight into PIEE and multicolor properties from the structural point of view and inspired the idea of capturing different colors by hydrostatic pressure, which will facilitate the design of and search for high-performance MRL materials.

Microfluidic spinning, as a combination of wet spinning and microfluidic technology, has been used to develop microfibers with special structures to facilitate cell 3D culture/co‐culture and microtissue formation in vitro. In this study, a simple microchip‐based microfluidic spinning strategy is presented for the fabrication of multicomponent heterogeneous calcium alginate microfibers. The use of two kinds of microchip enables the one‐step preparation of multicomponent heterogeneous microfibers with various arrangement patterns, including the preparation of one‐, two‐, and three‐component microfibers by a two‐layer microchip and preparation of four component microfibers with different arrangement by a membrane‐sandwiched three‐layer microchip. The obtained microfibers could be used to encapsulate various kinds of cells, such as the human non‐small cell lung cancer cell NCI‐H1650, the human fetal lung fibroblast HFL1, the normal pulmonary bronchial epithelial cell 16HBE, and human umbilical vein endothelial cells. By adding chitosan to the medium to keep the fibers stable, 3D long‐term in vitro cell co‐culture has been carried out up to 21 days. This method is very simple and easy to operate, continuously produces spatially well‐defined heterogeneous microfibers, has important applications for composite functional biomaterials, and shows great potential in organs‐on‐a‐chip and biomimetic systems.

Pressure-induced emission enhancement (PIEE) is a new phenomenon that has attracted widespread attention in the past few years for improving the solid-state emission efficiency of fluorophores. However, a thorny issue still remains in the study of PIEE. Thus, it is urgent and important to discover and design more PIEE systems for further enhancing the efficiency. In this paper, we found that triphenylethylene (TriPE) showed both conspicuous emission enhancement within the pressure range of 0.0–0.8 GPa and piezochromism behavior upon compression. More interestingly, infrared (IR) analysis indicated that ring-opening reaction of the phenyl ring occurred when pressure was beyond 14.2 GPa. Also, the ring-opening reaction of the phenyl ring led to irreversible optical changes. In situ high-pressure IR spectroscopy and angle-dispersive X-ray diffraction analysis demonstrated that the PIEE of TriPE was attributed to the related C–H···π and C–H···C hydrogen bonds that could inhibit or restrict the movement of aromatic parts remarkably, restraining the energy loss by intramolecular motion. Our study provides insights into the significant effect of intermolecular interactions on fluorescence emission properties.

Mechanoresponsive luminescent materials have attracted widespread attention for their potential applications, especially for these behaving pressure-induced emission enhancement (PIEE). Designing and seeking systems with high-efficiency PIEE are desirable and crucial for material science. Here, the mechanisms of different piezoresponsive luminescence of 2,3,4,5-tetraphenylthiophene (TPT) and 2,3,4,5-tetraphenylfuran (TPF) crystals are explored. The experimental results combined with density functional theory (DFT) theory calculation indicate that the PIEE phenomenon is possibly exhibited in V-shape arrangement for the reason of the weak π–π interactions. This study not only gains deep insight into the relationship between optical properties and structural evolution but also puts forward a strategy for designing PIEE materials from the point of molecular arrangement.

The control of molecular packing at the molecular design stage is significant but challenging. Herein, a strategy is provided to regulate the molecular packing of pyrene derivatives based on steric and electronic effects. Two tertiary butyl groups are introduced as isolation groups to enlarge the intermolecular distance to accommodate the tendency of monomer‐like packing. By increasing the electron‐withdrawing ability of substituents, tunable and tighter packing motifs can be realized owing to the decreasing electron density of the pyrene ring. Accordingly, coupled with quenched emissions in monomer‐like packing and bright emissions in dimer‐like packing, compound 4‐(2,7‐di‐tert‐butylpyren‐4‐yl)benzaldehyde (PPCHO) shows an off–on mechanochromism with high performance (contrast ratio reaching 400 compared with the normal figure of <100), demonstrating the power of molecular design. Encryption based on the unique off–on mechanochromism characteristic of PPCHO demonstrates good sensitivity and reversibility.