A chameleon under pressure: The observed piezochromic behavior of the title compound (BP2VA) was found to depend on its molecular aggregation state and specifically on the strength of the π–π interaction between the anthracene rings of adjacent molecules. When BP2VA is ground or placed under pressure, its molecular aggregation state changes, and a red shift in the fluorescence emission from green via orange to red occurs (see picture).

Solid-state organic photoswitches with reversible luminescence modulation property are highly attractive because of their wide prospects in advanced photonic applications, such as optical data storage, anticounterfeiting and bioimaging. Yet, developing such materials has long been a significant challenge. In this work, we construct an efficient solid-state photoswitch based on a spiropyran-functionalized distyrylanthracene derivative (DSA-2SP) that exhibits exceptional reversible absorption/luminescence modulation ability. Efficient photoswitching between DSA-2SP and its photoisomer DSA-2MC are facilitated by large free volumes induced by nonplanar molecular structures of DSA moieties, as well as the intramolecular hydrogen bonds between the DSA and MC moieties. Consequently, the excellent solid-state photochromic property of DSA-2SP is highly applicable as both anticounterfeiting inks and super-resolution imaging agents.

We have studied the crystal structures and photophysical properties of four 9,10-distyrylanthracene (DSA) derivatives. Their crystal structures exhibit nonplanar conformations due to the supramolecular interactions resulting in rigid molecules and relative tight stacking. The four DSA derivatives possess a typical aggregation-induced emission (AIE) property, i.e., they exhibit faint emission in their solutions but intense emission in their crystals as a result of the dominant nonradiative decay by free intramolecular torsion in the solution and the restricted torsional motion by supramolecular interaction in the crystal. The investigation of the relationship between the crystal structures and AIE properties of the four DSA derivatives indicates that DSA moiety is the key factor of AIE property because of the restricted intramolecular torsion between the 9,10-anthrylene core and the vinylene moiety.

Perovskite solar cells (PSCs) have been demonstrated as one of the most promising candidates for solar energy harvesting. Here, for the first time, a functionalized nanographene (perthiolated trisulfur-annulated hexa-peri-hexabenzocoronene, TSHBC) is employed as the hole transporting material (HTM) in PSCs to achieve efficient charge extraction from perovskite, yielding the best efficiency of 12.8% in pristine form. The efficiency is readily improved up to 14.0% by doping with graphene sheets into TSHBC to enhance the charge transfer. By the HOMO-LUMO level engineering of TSHBC homologues, we demonstrate that the HOMO levels are critical for the performance of PSCs. Moreover, beneficial from the hydrophobic nature of TSHBC, the devices show the improved stability under AM 1.5 illumination in the humidity about 45% without encapsulation. These findings open the opportunities for efficient HTMs based on the functionalized nanographenes utilizing the strong interactions of their functional groups with perovskite.

4005wileyonlinelibrary.com in a low contrast ratio in the luminescence recording.High-contrast luminescence recording requires not only the obvious two-color luminescence switching, but also the dramatic switching in the luminescence intensity which is diffi cult to realize for the traditional piezochromic luminescent materials. [ 4 ] Recently, a few piezochromic materials with on-off or off-on luminescence property have been reported. Pei and co-workers [ 5 ] reported a turn-on luminescence of cocrystallized complex of 2,5-di( E )-distyrylfuran and N -alkyl-substituted maleimides by breaking the donoracceptor (D-A) interaction after applying mechanical force. Park and co-workers [ 4b , 6 ] found the mechanically controlled photoinduced electron transfer in molecular assemblies of dicyanodistyrylbenzene derivative with the obvious off-on luminescence, and shear-induced luminescence onoff switching in stilbenic π-dimer crystals by reversible [2 + 2] cycloaddition. Tang and co-workers [ 7 ] and Wang and co-workers [ 8 ] reported some crystallization-induced emission enhancement (CIEE) materials with on-off emission under grinding, respectively. In addition, Tang [ 9 ] reported the mechanical force induced off-on emission of the defect-sensitive crystals based on diaminomaleonitrile-functionalized Schiffbase. Almost all the above researches focused on the luminescence change under the mechanical grinding. However, the magnitude of the grinding force cannot be precisely controlled and the direction of the grinding force is anisotropic, which is diffi cult to investigate the mechanism of the piezochromic luminescence by mechanical grinding. Instead, the research of piezochromic luminescence under hydrostatic pressure is a more effective and controllable method to explore the piezochromic mechanism. Our group [ 10 ] and Yamaguchi group [ 11 ] have reported piezochromic luminescence of 9,10-bis(( E )-2-(pyrid-2-yl)vinyl)anthracene and tetrathiazolylthiophene, respectively, which both showed gradually redshifted wavelength and decreased intensity of luminescence due to the enhanced π-π interaction under the hydrostatic pressure.Herein, a structurally well-defi ned donor-acceptor (D-A) molecule, AD-TPE ( Figure 1 a), incorporating a twisted TPE unit as an electron donor, and a rigid AD unit as an electron acceptor have been readily synthesized with high yield according to Scheme S1 (Supporting Information) via the C-N couplingThe molecular crystals of acridonyl-tetraphenylethene (AD-TPE) exhibit an intriguing turn-on and color-tuned luminescence in response to mechanical grinding and hydrostatic compression. On the basis of in-depth experimental and computational studies, it is hypothesized that the origin of the piezochromic behavior from the D-phase to the B-phase is the change of the intramolecular geometrical conformation, especially for the torsion angle between the TPE and AD moiety. The different molecular conformation in the two distinctive solid phases causes the substantial switching of the intramolecular cha...