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.

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...

Photoinduced electron transfer (PET) is one of the most important mechanisms for developing fluorescent probes and biosensors. Quantitative prediction of the quantum yields of these probes and sensors is crucial to accelerate the rational development of novel PET-based functional materials. Herein, we developed a general descriptor (ΔE) for predicting the quantum yield of PET probes, with a threshold value of ∼0.6 eV. When ΔE < ∼0.6 eV, the quantum yield is low (mostly <2%) due to the substantial activation of PET in polar environments; when ΔE > ∼0.6 eV, the quantum yield is high because of the inhibition of PET. This simple yet effective descriptor is applicable to a wide range of fluorophores, such as BODIPY, fluorescein, rhodamine, and Si-rhodamine. This ΔE descriptor enables us not only to establish new applications for existing PET probes but also to quantitatively design novel PET-based fluorophores for wash-free bioimaging and AIEgen development.

Two methoxy-substituted tetraphenylethylene (TPE) derivatives, tetra(4-methoxyphenyl)ethylene (TMOE) and tetra(3,4-dimethoxyphenyl)ethylene (TDMOE), were synthesized by McMurry reaction in high yields.The nearly centrosymmetric and natural propeller shape of TMOE and TDMOE excluded intermolecular effects, such as H or J-aggregation and p-p stacking, on their AIE (AIEE) and mechanofluorochromic performance. The crystal structures of TMOE and TDMOE, and theoretical calculations proved that their emission colours are determined by single molecular conjugation. These molecules were used to investigate pure conformational effects on molecular emissions. The spectral properties of these molecules in five environments of crystal(s), THF solution, THF-water binary solution, solidified THF and amorphous states, were investigated. The crystalline to amorphous phase transition by grinding resulted in good mechanofluorochromic performances with high quantum yields and distinguishable emission change, which was further explored as anti-counterfeiting inks on banknotes.

Two tetraphenylethene (TPE)-functionalized spiropyran (SP) molecules with very similar structure were designed and synthesized. The two molecules exhibit aggregation-induced emission (AIE) properties, as well as multistimuli-responsive color-changing properties, such as photochromism and acidchromism. The investigation of their different photochromic and acidchromic characteristics and dual-response fluorescent switch during isomerization indicated that the different link position between TPE and SP will significantly affect the extended π-conjugated system, resulting in completely different photochromic and acidchromic properties.

Rhodamine spirolactams with adjacent amino groups work as acid-resistant and photoswitchable fluorophores in single-molecule localization super-resolution imaging.

The mechanochromic property of tetrakis(4-(dimethylamino)phenyl)ethylene (TDMAPE) with natural propeller shape and nearly centrosymmetric structure was investigated. The destruction of the crystalline structure leads to the planarization of molecular conformation, which is considered as a possible reason for the red-shift of absorption and fluorescence spectra after grinding. And the polymorphism-dependent emissions of the two polymorphs of TDMAPE are mainly determined by the intramolecular conformation, which show the increased coplanarity or conjugation degree, ultimately leading to the bathochromic shift of the emissions.

A near-infrared (NIR) mechanophore was developed and incorporated into a poly­(methyl acrylate) chain to showcase the first force-induced NIR chromism in polymeric materials. This mechanophore, based on benzo­[1,3]­oxazine (OX) fused with a heptamethine cyanine moiety, exhibited NIR mechanochromism in solution, thin-film, and bulk states. The mechanochemical activity was validated using UV–vis–NIR absorption/fluorescence spectroscopies, gel permeation chromatography (GPC), NMR, and DFT simulations. Our work demonstrates that NIR mechanochromic polymers have considerable potential in mechanical force sensing, damage detection, bioimaging, and biomechanics.