Low-Pressure Sensitive Piezochromic Fluorescence Switching of Tetraphenylethylene-Anthraquinone.

Invited for the cover of this issue are Prof. Wenjing Tian and co-workers at Jilin University. The image depicts the highly sensitive piezochromic fluorescence switching of tetraphenylethylene-anthraquinone under low-pressure regimes (∼60 kPa). Read the full text of the article at 10.1002/chem.202301070.

Low-Pressure Sensitive Piezochromic Fluorescence Switching of Tetraphenylethylene-Anthraquinone.

Sensing of low-pressure signals is of great importance for cutting-edge technologies. Organic piezochromic molecules offer a promising library of pressure sensitive materials which can be tailor-designed toward specific requirements. However, very few examples of low-pressure sensitive piezochromic fluorescent molecules have been obtained till date, and the underlying mechanisms are still in its infancy. Herein, we report highly sensitive piezochromic fluorescent switching under low-pressure regimes (∼60 kPa) of tetraphenylethylene-anthraquinone (TPE-AQ) based on the controlled molecular design and polymorphic phase strategy. The influence of both intramolecular conformation effect and variations of intermolecular stacking modes on the piezochromic property of TPE-AQ is investigated. The underlying mechanism of the low-pressure sensitive piezochromic fluorescence switching is demonstrated to be closely related to the loosely packed molecular orientation, as confirmed by X-ray diffraction measurements combined with simulations. This work provides a way to design highly efficient pressure sensors based on organic molecular systems.

Photoinduced Fluorescence Switching in Molecular Aggregates by Topological [2+2] Cycloaddition.

The optical modulation of fluorescence characteristics in molecular aggregates, which mainly involves diverse molecular stacking and the consequent intermolecular interactions, remains a significant challenge for potential applications in optical anticounterfeiting, data storage, and imaging. Here we successfully realize in situ fluorescence switching in molecular aggregates of thianaphthene-dioxide derivatives by topological [2+2] photocycloaddition, which represents a promising way to regulate the molecular stacking and alter photophysical processes. Notably, 2-(3,5-bis-trifluoromethylphenyl)benzo[b]thiophene-dioxide (BTO-TF) in both crystal and powder forms exhibits a unique switching from an initial nonfluorescent state to a highly fluorescent state (ΦPL =0.46) upon UV irradiation, because of the destruction of the [2+2] cycloaddition process by volume expansion of the photodimer. Furthermore, we demonstrate such a [2+2] photocycloaddition can occur when 2-(4-carboxypheny)benzo[b]thiophene-dioxide (BTO-OH) is doped within selective polymer matrixes, and can be utilized for the visualization of macrophase separation in polymer blends.

Discrete Platinum(II) Metallacycles with Inner- and Outer-Modified 9,10-Distyrylanthracene: Design, Self-Assembly, and Luminescence Properties.

To completely unravel the relationship between structures and luminescence properties of inner- and outer-modified metallacycles, two rhombic metallacycles S1 and S2 with 9,10-distyrylanthracene (DSA) were constructed herein via the design of DSA moieties on the inside or outside of metallacycles. Similar building blocks of the two metallacycles led to the same emission wavelengths in a dilute solution. In contrast, their fluorescence emissions in the aggregation and solid states were significantly different and revealed interesting emission behaviors from structures with inner- and outer-modified design. Finally, based on their luminescence properties, a tunable solid-state fluorescence emissive material was easily obtained by the mixing of two supramolecules in different ratios. This unique design suggested that the modified position of fluorophores exerts a key impact on the adjustment of luminescence from a dilute solution to the aggregated state and will be of great significance for the development of luminescent materials based on supramolecules.

Reversible Photoswitching between Fluorescence and Room Temperature Phosphorescence by Manipulating Excited State Dynamics in Molecular Aggregates.

Regulation of fluorescence-phosphorescence pathways in organic molecular aggregate remains a challenge due to the complicated singlet-triplet excited state dynamics process. Herein, we demonstrated a successful example (o-BFT) to realize photoreversible fluorescence and room temperature phosphorescence (RTP) switching based on an effective strategy of integrating a phosphor (dibenzofuran) with a photoswitch (dithienylbenzothiophene). o-BFT exhibited dual emission of fluorescence and RTP in both powder and doping polymer film. Notably, the long-lived RTP of o-BFT could be repeatedly erased and restored through reversible photocyclization and decyclization under alternate ultraviolet and visible photoirradiation. In-depth theoretical and spectroscopic investigations revealed that the triplet inactivation was dominated by a photo-controlled triplet-to-singlet Förster resonance energy transfer from light-activated o-BFT to photoisomer c-BFT. Yet, the initial fluorescence could be preserved in this process to afford a photoreversible fluorescence-RTP switching.

Reversible Three-Color Fluorescence Switching of an Organic Molecule in the Solid State via "Pump-Trigger" Optical Manipulation.

In photoswitches that undergo fluorescence switching upon ultraviolet irradiation, photoluminescence and photoisomerization often occur simultaneously, leading to unstable fluorescence properties. Here, we successfully demonstrated reversible solid-state triple fluorescence switching through "Pump-Trigger" multiphoton manipulation. A novel fluorescence photoswitch, BOSA-SP, achieved green, yellow, and red fluorescence under excitation by pump light and isomerization induced by trigger light. The energy ranges of photoexcitation and photoisomerization did not overlap, enabling appropriate selection of the multiphoton light for "pump" and "trigger" photoswitching, respectively. Additionally, the large free volume of the spiropyran (SP) moiety in the solid state promoted reversible photoisomerization. Switching between "pump" and "trigger" light is useful for three-color tunable switching cell imaging, which can be exploited in programmable fluorescence switching. Furthermore, we exploited reversible dual-fluorescence switching in a single molecular system to successfully achieve two-color super-resolution imaging.

Folding-Induced Spin-Orbit Coupling Enhancement for Efficient Pure Organic Room-Temperature Phosphorescence.

For the direct luminescence of triplet excitons, different mechanisms have been proposed for realizing pure organic room-temperature phosphorescence (RTP). To further verify the mechanism of folding-induced spin-orbit coupling (SOC) enhancement, two analogues of thianthrene (TA) were introduced by gradually replacing the sulfur atom with an oxygen atom for a systematical comparison, corresponding to phenoxathiine (PX) and dioxins (DX) molecules with increasing folding dihedral angles (or decreasing degrees of folding). Photophysical measurements show an obviously enhanced RTP efficiency from DX and PX to TA, which is consistent with their greatly enhanced SOC with a decrease in folding dihedral angle. The folding angle-dependent SOC calculations for each molecule reveal that this enhanced RTP is dominated by folding-induced SOC enhancement, in contrast with the negligible heavy-atom effect from oxygen to sulfur. This work further validates the rationality of the folding-induced SOC enhancement mechanism, which provides an innovative molecular design strategy for developing efficient pure organic RTP materials using folding structures.

Exploiting radical-pair intersystem crossing for maximizing singlet oxygen quantum yields in pure organic fluorescent photosensitizers.

Fluorescent photosensitizers (PSs) often encounter low singlet oxygen (1O2) quantum yields and fluorescence quenching in the aggregated state, mainly involving the intersystem crossing process. Herein, we successfully realize maximizing 1O2 quantum yields of fluorescent PSs through promoting radical-pair intersystem crossing (RP-ISC), which serves as a molecular symmetry-controlling strategy of donor-acceptor (D-A) motifs. The symmetric quadrupolar A-D-A molecule PTP exhibits an excellent 1O2 quantum yield of 97.0% with bright near-infrared fluorescence in the aggregated state. Theoretical and ultrafast spectroscopic studies suggested that the RP-ISC mechanism dominated the formation of the triplet for PTP, where effective charge separation and an ultralow singlet-triplet energy gap (0.01 eV) enhanced the ISC process to maximize 1O2 generation. Furthermore, in vitro and in vivo experiments demonstrated the dual function of PTP as a fluorescent imaging agent and an anti-cancer therapeutic, with promising potential applications in both diagnosis and theranostics.

Protective effect of pantoprazole against sepsis-induced acute lung and kidney injury in rats.

To investigate the effect of pantoprazole on acute lung and kidney injury with sepsis and its possible mechanism. Rats were randomly divided into six groups, the status and lung wet/dry weight ratio were determined at various time points. Hematoxylin Eosin staining (HE) for pathological changes in the lungs and kidneys of rats with sepsis. Western blot (WB) and immunohistochemistry were used to detect the pulmonary surfactant protein A(SPA) and D(SPD). The levels of markers for kidney damage in serum and urine various time points were measured by ELISA. The apoptosis in lung and kidney tissue of rats were detected using TUNEL assay. Subsequently, the cell apoptosis of LPS-induced BEAS-2B and HK-2 cells after pantoprazole treatment were detected using flow cytometry. The levels of RHOA/ROCK signaling pathway proteins in the lung and kidney tissues and cells were detected using WB. Our results indicated that Pantoprazole could suppress the expression of inflammatory factors in the blood and alleviate pathological damage of lung and kidney tissues in rats with sepsis. Pantoprazole treatment could reduce apoptosis in lung and kidney tissues and inhibit cell apoptosis induced by LPS. In addition, pantoprazole can inhibit RHOA/ROCK signaling pathway proteins and the levels of inflammatory factors in LPS-induced BEAS-2B and HK-2 cells. Pantoprazole can improve the symptoms of acute lung and kidney injury in septic rats, which suggested that pantoprazole might be used to guide the treatment of sepsis.