Twisted Intramolecular Charge Transfer in Polydimethylsilylene Bearing Pyrenyl Groups

Polydimethylsilylenes bearing pyrenyl groups exhibit emissions fromtwisted intramolecular charge transfer state between the aromatic ring and thesilicon backbone both in polar and nonpolar solvents.

Spectral Properties and Solubilization Location of 2′-Ethylhexyl 4-（N,N-Dimethylamino）benzoate in Micelles

Dual fluorescence and UV absorption of 2′-ethylhexyl 4-（N,N-dimethylamino）benzoate （EHDMAB） were investigated in cationic, non-ionic and anionic micelles. When EHDMAB was solubilized in different micelles, the UV absorption of EHDMAB was enhanced. Twisted intramolecular charge transfer （TICT） emission with longer wavelength was observed in ionic micelles, whereas TICT emission with shorter wavelength was obtained in non-ionic micelles. In particular, dual fluorescence of EHDMAB was significantly quenched by the positively charged pyridinium ions arranged in the Stern layer of cationic micelles. UV radiation absorbed mainly decays via TICT emission and radiationless deactivation. The dimethylamino group of EHDMAB experiences different polar environments in ionic and non-ionic micelles according to the polarity dependence of TICT emission of EHDMAB in organic solvents. In terms of the molecular structures and sizes of EHDMAB and surfactants, each individual EHDMAB molecule should be buried in micelles with its dimethylamino group toward the polar head groups of different micelles and with its 2′-ethylhexyl chain toward the hydrophobic micellar core. Dynamic fluorescence quenching measurements of EHDMAB provide further support for the location of EHDMAB in different micelles.

Computational chemistry-assisted design of hydrazine-based fluorescent molecular rotor for viscosity sensors

Deep understanding of the fluorescence quenching mechanisms of probes plays a crucial role in developing their practical applications.The fluorescence quenching mechanism of hydrazine-based fluorescence probes needs to be clarified up to the present.Herein,we designed and synthesized a new hydrazine-based fluorescence probe(HA-Na)based on the naphthalimide skeleton.We clarified the molecular origin of the non-fluorescence of this probe with the aid of computational chemistry and spectroscopic analysis.We showed that the significant rotation of the hydrazine group in the excited state potential energy surface,which caused the complete charge separation,was responsible for the fluorescence quenching of the probe in an organic solvent.Once the rotation was prevented in an aggregative state or high-viscosity solution,the fluorescence of the probe recovered.In other words,the fluorescence quenching mechanism of hydrazine-based fluorescence probes was attributed to the formation of a twisted intramolecular charge transfer(TICT)state.More importantly,we demonstrated that this fluorescence molecular rotor could be used to monitor the autophagy process in living cells by detecting lysosomal viscosity changes during starvation.Altogether,this work provides an essential theoretical basis for the developing potential hydrazine-based fluorescence molecular rotors.

Theoretical investigation on the fluorescent sensing mechanism for recognizing formaldehyde: TDDFT calculation and excited-state nonadiabatic dynamics

Inspired by the activity-based sensing method, the hydrazine-modified naphthalene derivative(Naph1) was synthesized and used as a fluorescent probe to detect formaldehyde(FA) in living cells. Through the condensation reaction between the probe Naph1 and analyte FA, researchers observed a ~14 folds enhancement of fluorescent signal around 510 nm in an experiment, realizing the high selectivity and sensitivity detection of FA. However, a theoretical understanding of the sensing mechanism was not provided in the experimental work. Given this, the light-up fluorescent detecting mechanism was in-depth unveiled by performing the time-dependent density functional theory(TDDFT) and the complete active space self-consistent field(CASSCF) theoretical calculations on excited-state intramolecular proton transfer(ESIPT)and non-adiabatic excited-state dynamics simulation. The deactivation channel of S_1/T_2 intersystem crossing(ISC) was turned off to successfully recognize FA. Insight into the ESIPT-based fluorescent detecting mechanism indicated that ESIPT was essential to light-up fluorescent probes. This work would provide a new viewpoint to develop ESIPT-based fluorescent probes for detecting reactive carbon species in vivo or vitio.

Olefin-linked covalent organic frameworks with twisted tertiary amine knots for enhanced ultraviolet detection

Though Olefin-linked covalent organic frameworks(oCOFs)possess excellentπ-electron delocalization,the barely reversible olefin linkage brings challenges for oCOFs’synthesis and functionalization.Here,we synthesize new oCOFs with tertiary amine knots which have twisted configuration and electron-donating nature.Investigation into the structural variation and photoelectric performance shows that the twisted configuration of oCOF-TFPA could favor to the intramolecular charge transfer process and reduce the pos-sibility of aggregation-caused quenching.Photoelectrical measurements and electric band structure cal-culation both verify the superiority of this oCOFs’structure in photoelectric sensing.

D-A-D-structured boron-dipyrromethene with aggregation-induced enhanced phototherapeutic efficiency for near-infrared fluorescent and photoacoustic imaging-guided synergistic photodynamic and photothermal cancer therapy

Clinical phototheranostic agents suffer from low absorption in near-infrared(NIR)region,decreasing singlet oxygen quantum yield(^(1)O_(2)QY)caused by aggregation in water,and low photothermal conversion efficiency(PCE),all of which are factors weakening their phototheranostic efficacy.Herein,we designed and synthesized a donor-acceptor-donor(D-A-D)structured boron-dipyrromethene derivative(B-2TPA)which exhibited NIR absorption and fluorescence.After being encapsulated in amphiphilic distearoyl phosphoethanolamine polyethyleneglycol 2000(DSPE-PEG-2000),the water-soluble B-2TPA nanoparticles(NPs)had increasing^(1)O_(2)QY(6.7%)due to the intermolecular aggregation-induced decrease in the energy gap between singlet and triplet excited states.Moreover,the quenched fluorescence and stable twisted intramolecular charge transfer in aggregates further increased the PCE of B-2TPA NPs to 60.1%.In vitro and in vivo studies confirmed that B-2TPA NPs could be used in NIR fluorescence and photoacoustic imagingguided synergistic photodynamic and photothermal therapy in tumor treatment.

Thermal Energy-Driven Solid-State Molecular Rotation Monitored by Real-Time Emissive Color Switching

Inspired by nature’s molecular machines,the scientific research on solid-state molecular rotors is of great interest yet remains largely unexplored.Herein,we report a unique example of a thermal energydriven stimuli-responsive solid-state molecular rotor,which features an o-carborane moiety as a rotor that directly transduces the surrounding thermal energy into molecular rotations in the crystalline state.Its rotation is confirmed by X-ray diffraction.

Emission-Tunable Nanofluorophores through Self-assembly of Amphiphilic Block Copolymers:toward Application in Cell Imaging

Comprehensive Summary Nanofluorophores based on aggregation-induced emission(AIE)dyes have recently received considerable attention because of their unique optical properties and biocompatibility.In this work,we report an emission-tunable nanofluorophore constructed by the self-assembly of an amphiphilic block copolymer(denoted by PTN).The diblock copolymer was synthesized by RAFT polymerization.A polyethylene glycol-based trithiocarbonate was employed as the macromolecular chain transfer agent,and a near-infrared emitting tetraphenylethylene derivative with a vinyl terminal group was designed as the monomer.The block copolymers self-assembled in an aqueous solution to form nanospheres,which showed near-infrared emission at approximately 720 nm with a significant Stokes shift of approximately 260 nm.Furthermore,nanofluorophores have excellent biocompatibility,photostability,and pH-independent emission-tunable properties,and were successfully applied to label HeLa cells for fluorescence imaging.