Time-Dependent Stokes Shift from Solvent Dielectric Relaxation

The Stokes shift response function, which is related to the time dependent solvation energy, is calculated with the dielectric response function and a novel expression of nonequilibrium solvation energy. In the derivation, relationship between the polarization and the dielectric response function is used. With the dipole-in-a-sphere model applied to the system coumarin 343 and water as the solvent, encouraging agreement with the experimental data from Jimenez et al. is obtained [Nature 369, 471 （1994）].

A pyrene-based ratiometric fluorescent probe with a large Stokes shift for selective detection of hydrogen peroxide in living cells

Hydrogen peroxide(H2O2)plays a significant role in regulating a variety of biological processes.Dysregulation of H2O2 can lead to various diseases.Although numerous fluorescent imaging probes for H2O2 have been reported,the development of H2O2 ratiometric fluorescent probe with large Stokes shift remains rather limited.Such probes have shown distinct advantages,such as minimized interference from environment and improved signal-to noise ratio.In this work,we reported a new pyrene-based compound Py-VPB as H2O2 fluorescent probe in vitro.The probe demonstrated ratiometric detection behavior,large Stokes shift and large emission shift.In addition,the probe showed high sensitivity and selectivity towards H2O2 in vitro.Based on these excellent properties,we successfully applied Py-VPB to the visualization of exogenous and endogenous H2O2 in living cells.Cell imaging study also showed that our probe was localized in the mitochondria.We envision that the probe can provide a useful tool for unmasking the biological roles of mitochondrial H2O2 in living systems.

Inverted Solvatochromic Stokes Shift in GFP-like Chromophores with Extended Conjugation

Chrornophore structures inspired by natural green fluorescent protein （GFP） play an im- portant role in the field of bio-irnaging. In this work, photochemical properties of a new class of GFP-like chromophores are investigated using computational approaches. Thermo- dynamically stable isomers are identified in vacuum and in solvent. Spectral Stokes shifts are computed and compared to experiments. An inverted solvatochromic shift between absorption and emission emerging in this new class of GFP-like chromophores is observed, and attributed to the stabilized charge transfer and inhibited rotational structural reorganization in solvent.

A non-peptide-based chymotrypsin-targeted long-wavelength emission fluorescent probe with large Stokes shift and its application in bioimaging

As a hydrolase,chymotrypsin(CHT)is involved in many physiological activities,and its abnormal activity is closely related to diabetes,pancreatic fibrosis,chronic pancreatitis and pancreatic cancer.In this work,an innovative long-wavelength emission fluorescent probe TCF-CHT was designed and synthesized for the high specificity detection of CHT,which utilized TCF-OH and a mimetic peptide substrate 4-bromobutyryl as chromogenic group and recognition group,respectively.TCF-CHT exhibited excellent selectivity and eye-catching sensitivity(8.91 ng/m L)towards CHT,“off-on”long-wavelength emission at 670 nm and large Stokes shift(140 nm).Furthermore,the successful fulfillment and perfect performance in imaging endogenous CHT in complex organisms(P815 cells,HepG2 cells,zebrafish and tumor-bearing mice)verified its potential as a powerful tool for the recognition of CHT in complicated biological environments.

Fast Response Fluorescent Probe with a Large Stokes Shift for Thiophenol Detection in Water Samples and Cell Imaging

Herein,the 2,4-dinitrophenyl functional group acting as the thiophenol reactive site was introduced into a carbazole-chalcone fluorophore to synthesize probe-CCF2,which could result in a remarkable increase in fluorescence when reacting with thiophenols.The selectivity and accuracy of probe-CCF2 were investigated with thiophenols,hydrosulphide salt,aliphatic thiols,glutathione,cysteine,anions and metal cations.Probe-CCF2 exhibited a detection limit of 37 nmol/L(R^(2)=0.9951),a remarkable Stokes shift of approximately 130 nm,and a brief response time of 9 min with a remarkable increase in fluorescence of 90-fold.Probe-CCF2 was applied for thiophenol detection in water samples and imaging in living cells successfully,with high sensitivity and excellent selectivity.

The aromatic peptide protected gold nanoclusters with significant Stokes shift:Ligand-mediated two-step FRET

During the last decade,a great variety of ligand protected gold nanoclusters(AuNCs)have been synthesized,and their broad applications have been intensively reported.Although the spectroscopic properties of AuNCs have been comprehensively explored,the mechanism of the significant Stokes shift(>200 nm)and the specific role played by surface ligands have not been clearly explained yet.In this study,a series of fluorescent AuNCs with huge Stokes shift(up to 530 nm)were successfully prepared by employing the rationally designed tri-peptides as the protecting ligands,and their spectroscopic properties were systematically investigated.The detailed measurements on the example product,YCY-AuNCs(Tyr-Cys-Tyr liganded AuNCs),showed that the energy absorbed by the tyrosine(~250 nm)can be effectively transferred through the ligand-mediated two-step Förster resonance energy transfer(FRET)process and released as fluorescence emission in the near-infrared fluorescence(NIR)range(~780 nm),which resulted in the significant apparent Stokes shift.The YCY ligands play a critical role by offering the tyrosine groups(donor of the first FRET pair),generating the dityrosine-like structure on the AuNCs surface(acceptor of the first FRET pair and donor of the second FRET pair),and protecting the cores(acceptor of the second acceptor).The additional ligand exchange experiments and the investigation on the other AuNCs further demonstrated that the sufficient high density of the aromatic groups is also essential to mediate the two-step FRET and achieve the remarkable Stokes shift.We believe that the aromatic ligand-mediated FRET mechanism not only offers a new theoretical explanation for the huge Stokes shift exhibited in AuNCs,but also provides a general strategy for the construction of new materials with large Stokes shift.

Naphthalimide-modified near-infrared cyanine dye with a large stokes shift and its application in bioimaging

Developing the novel fluorescent dyes with a larger Stokes shift is still a challenge in the research of fluorescence probes. In this work, a naphthalimide-modified near-infrared cyanine dye with an emission at 785 nm has been synthesized for lysosome-targeting imaging. This fluorescent dye showed a large Stokes shift（up to 165 nm） and favorable lysosome-targeting property, which facilitated it to be a potential candidate for studying of lysosomal functions. The result also indicated that the probe is a promising contrast agent for in vivo imaging in mouse models.

Molecular engineering of ultra-sensitive fluorescent probe with large Stokes shift for imaging of basal HOCl in tumor cells and tissues

Fluorescent probes have been widely employed in biological imaging and sensing.However,it is always a challenge to design probes with high sensitivity.In this work,based on rhodamine skeleton,we developed a general strategy to construct sensitivity-enhanced fluorescent probe with the help of theoretical calculation for the first time.As a proof of concept,we synthesized a series of HOCl probes.Experiment results showed that with the C-9 of pyronin moiety of rhodamine stabilized by an electron donor group,probe DQF-S exhibited an importantly enhanced sensitivity(LOD:0.2 nmol/L)towards HOCl together with fast response time(<10 s).Moreover,due to the breaking symmetrical electron distribution by another electron donor group,the novel rhodamine probe DQF-S displayed a far red to near-infrared emission(>650 nm)and large Stokes shift.Bioimaging studies indicated that DQF-S can not only effectively detect basal HOCl in various types of cells,but also be successfully applied to image tumor tissue in vivo.These results demonstrate the potential of our design as a useful strategy to develop excellent fluorescent probes for bioimaging.

Rational design of far red to near-infrared rhodamine analogues with huge Stokes shifts for single-laser excitation multicolor imaging

Rhodamine dyes have been widely employed in biological imaging and sensing. However, it is always a challenge to design rhodamine derivatives with huge Stokes shift to address the draconian requirements of single-excitation multicolor imaging. In this work, we described a generally strategy to enhance the Stokes shift of rhodamine dyes by completely breaking their electronic symmetry. As a result, the Stokes shift of novel rhodamine dye DQF-RB-Cl is up to 205 nm in PBS, which is the largest in all the reported rhodamine derivatives. In addition, we successfully realized the single excitation trichromatic imaging of mitochondria, lysosomes and cell membranes by combining DQF-RB-Cl with commercial lysosomal targeting probe Lyso-Tracker Green and membrane targeting dye Dil. This is the organic synthetic dyes for SLE-trichromatic imaging in cells for the first time. These results demonstrate the potential of our design as a useful strategy to develop huge Stokes shift fluorophore for bioimaging.

Efficient One-Pot Access to 2,9-Dihydrothiopyrano[2,3-b]indole Scaffolds Showing Large Stokes Shifts

A simple, mild and efficient one-pot approach for the construction of 2-aryl-3-nitro-2,9-dihydrothiopyrano- [2,3-b]indole derivatives has been realized in CH2C12 medium at ambient temperature via three-component tandem reaction of N-protected-2-chloro-3-formylindoles, sodium hydrosulfide and β-substituted nitroolefins/δ-substituted nitrodienes using DABCO （10 mol%） as an organocatalyst, followed by dehydration in the presence of activated molecular sieves （4 A）. The significant advantages of this protocol are simple operation, shorter reaction time, high atom economy, good to high yields （73%-89%） and wider substrate scope. In addition, all the synthesized com- pounds have shown the large positive Stokes shift values （5632-6081 cm ^-1）.

Improved Ligand-Field Theory with Effect of Electron-Phonon Interaction

Traditional ligand-field theory has to be improved by taking into account both 'pure electronic' contribution and electron-phonon interaction one (including lattice-vibrational relaxation energy). By means of improved ligand-field theory, R1, R2, R'3, R'2, and R'1 lines, U band, ground-state zero-field-splitting (GSZFS), and ground-state g factors of ruby and/or GSGG: Cr3+ as well as thermal shifts of GSZFS, R1 line and R2 line of ruby have been calculated.The results are in very good agreement with the experimental data. Moreover, it is found that the value of cubic-field parameter given by traditional ligand-field theory is inappropriately large. For thermal shifts of GSZFS, R1 line and R2 line of ruby, several conclusions have also been obtained.

Excited state intramolecular proton transfer of novel conjugated derivatives containing hydroxy and imino groups

This letter presents excited state intramolecular proton transfer (ESIPT) of new conjugated derivatives containing hydroxy and imino groups. ESIPT occurrence in one photon process is confirmed by well-separated emission band for the derivatives. Two- photon absorption (TPA) induced ESIPT emission has been determined by Ti:sapphire femtosecond laser tuning from 700 nrn to 800 nm at the internals of 20 nm.

Synthesis and pH Sensitive Fluorescent Performance of 2'-Chloroseminaphthofluorescein with Dual Bands

A novel unsymmetrical fluorescein derivative substituted by chlorine and naphthol, 2 '-chloroseminaphthofluorescein, was prepared by the two-step synthetic method. This method can effectively control the reactive process,so the pure unsymmetrical fluorescein derivative can be obtained in high yield. The new fluorophore exhibited dual absorption bands,dual excitation bands and dual emission bands with long-wavelength,selectively exciting the acidic and basic forms of the fluorophore. Compared with the similar symmetrical fluorescein derivatives such as 2 ', 7 '-dichlorofluorescein and dinaphtofluorescein, this fluorophore was found to have larger Stokes shift,especially in the basic form. Based on the properties above,this unsymmetrical fluorescein derivative is expected as a good fluorescent probe to be used where the interference exists due to the presence of endogenous fluorescers.

N,O-Bidentated difluoroboron complexes based on pyridine-ester enolates:Facile synthesis,post-complexation modification,optical properties,and applications

An array of pyridine-ester enolate based organoboron complexes has been designed and synthesized via a one-pot cascade of Pd-catalyzedα-arylation and BF2complexation.The rapid structure-activity relationship(SAR)studies indicated that unsymmetrical N,O-chelated BF2complexes were highly fluorescent in solid state,and exhibited large Stokes shifts,excellent photostability,along with insensitivity to p H.Theα-aryl group could not only modulate the electronic effect but also inhibit the intermolecularπ-πstacking to promote the aggregation-induced emission(AIE)effect.DFT calculations and experiments identified that the intramolecular charge transfer properties of these N,O-chelates could be switched by the modification of substituents,resulting tunable fluorescence wavelengths.Furthermore,post-complexation modification was accomplished,including Suzuki-Miyaura cross-coupling,Buchwald-Hartwig amination,oxidative cleavage,along with a unique triple substitution reaction involving propargyl Grignard reagents.The exemplificative application of dimethylamine substituted boron complex as a reversible acidic vapor sensor was also demonstrated.

A near-infrared fluorescent probe for visualizing transformation pathway of Cys/Hcy and H2S and its applications in living system

Sulfydryl-contained(-SH)substances including hydrogen sulfide(H_(2)S),cysteine(Cys),homocysteine(Hcy)and glutathione(GSH)play crucial roles in living systems,and their variations are closely associated with various diseases.Herein,we developed a near-infrared intramolecular charge transfer(ICT)based fluorescent probe Y-NBD,achieving detection of Cys/Hcy and H_(2)S with different fluorescent signals(green-red for Cys/Hcy,red for H_(2)S),large Stokes shifts(∼100/105nm or 191 nm)and high signal-background-ratio,but not responding to GSH.Y-NBD was successfully applied to image exogenous/endogenous Cys/Hcy and H_(2)S in various living cancer cells(HeLa,A549,and HepG2)and in zebrafish.It not only visualized the transformation pathway of several thiols in HepG2 cells but also verified that the intestine is the main site for the activation and metabolism of Y-NBD in zebrafish,as well as realized to evaluate the degree of drug-induced liver injury.This work provides a promising tool for imaging Cys/Hcy and H_(2)S in living systems and shows great potency in evaluating drug-induced liver injury and its treatment.

A NIR fluorescent probe for imaging thiophenol in the living system and revealing thiophenol-induced oxidative stress

Thiophenol(PhSH)is an important raw material for organic synthesis,while its high toxicity to organisms makes it an environmental pollutant.Therefore,it is crucial to accurately detect PhSH and explore its metabolic process in the living system.Herein,a near-infrared(NIR)fluorescent probe TEM-FB was developed for sensing PhSH with a turn-on fluorescent signal at 719nm and a large Stokes shift(198 nm)based on generating the intramolecular charge transfer(ICT)process.TEM-FB shows high specificity and significant sensitivity towards PhSH(detection limit:10 nmol/L)via the aromatic nucleophilic substitution mechanism.Furthermore,it was successfully applied to image PhSH in multiple cell lines and in zebrafish.Notably,we revealed the oxidative stress process caused by PhSH and demonstrated that the hydrogen peroxide(H_(2)O_(2))in cells would alleviate the poisonousness from exogenous PhSH for the first time.This work provides a promising bioimaging tool for monitoring PhSH in living systems and visualizing the process of oxidative stress induced by PhSH.

Coumarin-based two-photon AIE fluorophores: Photophysical properties and biological application

Based on the coumarin skeleton, we deliberately designed two groups of fluorophores, termed as CoumR and Naph-Coum-R, using the diphenylamino group as the electron donor, which displayed longwavelength emissions(red spectral region), large Stokes shift(up to 204 nm), superior AIE performance,and large two-photon absorbance cross-sections(as high as 365 GM). The electron-withdrawing substituents at the 3-position of these dyes could induce a significant red-shift in their emission spectra.Preliminary imaging experiments demonstrated the capability of these dyes as two-photon fluorophores for specifically staining lipid droplets in living cells.

Synthesis of novel thieno-[3,4-b]-pyrazine-cored molecules as red fluorescent materials

Two novel thieno-[3,4-b]-pyrazine-based molecules, TP-E and TP-O, were designed and synthesized for potential application as red fluorescent emitters. The bulky tetraphenylethylene groups were attached at the periphery of the thieno-[3,4-b]-pyrazine core to form the non-planar molecules, as efficient solid- state emitting materials. The peripheral groups were grafted to the emissive core through either a conjugated acetylene bond, or a non-conjugated ether bond. These molecules exhibit strnng red fluorescence in both dilute solutions and in thin films with large Stokes shifts of over 100 nm. The cyclic voltammetry measurements showed the reversible oxidation and reduction behavior for both compounds. All these properties indicate the two compounds are possible functional materials for use in ontoelectronic devices.

Unusual Luminescence of Ca_8[Al_(12)O_(24)](WO_4)_2: Tb^(3+)

The luminescence properties of aluminate sodalite Ca8[Al12O24](WO4)2 (CAW) undoped and doped with Tb3+ are reported and discussed. At room temperature the emission of tetrahedral 2-4WO in CAW showed an abnor-mally small Stokes shift (9060 cm-1), which is related to the crystal structure of CAW. A strong absorption band in the excitation spectrum of the Tb3+-activated CAW is ascribed to the absorption of the charge transfer state Tb4+- W5+, into which the excitation resulted in the efficient emission from the 5D4 level of Tb3+, but not from the 5D3 level.

Donor-conformation-dependent energy transfer for dual-color fluorescent probe with high-resolution imaging

Herein,we presented a brand-new concept to construct the Forster resonance energy transfer(FRET)based cassette by integrating a vibration-induced emission(VIE)chromophore as the donor.Different from traditional donors only with a single emission,the VIE donor possessed well-separated dual emission bands by altering the excited state molecular configuration from the bent state to the planar state.By linking an acceptor such as a cyanine dye(Cy5),a novel VIE-FRET cassette(PPCy5)was prepared.The planar emission profile of the VIE donor moiety could fully cover the absorption of Cy5,and thus the complete FRET process enabled the excellent bimodal spectra difference of 142 nm and ultra-large pseudo-Stokes shift of up to 300 nm.Benefiting from the viscosity-dependent characteristic of the VIE donor,PPCy5 could clearly and intuitively reveal the different viscosity regions in vivo by dual-color and high-resolution imaging.The VIE-FRET paradigm provides an optional platform for developing donor-acceptor-based dual-color fluorescent probes with high-resolution imaging ability.