Single Fluorescence Emission Research Articles

ESIPT-induced intersystem crossing leads to tautomer fluorescence quenching for 3-mercapto-2-(4-(trifluoromethyl)phenyl)-4H-chromen-4-one molecule

ESIPT-induced intersystem crossing leads to tautomer fluorescence quenching for 3-mercapto-2-(4-(trifluoromethyl)phenyl)-4H-chromen-4-one molecule

Detection mechanism of glutathione by off–on fluorescent probe based on excited state intramolecular proton transfer

Detection mechanism of glutathione by off–on fluorescent probe based on excited state intramolecular proton transfer

A multidimensional quantitative fluorescent probe for high-fidelity monitoring of the polarity change in lysosomes during autophagy

A multidimensional quantitative fluorescent probe for high-fidelity monitoring of the polarity change in lysosomes during autophagy

Generalization of the Ratiometric Method to Extend pH Range Measurements of the BCECF Probe

There is a variety of fluorescent probes for pH measurements and which are mainly used for biological systems. In general, they can be classified into two groups. The first group includes fluorescent pH probes which exhibit a single fluorescence emission peak. For these probes, the fluorescence excitation profile is pH-dependent and the shape of the emission spectra remains almost constant. Hence, the ratiometric pH measurement-which makes pH determination independent of the probe concentration-is implemented when the excitation is performed at two excitation wavelengths and the fluorescence emission is measured at one wavelength. The second group exhibits a dual fluorescence emission peak. Here, each protonated or deprotonated form exhibits characteristics emission and/or absorption spectra. Shifts between spectra obtained for protonated and deprotonated species can be exploited in order to perform a ratiometric measurement. In this study we present a methodology that evaluates the precision of the ratiometric measurements based on multiple wavelengths excitation to determine the optimum wavelengths combination for pH determination in biological samples. This methodology using the BCECF probe is applied to measure the pH drift in cell culture medium. It exhibits a high precision and significantly extends the range of validity for pH measurements spanning from very acidic to basic.

Generation of Tunable Ultrastrong White‐Light Emission by Activation of a Solid Supramolecule through Bromonaphthylpyridinium Polymerization

AbstractHerein, we reported solid supramolecular bromonaphthylpyridinium polymers (P‐BrNp), which exhibit tunable phosphorescence emission in the amorphous state enabled by sulfobutylether‐β‐cyclodextrin (SBE‐β‐CD) and diarylethene derivatives. The monomer BrNp gave single fluorescence emission at 490 nm, while an apparent room‐temperature phosphorescence (RTP) at 550 nm emerged for P‐BrNp copolymers with various feed ratios. Through fluorescence‐phosphorescence dual emission, P‐BrNp‐0.1 displayed an ultrahigh white‐light emission quantum yield of 83.9 %. Moreover, the subsequent assembly with SBE‐β‐CD further enhanced the phosphorescent quantum yield of P‐BrNp‐0.1 from 64.1 % to 71.3 %, accompanied by the conversion of photoluminescence emission from white to yellow. Diarylethene monomers were introduced as photoswitches to realize reversible RTP emission, which can be used in switchable data encryption and multifunctional writing ink.

ESIPT and AIE characteristics of three Schiff base derivatives and the relevant photophysical mechanism analyses

Recently, three novel Schiff base derivatives (L 1-3 ) were experimentally found to show water-induced aggregation-induced emission (AIE) and ultrafast excited state intramolecular proton transfer (ESIPT) characteristics, which have potential applications in fields of both optical material and fluoride ion detection. However, the corresponding optical properties have not been recognized completely and the relevant theoretical mechanism is lacking in analysis. In this work, based on the constructed relaxed potential energy curves, we investigated the stable configurations and clarified the proton transfer reaction mechanism for L 1-3 with different substituents. The results show that the proton transfer associated with the interconversion from enol to keto isomer in S 0 state is increasingly activated as substituted from electron-withdrawing group to electron-donating group, while the reverse trend is observed in S 1 state. Above phenomenon can be ascribed to the change in strength of intramolecular hydrogen bond contributed to the reaction, which is demonstrated by hydrogen-bond parameters and interaction region indicator (IRI) analyses. Based on the optimized geometries, the single-fluorescence emission is found following the dual-absorption. The calculated fluorescence peaks (545 nm for L 1 , 536 nm for L 2 , 704 nm for L 3 ) show little difference from those of experiment, which are reassigned to the ESIPT induced formation of keto isomer instead of enol form. In addition, the mechanism of water-induced AIE is clarified by increasing radiative rate and orbital overlap. To essentially comprehend the photophysical properties of organic luminogens with AIE and ESIPT characteristics is of fundamental interests in molecular electronics and photonics, and is also helpful to design new optical materials. • The single fluorescence emission of L 1-3 is ascribed to the excited-state keto isomer instead of enol configuration. • The ESIPT (E*→K*) is increasingly activated as substituted from electron-donating group to electron-withdrawing group. • The water-induced AIE is clarified by increasing radiative rate and orbital overlap.

Preparation of Eu0.075Tb0.925-Metal Organic Framework as a Fluorescent Probe and Application in the Detection of Fe3+ and Cr2O72.

Luminescent Ln-MOFs (Eu0.075Tb0.925-MOF) were successfully synthesised through the solvothermal reaction of Tb(NO3)3·6H2O, Eu(NO3)3·6H2O, and the ligand pyromellitic acid. The product was characterised by X-ray diffraction (XRD), TG analysis, EM, X-ray photoelectron spectroscopy (XPS), and luminescence properties, and results show that the synthesised material Eu0.075Tb0.925-MOF has a selective ratio-based fluorescence response to Fe3+ or Cr2O72−. On the basis of the internal filtering effect, the fluorescence detection experiment shows that as the concentration of Fe3+ or Cr2O72− increases, the intensity of the characteristic emission peak at 544 nm of Tb3+ decreases, and the intensity of the characteristic emission peak at 653 nm of Eu3+ increases in Eu0.075Tb0.925-MOF. The fluorescence intensity ratio (I653/I544) has a good linear relationship with the target concentration. The detection linear range for Fe3+ or Cr2O72− is 10–100 μM/L, and the detection limits are 2.71 × 10−7 and 8.72 × 10−7 M, respectively. Compared with the sensor material with a single fluorescence emission, the synthesised material has a higher anti-interference ability. The synthesised Eu0.075Tb0.925-MOF can be used as a highly selective and recyclable sensing material for Fe3+ or Cr2O72−. This material should be an excellent candidate for multifunctional sensors.

Nanoscale coordination polymers with live-cell imaging property

The reaction of semi flexible ligand, 9,10-bis((4-carboxylatopyridinium-1-methylene)anthracene dihyrdrobromide ([H2cpma]Br2) with transition metal ions [Cu(II), Zn(II) and Cd(II)] in solvothermal condition resulted in the formation of three new coordination polymers i.e., Cu3(cpma)7/2(O)2(H2O)3Cl](NO3)2(H2O)2(S)} (Cu-cpma), {[Zn(cpma)Cl2] (S)} (Zn-cpma) and {[Cd(cpma)(Br)(NO3)]2(S)} (Cd-cpma) where cpma denotes 9,10-bis((4-carboxylatopyridinium-1-methylene)anthracene and S denotes the squeezed solvent molecules. These coordination polymers have been characterized by single crystal X-ray, powder XRD, TGA, IR, elemental analysis and fluorescence emission spectroscopy techniques. Single crystal X-ray studies revealed that both Cu-cpma and Zn-cpma are one dimensional chain whereas Cd-cpma has zero dimensional structure. The appropriate particle size of all CPs was calculated by the PXRD pattern using Debye-Scherrer equation and found that all the CPs is of nano range. These nano coordination polymers (NCPs) were evaluated in live-cell imaging assays using HCT-15 as a model cell-line. The results showed that Zn-cpma has highest fluorescence value.

B- and N-Embedded π-Conjugation Units Tuning Intermolecular Interactions and Optical Properties of Platinum(II) Complexes.

A new series of neutral and cationic platinum(II) complexes containing a B- or N-embedded π-conjugation unit has been prepared. Notably, significantly different intermolecular interactions (Pt-Pt, π-π, head to tail, and head to head) and interesting optical properties exist in these complexes, which can be attributed to the difference in spatial structures and π-electron properties between B- and N-embedded π-conjugation units. Unexpectedly, under a hypoxic atmosphere, N-embedded neutral complex PtNacac can display a distinct dual-emission with both fluorescence and phosphorescence, whereas only a single fluorescence emission was observed in the air, which is different from the B-embedded neutral complex PtBacac with only a single phosphorescence emission at any atmosphere, as well confirmed by lifetime measurement and oxygen sensing experiments. DFT calculations reveal that unusual ligand-to-metal charge transfer (LMCT) excited state character and low spin orbit coupling (SOC) elements can be found in N-embedded complexes due to the strong electron-donating ability of the N-embedded unit. Based on this, as a novel ratiometric oxygen probe with a simple structure, PtNacac can be successfully used to examine intracellular oxygen levels by monitoring both fluorescence and phosphorescence signals via ratiometric photoluminescence imaging and time-resolved luminescence imaging (TRLI) technology. This work provides a completely new idea for designing fluorescence/phosphorescence dual-emissive complexes.

Two-photon absorbing performance and interfacial coordination enhanced mechanism of TPPA-CdS hybrid

Abstract A novel organic/inorganic hybrid which consisted of N,N-diphenyl-4-(2,2':6′,2″-tepyridin-4-yl)aniline (abbreviated as TPPA) and CdS nanoparticles (NPs) had been prepared through interfacial coordination effect according to soft-hard-acid-base principle. The interfacial coupling coordination was analyzed by XRD, far-IR, FT-IR and HRTEM, which resulted in changeable morphology and tunable linear/nonlinear optical properties. Upon interfacial coordination, the hybrid showed a red-shifted (55 nm) UV–vis absorption band, weakened single photon fluorescence emission (84% decrease), and enhanced two-photon absorption cross-section (13 folds). Due to excellent two-photon absorbing character, the hybrid had good application in the field of optical power limiting with 43 W⋅cm−2 limiting threshold. The regulation mechanism of optical properties was thoroughly discussed upon single crystal structure of the interfacial coordination complex and quantum calculation, as well as the growing mechanism of the hybrid.

Regulation of optical properties for fluorescent triphenylamine-silver hybrid based on SPR effect.

In this study, a two photon absorbing (TPA) material consisting silver nanoparticles and triphenylamine-thiol derivative (TBS) has been prepared through interfacial coordination effect according to soft-hard-acid-base principle. The interfacial structure and morphology of the hybrid are researched in detail. Linear and nonlinear optical properties of the hybrid are studied. Upon interfacial coordination, the hybrid shows red-shifted UV-Vis absorption, causing from enhanced electronic drawing strength due to existence of Ag atom. The results also indicate that the surface Plasmon resonance (SPR) effect of Ag nanoparticles (~6 nm) brings about enhancement in single photon fluorescence emission and two photon absorption. Compared with free TBS, Ag-TBS hybrids show higher TPA cross-section (δ), which is 8784 GM for TBS and up to 103876 GM for Ag-TBS hybrid, showing ~12 fold increase. Due to excellent TPA property, the hybrids have good application in the field of optical power limiting and its limiting threshold is 0.49 J/cm-2. This type of interfacial coordination induced hybrid provides a promising strategy to regulate linear optical properties and optimize nonlinear performance.

Solution and solid-state Excited-State Intramolecular Proton Transfer (ESIPT) emitters incorporating Bis-triethyl-or triphenylsilylethynyl units

Abstract Excited-State Intramolecular Proton Transfer (ESIPT) emitters based on a 2-(2′-hydroxyphenyl)benzazole (HBX) scaffold, incorporating triethyl- or triphenylsilyl substituents either at the 3′,5′ positions of the benzoxazole ring or at the 3,5 positions of the phenol cycle have been synthesized through an expedite two-steps synthetic route. Upon excitation and depending on the substitution and environment, these fluorophores display either single (keto) or dual (enol/keto) fluorescence emission spanning from 400 to 570 nm. Unlike the majority of reported ESIPT emitters, these rigidified dyes display intense fluorescence intensity in the solution-state in either aprotic apolar (toluene) or protic polar (ethanol) solvents with observed emission quantum yields (QY) up to 52% and 44%, respectively. These values represent a drastic enhancement as compared to unsubstituted HBX dyes which feature QY between 1 and 2% in toluene. These fluorophores remain highly emissive in the solid-state, as dispersed in KBr pellets or doped in PMMA films (QY up to 77% and 60% respectively). Molecular engineering studies showed that it is possible to fine-tune the emission color with very small modifications of the HBX scaffold. The nature of the excited-states was also probed through ab initio calculations, evidencing in each case a transition from the K∗ state.

Ratiometric fluorescent nanosensor based on carbon dots for the detection of mercury ion

A novel ratiometric fluorescent nanosensor based on carbon dots has been synthesized via bonding rhodamine B hydrazide to the carbon dots surface by an amide reaction. The ratiometric fluorescent nanosensor showed only a single blue fluorescence emission around 450 nm. While, as mercury ion was added, due to the open-ring of rhodamine moiety bonded on the CDs surface, the orange emission of the open-ring rhodamine would increase obviously according to the concentration of mercury ion, resulting in the distinguishable dual emissions at 450 nm and 575 nm under a single 360 excitation wavelength. Meanwhile, the ratiometric fluorescent nanosensor based on carbon dots we prepared is more sensitive to qualitative and semi-quantitative detection of mercury ion in the range of 0–100 μM, because fluorescence changes gradually from blue to orange emission under 365 nm lamp with the increasing of mercury ion in the tested solution.

Luminescence Studies of Single Molecule Electron Transfer Events

Single electron transfer events in both immobilized and freely diffusing redox-active molecules can now be studied with some facility using a special kind of bimodal nanoelectrochemical-nanophotonic architecture – the electrochemical zero-mode waveguide (E-ZMW). The E-ZMW consists of a high density array of recessed dual-ring electrode nanopores that can moderate the interaction between single electron-transfer events and fluorescence emission, in the zeptoliter optical confinement volume of a zero-mode waveguide. The dual optical-electrochemical functionality makes it possible to perform single molecule spectroelectrochemical measurements under redox cycling conditions – both when the upper electrode is potential-controlled and using self-induced redox cycling. These have been performed with flavin mononucleotide, FMN, whose isoalloxazine chromophore is fluorescent in the oxidized state and dark in the reduced state, FMNH2. This property permits the redox state of single FMN molecules to be followed by fluorescence, with each high/low luminescence transition signaling single molecule cycling. Capture efficiencies are characterized as a function of the potential applied to the upper ring electrode, and single molecule electrochemical-spectroscopic cross-correlation measurements are performed as a function of nanopore occupancy down to <n> ~0.001.

Spectroscopic and theoretical studies of fluorescence effects in bio-active: 4-(5-(methyl-1,3,4-thiadiazol-2-yl))benzene-1,3-diol and 4-(5-(methylamino-1,3,4-thiadiazol-2-yl))benzene-1,3-diol compounds: Effect of molecular aggregation and amino group position

Abstract This work deals with the results of fluorescence studies of 4-(5-(methylamino-1,3,4-thiadiazol-2-yl))benzene-1,3-diol (MATB) and 4-(5-(methyl-1,3,4-thiadiazol-2-yl))benzene-1,3-diol (MTB) in an aqueous solution at various pH. The aqueous solutions of both compounds analysed exhibited interesting fluorescence effects: dual fluorescence for MTB and two clearly separated distinct (partially overlapping) fluorescence emissions for MATB. Such fluorescence effects were observed in the aqueous solutions at pH 1–7 for MTB and pH 1–5 for MATB. At higher pH values, single fluorescence emission band were observed for both compounds. Based on the results reported to date, it was concluded that the observed fluorescence effects were mainly influenced by aggregation factors (induced by concentration changes, conformational effects or other interactions, e.g. formation of hydrogen bonds) and charge transfer effects (pH-induced and structure (substituent)-dependent). The dual fluorescence effect was noted for the analysed MTB compound (which does not have the –NH– secondary amine group), whereas two distinctly separated fluorescence bands were observed for the MATB analogue (which has the secondary amine group). The results presented in this paper highlight the impact of the secondary amine moiety on the fluorescence effects observed a long the range of solvents tested. The experimental research is accompanied by density functional theory-based (DFT) molecular modelling, which provide some hypothesis of the microscopic origins of the phenomena observed.

不同基片对单量子点单光子荧光发射的调控

不同基片对单量子点单光子荧光发射的调控

Tuning the emission of a water-soluble 3-hydroxyflavone derivative by host-guest complexation.

3-Hydroxyflavone derivatives have great potential as fluorescent probes for bio-labeling in aqueous medium. They were extensively studied in various organic solvents for the "excited state intramolecular proton transfer" process, but seldom addressed in aqueous solution due to the poor water solubility. Herein, an amphiphilic molecule bearing 3-hydroxyflavone and oligo(ethylene oxide) (denoted as 3HF-EO) was designed and synthesized. Different from the fluorescence in organic solvents, 3HF-EO in aqueous solution showed a remarkable single fluorescence emission, which is ascribed to the fluorescence of its anionic species. We found that the fluorescence intensity could be efficiently tuned via host-guest complexation. α-CD has little effect on the emission, while β-CD and γ-CD lead to enhanced and reduced emissions of 3HF-EO, respectively. The 1H NMR and 2D NOESY NMR spectra indicate that α-CD barely had any interaction with 3HF-EO, while β-CD and γ-CD formed complexes with one and two 3HF-EO molecules, respectively. These results provide a sound explanation for the modulated fluorescence intensity.

Apoprotein heterogeneity increases spectral disorder and a step-wise modification of the B850 fluorescence peak position

It has already been established that the quaternary structure of the main light-harvesting complex (LH2) from the photosynthetic bacterium Rhodopseudomonas palustris is a nonameric 'ring' of PucAB heterodimers and under low-light culturing conditions an increased diversity of PucB synthesis occurs. In this work, single molecule fluorescence emission studies show that different classes of LH2 'rings' are present in "low-light" adapted cells and that an unknown chaperon process creates multiple sub-types of 'rings' with more conformational sub-states and configurations. This increase in spectral disorder significantly augments the cross-section for photon absorption and subsequent energy flow to the reaction centre trap when photon availability is a limiting factor. This work highlights yet another variant used by phototrophs to gather energy for cellular development.

Coherent interaction of single molecules and plasmonic nanowires

Quantum plasmonics opens the option to integrate complex quantum optical circuitry onto chip scale devices. In the past, often external light sources were used and nonclassical light was coupled in and out of plasmonic structures, such as hole arrays or waveguide structures. Another option to launch single plasmonic excitations is the coupling of single emitters in the direct proximity of, e.g., a silver or gold nanostructure. Here, we present our attempts to integrate the research of single emitters with wet-chemically grown silver nanowires. The emitters of choice are single organic dye molecules under cryogenic conditions, which are known to act as high-brightness and extremely narrow-band single photon sources. Another advantage is their high optical nonlinearity, such that they might mediate photon–photon interactions on the nanoscale. We report on the coupling of a single molecule fluorescence emission through the wire over the length of several wavelengths. The transmission of coherently emitted photons is proven by an extinction type experiment. As for influencing the spectral properties of a single emitter, we are able to show a remote change of the line-width of a single terrylene molecule, which is in close proximity to the nanowire.

Dual fluorescence of (E)-N-(4-(dimethylamino)benzylidene)-2H-1,2,4-triazol-3-amine (DMABA-Amtr): A ground state perspective

We present the absorption and fluorescence spectra of (E)-N-(4-(dimethylamino)benzylidene)-2H-1,2,4-triazol-3-amine (DMABA-Amtr), an electron donor-π-acceptor system. The molecule shows a single fluorescence emission band in non-polar solvents while dual emissions were observed in polar aprotic solvents. Although several researchers over the years provide different explanations for the mechanism of the phenomena, based on solvent assisted excited state geometry changes of such systems, it is still a matter of controversy since such systems are unique as they contradict Kasha's rule. The emission spectrum of the molecule shows strong dependence on solvent polarity and excitation wavelength. This observation together with a single iso-emissive point found in the area normalize emission spectra indicates the presence of two ground state equilibrium structures of the compound which are both fluorescent. Density functional theory (DFT) and time-dependent (TD-DFT) calculations also support the experimental findings.