Efficient Fluorophores Research Articles

A compact fluorescent probe based on o-phthalaldehyde for ultrasensitive detection of hydrazine in gas and solution phases

Because of the high toxicity of hydrazine, the development of ultrasensitive fluorescent probes for hydrazine has been challenging. In this work, an ultrasensitive fluorescent probe based on o-phthalaldehyde has been exploited for hydrazine. The probe was designed based on creating an efficient fluorophore by incorporating hydrazine into o-phthalaldehyde framework via an intermolecular condensation-cyclization reaction. The probe could quickly detect hydrazine and displayed a high sensitivity for hydrazine with a LOD of 1.9 nM (0.06 ppb), which is far below the U.S. Environmental Protection Agency standard (10 ppb). Moreover, the probe was successfully applied to the detection of hydrazine in real water samples and hydrazine vapor.

Linear dendronized polyols as a multifunctional platform for a versatile and efficient fluorophore design

Linear dendronized polyols (LDPs)as a modular platform for bright, stable, and biocompatible polymeric fluorophores applicable for fluorescent bioimaging studies.

Why Do Simple Molecules with "Isolated" Phenyl Rings Emit Visible Light?

π-Bonds connected with aromatic rings were generally believed as the standard structures for constructing highly efficient fluorophores. Materials without these typical structures, however, exhibited only low fluorescence quantum yields and emitted in the ultraviolet spectral region. In this work, three molecules, namely bis(2,4,5-trimethylphenyl)methane, 1,1,2,2-tetrakis(2,4,5-trimethylphenyl)ethane, and 1,1,2,2-tetraphenylethane, with nonconjugated structures and isolated phenyl rings were synthesized and their photophysical properties were systematically investigated. Interestingly, the emission spectra of these three molecules could be well extended to 600 nm with high solid-state quantum yields of up to 70%. Experimental and theoretical analyses proved that intramolecular through-space conjugation between the "isolated" phenyl rings played an important role for this abnormal phenomenon.

SNAP‐Tag‐Based Subcellular Protein Labeling and Fluorescent Imaging with Naphthalimides

Genetically encoded technologies provide methods for the specific labeling and imaging of proteins, which is essential to understand the subcellular localization of these proteins and their function. Herein, we employed naphthalimide, an efficient two-photon fluorophore, to develop O6 -benzylguanine (BG) derivatives for specific labeling of subcellular proteins and fluorescent imaging through the SNAP-tag. Three naphthalimide-BG derivatives, TNI-BG, QNI-BG, and ONI-BG, were conveniently synthesized through modular "click chemistry" in high yields. All of them showed high labeling efficiency with SNAP-tag in solution (≈1-2×103 s-1 m-1 ) and in bacteria. Among them, ONI-BG showed high specificity to diffused, histone H2B and mitochondria COX8A targeted SNAP-tag in mammalian cells. The protein-labeled naphthalimides exhibited high two-photon absorption cross-sections, which indicated their potential application in protein-specific two-photon fluorescent imaging, such as two-photon fluorescent lifetime imaging and two-photon multicolor imaging. Therefore, ONI-BG is a versatile tool that can be used to track subcellular proteins through multiple fluorescent techniques.

Planar 2-(2-hydroxyphenyl)benzothiazole-based dyes functionalized via triple bonds as exceedingly efficient solid-state fluorophores

Two planar 2-(2-hydroxyphenyl)benzothiazole-based dyes without sterically bulky groups as exceedingly efficient solid-state fluorophores due to the absence of strong π–π intermolecular interaction.

A perpendicular phenyl-induced exceedingly efficient solid-state excited state intramolecular proton transfer fluorophore based on 2-(2-hydroxyphenyl)benzothiazole

Fluorescent solid-state organic materials have been intensively researched in recent years. In this study, two 2-(2-hydroxyphenyl)benzothiazole (HBT) derivatives: phenylethylene-modified HBT (HBT-s-Ph) and diphenylethylene-modified HBT (HBT-d-Ph), were synthesized by facile Suzuki cross-coupling reactions. In toluene solutions, the fluorescence quantum yield (Φf) of HBT-s-Ph is slightly larger than that of HBT-d-Ph, because of the presence of a stronger intramolecular H-bond in HBT-s-Ph than in HBT-d-Ph. In crystalline forms, both of their Φf has substantial improvement, and the Φf of HBT-d-Ph reaches 78%, which is twice that of HBT-s-Ph. The crystal structure revealed that the striking emission enhancement of HBT-d-Ph was attributable to its distinct molecular packing model and the resultant relatively weak intermolecular interactions induced by the single phenyl group cis to the HBT moiety.

En Route to Stimuli-Responsive Boron-, Nitrogen-, and Sulfur-Doped Polycyclic Aromatic Hydrocarbons.

Replacing both meso carbon atoms of the polycyclic aromatic hydrocarbon (PAH) bisanthene by boron atoms creates an efficient blue fluorophore with a strong electron-accepting character. The corresponding meso-B,S-doped bisanthene exhibits a solvent-dependent green-to-orange photoluminescence and undergoes a reversible reduction at E1/2 =-2.06 V (vs. FcH/FcH(+) ). After oxidation of the sulfur atom, the resulting sulfoxide emits in the blue range of the spectrum, shows only negligible solvatochromism, and a reversible redox transition at E1/2 =-1.74 V. Several related B, N- and B, S-containing PAHs have been prepared following the same modular synthetic procedure and are also described herein. In order to systematically compare their optoelectronic properties, all products have been investigated by cyclic voltammetry as well as UV/Vis absorption/emission spectroscopy.

Optical Properties of Zinc(II) and Boron(III) Dipyrrinates with Different Structures

The spectral luminescent, photophysical, photochemical, lasing, nonlinear optical, and sensor characteristics of a series of new synthesized complexes of zinc and difluoroborate with dipyrrines of different structure have been studied. It is found that many of these compounds exhibit stimulated emission in different solvents when excited by the second (532 nm) and third (355 nm) harmonics of a Nd:YAG laser in the range of 548–692 nm. It is shown that not only efficient fluorophores belonging to dipyrrine difluoroborates (with a quantum fluorescence yield close to 1), but also compounds with a fluorescence yield equal to 0.3, generate laser radiation with a high resource; phosphorescence is also observed along with fluorescence. Transmission of UV radiation (355 nm) is shown to decrease with an increase in the pulsed excitation power density; this is a manifestation of nonlinear optical properties. The change of phosphorescence signal in dependence of the composition of the gas mixture around a solid-state sample colored by dipyrrinate complexes indicates that a number of the compounds under consideration exhibit sensor abilities.

Developing Sensors of Chemical Warfare Agent Simulants with Fluorescent Dye Molecules

Worldwide, as threats from chemical warfare (CW) agents have increased, the need for sensors and detectors for such agents has also risen. Many of the most dangerous CW agents are covalent inhibitors of acetylcholinesterase (AchE) which function by very similar chemistry, and hence have similar chemical properties overall. Here we show that a recently developed class of fluorescent molecules with phenylene ethynylene (PE) backbones can act as excellent sensors for a class of CW simulant molecules (malathion and its derivatives) when in complex with an anionic surfactant at very low concentrations. Oligo phenylene ethynylenes (OPEs) have recently been shown to be both efficient fluorophores and (depending on details of structure) sources of photo-generated reactive oxygen species, especially singlet oxygen. As such, the OPEs are attractive candidates as both potential CW sensors and potential CW-destroying agents. Here we show that several OPE variants are able to detect the CW simulant malathion when in aqueous complex with small concentrations of surfactants such as sodium dodecyl sulfate (SDS). At the correct molar ratios, the combination of the OPE molecule with SDS and malathion appears to form a cooperative triple complex that varies sharply in its fluorescence properties over a narrow range of malathion concentrations. With some OPE/surfactant combinations the complex acts as a “turn off” detector—fluorescence intensity decreases with malathion concentration—while other combinations can act as “turn on” detectors—fluorescence intensity increases with malathion concentration. Simulations designed to understand the nature of the triple complex, and further experiments to test the ability of triple complexes to destroy CW agents, are currently underway.

A Two-Photon Fluorescent Probe for Lysosomal Thiols in Live Cells and Tissues.

Lysosome-specific fluorescent probes are exclusive to elucidate the functions of lysosomal thiols. Moreover, two-photon microscopy offers advantages of less phototoxicity, better three dimensional spatial localization, deeper penetration depth and lower self-absorption. However, such fluorescent probes for thiols are still rare. In this work, an efficient two-photon fluorophore 1,8-naphthalimide-based probe conjugating a 2,4-dinitrobenzenesulfonyl chloride and morpholine was designed and synthesized, which exhibited high selectivity and sensitivity towards lysosomal thiols by turn-on fluorescence method quantitatively and was successfully applied to the imaging of thiols in live cells and tissues by two-photon microscopy.

Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties

A macrocyclic bisBODIPY (bis(boron-dipyrromethene)) complex [1B2] with a figure-of-eight helicity was synthesized and successfully resolved. [1B2] was proven to be one of the most efficient red-emitting CPL (circularly polarized luminescence) fluorophores reported to date (λ = 663 nm, |glum| = 9 × 10(-3), ΦF = 0.58).

NanoBRET--A Novel BRET Platform for the Analysis of Protein-Protein Interactions.

Dynamic interactions between proteins comprise a key mechanism for temporal control of cellular function and thus hold promise for development of novel drug therapies. It remains technically challenging, however, to quantitatively characterize these interactions within the biologically relevant context of living cells. Although, bioluminescence resonance energy transfer (BRET) has often been used for this purpose, its general applicability has been hindered by limited sensitivity and dynamic range. We have addressed this by combining an extremely bright luciferase (Nanoluc) with a means for tagging intracellular proteins with a long-wavelength fluorophore (HaloTag). The small size (19 kDa), high emission intensity, and relatively narrow spectrum (460 nm peak intensity) make Nanoluc luciferase well suited as an energy donor. By selecting an efficient red-emitting fluorophore (635 nm peak intensity) for attachment onto the HaloTag, an overall spectral separation exceeding 175 nm was achieved. This combination of greater light intensity with improved spectral resolution results in substantially increased detection sensitivity and dynamic range over current BRET technologies. Enhanced performance is demonstrated using several established model systems, as well as the ability to image BRET in individual cells. The capabilities are further exhibited in a novel assay developed for analyzing the interactions of bromodomain proteins with chromatin in living cells.

Photoactivatable Aggregation‐Induced Emission Fluorophores with Multiple‐Color Fluorescence and Wavelength‐Selective Activation

Photoactivatable (caged) fluorophores are widely used in chemistry, materials, and biology. However, the development of such molecules exhibiting photoactivable solid-state fluorescence is still challenging due to the aggregation-caused quenching (ACQ) effect of most fluorophores in their aggregate or solid states. In this work, we developed caged salicylaldehyde hydrazone derivatives, which are of aggregation-induced emission (AIE) characteristics upon light irradiation, as efficient photoactivatable solid-state fluorophores. These compounds displayed multiple-color emissions and ratiometric (photochromic) fluorescence switches upon wavelength-selective photoactivation, and were successfully applied for photopatterning and photoactivatable cell imaging in a multiple-color and stepwise manner.

Novel efficient fluorophores synthesized from citric acid

Citric acid was reacted with α,β-diamines, β-amino thiols and β-amino alcohols to produce fluorescent derivatives of 2-pyridone (QY up to ∼79%). The chemical structures of these compounds were confirmed by analyses of 1D, 2D NMR and ESI-MS data.

Elimination of hole-surface overlap in graded CdS(x)Se(1-x) nanocrystals revealed by ultrafast fluorescence upconversion spectroscopy.

Interaction of charge carriers with the surface of semiconductor nanocrystals plays an integral role in determining the ultimate fate of the excited state. The surface contains a dynamic ensemble of trap states that can localize excited charges, preventing radiative recombination and reducing fluorescence quantum yields. Here we report quasi-type-II band alignment in graded alloy CdSxSe1-x nanocrystals revealed by femtosecond fluorescence upconversion spectroscopy. Graded alloy CdS(x)Se(1-x) quantum dots are a compositionally inhomogeneous nano-heterostructure designed to decouple the exciton from the nanocrystal surface. The large valence band offset between the CdSe-rich core and CdS-rich shell separates the excited hole from the surface by confining it to the core of the nanocrystal. The small conduction band offset, however, allows the electron to delocalize throughout the entire nanocrystal and maintain overlap with the surface. Indeed, the ultrafast charge carrier dynamics reveal that the fast 1-3 ps hole-trapping process is fully eliminated with increasing sulfur composition and the decay constant for electron trapping (∼ 20-25 ps) shows a slight increase. These findings demonstrate progress toward highly efficient nanocrystal fluorophores that are independent of their surface chemistry to ultimately enable their incorporation into a diverse range of applications without experiencing adverse effects arising from dissimilar environments.

A theoretical study on diastereoselective oxidative dearomatization by iodoxybenzoic acid.

The reaction mechanism of diastereoselective oxidative dearomatization by iodoxybenzoic acid of key compounds involved in the total synthesis of epicocconone analogs, which are efficient fluorophores with a wide range of applications in protein staining and separation, was studied using density functional theory. In particular, the conformational space was investigated, as was the role of the so-called hypervalent twist move, which is thought to be the rate-determining step. Both kinetic and thermodynamical aspects of the mechanism were considered from static and dynamic viewpoints, including solvent effects. The results were then rationalized using conceptual density functional theory and Bader's atoms-in-molecules framework, which demonstrated how complementary these two approaches are when studying organic chemistry reactions theoretically.

Multiphoton Excited Fluorescent Materials for Frequency Upconversion Emission and Fluorescent Probes

Recent progress in developing various strategies for exploiting efficient MPA fluorophores for two emerging technological MPA applications including frequency upconversion photoluminescence and lasing as well as 2PA fluorescence bioimaging and biosensing are presented. An intriguing application of MPA frequency-upconverted lasing offers opportunity for the fabrication of high-energy coherent light sources in the blue region which could create new advantages and breakthroughs in various laser-based applications. In addition, multiphoton excitation has led to considerable progress in the development of advanced diagnostic and therapeutic treatments; further advancement is anticipated with the emergence of various versatile 2PA fluorescence probes. It is widely appreciated that the two-photon excitation offers significant advantages for the biological fluorescence imaging and sensing which includes higher spatial resolution, less photobleaching and photodamage as well as deeper tissue penetration as compared to the one-photon excited microscopy. To be practically useful, the 2PA fluorescent probes for biological applications are required to have a site-specificity, a high fluorescence quantum yield, proper two-photon excitation and subsequent emission wavelengths, good photodecomposition stability, water solubility, and biocompatibility besides large 2PA action cross-sections.

A water compatible turn ‘on’ optical probe for Cu2+ based on a fluorescein–sugar conjugate

A fluorescein–sugar conjugated chromo-fluorogenic turn ‘on’ probe (FG) has been synthesized for detection of Cu2+. The FG comprises of fluorescein as an efficient fluorophore and a sugar moiety, viz., galactose as the binding unit. The inclusion of galactose into FG led towards its good water compatibility. When Cu2+ was added in 70% aqueous HEPES buffered solution (pH 7.4) of FG, the absorbance and the fluorescence spectral pattern of the same were modulated dramatically with observation of absorption and emission bands at 632 and 515nm, respectively. The detection limit from fluorescence titration was calculated as 6.32nM which further establishes high sensitivity of FG towards Cu2+. The spectral studies for the interaction of FG with Cu2+ indicated towards metal ion triggered spirolactam ring opening of FG as the mechanistic pathway of the sensing phenomenon.

Evaluating Charge Transfer in Epicocconone Analogues: Toward a Targeted Design of Fluorophores

Through-space charge transfers upon photon absorption in aminated epicocconone analogues, which serve as promising proteins markers, are investigated within time-dependent density functional theory using total densities differences and various point-charge models (with a special emphasis on Bader's atoms-in-molecules theory). In particular, the distances and the amounts of charge transfer, as well as the transition dipole moments, are discussed from a methodological point of view, and their values are subsequently linked with the chemical structures of these efficient fluorophores. Finally, on the basis of these theoretical findings, several hints for the future improvement of the photochemical properties of these analogues are advanced.

Development of Nile red-functionalized magnetic silica nanoparticles for cobalt ion sensing and entrapping

A new type of hybrid nanoparticles (NPs) with combined magnetic and fluorescent properties in single particle was developed by incorporating magnetic silica NPs with highly fluorescent Nile red dyes. These NPs clearly exhibit Co2+ ion entrapping ability in aqueous milieu and Co2+-induced fluorescence enhancement features with high selectivity owing to the Co2+-triggered inhibition on the photoinduced electron transfer progress in the efficient fluorophore (Nile red derivative). Moreover, these dual-functional NPs display superparamagnetic features and the motion of these fluorescent NPs can be induced by the application of an external magnetic field, enabling a facile separation/removal of toxic Co2+ ion from the aqueous milieu and real-time monitoring via fluorescence measurements.