QUANTITATIVE SPECTROFLUORIMETRY-THE FLUORESCENCE QUANTUM YIELD OF QUININE SULFATE

Fluorescence Enhancement of Nonemissive Monodeprotonated Luteolin in a Poly(vinyl alcohol) Film

Solid polymer matrixes can modulate the electronic states of embedded chromophores and have been widely used in flexible optoelectronic and optical materials. Luteolin is one of the most common natural flavonoids, and its neutral and monodeprotonated forms are nonemissive in aqueous solution induced by ultrafast excited-state proton transfer (ESPT) followed by nonradiative relaxation. In this study, we have incorporated luteolin into poly(vinyl alcohol) (PVA) films and studied their fluorescence behaviors. Neutral and one monodeprotonated luteolin coexist in the PVA film. Weak steady-state fluorescence of neutral luteolin peaking at about 440 nm is observed for the first time. In addition, the monodeprotonated luteolin in PVA film exhibits obvious fluorescence peaking at 500 nm, with a fluorescence quantum yield of as high as 0.4 and a fluorescence lifetime of as long as 2.4 ns. Time-dependent density functional theory calculations have determined that the ESPT of neutral luteolin is barrierless but that of monodeprotonated luteolin needs to surmount a barrier, explaining their distinct emission properties. These results indicate the modulation ability of the PVA film in both ground-state deprotonation and ESPT, broadening the application areas of the solid polymer matrix.

7-membered-ring effect on fluorescence quantum yield: does metal-complexation-induced twisting-inhibition of an amino GFP chromophore derivative enhance fluorescence?

To investigate two aspects, namely, (1) the 7-membered-ring effect on fluorescence quantum yield and (2) whether metal-complexation-induced twisting-inhibition of an amino green fluorescent protein (GFP) chromophore derivative is bound to enhance fluorescence, a novel GFP-chromophore-based triamine ligand, (Z)-o-PABDI, is designed and synthesized. Before complexation with metal ions, the S₁ excited state of (Z)-o-PABDI undergoes τ-torsion relaxation (Z/E photoisomerization) with a Z/E photoisomerization quantum yield of 0.28, forming both ground-state (Z)- and (E)-o-PABDI isomers. Since (E)-o-PABDI is less stable than (Z)-o-PABDI, it is thermo-isomerized back to (Z)-o-PABDI at room temperature in acetonitrile with a first-order rate constant of (1.366 ± 0.082) × 10^-6 s^-1. After complexation with a Zn²⁺ ion, (Z)-o-PABDI as a tridentate ligand forms a 1 : 1 complex with the Zn²⁺ ion in acetonitrile and in the solid state, resulting in complete inhibition of the φ-torsion and τ-torsion relaxations, which does not enhance fluorescence but causes fluorescence quenching. (Z)-o-PABDI also forms complexes with other first-row transition metal ions Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺ and Cu²⁺, generating almost the same fluorescence quenching effect. By comparison with the 2/Zn²⁺ complex, in which a 6-membered ring of Zn²⁺-complexation enhances fluorescence significantly (a positive 6-membered-ring effect on fluorescence quantum yield), we find that the flexible 7-membered rings of the (Z)-o-PABDI/Mⁿ⁺ complexes trigger their S₁ excited states to relax through internal conversion at a rate much faster than fluorescence (a negative 7-membered-ring effect on fluorescence quantum yield), leading to fluorescence quenching regardless of the type of transition metal that complexes with (Z)-o-PABDI.

Enhanced Fluorescence by Inter/Intramolecular Hydrogen Bonding in Si-Substituted Coumarins

Introducing heteroatoms in organic fluorophores offers a unique strategy to tune their photophysical properties without dangling structural decorations. Silicon-substituted coumarins (Si-coumarins) are the analogues of coumarin with the substitution of ester oxygen atoms by silicon atoms. In Si-coumarins, significant fluorescence enhancement in protic solvents through the formation of inter/intramolecular hydrogen bonds (H-bonds) offered great potential in various aspects with many unique photophysical properties. The energies of nπ* and ππ* states in Si-coumarins are elaborately tuned by inter/intramolecular H-bonds and solvents after incorporating silicon atoms. For example, the inter/intramolecular H-bonds elevate the energy of the nπ* state in protic solvents, leading to an enlarged energy gap between the nπ* and ππ* states. Thus, fluorescence is enhanced by reducing the nonradiative transition through the nπ* state in coumarins, resulting in many unique photophysical properties. The understanding of H-bonds in Si-coumarins offers more potential strategies for the design of novel fluorophores.

Quantum dots assembled from an aziridinium based hybrid perovskite displaying tunable luminescence

3D hybrid perovskites based upon small organic cations gave start to a new intensively growing class of semiconducting materials. Here we report on the elaboration of quantum dots of a recently emerged new perovskite (AzrH)PbBr₃ (AzrH = aziridinium cation). By employing the antisolvent precipitation technique and stabilization with a cationic surfactant we succeeded in obtaining quantum dots that display tunable luminescence. This piece of work shows the perspective of aziridinium-based materials for the elaboration of advanced photonic nanostructures.

Photoantibacterial Poly(vinyl)chloride Films Applying Curcumin Derivatives as Bio-Based Plasticizers and Photosensitizers

Herein we describe the design of natural curcumin ester and ether derivatives and their application as potential bioplasticizers, to prepare photosensitive phthalate-free PVC-based materials. The preparation of PVC-based films incorporating several loadings of newly synthesized curcumin derivatives along with their standard solid-state characterization is also described. Remarkably, the plasticizing effect of the curcumin derivatives in the PVC material was found to be similar to that observed in previous PVC-phthalate materials. Finally, studies applying these new materials in the photoinactivation of S. aureus planktonic cultures revealed a strong structure/activity correlation, with the photosensitive materials reaching up to 6 log CFU reduction at low irradiation intensities.

Investigation of the role of pH and the stoichiometry of the N-dopant in the luminescence, composition and synthesis yield of carbon dots

Carbon dots (CDs) are carbon-based nanoparticles with very attractive luminescence features, which simplicity and flexibility of their fabrication can lead to an endless number of CDs with distinct properties and applications. High fluorescence quantum yields (QY_FL) are generally a necessary feature for various applications of CDs. One commonly employed strategy to improve the fluorescence properties of CDs is heteroatom-doping using precursors containing desired heteroatoms (with focus on N-doping). In this work, we report the synthesis and systematic investigation of an array of N-doped CDs, obtained from the dry heating of solid mixtures of glucose and urea in different molar ratios with two main objectives: to study the role of stoichiometry in the optical properties and composition of CDs and to investigate the formation of possible alkaline-responsive nanoparticles and the potential of this procedure for obtaining CDs with higher synthesis yields. We have characterized the optical properties of this diverse array of glucose and urea-based CDs using both UV-Vis and fluorescence spectroscopies. In addition, we have also examined the CDs by using high-resolution transmission electron microscopy (HR-TEM) and X-Ray photoelectron (XPS) spectroscopy, as well as by assessing the thermal stability of the nanoparticles. We have found that this fabrication process generates two types of CDs, one readily soluble in water and other only soluble at basic pH. The latter was characterized by higher synthesis yields, and lower QY_FL and thermal stability, when compared with those of the former. Furthermore, the stoichiometry of the N-dopant does not appear to be correlated with the QY_FL of the obtained CDs. This study provides novel information that should be useful for the future rational development of CDs with higher QY_FL and synthesis yields.

Magnetoliposomes Containing Multicore Nanoparticles and a New Antitumor Thienopyridine Compound with Potential Application in Chemo/Thermotherapy

Multicore magnetic nanoparticles of manganese ferrite were prepared using carboxymethyl dextran as an agglutinating compound or by an innovative method using melamine as a cross-coupling agent. The nanoparticles prepared using melamine exhibited a flower-shape structure, a saturation magnetization of 6.16 emu/g and good capabilities for magnetic hyperthermia, with a specific absorption rate (SAR) of 0.14 W/g. Magnetoliposome-like structures containing the multicore nanoparticles were prepared, and their bilayer structure was confirmed by FRET (Förster Resonance Energy Transfer) assays. The nanosystems exhibited sizes in the range of 250–400 nm and a low polydispersity index. A new antitumor thienopyridine derivative, 7-[4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl]thieno[3,2-b]pyridine, active against HeLa (cervical carcinoma), MCF-7 (breast adenocarcinoma), NCI-H460 (non-small-cell lung carcinoma) and HepG2 (hepatocellular carcinoma) cell lines, was loaded in these nanocarriers, obtaining a high encapsulation efficiency of 98 ± 2.6%. The results indicate that the new magnetoliposomes can be suitable for dual cancer therapy (combined magnetic hyperthermia and chemotherapy).

Structure and Dynamics of the Flexible Cardiac Troponin T Linker Domain in a Fully Reconstituted Thin Filament

The structural analysis of large protein complexes has been greatly enhanced through the application of electron microscopy techniques. One such multiprotein complex, the cardiac thin filament (cTF), has cyclic interactions with thick filament proteins to drive contraction of the heart that has recently been the subject of such studies. As important as these studies are, they provide limited or no information on highly flexible regions that in isolation would be characterized as inherently disordered. One such region is the extended cardiac troponin T (cTnT) linker between the regions of cTnT which have been labeled TNT1 and TNT2. It comprises a hinge region (residues 158-166) and a highly flexible region (residues 167-203). Critically, this region modulates the troponin/tropomyosin complex's position across the actin filament. Thus, the cTnT linker structure and dynamics are central to the regulation of the function of cardiac muscles, but up to now, it was ill-understood. To establish the cTnT linker structure, we coupled an atomistic computational cTF model with time-resolved fluorescence resonance energy transfer measurements in both ±Ca²⁺ conditions utilizing fully reconstituted cTFs. We mapped the cTnT linker's positioning across the actin filament, and by coupling the experimental results to computation, we found mean structures and ranges of motion of this part of the complex. With this new insight, we can now address cTnT linker structural dynamics in both myofilament activation and disease.

Copper(II)-Doped Carbon Dots as Catalyst for Ozone Degradation of Textile Dyes

A catalytic ozonation advanced oxidation process (AOP) with a copper(II)-doped carbon dot as catalyst, Cu-CD (using L-cysteine and polyethylene glycol (PEG) as precursors and passivation agents), was developed for textile wastewater treatment (T = 25 °C and pH = 7). Four dyes were analyzed—Methyl Orange (MO), Orange II sodium salt (O-II), Reactive Black 5 (RB-5) and Remazol Brilliant Blue R (RBB-R), as well as a real effluent from the dying and printing industry. The Cu-CD, with marked catalytic ozonation properties, was successfully synthesized by one-pot hydrothermal procedure with a size of 4.0 nm, a charge of −3.7 mV and a fluorescent quantum yield of 31%. The discoloration of the aqueous dye solutions followed an apparent first-order kinetics with the following rate constants (kap in min−1): MO, 0.210; O-II, 0.133; RB-5, 0.177; RBB-R, 0.086. In the presence of Cu-CD, the following apparent first-order rate constants were obtained (kapc in min−1) with the corresponding increase in the rate constant without catalyst (%Inc): MO, 1.184 (464%); O-II, 1.002 (653%); RB-5, 0.709 (301%); RBB-R, 0.230 (167%). The presence of sodium chloride (at a concentration of 50 g/L) resulted in a marked increase of the discoloration rate of the dye solution due to generation of other radicals, such as chlorine and chlorine oxide, resulting from the reaction of ozone and chloride. Taking into consideration that the real textile effluent under research has a high carbonate concentration (>356 mg/L), which inhibits ozone decomposition, the discoloration first-order rate constants without and with Cu-CD (kap = 0.0097 min−1 and kapc = 0.012 min−1 (%Inc = 24%), respectively) were relatively small. Apparently, the Cu-CD, the surface of which is covered by a soft and highly hydrated caramelized PEG coating, accelerates the ozone decomposition and dye adsorption, increasing its degradation.

Influence of a series of pyridine ligands on the structure and photophysical properties of Cd(ii) complexes

Five Cd(ii) complexes based on α-acetamidocinnamic acid (HACA) and a set of N,N^N and N^N^N-pyridine (dPy) yield complexes with diverse nuclearities and enhanced quantum yields, benefiting from the chelation enhanced effect (CHEF) of dPy.

Quantifying Cytosolic Cytochrome c Concentration Using Carbon Quantum Dots as a Powerful Method for Apoptosis Detection

BACKGROUND

Cytochrome c (Cyt c) is a key biomarker for early apoptosis, and many methods were designed to detect its release from mitochondria. For a proper evaluation of these programed cell death mechanisms, fluorescent nanoparticles are excellent candidates due to their valuable optical properties. Among all classes of nanoparticles developed thus far, carbon-based quantum dots bring qualitative and efficient imaging strategies for biomedical applications as a consequence of their biocompatibility and low cytotoxicity.

METHODS

In this study, we synthesized carbon quantum dots smaller than 5 nm from sodium citrate and polyethylene imine. These nanoparticles were rigorously characterized, and their quenching capacity in apoptotic events was assessed in A549 cells treated with staurosporine and etoposide. For the evaluation of Cyt c release, a phenomenon directly correlated with apoptotic events, we ran a semiquantitative analysis using confocal laser scanning microscopy.

RESULTS

Carbon quantum dots were synthesized and were successfully employed for Cyt c detection by means of fluorescence microscopy. Significant drops in fluorescence intensity were observed in the case of cells treated with apoptosis-inducing therapeutic compounds compared to untreated cells, confirming Cyt c release from mitochondria to cytosol.

CONCLUSION

Considering these results, we strongly believe this method can contribute to an indirect in vitro evaluation of apoptosis.

Tyrosine-Templated Dual-Component Silver Nanomaterials Exhibit Photoluminescence and Versatile Antimicrobial Properties through ROS Generation

The role of small molecules in the preparation of metal nanomaterials generates considerable interest in the fields from materials science to interdisciplinary sciences. In this study, a small amino acid, l-tyrosine (Tyr), has been used as a ligand precursor for the preparation of silver nanomaterials (AgNMs) comprising a dual system: smaller silver nanoclusters (responsible exclusively for the photophysical properties) and larger silver nanoparticles (responsible exclusively for the antimicrobial properties). The luminescent properties of this AgNM system substantiate the role played by Tyr as a capping and a reducing agent outside the protein environment. An interesting feature of this report is the promising antimicrobial properties of the AgNMs against Saccharomyces cerevisiae, Candida albicans, Escherichia coli, and Bacillus cereus cell lines. The importance of this work is that this investigation demonstrates the combating ability of our AgNM system against pathogenic strains (C. albicans and B. cereus) as well. Moreover, the mechanistic aspects of the antimicrobial activity of the AgNMs were elucidated using various methods, such as propidium iodide staining, monitoring reactive oxygen species generation, leakage of proteins, DNA cleavage, etc. We propose that AgNM-mediated cytotoxicity in S. cerevisiae stems from the generation of singlet oxygen (¹O₂) species that create oxidative stress, disrupting the cell membrane and thereby resulting in leakage of proteins from the cells. This study can pave the way toward elucidating the role of a small molecule, Tyr, in the formation of NMs and describes the use of new NMs in potential antimicrobial applications.

A conjugated fluorescent polymer sensor with amidoxime and polyfluorene entities for effective detection of uranyl ion in real samples

It is an important challenge to develop a chemosensor for trace uranyl ion in an aqueous medium for sustainable development of nuclear energy and environmental conservation. A conjugated fluorescent polymer sensor P2 based on amidoxime groups and polyfluorene, which showed good hydrophilous resulting adequate contact with uranyl ions and selectivity and sensitivity even in the presence of other metal ions in DMA/H₂O (v/v = 20:80, pH = 6.0) solution, for uranyl ion was designed and prepared in this work. And it possesses good thermal stability and a larger Stokes shift (108 nm). Importantly, the fluorescence quenching occurred when P2 combining uranium. It had a good linear relationship with UO₂²⁺ concentration in the range of 10 to 200 nM with a fairly low LOD 7.4 × 10^-9 M. Interaction properties between the sensor P2 and UO₂²⁺ and the fluorescent mechanism were investigated by density functional theory (DFT). More importantly, the sensor can be successfully used for the detection of uranyl ion in environmental solutions. This work suggests that conjugated fluorescent polymer with amidoxime groups will be a prospective sensor of uranyl ion in the environmental sample.

Evaluation of Different Bottom-up Routes for the Fabrication of Carbon Dots

Carbon dots (CDs) are carbon-based nanoparticles with very attractive luminescence features. Furthermore, their synthesis by bottom-up strategies is quite flexible, as tuning the reaction precursors and synthesis procedures can lead to an endless number of CDs with distinct properties and applications. However, this complex variability has made the characterization of the structural and optical properties of the nanomaterials difficult. Herein, we performed a systematic evaluation of the effect of three representative bottom-up strategies (hydrothermal, microwave-assisted, and calcination) on the properties of CDs prepared from the same precursors (citric acid and urea). Our results revealed that these synthesis routes led to nanoparticles with similar sizes, identical excitation-dependent blue-to-green emission, and similar surface-functionalization. However, we have also found that microwave and calcination strategies are more efficient towards nitrogen-doping than hydrothermal synthesis, and thus, the former routes are able to generate CDs with significantly higher fluorescence quantum yields than the latter. Furthermore, the different synthesis strategies appear to have a role in the origin of the photoluminescence of the CDs, as hydrothermal-based nanoparticles present an emission more dependent on surface states, while microwave- and calcination-based CDs present an emission with more contributions from core states. Furthermore, calcination and microwave routes are more suitable for high-yield synthesis (~27-29%), while hydrothermal synthesis present almost negligible synthesis yields (~2%). Finally, life cycle assessment (LCA) was performed to investigate the sustainability of these processes and indicated microwave synthesis as the best choice for future studies.

Bridge between Temperature and Light: Bottom-Up Synthetic Route to Structure-Defined Graphene Quantum Dots as a Temperature Probe In Vitro and in Cells

Owing to their unique superiorities in chemical and photoluminescence (PL) stability, low toxicity, biocompatibility, and easy functionalization, graphene quantum dots (GQDs) are widely used in cell imaging, probes, and sensors. However, further development and deeper research of GQDs are restricted by their imprecise and complex structure and accompanying controversial PL mechanism. In this work, two kinds of structure-defined water-soluble GQDs, with different oxidation degrees, are synthesized from molecules using bottom-up syntheses methods. After being studied by a series of characterizations, their optical properties, functional groups, molecular weight, and structural information were obtained. The optical properties of GQDs could be optimized by controlling their oxidation degree. The PL mechanism of GQDs was investigated by comparing their structure and properties. Furthermore, robust, stable, and precise temperature probes were designed using the GQDs, which exhibited an excellent wide response range, covering the whole physiology temperature range, from 0 to 60 °C in water. Moreover, the GQDs were successfully applied as temperature-responsive fluorescence probes in the HeLa cell line. These works laid a solid foundation for further applications of GQDs as biological thermoprobes and selectively temperature detectors in vitro cellular and in vivo.

N-Heterocyclic Carbenes as Reversible Exciton-Delocalizing Ligands for Photoluminescent Quantum Dots

Delocalization of excitons within semiconductor quantum dots (QDs) into states at the interface of the inorganic core and organic ligand shell by so-called "exciton-delocalizing ligands (EDLs)" is a promising strategy to enhance coupling of QD excitons with proximate molecules, ions, or other QDs. EDLs thereby enable enhanced rates of charge carrier extraction from, and transport among, QDs and dynamic colorimetric sensing. The application of reported EDLs-which bind to the QDs through thiolates or dithiocarbamates-is however limited by the irreversibility of their binding and their low oxidation potentials, which lead to a high yield of photoluminescence-quenching hole trapping on the EDL. This article describes a new class of EDLs for QDs, 1,3-dimethyl-4,5-disubstituted imidazolylidene N-heterocyclic carbenes (NHCs), where the 4,5-substituents are Me, H, or Cl. Postsynthetic ligand exchange of native oleate capping ligands for NHCs results in a bathochromic shift of the optical band gap of CdSe QDs (R = 1.17 nm) of up to 111 meV while the colloidal stability of the QDs is maintained. This shift is reversible for the MeNHC-capped and HNHC-capped QDs upon protonation of the NHC. The magnitude of exciton delocalization induced by the NHC (after scaling for surface coverage) increases with the increasing acidity of its π system, which depends on the substituent in the 4,5-positions of the imidazolylidene. The NHC-capped QDs maintain photoluminescence quantum yields of up to 4.2 ± 1.8% for shifts of the optical band gap as large as 106 meV.

Evaluation of the Environmental Impact and Efficiency of N-Doping Strategies in the Synthesis of Carbon Dots

The efficiency and associated environmental impacts of different N-doping strategies of carbon dots (CDs) were evaluated. More specifically, N-doped CDs were prepared from citric acid via two main synthesis routes: Microwave-assisted hydrothermal treatment with addition of N-containing small organic molecules (urea and ethylenediamine (EDA)); and microwave-assisted solvothermal treatment in N-containing organic solvents (n,n-dimethylformamide (DMF), acetonitrile and pyridine). These syntheses produced CDs with similar blue emission. However, XPS analysis revealed that CDs synthesized via both hydrothermal routes presented a better N-doping efficiency (~15 at.%) than all three solvothermal-based strategies (0.6-7 at.%). However, from the former two hydrothermal strategies, only the one involving EDA as a nitrogen-source provided a non-negligible synthesis yield, which indicates that this should be the preferred strategy. This conclusion was supported by a subsequent life cycle assessment (LCA) study, which revealed that this strategy is clearly the most sustainable one from all five studied synthesis routes.

Thieno[3,2-c]pyran: an ESIPT based fluorescence “turn-on” molecular chemosensor with AIE properties for the selective recognition of Zn2+ ion

Thieno[3,2-c]pyran was synthesized as a fluorescent turn-on chemosensor for the selective recognition of Zn²⁺ ions with a low detection limit (0.67 μM), and it also exhibited AIE properties.

Synthesis and Fluorescent Properties of Novel Isoquinoline Derivatives

Isoquinoline derivatives have attracted great interest for their wide biological and fluorescent properties. In the current study, we focused on the synthesis of a series of novel isoquinoline derivatives substituted at position 3 of the heteroaromatic ring. Compounds were obtained in a Goldberg-Ullmann-type coupling reaction with appropriate amides in the presence of copper(I) iodide, N,N-dimethylethylenediamine (DMEDA), and potassium carbonate. The structures of novel isoquinolines were confirmed by IR, NMR, and elemental analysis, as well as X-ray crystallography. In the course of our research work, the visible fluorescence of this class of compounds was observed. The above findings prompted us to investigate the optical properties of the selected compounds.

Ultrafast ring closing of a diarylethene-based photoswitchable nucleoside

Deoxyuridine nucleosides embodied into diarylethenes form an especial class of photoswitchable compounds that are designed to stack and pair with DNA bases. The molecular geometry can be switched between "open" and "closed" isomers by a pericyclic reaction that affects the stability of the surrounding double helix. This potentially enables light-induced control of DNA hybridization at microscopic resolution. Despite its importance for the optimization of DNA photoswitches, the ultrafast photoisomerization mechanism of these diarylethenes is still not well understood. In this work, femtosecond transient absorption spectroscopy is applied to study the ring closing reaction upon UV excitation with 45 fs pulses. Excited-state absorption decays rapidly and gives rise to the UV-Vis difference spectrum of the "closed" form within ≈15 ps. Time constants of 0.09, 0.49 and 6.6 ps characterize the multimodal dynamics, where a swift recurrence in the signal anisotropy indicates transient population of the intermediate 21A-like state.

Tuning the Optical Properties of Sulfonylaniline Derivatives: Degeneracy Breaking of Benzene Orbitals and Linkage through Nodal Planes

The orbital degeneracy of benzene rings is resolved by an asymmetric push-pull system in 2,6-bis(methylsulfonyl)aniline (BMeSA), in which the highest occupied molecular orbital (HOMO) is located at the 4-position, while the lowest unoccupied molecular orbital (LUMO) is located at a different position and has a nodal plane through the carbon atoms at the 1- and 4-positions. Therefore, the π-extension of BMeSA at the 4-position reveals a strong overlap in the HOMO and a minimal overlap in the LUMO. Consequently, π-extended BMeSA derivatives exhibit longer absorbance and emission wavelengths in the order of the electron-donating abilities of their substituents at the 4-position, which is based on a decrease in an absolute HOMO-level-dependent HOMO-LUMO gap in accordance with the nodal arrangement. Positive fluorescent solvatochromism with polarity-dependent decrease in fluorescent intensity was also observed. The biaryls exhibited more planar geometries in the excited state than in the ground state. The charge transfer mechanism, which can be described as node-induced intramolecular charge transfer (NICT), differs from the planar intramolecular charge transfer (PICT) and twisted intramolecular charge transfer (TICT).

S1/S0 Potential Energy Surfaces Experience Different Types of Restricted Rotation: Restricted Z/ E Photoisomerization and E/ Z Thermoisomerization by an Out-of-Plane Benzyl Group or In-Plane m-Pyridinium Group?

Any method that can enhance the fluorescence of fluorophores is highly desirable. Fluorescence enhancement accomplished by restricted Z/ E photoisomerization through intramolecular steric hindrance or relatively high bond order of a C═C double bond in a S₁ excited state has rarely been studied. In this article, we used green fluorescent protein (GFP) chromophore analogues as a model to get new physical insights into the restricted Z/ E photoisomerization and E/ Z thermoisomerization phenomena. We found that the S₁ and S₀ potential energy surfaces (PESs) of the GFP chromophore analogues experience two dramatically different types of restricted rotation, and 2b can be a representative example. In its S₁ PES, it is not the intramolecular steric hindrance between the out-of-plane benzyl group and the in-plane m-pyridinium group but the relatively high bond order of the I-bond in the S₁ excited state of 2b that makes it have a higher barrier for the Z/ E photoisomerization, a smaller Z/ E photoisomerization quantum yield, and a higher fluorescence quantum yield. In its S₀ PES, it is not the reduced bond order of the I-bond in the S₀ ground state of 2b but the intramolecular steric hindrance between the out-of-plane benzyl group and the in-plane m-pyridinium group that makes it have an extra higher barrier for E/ Z thermoisomerization and a much smaller E/ Z thermoisomerization rate constant.

Concentration-tuned multicolor carbon dots: microwave-assisted synthesis, characterization, mechanism and applications

A new and simple way to obtain multicolor-emission carbon dots and an exploration of their mechanism and applications.

Microwave-assisted synthesis, characterization, cell imaging of fluorescent carbon dots using l-asparagine as precursor

Structure-analyzed carbon dots fabricated from a green raw material by a time-saving method.

Dinuclear Au(i) N-heterocyclic carbene complexes derived from unsymmetrical azolium cyclophane salts: potential probes for live cell imaging applications

We have synthesized a new series of azolium cyclophanes and used them as precursors of inherently luminescent dinuclear Au(i)-N-heterocyclic carbene (NHC) complexes. The azolium cyclophanes contained two azolium groups (either imidazolium or benzimidazolium), an o-xylyl group, and an alkyl linker chain (either C2, C3 or C4). All of the azolium cyclophanes were characterised by X-ray diffraction studies and VT NMR studies, and all were fluxional in solution on the NMR timescale. The C3- and C4-linked azolium cyclophanes served as precursors of Au2L2(2+) complexes (L is a cyclophane bis(NHC) ligand). Due to the unsymmetrical nature of the azolium cyclophanes, the Au2L2(2+) complexes each existed as cis and trans isomers. X-ray diffraction studies showed that the Au2L2(2+) complexes had short intramolecular AuAu distances, in the range 2.9-3.3 Å, suggestive of an aurophilic attraction, presumably as a consequence of the geometrical constraints imposed by the cyclophane bis(NHC) ligands. The complexes having the shortest AuAu distances (i.e., those based on C3-linked cyclophanes) exhibited intense luminescence in solution. The uptake of one of the dinuclear Au-NHC complexes by tumorigenic cells, and its subsequent distribution and toxicity in the cells, was monitored by luminescence microscopy over 6 h and proliferation measurements, respectively.

Targetable, two-photon fluorescent probes for local nitric oxide capture in the plasma membranes of live cells and brain tissues

A plasma membrane-targetable two-photon fluorescent probe for capturing nitric oxide in cells and brain tissues.

Synthetic green fluorescent protein chromophore analogues with a positive charge at the phenyl-like group

Synthetic green fluorescent protein (GFP) chromophore analogues with a positive charge at the phenyl-like group have the highly electrophilic amidine carbon, smaller LUMO-HOMO energy gap, red-shifted electronic absorptions and fluorescent emissions, and accelerated E-Z thermoisomerization rates. They are water-labile and their hydrolysis results in ring-opening of the imidazolinone moiety with a half life around 25-37 h in D₂O at 25 °C.

Synthesis and evaluation of benzothiazole-triazole and benzothiadiazole-triazole scaffolds as potential molecular probes for amyloid-β aggregation

Fluorescent scaffolds that can be easily modifiedviaclick chemistry were investigated as probes for Aβ-plaque deposits in mouse tissue.

Synthesis and structural characterization of metal complexes with macrocyclic tetracarbene ligands

Fourteen Ag(i), Au(i), Ni(ii), Pd(ii) and Pt(ii) complexes were prepared with macrocyclic tetradentate N-heterocyclic carbene (NHC) ligands.

Can a Six-Letter Alphabet Increase the Likelihood of Photochemical Assault to the Genetic Code?

In 2014, two unnatural nucleosides, d5SICS and dNaM, were shown to selectively base pair and replicate with high fidelity in a modified strain of E. coli, thus effectively expanding its genetic alphabet from four to six letters. More recently, a significant reduction in cell proliferation was reported in cells cultured with d5SICS, and putatively with dNaM, upon exposure to brief periods of near-visible radiation. The photosensitizing properties of the lowest-energy excited triplet state of both d5SICS and dNaM were implicated in their cytotoxicity. Importantly, however, the excited-state mechanisms by which near-visible excitation populates the triplet states of d5SICS and dNaM are currently unknown. In this study, steady-state and time-resolved spectroscopies are combined with quantum-chemical calculations in order to reveal the excited-state relaxation mechanisms leading to efficient population of the triplet states in these unnatural nucleosides in solution. It is shown that excitation of d5SICS or dNaM with near-visible light leads overwhelmingly to ultrafast population of their triplet states on the femtosecond time scale. The results presented in this work lend strong support to the proposal that photoexcitation of these unnatural nucleosides can accelerate oxidatively generated damage to DNA and other biomolecules within the cellular environment.

A Three-Photon Active Organic Fluorophore for Deep Tissue Ratiometric Imaging of Intracellular Divalent Zinc

Deep tissue bioimaging with three-photon (3P) excitation using near-infrared (NIR) light in the second IR window (1.0-1.4 μm) could provide high resolution images with an improved signal-to-noise ratio. Herein, we report a photostable and nontoxic 3P excitable donor-π-acceptor system (GMP) having 3P cross-section (σ3 ) of 1.78×10(-80)  cm(6)  s(2)  photon(-2) and action cross-section (σ3 η3 ) of 2.31×10(-81)  cm(6)  s(2)  photon(-2) , which provides ratiometric fluorescence response with divalent zinc ions in aqueous conditions. The probe signals the Zn(2+) binding at 530 and 600 nm, respectively, upon 1150 nm excitation with enhanced σ3 of 1.85×10(-80)  cm(6)  s(2)  photon(-2) and σ3 η3 of 3.33×10(-81)  cm(6)  s(2)  photon(-2) . The application of this probe is demonstrated for ratiometric 3P imaging of Zn(2+) in vitro using HuH-7 cell lines. Furthermore, the Zn(2+) concentration in rat hippocampal slices was imaged at 1150 nm excitation after incubation with GMP, illustrating its potential as a 3P ratiometric probe for deep tissue Zn(2+) ion imaging.

Synthesis of Ethano-Bridged Diazapolycenes as Potential Precursors for Diazapolycenes and Their Properties

A series of ethanodiazapolycenes were prepared in 87%-89% yields by Friedländer reactions of three o-aminoarenecarbaldehydes with bicyclo[2.2.2]octane-2,5-dione and their spectral, thermal, and structural properties were studied. Subsequent attempts to convert them to diazapolycenes have proved unsuccessful.

Reaction-Based Probes for Imaging Mobile Zinc in Live Cells and Tissues

Chelatable, or mobile, forms of zinc play critical signaling roles in numerous biological processes. Elucidating the action of mobile Zn(II) in complex biological environments requires sensitive tools for visualizing, tracking, and manipulating Zn(II) ions. A large toolbox of synthetic photoinduced electron transfer (PET)-based fluorescent Zn(II) sensors are available, but the applicability of many of these probes is limited by poor zinc sensitivity and low dynamic ranges owing to proton interference. We present here a general approach for acetylating PET-based probes containing a variety of fluorophores and zinc-binding units. The new sensors provide substantially improved zinc sensitivity and allow for incubation of live cells and tissue slices with nM probe concentrations, a significant improvement compared to the μM concentrations that are typically required for a measurable fluorescence signal. Acetylation effectively reduces or completely quenches background fluorescence in the metal-free sensor. Binding of Zn(II) selectively and quickly mediates hydrolytic cleavage of the acetyl groups, providing a large fluorescence response. An acetylated blue coumarin-based sensor was used to carry out detailed analyses of metal binding and metal-promoted acetyl hydrolysis. Acetylated benzoresorufin-based red-emitting probes with different zinc-binding sites are effective for sensing Zn(II) ions in live cells when applied at low concentrations (∼50-100 nM). We used green diacetylated Zinpyr1 (DA-ZP1) to image endogenous mobile Zn(II) in the molecular layer of mouse dorsal cochlear nucleus (DCN), confirming that acetylation is a suitable approach for preparing sensors that are highly specific and sensitive to mobile zinc in biological systems.

Synthesis and Photophysical and Electroluminescent Properties of Poly(1,4-phenylene-ethynylene)-alt-poly(1,4-phenylene-vinylene)s with Various Dissymmetric Substitution of Alkoxy Side Chains

The synthesis and characterization of a set of conjugated polymers, poly(1,4-phenylene–ethynylene)-alt-poly(1,4-phenylene–vinylene)s (PPE–PPVs), with a dissymmetrical configuration (partial or total) of alkoxy side chains is reported. Five new polymers bearing octyloxy and/or octadecyloxy side chains at the phenylene–ethynylene and phenylene–vinylene segments, respectively, were obtained. Two symmetrical substituted polymers were used for comparison. Polymers with weight-average molecular weight, M_w, up to 430 000 g/mol and degree of polymerization between 17 and 322 were obtained by a Horner–Wadsworth–Emmons olefination polycondensation reaction of the respective luminophoric dialdehydes and bisphosphonates. As expected, identical conjugated backbones in all polymers results in very similar photophysical response in dilute solution, with high fluorescence quantum yields between 50% and 80%. In contrast, the thin film properties are dependent on the combinatorial effects of side chain configuration, molecular weight, and film thickness parameters, which are the basis of the resulting comparison and discussion.

Friend or foe? The role of solvents in non-triplet, intraligand charge transfer sensitization of lanthanide(iii) luminescence

A comprehensive photophysical and solvatochromic study is conducted to evaluate the luminescence properties of our Eu(iii), Sm(iii) and Yb(iii) complexes.

Impact of the different electron-releasing subunits on the dye-sensitized solar cell performance of new triphenylamine-benzimidazole based molecules

New triphenylamine-benzimidazole type small molecules with different electron-releasing groups were designed and synthesized to investigate their photovoltaic performances in dye sensitized solar cells (DSSCs). Their good visible absorptions covering the 400-535 nm in addition to suitable lowest unoccupied molecular orbital (LUMO) energy levels between -3.03 and -3.11 eV make good candidates them for DSSC devices. Fluorescence quenching studies of the dyes with pristine titania support the good electron injection to conduction band of TiO2. Time resolved measurements of the dyes in solutions indicate the occurence of charge generation during the excited state. One of the used dyes in DSSC devices, TPA5a, carrying a methoxy group in triphenylamine part of the structure, gave much higher power conversion efficiency (PCE) value of 4.31% as compared to the other derivatives. Device fabricated from TPA5a dye gives good external quantum efficiency (EQE) value above 70% at 460 nm. Also, electron impedance spectroscopy (EIS) analysis of the devices gives a good explanation of the understanding of the cell performances.

Highly efficient quencher-free molecular beacon systems containing 2-ethynyldibenzofuran- and 2-ethynyldibenzothiophene-labeled 2'-deoxyuridine units

We have prepared two fluorescent DNA probes--UDBF and UDBT, containing 2-ethynyldibenzofuran and 2-ethynyldibenzothiophene moieties, respectively, covalently attached to the base dU--and incorporated them in the central positions of oligodeoxynucleotides (ODNs) so as to develop new types of quencher-free linear beacon probes and investigate the effect of functionalization of the fluorene scaffold on the photophysical properties of the fluorescent ODNs. The ODNs containing adenine flanking bases (FBs) displayed a selective fluorescence "turn-off" response to mismatched targets with guanine bases; this suggests that these probes could be used as base-discriminating fluorescent nucleotides. On the other hand, we observed a "turn-on" response to matched targets when the UDBF and UDBT units of ODNs containing pyrimidine-based FBs were positioned opposite the four natural nucleobases. In particular, an ODN incorporating UDBT and cytosine FBs has potential use in single-nucleotide polymorphism typing.