Shift In Emission Spectra Research Articles

Dicyanovinyl substituted push-pull chromophores: effects of central C[double bond, length as m-dash]C/phenyl spacers, crystal structures and application in hydrazine sensing.

To discern the distinctive effect of the C[double bond, length as m-dash]C bond and the phenyl bridge on the photophysical and chemical properties of D-π-A molecular systems, three new dicyanovinyl substituted push-pull chromophores 1-3 containing either a C[double bond, length as m-dash]C bond or a phenyl ring as the central π-linker were synthesized by the Suzuki-Miyaura and Knoevenagel reactions. Together with the counterpart of 1 developed by Zhang's group (TPE-z), their optical properties and single crystal structures were systematically and comparatively investigated. Notably, the simple π-extension of a C[double bond, length as m-dash]C linker to a phenyl ring between electron donor and electron acceptor moieties could greatly affect the photophysical properties of chromophores, particularly leading to significant hypsochromic shifts in both absorption and emission spectra. Meanwhile, as a node of twisted sections in chromophores, the C[double bond, length as m-dash]C bond was demonstrated to play an important role in the nonradiative relaxation of excited states, as compared to the rigid phenyl spacer. Moreover, the three chromophores were found to display spectral responses to hydrazine with slightly different sensitivities, and visual detection of hydrazine in the gaseous state was achieved via using readily fabricated paper test strips.

A coumarin-based fluorescent probe for ratiometric detection of hydrazine and its application in living cells.

A new ratiometric fluorescent probe (1) was developed for the detection of hydrazine. The probe was obtained by incorporating the recognition moiety of acetyl group onto a coumarin fluorophore. Probe 1 displayed a distinct cyan emission in a 100% aqueous phosphate buffer solution. In the presence of hydrazine, probe 1 undergoes a hydrazinolysis process to release the coumarin fluorophore, which exhibited significant hypsochromic shifts in both absorption and emission spectra, and thus achieving a ratiometric response. This ratiometric probe is highly selective and sensitive towards hydrazine detection. The limit of detection (LOD) was calculated to be 34 nM. Moreover, cellular toxicity and imaging experiments suggested that probe 1 is can be used to monitor hydrazine in live cells.

Small Changes With Big Consequences: Swapping Two Atoms In Side Chains Changes Phenylene-Ethynylene Packing And Fluorescence.

Engineering the properties of conjugated materials in the solid state is an unsolved, ongoing challenge important to fundamental understanding of how non-covalent interactions dictate packing and key properties, as well as the development of technologies based in organic optoelectronics. The most common design paradigm of such materials divide them into a "main chain" with extended conjugation, the chemical structure of which determines optoelectronic properties, and "side chains" not conjugated to the backbone, which provide solubility when they are long alkyl chains. This paper describes comparisons between phenylene-ethynylene molecules in which slight changes to the structure of "side chains"-swapping hydrogen and fluorine atomic position on an aromatic ring-results in unexpectedly large changes in the solid-state optical properties. In a pair of anisyl-terminated three-ring phenylene-ethynylenes, switching the side chain arenes of benzyl esters from 2,4,6-trifluoro to 2,3,6-trifluoro results in a shift in fluorescence emission spectra of over 100 nm, as well as the opposite direction of force-induced shifting of emission. Through a combination X-ray crystal structures, electronic structure calculations, and comparisons with other derivatives, we describe how the 2,4,6-trifluorinated side chains yield cofacial fluoroarene-arene stacking interactions that twist the PE backbone out of conjugation, while the 2,3,6-trifluoro side chains do not stack, instead yielding more coplanar PE backbones that form intermolecular aggregates. Overall, this work demonstrates how slight modifications to parts of conjugated materials normally considered ancillary to optoelectronic properties can determine their solid-state properties, epitomizing the challenge of rational design but at the same time offering opportunities for materials discovery and improved understanding of non-covalent interactions.

State transition identification in multivariate time series (STIMTS) applied to rotational jump trajectories from single molecules.

Time resolved data from single molecule experiments often suffer from contamination with noise due to a low signal level. Identifying a proper model to describe the data thus requires an approach with sufficient model parameters without misinterpreting the noise as relevant data. Here, we report on a generalized data evaluation process to extract states with piecewise constant signal level from simultaneously recorded multivariate data, typical for multichannel single molecule experiments. The method employs the minimum description length principle to avoid overfitting the data by using an objective function, which is based on a tradeoff between fitting accuracy and model complexity. We validate our method with synthetic data from Monte Carlo simulations modeling fluorescence resonance energy transfer and rotational jumps, respectively. The method is applied to quantify rotational jump dynamics of single terrylene diimide (TDI) molecules deposited on a solid substrate. Depending on the substitution pattern of the TDI molecules and the chosen substrate materials, we find significant differences in time scale and geometry of molecular reorientation. From an additional application of our state transition identification in multivariate time series approach, a significant correlation between shifts of emission spectra and the occurrence of rotational jumps was found.

A waterborne polyurethane-based polymeric dye with covalently linked disperse red 11

A red fluorescent sulfonated waterborne polyurethane-based dye WPU-DR11 was synthesized by conjugating Disperse Red 11 (DR11) into polyurethane backbones. The expected structure of WPU-DR11 was characterized by FT-IR and UV–vis spectra. Containing the well-known dye of anthraquinone chromophores, WPU-DR11 exhibits intriguing optical behaviors. Compared with DR11, WPU-DR11 shows an obvious bathochromic shift in absorption spectra, whereas a evident hypsochromic shift in emission spectra. The fluorescence intensity of WPU-DR11 is dramatically enhanced compared with that of DR11. The fluorescence intensity of WPU-DR11 increases with the temperature, which is different from that of ordinary fluorescent materials. It is found that the fluorescence intensity of WPU-DR11 gradually increase with the increase of concentration, and then decrease. Migration rate of WPU-DR11 are only 2.0–4.0%, which is well below migration rate of DR11. The polyester fibers dyed with WPU-DR11 show high color yield, excellent breaking strength retention, good air permeability and anti-wrinkle resistance. According to the experimental results, WPU-DR11 exhibits excellent fluorescent and dyeing performance.

Size-dependent structural phase transitions and their correlation with photoluminescence and optical absorption behavior of annealed Zn0.45Cd0.55S quantum dots

In this paper, we investigate the effect of thermally induced structural phase transitions on the photoluminescence (PL) and optical absorption behaviour of Zn0.45Cd0.55S nanoparticles (NPs). Analysis of X-ray diffraction (XRD) patterns and high-resolution electron microscope (HRTEM) images reveal that the as-synthesized sample possesses zinc-blende-type cubic structure. In addition, at annealing temperature (Ta) 400 °C, the cubic structure transforms completely into the wurtzite-type hexagonal structure. Furthermore, the second phase transition of the as-synthesized sample has observed at 700 °C, where the cubic structure has transformed into mixed polycrystalline phases of hexagonal ZnO, cubic CdO, monoclinic CdSO3, and orthorhombic ZnSO4 structures. These new phases have also confirmed from the analysis of Raman and FTIR spectra. Analysis of UV–visible optical absorption spectra demonstrates that Increasing Ta results in the decrease of optical band gap due the improvement in crystallinity accompanied by the increase in the particle size. The PL emission bands at an excitation energy of 3.818 eV exhibit redshift and a decrease in the intensity with increasing Ta up to 500 °C. Meanwhile, further increase in Ta up to 700 °C results in the enhancement of green emission intensity. On the other hand, PL emission spectra at 3.354 eV and Ta 700 °C, reveal a dramatic increase in the emission intensity nearly by one-order of magnitude with respect to its value of the as-synthesized sample. This behaviour is ascribed to the incorporation of oxygen-related defects via thermal annealing in air, which act as additive radiative centers. Also, we have interpreted the observed spectral blue shift of PL emission spectrum with increasing excitation energy.

Photophysical properties of 1-pyrene-based derivatives for nitroaromatic explosives detection: Experimental and theoretical studies

Novel pyrene-based derivatives, 4-(p-tolylethynyl)pyrene (Py-ET) and 9-(pyren-3-yl)-9H-carbazole (Py-CZ), were synthesized for application of nitroaromatic explosives detections. Introduction of groups into pyrene moieties resulted in a bathochromic shift in absorption and emission spectra. The fluorescence quantum yield varied between 0.26 and 0.44. Fluorescence quenching behavior of 1-pyrene-based derivatives for sensing of nitroaromatic explosives, which are 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), in dichloromethane solution was studied. It was found that the Py-ET had a higher sensitivity and quenching efficiency than Py-H and Py-CZ with detection limits of 2.32 and 3.09 ppm for DNT and TNT, respectively. This was explained by using theoretical studies with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. It revealed that Py-ET was quenched by nitroaromatic explosives via intermolecular π–π interaction with highest binding energy and lowest energy gap. Most of electrons (>90%) were transferred from HOMO of the pyrene derivatives to the LUMO of quencher molecules during the quenching process.

Photoluminescence Spectra From The Direct Energy Gap of a-SiQDs

A theoretical model for radiative recombination in amorphous silicon quantum dots (a-SiQDs) was developed. In this model, for the first time, the coexistence of both spatial and quantum confinements were considered. Also, it is found that the photoluminescence exhibits significant size dependence in the range (1-4) nm of the quantum dots. a-SiQDs show visible light emission peak energies and high radiative quantum efficiency at room temperature,in contrast to bulk a-Si structures. The quantum efficiency is sensitive to any change in defect density (the volume nonradiative centers density and/or the surface nonradiative centers density) but, with small dots sizes, the quantum efficiency is insensitive to such defects. Our analysis shows that the photoluminescence intensity increases or decreases by the effect of radiative quantum efficiency. By controlling the size of a-SiQDs, we note that the energy of emission can be tuned. The blue shift is attributed to quantum confinement effect. Meanwhile, the spatial confinement effect is clearly observed in red shift in emission spectra. we found a good agreement with the experimental published data. Therefore, we assert that a-SiQDs material is a promising candidate for visible, tunable, and high performance devices of light emitting.

Synthesis and Photophysical Properties of α‐Pyrone‐fused‐pyrido[3, 2,1‐jk]carbazolone Derivatives : DFT/TD‐DFT Insights

AbstractThe present paper discloses an interesting microwave‐assisted solvent‐free protocol for the synthesis of thermally stable, highly fluorescent pyrano[2′, 3′:4,5]pyrido[3, 2,1‐jk]carbazole‐5,8‐diones in good to high yields with good quantum yields (Ø ≥ 0.70) through a [3+3] annulation reaction of aryl‐substituted Morita‐Baylis‐Hillman acetates with a 4‐hydroxy‐6H‐pyrido[3, 2,1‐jk]carbazol‐6‐one in the presence of Hünig's base. The solvatochromic properties of synthesized compounds have been determined which showed blue shifts in absorption and emission spectra with increasing the polarity of solvents. Similarly, the higher quantum yields were also observed in case of non‐polar solvents as compared to polar ones. Interestingly, the experimental results of photophysical properties were in good agreement with theoretical data obtained using B3LYP/6‐311G++(d,p) level of theory. Furthermore, the synthesized chromophoric scaffolds exhibited good thermal stability (342‐387 °C) and average fluorescence lifetime in the range of 2.011‐2.139 ns for 408 nm, 2.268‐2.277 ns for 428 nm.

Synthesis and fluorescence characteristics of selective ratiometric fluorescent sensors for silver ions based on 3-indolyl-4-indazolyl maleimide derivatives

Selective ratiometric fluorescent sensor b for detection of silver ions and its counterparts (sensor a and c) were efficiently synthesized based on 3-indolyl-4-indazolyl maleimide, and their photophysical properties and activities towards metal ions were examined. The experimental results were verified by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The results demonstrated that sensor b could selectively and sensitively recognize Ag+ compared with other competing metal ions in tetrahydrofuran (THF). It probably forms a 1:1 complex with Ag+, displaying a 52-nm bathochromic shift of the fluorescence emission spectrum. Moreover, the binding mechanism was investigated using binding stoichiometry titration and 1H, 13C nuclear magnetic resonance (NMR).

One pot synthesis, physicochemical and photophysical investigation of biologically active pyridine-3-carboxylate (ECPC) as probe to determine CMC of surfactants in organized media

Ethyl 4 - (9-ethyl-9H-carbazol-3-yl) – 2 – methyl - 5- oxo - 4, 5 - dihydro-1H-indeno[1,2-b]pyridine-3-carboxylate (ECPC) was prepared by one pot multi component reaction of 9-ethyl-9H-carbazole-3-carbaldehyde, indane-1,3-dione, ethyl acetoacetate and ammonium acetate in the presence few drops of piperidine. Structure of the title compound (ECPC) was confirmed by the spectroscopic techniques (FT-IR, 1H-NMR, 13C-NMR, EI-MS) and elemental analysis. Photophysical parameter of the ECPC such as transition dipole moment, extinction coefficient, stokes shift, oscillator strength, fluorescence quantum yield were calculated by using the different solvents (based on the polarity). The results of compound ECPC showed red shift in absorbance and emission spectrum with increase in the polarity of the solvents from n-heptane to DMSO. Emission spectrum of ECPC effected with anionic and cationic surfactant so ECPC can be used as probe to determine critical micelle concentrations (CMC) of anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB) surfactant. The in-vitro antibacterial activity of ECPC was examined by the disk diffusion and minimum inhibitory concentration (MIC) methods against two Gram-positive and two Gram-negative bacteria by using Tetracycline as reference drug.

Impact of Ga3+ on the phase transition and luminescence properties of substituted Sr2SiO4:Eu2+ phosphor synthesized from a highly homogeneous oxide precursor based on a novel water-soluble silicon compound

A series of samples with the compositions Sr2(1−x-z/2)Eu2xLazSi1−zGazO4 were synthesized by an advanced solution method employing a water-soluble silicon (WSS) compound. It has been observed that the substitution of Si4+ by Ga3+ in charge compensated Sr2(1−x-z/2)Eu2xLazSi1−zGazO4 samples causes a phase transition from β-phase to the α-phase of Sr2SiO4 accompanied by a considerable red shift in the photoluminescence emission spectra. Internal quantum efficiencies are found to be 95% and 77% for Sr1.98Eu0.02SiO4 and Sr1.93Eu0.02La0.05Si0.95Ga0.05O4 respectively. The high quantum efficiency of the phosphors owe to the synthesis procedure as well as use of SrCl2 as flux during the heat treatment in H2/Ar atmosphere. To demonstrate its potential application, we fabricated a warm white light-emitting diode (WLED) using the Sr1.93Eu0.02La0.05Si0.95Ga0.05O4 phosphor, pumped with a 365nm n-UV LED chip, which reflects the good color rendering index and color temperature.

Analysis and optimization on the angular color shift of RGB OLED displays

Microcavites contribute to enhancing the optical efficiency and color saturation of an organic light emitting diode (OLED) display. A major tradeoff of the strong cavity effect is its apparent color shift, especially for RGB-based OLED displays, due to their mismatched angular intensity distributions. To mitigate the color shift, in this work we first analyze the emission spectrum shifts and angular distributions for the OLEDs with strong and weak cavities, both theoretically and experimentally. Excellent agreement between simulation and measurement is obtained. Next, we propose a systematic approach for RGB-OLED displays based on multi-objective optimization algorithms. Three objectives, namely external quantum efficiency (EQE), color gamut coverage, and angular color shift of primary and mixed colors, can be optimized simultaneously. Our optimization algorithm is proven to be effective for suppressing color shift while keeping a relatively high optical efficiency and wide color gamut.

Effects of Hydrophobic Amino Acid Substitutions on Antimicrobial Peptide Behavior.

Antimicrobial peptides (AMPs) are naturally occurring components of the immune system that act against bacteria in a variety of organisms throughout the evolutionary hierarchy. There have been many studies focused on the activity of AMPs using biophysical and microbiological techniques; however, a clear and predictive mechanism toward determining if a peptide will exhibit antimicrobial activity is still elusive, in addition to the fact that the mechanism of action of AMPs has been shown to vary between peptides, targets, and experimental conditions. Nonetheless, the majority of AMPs contain hydrophobic amino acids to facilitate partitioning into bacterial membranes and a net cationic charge to promote selective binding to the anionic surfaces of bacteria over the zwitterionic host cell surfaces. This study explores the role of hydrophobic amino acids using the peptide C18G as a model system. These changes were evaluated for the effects on antimicrobial activity, peptide-lipid interactions using Trp fluorescence spectroscopy, peptide secondary structure formation, and bacterial membrane permeabilization. The results show that while secondary structure formation was not significantly impacted by the substitutions, antibacterial activity and binding to model lipid membranes were well correlated. The variants containing Leu or Phe as the sole hydrophobic groups bound bilayers with highest affinity and were most effective at inhibiting bacterial growth. Peptides with Ile exhibited intermediate behavior while those with Val or α-aminoisobutyric acid (Aib) showed poor binding and activity. The Leu, Phe, and Ile peptides demonstrated a clear preference for anionic bilayers, exhibiting significant emission spectrum shifts upon binding. Similarly, the Leu, Phe, and Ile peptides demonstrated greater ability to disrupt lipid vesicles and bacterial membranes. In total, the data indicate that hydrophobic moieties in the AMP sequence play a significant role in the binding and ability of the peptide to exhibit antibacterial activity.

Self-Trapped Exciton and Large Stokes Shift in Pristine and Carbon-Coated Silicon Carbide Quantum Dots

SiC quantum dots have potential applications in the fields of optoelectronics, biological imaging, etc. However, the theoretical studies of their optical spectra have been limited to the energy gap calculations, and the microscopic mechanism of the photoluminescence process has not been clearly understood. Here, we study the optical absorption and emission spectra for pristine and carbon-coated SiC quantum dots via time-dependent density functional tight-binding method. The results show that optical absorption spectra of pristine SiC quantum dots are generally governed by the quantum confinement effect, which however will break down for the carbon-coated SiC quantum dots. Large Stokes shift in the optical emission spectra for all quantum dots is found, which is attributed to the self-trapped exciton accompanying with stretched chemical bond. The location of self-trapped exciton and the type of stretched bond will be affected by the coated carbon shell, which can be utilized to tune the optical emission properties.

Spectroscopic, Photophysical Investigation and Micellization for Critical Micelle Concentration of 3-(3,4-Dimethoxyphenyl)-1-(2,5-Dimethylfuran-3-Yl)Prop-2-En-1-One Dye

3-(3,4-Dimethoxyphenyl)-1-(2,5-dimethylfuran-3-yl)prop-2-en-1-one (DDFP) was prepared by the reaction of 3-acetyl-2,5-dimethylfuran and 3,4-dimethoxybenzaldehyde. Data obtained from FT-IR, 1H-NMR, 13C-NMR, EIMS, and elemental analysis were consistent with the chemical structure of the newly prepared DDFP. Electronic absorption and emission spectrum of DDFP have been measured in different solvents. DDFP dye exhibits red shift in emission spectrum as solvent polarity increases, indicating a large change in dipole moment of DDFP molecule upon excitation due to intramolecular charge transfer in excited DDFP. Excited state intermolecular hydrogen bonding affects the energy of emission spectrum and fluorescence quantum yield of DDFP molecule. DDFP dye undergoes solubilization in different micelles and may be used as a probe or quencher to determine the critical micelle concentration (CMC) of CTAB and SDS. The pho to reactivity and net photochemical quantum yield (φc) of DDFP are determined in solvents CHCl3, CH2Cl2, CCl4, and DMSO. The dye is relatively photostable in DMSO and displays photodecomposition in chloromethane solvents.

A highly selective and ratiometric fluorescent probe for cyanide by rationally altering the susceptible H-atom

A highly selective and ratiometric fluorescent probe for cyanide was rationally designed and synthesized. The probe comprises a fluorophore unit of naphthalimide and a CN- acceptor of methylated trifluoroacetamide group. For these previous reported trifluoroacetamide derivative-based cyanide chemosensors, the H-atom of amide adjacent to trifluoroacetyl group is susceptible to be attacked by various anions (CN- itself, F-, AcO-, et al.) and even the solvent molecule, which resulted in the bewildered reaction mechanism and poor selectivity of the assay. In this work, the susceptible H-atom of trifluoroacetamide was artfully substituted by alkyl group. Thus a highly specific fluorescent probe was developed for cyanide sensing. Upon the nucleophilic addition of cyanide anion to the carbonyl of trifluoroacetamide moiety of the probe, the ICT process of the probe was significantly enhanced and leading to a remarkable red shift in both absorption and emission spectra of the probe. This fluorescent assay showed a linear range of 1.0–80.0µM and a LOD (limit of detection) of 0.23µM. All the investigated interference have no influence on the sensing behavior of the probe toward cyanide. Moreover, by coating on TLC plate, the probe can be utilized for practical detection of trace cyanide in water samples.

Unsymmetrically functionalized 5,5″-diaryl- and 5,6,5″-triaryl-2,2′:6′,2″-terpyridines: an efficient synthetic route and photophysical properties

An efficient approach for the synthesis of 5,5″- or 5,6,5″-aryl substituted 2,2′:6′,2″-terpyridines, bearing an anneleted cyclopentene unit in one of the side-chain pyridine rings for the improved solubility in organic solvents, via their 1,2,4-triazine analogues has been developed. By using this approach, various aromatic substituents were introduced in the 2,2′:6′,2″-terpyridine core. Depending on the nature of the aromatic substituents, the obtained terpyridines exhibited an intense emission in a range of ca. 344–394 nm in acetonitrile solutions. For the most representative compounds, pronounced bathochromic shifts in both absorption and emission spectra were observed compared with previously reported substituted terpyridines.

Remarkable enhancement of La(1-x)SmxCrO3 nanoperovskite properties: An influence of its doping concentrations

Rare earth orthochromites of type La(1-x)SmxCrO3 ((LSCO) x=0, 0.1, 0.3, 0.5) have been synthesized through solid state reaction. These polycrystalline samples exhibit orthorhombic crystal structure and its corresponding distortion depends on the dopant concentrations. With increasing dopant stoichiometry, the A-O bond length changes resulting in the augmentation of perovskite’s physical properties. The occupancy of relatively less ionic radii dopant influences the decrease in crystallite size, blue shift in emission spectrum and intensification of the phonon characteristic vibrations. The finer particles aggregate to form dendritic morphology and become distinct on Sm/La ratio increments as identified from electron micrographs and atomic force microscopy. Ambient temperature magnetization analysis reveals the enhancement of antiferromagnetic nature upon dopant increments.

Composition and strain effects in Type I and Type II heterostructure ZnSe/Cd(Zn)S and ZnSe/Cd1-xZnxS core/shell quantum dots

We investigated the effect of ternary shell alloy composition on the bandgap and diameter of core of ZnSe/Cd1−xZnxS heterostructure core/shell quantum dots, which were synthesized by using a simple colloidal technique. Characterization by using the x-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Vis absorption and fluorescence emission spectroscopic techniques indicate that (i) there is a transition of ZnSe/Cd0.6Zn0.4S Type-I heterostructure (electrons and holes tend to localize in core) to ZnSe/Cd0.75Zn0.25S quasi-Type-II heterostructures (holes tend to localized in the core and electrons are delocalized) and (ii) then after large red shift and Stock-shift in PL emission spectra but not a distinct absorption peak in UV spectra become noticeable in ZnSe/Cd0.75Zn0.25 S quasi-Type II and ZnSe/CdS Type II heterostructures (electrons are localized in core and holes are localized in shell). Furthermore, the increase of Cd:S ratio in shell alloy composition shifts the XRD peaks to lower 2θ degrees which corresponds to tensile strain in the ZnSe core. Finally, the hydrostatic interfacial strain has effect on the squeezing or stretching the capped core: A decrease of compressive force on core from ZnSe/ZnS to tensile force in ZnSe/CdS with increase in Cd:S ratio indicates that transition of compressive strain to tensile strain takes place with the transition from Type-I to II heterostructure.