Red-edge Effect Research Articles

750 nm laser based on an BaGa4Se7 optical parametric oscillator

The red edge effect of plants is extensively utilized in vegetation remote sensing, particularly by applying hyperspectral LiDAR (HSL) technology. This technology effectively captures spectral information from targets together with range measurements by processing recorded waveforms in the red-edge spectral bands. Despite its widespread use, there is still potential for enhancing the tuning accuracy and the energy output of each channel. What we believe to be a novel nonlinear crystal, BaGa4Se7 (BGSe), has been employed to achieve laser output in the red edge spectral band with a wide tuning range and high tuning precision for the first time. Successful generation of laser radiation at 1512 nm was achieved, with an angular tuning resolution of 35.9 nm/°. When the pump light energy was 17.81 mJ, the energy of the 1512 nm near-infrared laser was 3.210 mJ, with a slope efficiency of 31.2% and an optical-to-optical conversion efficiency (pump to signal) of 18.0%. Subsequent pumping of the second harmonic generation crystal KTiOPO4 (KTP) with the 1512 nm laser output from the BGSe optical parametric oscillator (OPO) facilitated the generation of 756 nm red light laser output. Angle tuning of the BGSe OPO eventually enabled the tunable output of the red edge spectral laser ranging from 701 nm to 780 nm with output energy of approximately 2 mJ, which is several orders of magnitude higher than traditional supercontinuum laser source solution. Such improvement becomes a solid cornerstone for long-range HSL applications.

A near-infrared HBT-based fluorescent probe for tracking carbon monoxide-releasing CORM-3

Tricarbonylchloro(glycinato)ruthenium (CORM-3) has important application in the treatment of clinical diseases because of anti-inflammatory and heart-protecting properties, and is also used to study the metabolic mechanism of endogenous carbon monoxide as a safe and convenient carbon monoxide-releasing agent in vivo due to good water solubility and releasing controlled amounts of CO. Thus the development of effective detection methods to achieve the analysis of CORM-3 is of great significance in monitoring CORM-3 and studying the specific mechanism of endogenous CO in biological samples. Herein a small molecule fluorescent probe was developed by selecting 2-(2-hydroxyphenyl)benzothiazole (HBT) derivative as the optical signal unit and 4-nitrobenzyl moiety as the reactive unit. It could quickly detect CORM-3 within 15 min by the enhanced near-infrared fluorescence at 720 nm without the participation of heavy metal ions, accompanied by the large Stokes movement of 195 nm. The detection limit and linear range of the probe toward CORM-3 were achieved 0.11 µM and 0 – 175 µM, respectively. Besides, this probe displayed a red-edge effect, and the excitation wavelength and emission wavelength may be adjusted reasonably according to the test requirement to avoid interference signal. More importantly, it has been successfully used for the detection of CORM-3 with high resolution of fluorescence imaging in living cells and Zebrafish.

Red edge effect and chromoselective photocatalysis with amorphous covalent triazine-based frameworks

Chromoselective photocatalysis offers an intriguing opportunity to enable a specific reaction pathway out of a potentially possible multiplicity for a given substrate by using a sensitizer that converts the energy of incident photon into the redox potential of the corresponding magnitude. Several sensitizers possessing different discrete redox potentials (high/low) upon excitation with photons of specific wavelength (short/long) have been reported. Herein, we report design of molecular structures of two-dimensional amorphous covalent triazine-based frameworks (CTFs) possessing intraband states close to the valence band with strong red edge effect (REE). REE enables generation of a continuum of excited sites characterized by their own redox potentials, with the magnitude proportional to the wavelength of incident photons. Separation of charge carriers in such materials depends strongly on the wavelength of incident light and is the primary parameter that defines efficacy of the materials in photocatalytic bromination of electron rich aromatic compounds. In dual Ni-photocatalysis, excitation of electrons from the intraband states to the conduction band of the CTF with 625 nm photons enables selective formation of C‒N cross-coupling products from arylhalides and pyrrolidine, while an undesirable dehalogenation process is completely suppressed.

Synthesizing luminescent carbon from condensed tobacco smoke: bio-waste for possible bioimaging

Used cigarette filters, a waste material and a major source of land pollution, were used as raw material to study the nature of condensed tobacco smoke (tar) using microscopy, optical, IR, photoluminescence, and Raman spectroscopy, as well as X-ray diffraction and electron and fluorescence microscopy. The tar present in the cigarette filter bud was used to synthesize luminescent low dimensional carbon using a simple methanol extraction technique. The collected material shows light blue emission under UV excitation with emission peak energy depending strongly on the excitation wavelength. Such excitation energy dependent emission is observed from the extract solution and the dried film. Careful analysis was carried out to understand its origin, which revealed the presence of a giant red-edge effect in the samples. A correlation between room temperature photoluminescence spectroscopy and fluorescence microscopy was carried out. The presence of amorphous phase carbon was established using Raman spectroscopy, and a quantum yield of more than 9% was estimated, which was moderately high in comparison with the one shown by carbon dots prepared by using other sources and can be used for bioimaging applications.

Red-Edge Effect of Auramine O in Saccharide Glasses

Red-Edge Effect of Auramine O in Saccharide Glasses

Composition and excitation wavelength dependent photoluminescence color tuning in nanocomposite of PMMA and ZnO nanorods for PLED

Semiconducting nanocomposites of PMMA and ZnO are obtained by bulk polymerization of MMA in presence of hydrothermally synthesized ZnO nanorods. Three different phenomena i.e. FRET from PMMA to ZnO, red edge effect in PMMA, self-absorption in ZnO are found to be mainly responsible for the tunable luminescence in PMMA-ZnO nanocomposite. At excitation wavelength 285 nm, due to significant overlap between emission spectrum of PMMA and absorption spectrum of ZnO, FRET occurs from PMMA to ZnO and enhanced blue emission from the composite is obtained. Due to self-absorption in ZnO, the emission shows red shift up to few nanometers with increase in ZnO content. Again the energy transfer efficiency decreases with increase in ZnO content in the composite due to which emission intensity also decreases. Due to red edge effect the emission from PMMA shifts towards higher wavelength with the red shift of excitation wavelength. This causes no spectral overlap between PMMA and ZnO and no significant FRET occurs at excitation wavelength 377 nm. Here the emission from both PMMA and ZnO is observed and with increment of ZnO content the emission from ZnO becomes dominant. Thus with proper tuning of ZnO content in the composite, the emission from the composites excellently changes from deep blue to white upon illumination with photon of wavelength 377 nm. To get an insight of the applicability of the composites for polymer light emitting diode (PLED), electroluminescent property of the composites is investigated with the help of a mathematical model. From the calculated results, the external quantum efficiency (ηext) using the nanocomposite with 5 wt% of ZnO as emissive layer which emits light of wavelength 440 nm, is found to be the highest i.e. 5% at a turn-on voltage of 2.6 V. The other composites also show quite good ηext and hence become promising candidates for application in blue as well white light emitting PLED.

N-Doped Yellow-Emissive Carbon Nanodots from Gallic Acid: Reaction Engineering, Stimuli-Responsive Red Emission, and Intracellular Localization

An easy one-pot method is utilized for the synthesis of carbon nanodots, which has been investigated primarily from material perspectives. However, this preferred one-pot synthesis method suffers from the untraceability of steps leading to the infusion of the photoluminescence property in the nanodot. To resolve the steps involved, a single-precursor approach has been adopted here for the synthesis of the yellow-fluorescent probe by using a bioresource, gallic acid. The synthesized probe exhibits excitation-energy-independent emission, a typical molecular behavior, but shows an emission-wavelength-dependent lifetime that is often attributed to the red-edge effect most commonly observed for nanodots. We propose here that the observation of the red-edge effect for a synthesized probe in neat solvents is due to proton-transfer controlled solvation, a unique photoprocess. Characterization and computational results of the synthesized product clearly suggest the formation of a molecular fluorophore. Unprecedentedly, the synthesized probe shows proton-triggered red emission. The addition of a proton resulted in molecular aggregation due to a strong H-bonded interaction among product molecules. The presence of multiple phenolic−OH groups in the probe allows the easy formation of molecular chains of crystals on transmission electron microscopy grids, causing the observation of lattice spacing that remains unchanged in an aggregated state as well. We have also explored its possible applications in bioimaging and trivalent metal ion sensing. It has better cell-membrane permeability but remains predominantly in the cytoplasm. Both green and red fluorescence are observed inside the cell. The product molecule possesses a submicromolar detection limit for aluminum ions as well, further confirming the unaltered position of phenolic–OH groups present in the product and substrate.

Self-assembled natural biomacromolecular fluorescent hydrogels with tunable red edge effects

At present, fluorescent hydrogels have attracted more and more attention due to their wide applications in medical diagnosis, biological imaging and drug delivery. However, the luminescence of traditional fluorescent hydrogels usually requires specific fluorophores, and most of the fluorophores were rigid planar structures containing benzene rings or heterocyclic structures, making traditional fluorescent hydrogels have higher cytotoxicity and lower water solubility, thus limiting their practical applications. Here, we reported a fluorescent hydrogel, which can generate hydrogen bonds without emitting specific fluorophores, and it was found that the fluorescence intensity could be strengthened with the increase of concentration. At the same time, the fluorescence emission peak has the response of excitation wavelength and is not affected by the pH and concentration. Therefore, this special discovery in present work opens new application prospects for fluorescent hydrogels.

Red-edge excitation effect on the intersystem crossing of indole solution in ethanol at 77 K

Excitation-wavelength dependence of the luminescence spectra indole solution in ethanol at 77 K was measured. It was found that the ratio of the intensities of phosphorescence and fluorescence decreases at the red edge excitation. This decreasing is associated with a decrease in the ratio of the quantum yields of intersystem crossing and fluorescence φisc/φfl. Because of for the indole solution in ethanol at 77 K both singlet ππ* states of 1La and 1Lb are fluorescent, this result is explicated by increasing the contribution the 1La state to the processes of radiation and intersystem crossing at the red edge excitation.

Sphingomyelin-induced structural modification of native human hemoglobin and its chemically and thermally disrupted secondary structure: A photophysical exploration

Sphingomyelin-induced structural modification of Human Hemoglobin (Hb) has been investigated in its native and unfolded conformers that are partially denatured in presence of ∼ 4 M urea, completely denatured in ∼ 8 M urea and thermally disrupted (at ∼ 65 °C) state. The absorption studies unveil ground state complexation between Hb and SM. From steady-state fluorescence and quenching studies alteration of the micro-environments around Trp residues of Hb in above mentioned different cases has been determined. Moreover, lesser exposure of Trp residues to SM in thermally disrupted Hb can be accounted for the exceptionally interesting outcomes in other experiments. The alterations in the time-resolved decay profiles of native Hb, partially and totally chemically denatured as well as thermally disrupted Hb with gradual addition of SM also affirm the amendment of the proteinous micro-environment surrounding Trp residues in a view of FRET between Trp residues and heme group. Wavelength-sensitive emission spectral studies reveal that the protein shows red edge effect in its different conformations in presence and absence of SM. Interestingly, the wavelength-responsive time-resolved study at a constant excitation wavelength demonstrates that with addition of lipid the increment of the average fluorescence lifetime signifies a considerable modulation of solvation dynamics of the fluorescent Trp residues in their excited state being greatest in case of thermally disrupted Hb. Nevertheless, the loss of α-helicity of Hb at its various conformers with addition of SM has been portrayed thoroughly by means of far-UV CD spectral studies in a view of disruption of secondary structure of the protein.

Study of Organization and Dynamics of Multi-Tryptophan Protein Molecules Utilizing Red Edge Excitation Shift Approach

A shift in the fluorescence emission maxima with gradual increase in excitation wavelength is termed as red edge excitation shift (REES). Tryptophan residues are widely utilized as intrinsic fluorescence probe to investigate the protein structures. Wavelength selective tryptophan fluorescence can explore the dynamics of surrounded water molecules, the ubiquitous biological solvent. Thus REES experiment of various protein conformational states can provide significant input to the study of protein folding pathway and it can also be useful to study interaction of proteins with others. In this review article, we shall focus on red edge effect of various multi-tryptophan proteins in their respective native, intermediate and denatured state.

Photochemistry of Benzophenone in Solution: A Tale of Two Different Solvent Environments.

A long-standing ambition of photochemists is to excite species selectively in a complex liquid solution and in turn instigate a controlled chemical reaction. Benzophenone (Bzp) has been studied over six decades as a model system for understanding the photophysics and photochemistry of organic chromophores. Herein, we exploit the red-edge excitation effect to demonstrate that by subensemble selective excitation of Bzp molecules, either coordinated or noncoordinated to phenol through hydrogen bonding in a dichloromethane solution, the rate of an H atom abstraction reaction can be accelerated by a factor of ∼40. To this end, we have employed femtosecond time-resolved electronic and vibrational absorption spectroscopy in conjunction with DFT/TD-DFT calculations. The outcomes have implications for deductions drawn from single-excitation-wavelength studies of the photochemistry of similar molecular systems and especially of charge-transfer chromophores.

The Characteristic Analysis of Canopy Spectrum and Moisture Content of 10 Typical Arid Desert Plants

Plant water is a main factor to affect physiological and biochemical indexes of plants like photosynthesis, respiration, and biomass and so on. The investigation of plant water content is an important part of vegetation research. The study of the relationship between water content and canopy spectrum of typical desert plants by hyper spectral has great significance for remote sensing monitoring of vegetation in arid desert areas. The canopy spectral curves of 10 typical desert plants were determined by ASD portable ground spectrometer in this study. The correlation coefficient method and vegetation index method were used to analyze the spectral characteristics of different desert plants and their relationship with canopy moisture content. The results show: 1) the reflectance curve of desert plants has the general characteristics of green plants in the visible-near-infrared band, with obvious "green peak" characteristics and "red edge effect". 2) In the three wavebands of 954-973 nm, 1184-1198 nm and 1440-1462 nm, desert plants have obvious water absorption valleys. Among them, the correlation coefficient between spectral reflectance and water content in the 1440-1462 nm band is greater than 0.8, and they have strong linear correlation. 3) WBI (Water Band Index), NDWI (Normalized Difference Water Index), NDII (Normalized Difference Infrared Index), MSI (Moisture Stress Index) were significantly correlated with plant water content (P<0.05), and the measured values of canopy moisture content index and vegetation moisture have high consistency and can reflect the change of moisture content of desert vegetation.

Rotation and translation dynamics of coumarin 153 in choline chloride-based deep eutectic solvents.

The equilibrium and dynamic solvation responses of coumarin 153 (C153) in a range of deep eutectic solvents (DESs) based on choline chloride with either urea (molar ratio 1:2, ChCl:U), glycerol (1:2, ChCl:G), ethylene glycol (1:2, ChCl:E), or malonic acid (1:1, ChCl:Mal) were investigated using both steady-state and time-resolved fluorescence emission spectroscopy at room temperature (298 K). From steady-state fluorescence data, "red-edge effects" were observed in all the DESs studied, attributed to spatial heterogeneity of the DES matrix. Time-resolved Stokes shifts were used to quantify dynamic solvation with the solvation response function in DES found to be a biexponential function of time, which were used to obtain average solvation times (⟨τ s ⟩) which are generally faster in DES than in ionic liquids of comparable viscosity. Average solvation times showed a partial correlation with viscosity between different DESs. The choline chloride-glycerol DES showed deviation from the viscosity trend observed in the other DES for both dynamic and steady-state results. Rotational reorientation times obtained from dynamic anisotropy (r(t)) measured for these DESs showed a partial correlation with viscosity between different DESs. Determination of the DES rotational coupling with C153 showed more "slip"-like behavior than the previously reported ionic liquids and dipolar solvents.

A benzocoumarin based two-photon fluorescent probe for ratiometric detection of bisulfite

Bisulfite, an equilibrium species with sulfite, is generated from endogenous sulfur dioxide in cell from biothiols. At its elevated level, bisulfite can cause several physiological disorder and diseases. To study such “bisulfite biology” in cell and in tissue, a two-photon fluorescent probe with ratiometric imaging capability is in great demand. To this end, we investigated an aryl aldehyde-type probe derived from a dipolar benzocoumarin dye. The probe sensed bisulfite through formation of the corresponding aldehyde–bisulfite adduct in aqueous buffer at pH 7.4, with excellent selectivity over other biologically relevant species and with well-resolved ratiometric fluorescence changes from 625 nm to 552 nm. The high sensitivity (LOD = 0.08 μM) and reactivity (within 30 s) of the probe towards bisulfite enabled us to quantify an endogenous bisulfite level present in human serum. The promising in vitro ratiometric behavior, however, was deteriorated in the cellular environment, owing to large red-edge and blue-shift effects, observed for both the probe and its bisulfite adduct in cell, which occurred into the unfavorable direction. Thus the cellular imaging with the probe was confined to observe the bisulfite level changes, using one-photon as well as two-photon microscopy.

Detail Photophysical Studies of Sulfonated Polyaniline in Aqueous Medium.

Sulfonated polyaniline (SPANI) has emerged as a promising polymer in the past few decades due to its solubility in water and relatively moderate conductivity. However, to date, literature data on the optical characterization of SPANI are very limited and preliminary in nature. In the present work, SPANI is synthesized by direct sulfonation of emeraldine salt form of polyaniline with chlorosulfonic acid in an inert solvent. Detail photophysical properties of SPANI are investigated in aqueous medium by using steady state (concentration, temperature, pH, and excitation wavelength dependence) and time-resolved spectroscopic techniques. The steady state fluorescence emission measurements are carried out carefully to avoid inner filter effect (especially secondary inner filter effect or reabsorption effect) as well as scattering. Two ground state conformations of SPANI are suggested to exist in aqueous medium. Excitation wavelength dependence of the fluorescence emission spectra is attributed to red-edge effect. All these observations are nicely corroborated by the fluorescence lifetime data of SPANI obtained from time-resolved measurements. All these new findings are extremely important in view of the potential applications of SPANI in polymer optoelectronics.

Breakdown of Kasha\u2019s Rule in a Ubiquitous, Naturally Occurring, Wide Bandgap Aluminosilicate (Feldspar)

Excitation-energy-dependent emission (EDE) is well known from photoluminescence (PL) studies of polar solvents and carbon-based nanostructures. In polar solvents, this effect known as the ‘red edge effect’ (REE) is understood to arise from solute-solvent interactions, whereas, in case of carbon-based nanostructures, the origin is highly debated. Understanding this effect has important bearings on the potential applications of these materials. EDE has never been reported from large crystalline materials, except very recently by our group. Here, we make detailed investigations to understand the universality and the mechanism behind the EDE in a wide band gap aluminosilicate (feldspar), which comprises more than half of the Earth’s crust, and is widely used in geophotonics (e.g., optical dating). We observe EDE up to 150 nm at room temperature in our samples, which is unprecedented in rigid macroscopic structures. Based on PL investigations at 295 K and 7 K, we present a novel model that is based on photoionisation of a deep lying defect and subsequent transport/relaxation of free electrons in the sub-conduction band tail states. Our model has important implications for potential photonic applications using feldspar, measurement of band tail width in wide bandgap materials, and understanding the EDE effect in other materials.

Differential Perturbation of the Protrotropic Equilibrium of a Biological Photosensitizer within Bile Salt Aggregates of Varying Hydrophobicity: A Fluorimetric Investigation.

The present work reveals the binding interactions of a credible cancer cell photosensitizer, harmane (HM), with some selected bile salt aggregates of dissimilar hydrophobicity viz. sodium deoxycholate (NaDC), sodium cholate (NaC) and sodium taurocholate (NaTC). The explicit variation of the prototropic equilibrium of the photosensitizer both in the ground and excited state has been utilized to scrutinize the interaction phenomena. Differential modulation in the prototropic equilibrium of HM in the aforesaid aggregates has been explained on the basis of the structural dissimilarities of the bile salt monomers. The contrived hydrophobic surroundings provided by the aggregates have been reflected on the spectroscopic results, especially in the time-resolved fluorescence and the rotational dynamical behavior of the molecule of interest. Slow solvent reorientation time with regard to the lifetime of HM proliferated by the red-edge effect in two specific bile salts namely NaC and NaTC, whereas its absence in NaDC aggregates has also been elucidated on the basis of accessibility of the solvent molecules within the aggregates.

Adjustment of Sentinel-2 Multi-Spectral Instrument (MSI) Red-Edge Band Reflectance to Nadir BRDF Adjusted Reflectance (NBAR) and Quantification of Red-Edge Band BRDF Effects

Optical wavelength satellite data have directional reflectance effects over non-Lambertian surfaces, described by the bidirectional reflectance distribution function (BRDF). The Sentinel-2 multi-spectral instrument (MSI) acquires data over a 20.6° field of view that have been shown to have non-negligible BRDF effects in the visible, near-infrared, and short wave infrared bands. MSI red-edge BRDF effects have not been investigated. In this study, they are quantified by an examination of 6.6 million (January 2016) and 10.7 million (April 2016) pairs of forward and back scatter reflectance observations extracted over approximately 20° × 10° of southern Africa. Non-negligible MSI red-edge BRDF effects up to 0.08 (reflectance units) across the 290 km wide MSI swath are documented. A recently published MODIS BRDF parameter c-factor approach to adjust MSI visible, near-infrared, and short wave infrared reflectance to nadir BRDF-adjusted reflectance (NBAR) is adapted for application to the MSI red-edge bands. The red-edge band BRDF parameters needed to implement the algorithm are provided. The parameters are derived by a linear wavelength interpolation of fixed global MODIS red and NIR BRDF model parameters. The efficacy of the interpolation is investigated using POLDER red, red-edge, and NIR BRDF model parameters, and is shown to be appropriate for the c-factor NBAR generation approach. After adjustment to NBAR, red-edge MSI BRDF effects were reduced for the January data (acquired close to the solar principal where BRDF effects are maximal) and the April data (acquired close to the orthogonal plane) for all the MSI red-edge bands.

Fluorescence and Sensing Applications of Graphene Oxide and Graphene Quantum Dots: A Review.

Graphene oxide and graphene quantum dots are attractive fluorophores that are inexpensive, nontoxic, photostable, water-soluble, biocompatible, and environmentally friendly. They find extensive applications in fluorescent biosensors and chemosensors, in which they serve as either fluorophores or quenchers. As fluorophores, they display tunable photoluminescence emission and the "giant red-edge effect". As quenchers, they exhibit a remarkable quenching efficiency through either electron transfer or Förster resonance energy transfer (FRET) process. In this review, the origin of fluorescence and the mechanism of excitation wavelength-dependent fluorescence of graphene oxide and graphene quantum dots are discussed. Sensor design strategies based on graphene oxide and graphene quantum dots are presented. The applications of these sensors in health care, the environment, agriculture, and food safety are highlighted.