Red Absorption Band Research Articles

Tuning optical excitations of graphene quantum dots through selective nitrogen doping

Our research has revealed that the nitrogen doping configuration has a significant impact on the absorption properties and band gap of nitrogen doped graphene quantum dots (NGQDs). By analyzing the composition and character of optical transitions, we have observed that nitrogen doping causes a redistribution of oscillator strength between significant peaks and the emergence of new optical features. These changes lead to broken molecular orbital degeneracies, optical peak splitting, and activation of dark states in the visible to near-infrared (NIR) region. These findings shed light on the mechanisms that govern alterations in the spectral properties of NGQDs within the visible and near-infra red (NIR) absorption bands. Furthermore, selective manipulation of optoelectronic properties via distinct N-doping patterns could pave the way for the development of novel optoelectronic nanodevices and functional materials.

LH2 Complex from Sulfur Bacteria Allochromatium vinosum – Natural Singlet Oxygen Sensor

LH2 Complex from Sulfur Bacteria Allochromatium vinosum – Natural Singlet Oxygen Sensor

Synergistically Improving the Absorption, Energy Level, and Crystallization of PM6 by a Dicyanobenzothiadiazole Block-Based Terpolymer Strategy

The current top performing polymer solar cells (PSCs) are predominately based on the polymer donor material PM6 paired with Y-series small-molecule acceptors. For the limited improvement space for the Y-series acceptors, it is of great importance to explore strategies to optimize the molecular structure of PM6 for further elevation of the power conversion efficiencies (PCEs). Evidently, the terpolymer strategy is an effective method to improve the inherent properties of PM6 by introducing units with different electron states as building blocks in the copolymer backbone. In this work, a dicyanobenzothiadiazole (CNBT) group was selected and incorporated into the backbone of PM6 to form random terpolymers in a (D–A1)n–(D–A2)m structure with various CNBT contents. The electron-deficient CNBT group induced a strong intermolecular charge transfer, resulting in the rise of a red absorption band, which covered the absorption gap between PM6 and L8-BO around 700 nm. The high electron deficiency of CNBT groups also enabled a downshift in the highest occupied molecular orbital (HOMO) of PM6 for causing improvement of Voc. Furthermore, the high dipole moment of CNBT groups enhanced intermolecular aggregation, which helped to overcome the crystallization reduction effect of the terpolymer structures, leading to optimization of the thin-film morphology. The synergistically enhanced absorption, energy level matching, and crystallization tendency led to simultaneously increased Voc, Jsc, and FF, which all contributed to a significantly increased PCE of up to 18.01% compared with the PM6-based devices.

Solvent Effect on the spectral and photophysical properties of the Acridone

UV/Vis absorption, emission, and excitation spectroscopy with various solvents (dimethyl sulfoxide (DMSO), N,N-Dimethylformamide (DMF), and tetrahydrofuran (THF) and Acetone) at two concentrations (10−4 and 10−5) Mol/L were used to investigate the spectra and photophysical properties of Acridone. Using the integrated emission spectra, the fluorescence quantum yields are calculated. The emission maxima were determined using the red absorption band’s positions and bandwidths. The maximum absorption and emission wavelengths were found to be 390–399 nm and 399–413 nm, respectively, resulting in Stokes shifts of 318.05 and 1142.62 cm-1. Fluorescence spectra have a broad spectral range so that as concentration is increased, each peak shifts toward a long wavelength. It has been discovered that as concentrations increase, the quantum efficiency decreases. The fluorescence quantum yield magnitude is affected by solvents, with THF having the highest value.

Designing the optoelectronic properties of BODIPY and their photovoltaic applications for high performance of organic solar cells by using computational approach

A series of four novel pi-conjugated chromophores named BDP1-BDP4 have been designed in quest to enhance the PCE of organic photovoltaic cells. These chromophores were developed by using 4,4-difluroboradiaza-s-indacene (BODIPY) as a core, Triphenylamine (TPA) as donor and different end-capped acceptors i.e., 2-ethylidene malononitrile (BDP1), methyl-2-cyanobut-2-enoate (BDP2), 4-ethylidene-2-methyl-5-thiooxoisothiazolidin-3-one (BDP3), 2-(2-ethylidene-5,6-difluoro-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (BDP4). DFT and TD-DFT approach using B3LYP functional was employed to assess the photophysical, as well as opto-electronic properties of designed chromophores BDP1-BDP4. FMOs and Transition Density Matrix evaluations were executed to get insights about charge distribution, chemical reactivity, and stability of all molecules under investigation. Exciton binding energy and reorganization energy values have been computed to investigate exciton dissociation and charge carrier mobilities, respectively. All the newly developed molecules exhibit reduced band gap, red shift absorption bands, low exciton binding energy, small reorganization energy values and moderate Voc value in comparison to reference molecule which demonstrate that these newly developed molecules can be utilized as favorable photovoltaic materials. BDP4 considered to be promising acceptor molecule with highest λmax (883 nm), narrow band gap (1.22eV) and lowest λe value (0.01136). This theoretical and computational study revealed that the designed chromophores could be employed as efficient acceptors, in order to upsurge the quantum efficiency of organic photovoltaic devices.

Mode-dependent dye absorption in phthalocyanine-doped acrylic optical fiber

Phthalocyanine has attractive features as a dopant for plastic optical fibers. Its planar molecular structure and red absorption band are suitable for the design of fiber-optic strain sensors that use the dynamic orientation of dye induced by the deformation of the host matrix. The guidelines to achieve a phthalocyanine-doped fiber with a ruled dispersing manner were investigated. A synthesized fiber using phthalocyanine decorated with tertiary butyl groups showed mode-dependent absorption, which suggested gradual dye distribution in the core radial direction.

LUMINESCENT COATINGS BASED ON PR-CONTAINING COMPLEX OXIDES FOR THE ELABORATION OF PHYTO-LEDS

Plants in greenhouses are grown under special lighting conditions, i.e. when partially or completely artificial lighting is used. For this purpose, various lamps are used - xenon, high or low pressure sodium, mercury, LED, etc. Recent studies have shown that LED lamps can achieve about 60 % more efficiency in greenhouse lighting than sodium lamps. The increased energy efficiency of LED lamps (phyto-lamps) is associated with the coincidence of their emission bands with the spectra of photosynthetic active radiation. The simplest phyto-lamps are devices consisting of several blue and red light LEDs (phyto-LEDs). A significant disadvantage of red LEDs those are based on the semiconductor structures is their cost, which is much higher than that of blue phyto-LEDs. One of the ways to reduce the price of red LEDs can be their elaboration on the basis of an InGaN semiconductor structure (chip) with a blue light emission, with a deposited layer of an inorganic phosphor. Phosphors with a red emission can be created on the basis of oxide materials with ions of transition or rare earth metals, such as Pr3+. The advantage of praseodymium over transition element ions is that the main absorption bands of Pr3+ ions in the visible region located in the range of 430–490 nm, namely in the emission region of blue LEDs. The position of these bands weakly depends on the type of crystalline or glass matrix. In this work, luminescent coatings based on KBi(MoO4)2 and K2Bi(PO4)(MoO4) crystals doped with Pr3+ ions are considered. The coating on the LED was carried out using a polymer - cyanoacrylate glue. It has been found that the polymer used weakly absorbs LED radiation and does not exhibit significant luminescence in the visible region upon excitation at 446 nm. For a coating based on K2Bi0.99Pr0.01(PO4)(MoO4), it was shown that, in terms of the position of the oxide luminescence bands, it agrees well with the red absorption band of chlorophyll b and with weak absorption bands of chlorophyll in the range of 590–620 nm. However, the efficiency of blue into red light converting for this coating is rather low. Better results can be achieved with KBi0.9Pr0.1(MoO4)2, which has a better correlation with chlorophyll’s absorption bands, as well as a higher blue-to-red conversion efficiency. In our opinion, by varying the content of praseodymium in KBi1-xPrx(MoO4)2 and optimizing the deposition method, it is possible to increase the efficiency of such luminescent coatings for the development of phyto-LEDs.

Theoretical investigations about the effect of electron-withdrawing groups on proprieties of A-π-D-π-A type small molecules donor for organic solar cells.

Taking the reporting donor SM0 as reference, three new A-π-D-π-A type small molecules donors (SM1, SM2, and SM3) were designed via replacing acceptor moieties. The molecular proprieties affecting the cell performance, such as, frontier molecular orbital, open circuit voltage (Voc), absorption spectrum, vertical and adiabatic ionization potential, vertical and adiabatic electronic affinity, and energy driving force ΔEL-L were investigated through the density functional theory (DFT) and the time dependent density functional theory (TD-DFT). All new designed molecules exhibit reduced energy gap, show a red shift absorption band, small energy binding Eb, moderate Voc, and improve the creation of hole and electron as compared to SM0, which demonstrate that these new designed molecules could be used as a promising donors materials for organic solar cell. Additionally, the three new designed molecules present a larger amount charge transfer qCT, a longer length charge transfer DCT than SM0 and have a smaller reorganization energy of hole λ(h) which improve the charge carrier mobilities.

Photonics of Molecular Oxygen in Aqueous Solutions

The main stages in the development of research in the field of molecular-oxygen photonics and the most important methodical approaches to investigation of the lowest singlet states of oxygen molecules in organic and aqueous solutions are briefly outlined. The contemporary views on the kinetic and radiative parameters of singlet oxygen in water and deuterium oxide as well as the results of most recent studies of the red and IR absorption bands of oxygen molecules dissolved in water under normal conditions are presented. The data are compared with the absorption and luminescence parameters of oxygen in the gas phase and in organic media. The importance of the results of these studies for specialists in various fields of knowledge from molecular photophysics and spectroscopy to photodynamic and laser medicine is emphasized.

Instrument predevelopment activities for FLEX mission

The fluorescence imaging spectrometer (FLORIS) is the payload of the fluorescence explorer mission (FLEX) of the European Space Agency. The mission objective is to perform quantitative measurements of the solar-induced vegetation fluorescence aiming at monitoring photosynthetic activity. FLORIS works in a push-broom configuration, and it is designed to acquire data in the 500 to 780 nm spectral range with a sampling of 0.1 nm in the oxygen bands (759 to 769 nm and 686 to 697 nm) and 0.5 to 2.0 nm in the red edge, chlorophyll absorption, and photochemical reflectance index bands. FLEX will fly in formation with Sentinel-3 to benefit from the measurements made by Sentinel-3 instruments, OLCI, and SLSTR, particularly concerning the cloud screening, the proper characterization of the atmospheric state, and the determination of the surface temperature. The instrument concept is based on a common telescope and two modified Offner spectrometers with reflective concave gratings both for the high resolution (HR) and low resolution (LR) spectrometers. In the frame of the instrument predevelopment, Leonardo Company (Italy) has built and tested an elegant breadboard of the instrument consisting of the telescope and the HR spectrometer. OHB System AG (Germany) is in charge of the development of the LR spectrometer. The main objectives of the activity are to anticipate the development of the instrument and provide early risk retirement of the critical components; evaluate the system performances such as imaging quality parameters, straylight, ghost, polarization sensitivity, and environmental influences; verify the adequacy of critical tests such as spectral characterization and straylight; and define and optimize instrument alignment procedures. Following a brief overview of the FLEX mission, we will cover the design and the development of the optics breadboard with emphasis on the results obtained during the tests and the lessons learned for the flight unit.

Monitoring the binding of serotonin to silver nanoparticles: A fluorescence spectroscopic investigation

Serotonin (5-HT) is an important monoamine neurotransmitter that plays a vital role in the regulation of various cognitive and behavioural functions including sleep, mood, pain, depression, anxiety, aggression, learning etc. From the nanotoxicity and neurotoxicity point of view, interaction studies between serotonin and nanoparticles are highly essential to develop an indispensable understanding on the effect of nanoparticles on monoamine neurotransmitters. In the present work, steady-state and time-domain fluorescence measurements were carried out along with binding energy measurements through X-ray photoelectron spectroscopic (XPS) technique to understand the interaction of 5-HT with silver nanoparticles (AgNPs). The emergence of a week red absorption band and quenching of fluorescence intensity along with decrease in full width half maximum, but not the excited state decay time of 5-HT in the addition of AgNPs suggest the formation of a non-fluorescent complex in the ground state that indicates static quenching along with radiative energy transfer among them. This is also confirmed by the low energy shift of Ag transition in 3d3/2 and 3d5/2 in XPS measurements and a coupling of Lb transition with the surface plasmons of AgNPs in the excitation spectra. The obtained thermodynamic parameters from the fluorescence quenching reveal the nature of interaction between 5-HT and AgNPs is hydrophobic. The increase in binding constant with increasing temperature suggested an enhancement in the strength of this interaction due to rise in the mobility of the molecules and hence increases the sensitivity and association of 5-HT with AgNPs.

Characterization of mercury(II)-induced inhibition of photochemistry in the reaction center of photosynthetic bacteria.

Mercuric contamination of aqueous cultures results in impairment of viability of photosynthetic bacteria primarily by inhibition of the photochemistry of the reaction center (RC) protein. Isolated reaction centers (RCs) from Rhodobacter sphaeroides were exposed to Hg2+ ions up to saturation concentration (~ 103 [Hg2+]/[RC]) and the gradual time- and concentration-dependent loss of the photochemical activity was monitored. The vast majority of Hg2+ ions (about 500 [Hg2+]/[RC]) had low affinity for the RC [binding constant Kb ~ 5mM-1] and only a few (~ 1 [Hg2+]/[RC]) exhibited strong binding (Kb ~ 50μM-1). Neither type of binding site had specific and harmful effects on the photochemistry of the RC. The primary charge separation was preserved even at saturation mercury(II) concentration, but essential further steps of stabilization and utilization were blocked already in the 5 < [Hg2+]/[RC] < 50 range whose locations were revealed. (1) The proton gate at the cytoplasmic site had the highest affinity for Hg2+ binding (Kb ~ 0.2μM-1) and blocked the proton uptake. (2) Reduced affinity (Kb ~ 0.05μM-1) was measured for the mercury(II)-binding site close to the secondary quinone that resulted in inhibition of the interquinone electron transfer. (3) A similar affinity was observed close to the bacteriochlorophyll dimer causing slight energetic changes as evidenced by a ~ 30nm blue shift of the red absorption band, a 47meV increase in the redox midpoint potential, and a ~ 20meV drop in free energy gap of the primary charge pair. The primary quinone was not perturbed upon mercury(II) treatment. Although the Hg2+ ions attack the RC in large number, the exertion of the harmful effect on photochemistry is not through mass action but rather a couple of well-defined targets. Bound to these sites, the Hg2+ ions can destroy H-bond structures, inhibit protein dynamics, block conformational gating mechanisms, and modify electrostatic profiles essential for electron and proton transfer.

Characterization of Hematite Red Pigment for Porcelain Surface Coating

In this study, an α-Fe2O3 (hematite) coated porcelain plate was sintered in a temperature range from 1100 oC to 1250 °C using ferrous sulfate. The specimens were investigated by X-ray diffractometer (XRD), scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), and UV-visible spectrophotometer. It was confirmed that α-Fe2O3 (hematite) was densely fused to the surface at several tens of μm, the α-Fe2O3 (hematite) was in the form of thin platelet and polyhedra, and no other compounds appeared in the sintering process. In the specimen coated with α-Fe2O3 (hematite), the reflectance spectra show a red absorption band of 560-650 nm. The L* value decreased from 53.18 to 46.94 with the firing temperature. The values of a* and b* were at 19.03 and 15.25 at 1100 °C and gradually decreased with increasing temperature; these values decreased rapidly at 1250 °C to 11.54 and 7.98, respectively. It is considered that the new phases are formed by the phase transition of the porcelain plate (clay), and thus the a* and b* values are greatly influenced.

Radioprotective Action of Low-Intensity Light into the Red Absorption Band of Endogenous Molecular Oxygen

Application of ionizing radiation in oncology (radiation therapy) is a widespread way to eliminate malignant tumors. Normal tissues are inevitable included in any radiation field, and their reliable protection is actual till now. All attempts to solve the problem are based on search of effective radioprotectors, i.e. chemical compounds of various classes, which should be entered into the patient. To date about 50,000 compounds with some radioprotection properties had been tested, but the most effective of them have been simultaneously the most toxic. Here the preliminary results of researches devoted to development of an optical technique on basis of the light-oxygen effect for the protection of women with breast cancer from side effects of the radiation therapy are presented. A low intensity emission of the semiconductor laser in a red spectral interval was used to excite a very small quantity of endogenous molecular oxygen in O2(1Δg) state. It is shown, that application of the method at occurrence of earliest signs of radiation injury allows notably reducing dangerous breaks in radiation therapy course.

Fine Tuning of Chlorophyll Spectra by Protein‐Induced Ring Deformation

AbstractThe ability to tune the light‐absorption properties of chlorophylls by their protein environment is the key to the robustness and high efficiency of photosynthetic light‐harvesting proteins. Unfortunately, the intricacy of the natural complexes makes it very difficult to identify and isolate specific protein–pigment interactions that underlie the spectral‐tuning mechanisms. Herein we identify and demonstrate the tuning mechanism of chlorophyll spectra in type II water‐soluble chlorophyll binding proteins from Brassicaceae (WSCPs). By comparing the molecular structures of two natural WSCPs we correlate a shift in the chlorophyll red absorption band with deformation of its tetrapyrrole macrocycle that is induced by changing the position of a nearby tryptophan residue. We show by a set of reciprocal point mutations that this change accounts for up to 2/3 of the observed spectral shift between the two natural variants.

Fine Tuning of Chlorophyll Spectra by Protein-Induced Ring Deformation.

The ability to tune the light-absorption properties of chlorophylls by their protein environment is the key to the robustness and high efficiency of photosynthetic light-harvesting proteins. Unfortunately, the intricacy of the natural complexes makes it very difficult to identify and isolate specific protein-pigment interactions that underlie the spectral-tuning mechanisms. Herein we identify and demonstrate the tuning mechanism of chlorophyll spectra in type II water-soluble chlorophyll binding proteins from Brassicaceae (WSCPs). By comparing the molecular structures of two natural WSCPs we correlate a shift in the chlorophyll red absorption band with deformation of its tetrapyrrole macrocycle that is induced by changing the position of a nearby tryptophan residue. We show by a set of reciprocal point mutations that this change accounts for up to 2/3 of the observed spectral shift between the two natural variants.

Ruthenium porphyrin-induced photodamage in bladder cancer cells

Photodynamic therapy (PDT) is a noninvasive treatment for solid malignant and flat tumors. Light activated sensitizers catalyze photochemical reactions that produce reactive oxygen species which can cause cancer cell death. In this work we investigated the photophysical properties of the photosensitizer ruthenium(II) porphyrin (RuP), along with its PDT efficiency onto rat bladder cancer cells (AY27). Optical spectroscopy verified that RuP is capable to activate singlet oxygen via blue and red absorption bands and inter system crossing (ISC) to the triplet state. In vitro experiments on AY27 indicated increased photo-toxicity of RuP (20μM, 18h incubation) after cell illumination (at 435nm), as a function of blue light exposure. Cell survival fraction was significantly reduced to 14% after illumination of 20μM RuP with 15.6J/cm2, whereas the “dark toxicity” of 20μM RuP was 17%. Structural and morphological changes of cells were observed, due to RuP accumulation, as well as light-dependent cell death was recorded by confocal microscopy. Flow cytometry verified that PDT-RuP (50μM) triggered significant photo-induced cellular destruction with a photoxicity of (93%±0.9%). Interestingly, the present investigation of RuP-PDT showed that the dominating mode of cell death is necrosis.RuP “dark toxicity” compared to the conventional chemotherapeutic drug cisplatin was higher, both evaluated by the MTT assay (24h).In conclusion, the present investigation shows that RuP with or without photoactivation induces cell death of bladder cancer cells.

Absorption spectrum of gafchromic® EBT2 film with angular rotation

Study of the absorption spectrum in film dosimetry is important because the spectral absorbance of the film is related to the film’s total absorption dose. We investigated the absorption spectra of Gafchromic EBT2 film at various rotational angles in a visible wavelength band. The film was irradiated with 6- MV photon beams for a total dose of 300 cGy. The absorption spectra for different angles of rotation were obtained 24 h after the irradiation and we fitted the spectra by using Lorentzian functions. Two dominant absorption peaks, one at approximately 586 nm (green) and the other at 634 nm (red) were observed. The measured spectrum was decomposed into peaks at 542 nm, 558 nm, 578 nm, 586 nm, 626 nm, 634 nm, and 641 nm. The maximum total area of the red absorption band occurred at 45° (225°) and the minimum at 90° (270°). As the angle of rotation changed, the intensities and integrated areas of the blue and the green peaks also changed with a 180° period, with minima at 90° and 270°, and maxima at 0° and 180°, although the overall absorbance was very low. The spectral peak wavelengths remained constant within ±1.2 nm for all angles. The absorption spectrum of the film should no hysteresis of; spectra taken at 0° and 360° were substantially the same and showed similar behaviors for all rotational angles. The change in the absorbance with the rotational angle of the film affected the dosimetric properties, resulting in rotational variations of the film’s dosimetry in each red-green-blue channel.

Structure Determination from Powder X-ray Diffraction Data of Black Azo (Hydrazone) Pigments

Abstract Crystal structures of two black monoazo (hydrazone) pigments have been determined from powder X-ray diffraction data combined with DFT calculations. The DFT calculations suggested the molecules are in hydrazone forms but not in azo forms in both crystal structures. The molecular arrangements in the crystal structures suggested Davydov splitting may occur by excitonic interactions and it causes the red absorption band shift in the crystalline state leading to the characteristic black colors.

D–A–π–A featured sensitizers containing an auxiliary acceptor of benzoxadiazole: molecular engineering and co-sensitization

Benzoxadiazole-based D–A–π–A organic sensitizers can red shift absorption bands and predominantly deepen the LUMO level, realizing photovoltaic efficiency as high as 9.72% via a co-sensitization process.