Shift In Absorption Spectra Research Articles

Improved Photophysical Properties of Ionic Material-Based Combination Chemo/PDT Nanomedicine.

Herein, a cost-effective and prompt approach to develop ionic material-based combination nanodrugs for cancer therapy is presented. A chemotherapeutic (phosphonium) cation and photodynamic therapeutic (porphyrin) anion are combined using a single step ion exchange reaction. Afterward, a nanomedicine is prepared from this ionic materials-based combination drug using a simplistic strategy of reprecipitation. Improved photophysical characteristics such as a slower nonradiative rate constant, an enhanced phosphorescence emission, a longer lifetime, and a bathochromic shift in absorbance spectra of porphyrin are observed in the presence of a chemotherapeutic countercation. The photodynamic therapeutic activity of nanomedicines is investigated by measuring the singlet oxygen quantum yield using two probes. As compared to the parent porphyrin compound, the synthesized combination material showed a 2-fold increase in the reactive oxygen species quantum yield, due to inhibition of face-to-face aggregation of porphyrin units in the presence of bulky chemotherapeutic ions. The dark cytotoxicity of combination therapy nanomedicines in the MCF-7 (cancerous breast) cell line is also increased as compared to their corresponding parent compounds in vitro. This is due to the high cellular uptake of the combination nanomedicines as compared to that of the free drug. Further, selective toxicity toward cancer cells was acquired by functionalizing nanomedicine with folic acid followed by incubation with MCF-7 and MCF-10A (noncancerous breast). Light toxicity experiments indicate that the synthesized ionic nanomedicine shows a greater cell death than either parent drug due to the improved photophysical properties and effective combination effect. This facile and economical strategy can easily be utilized in the future to develop many other combination ionic nanomedicines with improved photodynamics.

Ligand Exchange and Impurity Doping in 2D CdSe Nanoplatelet Thin Films and Their Applications

AbstractThe effects of halide‐ligand exchange and Cu and Ag doping are studied on structural, optical, and electrical properties of four monolayer CdSe nanoplatelet (NPL) and NPL thin films. Combinational study shows that NH4Cl‐treatment on CdSe NPL and NPL thin films show tetragonal lattice distortion of NPL, side‐to‐side attachment between NPLs, bathochromic shift in absorption spectra, and complete quenching of band‐edge and dopant‐induced emissions. First‐principle calculations reveal that Cl creates states below valence band maximum while Ag and Cu dopants create acceptor‐like states, explaining the change of their optical property. Field‐effect transistors are fabricated to investigate the effect of doping and reduced interplatelet distance on electrical properties of CdSe NPL thin films, demonstrating Cu and Ag dopants mitigate n‐type character of CdSe NPL thin films. Temperature‐dependent electrical characterization is conducted to further understand charge transport behavior depending on the existence of dopants. This work provides scientific information on the influence of surface chemistry and impurity doping on quantum confined semiconductors and new directions for the design of high‐performance nanomaterial‐based electronic and optoelectronic devices.

Colorimetric and fluorimetric detection of fluoride ion using thiazole derived receptor

Thiazole based receptor 3, was designed and synthesized by condensation reactionof5–chlorosalicylaldehyde with 4-(4-phenylthiazol-2-yl)semicarbazide for colorimetric and fluorimetric detection of fluoride ion. Receptor 3 was characterized by 1H NMR, 13C NMR, and HRMS, and shows absorption in 280–400 nm region with emission at 442 nm in tetrahydrofuran (THF). Addition of fluoride ion to the THF solution of receptor 3 results in color change from colorless to yellow with significant change in UV–Visible absorption. The receptor–anion interaction occurs via hydrogen bonding followed by deprotonation which results in large bathochromic shift in absorption spectra and naked-eye color change. The colorimetric changes show selective response for fluoride ions over other anions. Fluorescence studies exhibit remarkable enhancement in emission intensity upon addition of fluoride ion with a limit of detection (LOD) of 8.6 nM. The 1H NMR titration studies exhibit deprotonation of the –OH proton of the salicylaldimine moiety resulting significant colorimetric and fluorimetric changes.

The excited state effective dipole moment of 2,3-benzofuran from thermochromic shifts in absorption and emission spectra

The excited state dipole moment of the lowest excited singlet state of 2,3-benzofuran in ethylacetate solution is determined using thermochromic spectroscopy and compared to the values which are obtained for the isolated molecule from electronic Stark spectroscopy (Hebestreit et al., 2020) and to the results of ab initio calculations at coupled cluster level of theory. It is shown that the dipole moment from thermochromic shifts in solution deviates considerably from that of the isolated molecule. This finding can be traced back to a field induced mixing by the strong reaction field of the solvent, which exceeds the external Stark field applied in gas phase measurements by a factor of 10.000. Depending on the dipole moments of the perturbing state and its energy gap to the excited state, dipole moments from thermochromic shifts (and consequently also of solvatochromic shifts) might be considerably different to gas phase values. However, the alteration of the electronic configuration of the molecule via the reaction field of the solvent can be deperturbed in the high-field limit.

Dynamical phase shift in x-ray absorption and ionization spectra by two delayed x-ray laser fields

We study theoretically x-ray absorption and ionization spectra of an atom or molecule by two coherent x-ray pulses that show a relative phase shift resulting in a time delay of the pulse envelopes. We demonstrate that the phase modulation of the spectra is shifted with respect to the phase oscillation comb of the x-ray double pulse. The reason for this shift is the dynamics of the process defined by the interplay of the delay time, the pulse width, the detuning, and the lifetime of the core-excited state.

Research on Correction Method of Water Quality Ultraviolet-Visible Spectrum Data Based on Compressed Sensing

The turbidity interference caused by suspended particles in water seriously affects the accuracy of ultraviolet-visible spectroscopy in detecting water quality chemical oxygen demand. Based on this, the application of ultraviolet-visible spectroscopy to detect water quality chemical oxygen demand usually requires physical and mathematical methods to correct the spectral baseline interference caused by turbidity. Because of the slow response speed and unstable compensation effect of traditional correction methods, this paper proposes to use a compressed sensing algorithm to perform baseline correction and achieve good results. In the experiment, we selected formazin turbidity solution and sodium oxalate standard solution and carried out the research on the algorithm of turbidity correction for detecting chemical oxygen demand of water quality by ultraviolet-visible spectroscopy. The experiment obtains the absorption spectra of different concentrations of formazine turbidity solutions and the same concentration of sodium oxalate with different turbidity standard solutions at 210∼845 nm and analyzes the nonlinear effect of absorbance on turbidity. This article uses standard solution experiments to explore the compressed sensing theory for turbidity correction, and through the correction of the absorption spectrum of the actual water sample, it verifies the feasibility of the compression theory for turbidity correction. The method effectively corrects the baseline shift or drift of the water quality ultraviolet-visible absorption spectrum caused by suspended particles, while retaining the absorption characteristics of the ultraviolet spectrum, and it can effectively improve the accuracy and accuracy of the ultraviolet-visible spectroscopy water quality chemical oxygen demand detection.

Influence of Cu2+ and Sn2+ ions on optical properties of MgS Nanoparticles: A comparative Analysis

Cu2+ and Sn2+ ions doped MgS nanoparticles were synthesized by chemical route without the aid of any capping agent. The role of Cu2+ and Sn2+ ions on the structural, optical, photoluminescence properties of MgS nanoparticles have been investigated through various analyses like XRD, TEM, EDX UV- vis absorption, transmittance studies, PL spectra and FT-IR. The average particle size was calculated as ∼ 10 nm and it was varied based on the ionic radius of the dopant. From this comparative study, it was observed that Cu2+ (2%) doped MgS showed a blue shift in Absorbance spectra, wide optical band gap and also exhibited better photoluminescence property. A strong PL emission was received in UV region and in the Red region. This combination of materials can be utilized in solar panel manufacturing as buffer material, optoelectronic devices and in red-emitting luminescent displays.

Anionic Polyelectrolyte-Induced Aggregation of Basic Orange 21: A Clue toward Metachromasia.

The change in the color of chromophore upon being embedded in a biological tissue is known as metachromasia. Basic Orange 21 (BO21) is a cationic polymethine dye that has been implied as a supravital dye, which produces metachromasia in leukocytes. An improved differential counting of leukocytes has been achieved in the clinical setup based on characteristic metachromatic expressions of BO21 for different types of leukocytes. Although BO21 has been utilized as a chromatic indicator for leukocyte counting, there are limited number of investigations that focus on the factors that may be responsible for the spectral shift in absorption and emission spectra of BO21, which leads to its metachromatic behavior. In this work, we have investigated the effect of a synthetic anionic polyelectrolyte, polystyrene sulfonate (PSS), on the photophysical properties of BO21, using steady-state emission, ground-state absorption, and time-resolved emission measurements, to get an understanding of the factors that may be responsible for the spectral shift of BO21 in the cellular environment. PSS induces aggregation of BO21 molecules with large changes in its photophysical properties; this appears to be most likely the mechanism of spectral shift for BO21 reported in the cellular environment. The employment of external stimulus reveals BO21 aggregates to be significantly responsive toward external stimuli, for example, temperature and presence of salt in the medium, which further strengthens the proposal of aggregate formation. Further, we have also employed fluorescence upconversion spectroscopy with subpicosecond time resolution to estimate the excited-state lifetime of BO21.

Modulation of stimuli‐responsiveness toward acid vapor between real‐time and write‐erase responses based on conjugated polymers containing azobenzene and Schiff base moieties

AbstractWe developed three types of film‐type stimuli‐responsive polymers based on aza‐substituted conjugated polymers involving azobenzene, N_bith, N_fluo and Schiff base moieties, C_bith. All polymer films showed bathochromic shifts in absorption spectra followed by chromic behaviors by fuming trifluoroacetic acid (TFA). In particular, we disclosed that there were three significant differences on acid detecting ability between azobenzene and Schiff base derivatives in terms of absorption wavelengths, stability, and proton holding time. The azobenzene polymers exhibited real‐time responses toward vapor fuming, meanwhile write and erase chromic behaviors were reversibly accomplished with the Schiff base polymer by exposing to acid and amine vapor. Theoretical calculation revealed that red‐shifted absorption bands should be induced by protonation on nitrogen atoms in the aza‐substituted positions. Diverse responses through dynamic regulation of electronic properties of main‐chain conjugation can be accomplished by introducing the aza‐substituents in polymers.

Investigation of optical properties for N- and F-doped triangular shaped carbon molecules.

Optical properties of N- and F-doping triangular-shaped carbon molecules have been investigated in theory and experiment. The theoretical results showed that carbon molecules with impurity F and Cl have the same characters with pure carbon. Doping N into pure carbon molecule would change the optical rotation at 589nm. For doping N replacing hydrogen atom structures (N-doping 1 and N-doping 2 molecules), the absorption spectra of them are similar to pure carbon molecule. However, for molecules with impurity N atom in benzene ring (N-doping 3 and N-doping 4 molecules), the peaks of wavelength of absorption spectra shift to long wavelength compared to that of pure carbon molecule. Moreover, the delocalization of molecular orbital (MO) is different from pure carbon molecule, which is caused by the impurity N changing the electrons distribution of benzene ring. We have calculated 3 without H and 4 without H molecules which are removing hydrogen atom in nitrogen atom from N-doping 3 and 4. 3 without H and 4 without H molecules have similar optical properties with pure carbon molecule. The results testified that the impurity N and F would not change the optical properties of carbon molecule if impurity did not change the delocalization of all benzene rings. Optical properties of nitrogen- and fluorine-doping carbon molecules investigating in theory and experiment.

An insight into the solvatochromic and photophysical behaviours of biowaste-origin carbon nanodots

In this work, C-dots were synthesised inexpensively, using hydrothermal, one-step pathway from persimmon peel biowaste. The prepared C-dots were investigated by UV–Vis spectroscopy, photoluminescence spectroscopy, XRD, TEM, CHN, FE-SEM and FT-IR. It was found that the C-dot is amorphous in nature, spherical in shape, narrow-sized, monodispersed, polar functionalised with average 2 nm size and highly dispersible in aqueous and non-aqueous media. Optical study in wide range of solvents, exhibited excitation wavelength dependency of photoluminescence, bathochromic and hypsochromic shifts in absorption and emission spectra and incredibly high quantum yields ranging from 10% to 60%. It was shown that the C-dot could be exploited as nanoprobe for polarity of medium in addition as fluorescent chemical sensing platform for some metal ions. Analyses resulted in different functional groups on the surface (carboxylic, carbonyl, amine, amide and hydroxyl) and led us to treat the solvatochromic method as convincing argument to resolve the dilemma of whether or not which functional groups are responsible for the intriguing observed optical properties. The increasing trend of emission efficiencies of homologues alcohols was interpreted in terms of exoergic (specific and non-specific) interaction parameters included in Kamlet-Taft’s equation along with the endoergic solubility parameters and correspondingly the stiffness of solvent.

Electronic and optical characteristics of 5d-transition metal doped 2D-NbSe2 monolayer for nanoelectronic device applications: An ab-initio-analysis

Novel physical properties can be realized in 2D transition metal dichalcogenides (TMDCs) 2H-NbSe2 via chemical doping. Using first-principles calculations, we have investigated the electronic and optical properties of pristine and 5d-transition metal atoms (M = Hf, Ta, W, Re, Ir, and Pt) doped 3 × 3 supercells of NbSe2 monolayers. The physical properties of M-doped NbSe2 monolayers are found to be tunable upon doping with transition metals; making these modifications of NbSe2 attractive 2D materials for applications in nanoelectronics. The calculated electronic properties reveal that transition metal doping remarkably affects the electronic structures because charge transfer varies only due to 5d-transition metal substitution instead of Nb atom. Consequently, variation in the density of states around Fermi level (EF) is observed. A hybridization between 5d-states of transition metals (TM) and 4p states of Se results TM-Se covalent bonds. Hence, doping can significantly tune the electronic properties of NbSe2 monolayer. The optical properties such as optical absorption coefficient, optical conductivity, reflectivity and energy loss function are also computed and discussed for 2D applications of the studied TM doped NbSe2 monolayers. In particular, our results indicate that the absorption spectra shift to lower photon energies upon TM doping. Such tuning of the physical properties suggest the use of these 2D-materials with graphene, to fabricate viable electronic devices, such as logic circuits and field-effect transistors.

Unusual shift in the visible absorption spectrum of an active ctenophore photoprotein elucidated by time-dependent density functional theory.

Active hydromedusan and ctenophore Ca2+-regulated photoproteins form complexes consisting of apoprotein and strongly non-covalently bound 2-hydroperoxycoelenterazine (an oxygenated intermediate of coelenterazine). Whereas the absorption maximum of hydromedusan photoproteins is at 460-470nm, ctenophore photoproteins absorb at 437nm. Finding out a physical reason for this blue shift is the main objective of this work, and, to achieve it, the whole structure of the protein-substrate complex was optimized using a linear scaling quantum-mechanical method. Electronic excitations pertinent to the spectra of the 2-hydroperoxy adduct of coelenterazine were simulated with time-dependent density functional theory. The dihedral angle of 60°of the 6-(p-hydroxy)-phenyl group relative to the imidazopyrazinone core of 2-hydroperoxycoelenterazine molecule was found to be the key factor determining the absorption of ctenophore photoproteins at 437nm. The residues relevant to binding of the substrate and its adopting the particular rotation were also identified.

A phenothiazine-based turn-on fluorescent probe for selective quantification of HClO in living cells

A simple phenothiazine-hemicyanine based probe PTZ-2Cy for selective in vitro and in vivo detection of ClO− was obtained. The detection mechanism was elucidated by absorption spectroscopy, emission spectroscopy, and ESI-MS analysis. With the increase in ClO− concentration, PTZ-2Cy first oxidize into sulfoxide product OPTZ-2Cy, and the additional concentration of hypochlorite ion leads to the cleavage of one or two CC bonds (OPTZ-Cy-CHO or OPTZ-2CHO). This is accompanied by the color change from light pink to light yellow, absorption spectra shift from 580 to 493 nm, and significant enhancement of fluorescence emission at 595 nm. The low limit of detection of ClO− ions (LOD = 0.038 μM) was obtained for the PTZ-2Cy probe in the 0–20 μM concentration range. The probe shows excellent selectivity for ClO− ions owing to dual-wavelength fluorimetric detection at 488 and 600 nm. The probe is applicable for imaging HClO in L929 cells and is a promising candidate for the development of a fluorescence sensor for hypochlorite ions detection in biological samples.

Femtosecond Charge Density Modulations in Photoexcited CuWO4.

Copper tungstate (CuWO4) is an important semiconductor with a sophisticated and debatable electronic structure that has a direct impact on its chemistry. Using the PAL-XFEL source, we study the electronic dynamics of photoexcited CuWO4. The Cu L3 X-ray absorption spectrum shifts to lower energy upon photoexcitation, which implies that the photoexcitation process from the oxygen valence band to the tungsten conduction band effectively increases the charge density on the Cu atoms. The decay time of this spectral change is 400 fs indicating that the increased charge density exists only for a very short time and relaxes electronically. The initial increased charge density gives rise to a structural change on a time scale longer than 200 ps.

Electric and steric hindrance effects of substituents on luminescence and force-stimuli response of cyanovinyl phenothiazine derivatives

Six cyanovinyl phenothiazine derivatives bearing substituents with different sizes, and electron-donating and -withdrawing abilities were designed and synthesized. The effect of substituents on photophysical properties in solution and solid states were systematically investigated. The results suggested that electron-donating groups almost did not influence absorption and emission properties in solutions because the distributions of molecular HOMOs and LUMOs were independent of electron-donating groups. In contrast, trifluoromethyl (CF3) and cyano as electron-withdrawing units induced bathochromic shifts in both absorption and fluorescence spectra owing to the decrease in LUMO energy levels. Furthermore, it was found that the photophysical properties in crystal states strongly depended on the terminal substituent. Larger tert-butyl (t-butyl), methoxy and CF3 groups resulted in smaller spectral shifts in relative to smaller groups after crystallization. Single crystal structures suggested both CF3 and CN units lead a poor π-stacking, but charge transfer existed in PCVCN crystals. J-type dimers were found in PCVH and PCVN crystals. More interestingly, t-butyl, CF3 and methoxy moieties induced obvious color conversion and larger spectral shifts of 76 nm, 66 nm and 55 nm, respectively, under force stimuli. On the other hand, the compounds with terminal hydrogen atom, naphthyl and cyano group possessed shifts of 46 nm, 34 nm and 23 nm.

Arylphosphonate-Tethered Porphyrins: Fluorescence Silencing Speaks a Metal Language in Living Enterocytes*.

We report the application of a highly versatile and engineerable novel sensor platform to monitor biologically significant and toxic metal ions in live human Caco‐2 enterocytes. The extended conjugation between the fluorescent porphyrin core and metal ions through aromatic phenylphosphonic acid tethers generates a unique turn off and turn on fluorescence and, in addition, shifts in absorption and emission spectra for zinc, cobalt, cadmium and mercury. The reported fluorescent probes p‐H8TPPA and m‐H8TPPA can monitor a wide range of metal ion concentrations via fluorescence titration and also via fluorescence decay curves. Cu‐ and Zn‐induced turn off fluorescence can be differentially reversed by the addition of common chelators. Both p‐H8TPPA and m‐H8TPPA readily pass the mammalian cellular membrane due to their amphipathic character as confirmed by confocal microscopic imaging of living enterocytes.

Unusual photodegradation reactions of Asteraceae and Poaceae grass pollen enzymatic extracts on P25 photocatalyst.

In previous studies, it was demonstrated that photocatalysis by TiO2 nanoparticles can be effective for decomposition of pollen grains and pollen allergen extracts (PAEs) for Cupressus arizonica and Platanus hybrida species. In this work, the chemical and photochemical processes of five types of PAEs belonging to family Asteraceae, tribe Astereae, and family Poaceae, tribes Poeae and Triticea, were studied. It was confirmed that the PAEs suffered almost complete decomposition, which likely led to gaseous final products. For the species of Poeae tribe, i.e., Poa pratensis, Festuca pratensis, and Avena sativa, an unusual surface chemical modification of the photocatalyst consisting in the appearance of new bands on fine core level spectra of Ti 2p, C 1s, and O 1s was observed. These changes were associated with possible doping of TiO2 with C and N by pollen extracts. This was accompanied by a red shift of absorption spectra. The results suggest that some components of Poeae pollen can be grafted on TiO2 surface and they can activate the photocatalyst in the visible range. These findings can open a new pathway to eco-friendly chemical engineering of photocatalysts using organic biological compounds.

Quantum chemical design of near‐infrared sensitive fused ring electron acceptors containing selenophene as π‐bridge for high‐performance organic solar cells

AbstractEnd‐capped acceptors modification of fused ring electron acceptors (FREAs) is an attractive strategy to boost the optoelectronic and photovoltaic properties of the materials. FREAs are also proven beneficial due to their tremendous applications in organic solar cells (OSCs). Among fused‐ring electronic species, small fullerene‐free FREAs have already been drawn more attention due to their near‐infrared sensitivity and constantly increasing efficiencies. Therefore, we have designed six new FREAs (K1–K6) having selenophene as π‐bridge in between the central alkylated indaceno[1,2‐b:5,6b]dithiophene (IDT) unit after the incorporations of various end‐capped acceptors on to the recently synthesized IDT2SeC2C4‐4F molecule. Structural–property relationship and photophysical and photovoltaic properties of newly designed molecules are studied with the help of density functional theory (DFT) and time‐dependent DFT (TD‐DFT). Certain critical specifications like frontier molecular orbitals (FMOs) alignment, density of states (DOS), absorption maxima, excitation energy, binding energy (BE) along with transition density matrix (TDM), and the specifically estimated reorganizational energy values of electron and hole and the open circuit voltages of newly designed molecules are computed and compared with reference molecule. Generally, a red‐shifting absorption behavior of FREAs is considered the most important reason for their high efficiencies in OSCs. Our novel designed molecules exhibit red shift in absorption spectrum. Similarly, low excitation and binding energies of designed molecules offer improved power conversion efficiencies (PCEs) with highest possible charge photocurrent density (Jsc) in OSCs devices. Furthermore, study of PTB7‐Th/K1 complex is also done in order to examine charge transfer between within complex. By introducing the efficient end‐capped acceptor moieties in reference molecule, enhancement in charge mobilities is noted. The large open circuit voltage, low reorganizational energies, narrower highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap, lower binding and excitation energies, and highly red shifting in absorption phenomenon indicate an efficient designing of molecules, which could be best fitted for high efficiency OSCs. Finally, theorized molecules are much superior related to their photovoltaic and electronic properties and thus are recommended to experimentalist for their synthesis and out‐looking future developments of highly efficient solar cells devices.

Study of excited state relaxation by time-resolved spectroscopy in conjugated substituted polyene bis-oxazoles

The simultaneous quantum-chemical and spectral investigations of the possible relaxation pathways in the excited state for the two α,ω-di-substituted polyenes were performed. Lengthening of the polymethine chain is accompanied by the considerable decreasing of the first electron transition and hence is manifested as the bathochromic shift of both absorption and fluorescence spectra; however, the nature of transition does not change. It is established that the considerable changes of the bond lengths in polymethine chain for both vinylogs in the excited state cause firstly the appearance of the fast component in short wavelengths spectral region; after relaxation, the intensity of the fast component decreases, and it disappears, but then the spectral band, shifted bathochromically, appears, so that its maximum coincide with the band maximum in the steady-state fluorescence maximum, what corresponds to the final symmetrical relaxation of bond lengths. The parallel quantum-chemical calculation shows that two highest levels are mainly formed by the donor levels of both terminal groups and hence twice occupied splitting levels. Upon excitation, one of the splitting MO (HOMO) becomes single occupied; this causes the molecule in the excited state to be unstable and could transform it to the unsymmetrical form. Such relaxation path is confirmed by the time-resolved spectra: the spectral band in both molecules, with the different polymethine chains, undergoes the subsequent bathochromical shifting.