Experimental Fluorescence Spectra Research Articles

Performance of Density Functionals for Excited-State Properties of Isolated Chromophores and Exciplexes: Emission Spectra, Solvatochromic Shifts, and Charge-Transfer Character.

This study assesses the performance of various meta-generalized gradient approximation (meta-GGA), global hybrid, and range-separated hybrid (RSH) density functionals in capturing the excited-state properties of organic chromophores and their excited-state complexes (exciplexes). Motivated by their uses in solar energy harvesting and photoredox CO2 reduction, we use oligo-(p-phenylenes) and their excited-state complexes with triethylamine as model systems. We focus on the fluorescence properties of these systems, specifically emission energies. We also consider solvatochromic shifts and wave function characteristics. The latter is described by using reduced quantities such as natural transition orbitals (NTOs) and exciton descriptors. The functionals are benchmarked against the experimental fluorescence spectra and the equation-of-motion coupled-cluster method with single and double excitations. Both in isolated chromophores and in exciplexes, meta-GGA functionals drastically underestimate the emission energies and exhibit significant exciton delocalization and anticorrelation between electron and hole motion. The performance of global hybrid functionals is strongly dependent on the percentage of exact exchange. Our study identifies RSH GGAs as the best-performing functionals, with ωPBE demonstrating the best agreement with experimental results. RSH meta-GGAs often overestimate emission energies in exciplexes and yield larger hole NTOs. Their performance can be improved by optimally tuning the range-separation parameter.

Genetic algorithm for obtaining potential energy curve of diatomic molecules based on dispersed fluorescence spectra

The method for reconstruction of an adiabatic potential energy curve from experimental dispersed fluorescence spectra has been developed. The novelty of the method relies on a unique approach of simultaneous use of bound rightarrow bound and bound rightarrow free parts of the spectrum. The method is based on the Genetic Algorithm (GA) procedure and determines potential energy curve integrally, below and above the dissociation energy limit. The method was tested on the artificially generated reference spectrum as well as experimental spectrum of G0_u^+(upsilon ^{prime }=39) rightarrow X0_g^+ transition in Hg_2. The tests show very good accuracy of simulation based on GA results with artificially generated reference spectrum as well as with the experimental one.

Density effect on electronic structure of warm dense matter based on X-ray fluorescence spectroscopy

Warm dense matter (WDM), a kind of transition state of matter between cold condensed matter and high temperature plasma, is one of the main research objects of high energy density physics (HEDP). Compared with the structure of isolated atom, the electron structure of WDM will change significantly because of the influences of density and temperature effect. As WDM is always strongly coupled and partly degenerate, accurate theoretical description is very complicated and the accurate experimental research is also very challenging. In this paper, the density effect on the warm dense matter electron structure based on the X-ray fluorescence spectroscopy is studied. The warm dense titanium with density larger than solid density is produced experimentally based on a specially designed hohlraum. Then, the titanium is pumped to emit fluorescence by using the characteristic line spectrum emitted by the laser irradiating the pump material (Vanadium). The X-ray fluorescence spectra of titanium with different states are diagnosed by changing the delay time between the pump laser and drive laser. The experimental fluorescence spectrum indicates that the difference in energy between <inline-formula><tex-math id="M5">\begin{document}${\mathrm{K}}_{\text{β}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231215_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231215_M5.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M6">\begin{document}$ {\mathrm{K}}_{\text{α}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231215_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231215_M6.png"/></alternatives></inline-formula> (<inline-formula><tex-math id="M7">\begin{document}$\Delta E_{{\mathrm{K}}_{\text{β}}\text{-}{\mathrm{K}}_{\text{α}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231215_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231215_M7.png"/></alternatives></inline-formula>) of the compressed titanium (7.2–9.2 g/cm<sup>3</sup>, 1.6–2.4 eV) is about 2 eV smaller than that of cold titanium. Two theoretical methods, i.e. finite-temperature relativistic density functional theory (FTRDFT) and two-step Hartree-Fock-Slater (TSHFS), are used to calculate the fluorescence spectrum of warm dense titanium. The calculated results indicate that the energy difference (<inline-formula><tex-math id="M10">\begin{document}$\Delta E_{{\mathrm{K}}_{\text{β}}\text{-}{\mathrm{K}}_{\text{α}}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231215_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20231215_M10.png"/></alternatives></inline-formula>) decreases with the increase of density but changes slowly with the increase of temperature during the calculated state (4.5–13.5 g/cm<sup>3</sup>, 0.03–5 eV). The FTRDFT overestimates the density effect on the line shift, while TSHFS underestimates the density effect. The future work will focus on optimizing the experimental method of X-ray fluorescence spectroscopy, obtaining X-ray fluorescence spectrum of titanium with more states, and then testing the theoretical method for warm dense matter.

Theoretical study of the absorption and emission spectrum and non‐adiabatic excited state dynamics of gas‐phase xanthone

AbstractThe ground, singlet, and triplet excited state structures (S1, S2, T1, and T2) of xanthone have been calculated and characterized in the adiabatic representation by using time‐dependent density functional theory (TDDFT). However, the fast intramolecular transition mechanisms of xanthone are still under debate, and so we perform non‐adiabatic excited state dynamics of the photochemistry of xanthone gas phase and find that it follows El‐Sayed's rule. Electronic transition mechanism of xanthone is sequential from the S2 state: the singlet internal conversion (IC) time from S2 (1ππ*) to S1 (1nπ*) is 3.85 ps, the intersystem crossing (ISC) from S1 (1nπ*) to T2 (3ππ*) takes 4.76 ps, and the triplet internal conversion from T2 (3ππ*) to T1 (3nπ*) takes 472 fs. The displaced oscillator, Franck–Condon approximation, and one‐photon excitation equations were used to simulate the absorption spectra of S0 → S2 transition, with v55 being most crucial for S0 structure; the fluorescence spectra of S1 → S0 transition with v47 for S1; and the phosphorescence spectra of T1 → S0 transition with v4 for T1. Our method can reproduce the experimental absorption, fluorescence, and phosphorescence spectra of gas‐phase xanthone.

Novel adamantane substituted polythiophenes as competitors to Poly(3-Hexylthiophene)

The investigation of poly(3-alkylthiophenes) (P3ATs) has gained great attention in the last decades. Here, we present the synthesis, experimental and theoretical study of the novel regioregular poly(3-adamantylmethylthiophene) (PMAT) and poly(3-adamantylethylthiophene) (PEAT) , characterised by a bulky adamantane side group. The prepared compounds are solution-processable in common organic solvents, possess excellent thermal stability up to 491 °C and have unique chemical endurance. The molecular ordering of the polymers was investigated by the GIWAXS technique, and PMAT was found to have the higher content of crystalline phase. The experimental absorption and fluorescence spectra of investigated polymers indicate a higher rigidity of the adamantane side group with respect to torsional rotation in solutions and in thin layers. Electrical measurements exhibit charge carrier mobilities comparable to poly(3-hexylthiophene) (P3HT) . In contrast to P3HT , adamantyl-substituted polymers show quasi-reversible reduction alongside the expected quasi-reversible oxidation, which in theory supports the ability to transport both types of electric charges. The newly synthetized regioregular adamantane substituted polythiophenes are serious competitors for a wide range of applications in electronics and optoelectronics. • Novel derivates of polythiophene, featuring the bulky adamantyl groups were synthesized. • These materials exhibit high thermal stability as well as electrical conductivity comparable to poly(3-hexylthiophene). • The materials absorb light in the 400 – 500 nm wavelength range, making them serious candidates for use in optoelectronics.

Electronically excited state structures and stabilities of organic small molecules: A DFT study of triphenylamine derivatives

• B3LYP was used in the excited state studies of 4-vinyl- N , N -di(p-tolyl)aniline derivatives. • Functionalization of MTPA results in varying degrees of geometry change at the excited states. • Structural stability of the excited MTPAs without forming charge separation is similar. • Structural stability of excited charge-separated molecule is sensitive to substitution. Information on the structures and stabilities of electronically excited organic small molecules is critically important for their many applications. In this work, we report the results of excited state structures and stabilities of eight triphenylamine-based molecules from density functional theory calculations. Four functionals, B3LYP, M06-2X, CAM-B3LYP, and ωB97X-D were tested and comparisons with the experimental fluorescence spectra show that B3LYP is a feasible choice. The results illustrated that functionalization of 4-vinyl- N , N -di(p-tolyl)aniline (MTPA) with electron donating groups enhances the C C bond conjugation in the excited state while that with strong electron withdrawing groups does not. With the increase in the electron-withdrawing ability of the substituent, the structural stability of the excited state is relatively independent of the functional groups if the molecule does not form charge separated states. These results will be very helpful for their applications in molecular engineering and rational design of organic photovoltaic materials.

Species Identification and Effects of Aromatic Hydrocarbons on the Fluorescence Spectra of Different Oil Samples in Seawater

The identification of oil species and their characteristics in oil spills is particularly important for their efficient disposal. Since aromatic hydrocarbons (AHs) with various characteristics are the major fluorescent components of oils in seawater, they can be used to detect different oil species in seawater. Here, we developed a composition method using the fluorescence spectra of eight AH categories analyzed by gas chromatography-mass spectrometry (GC-MS) to evaluate the contribution of AHs to the total fluorescence of six different oil species. Qualitative and quantitative difference analysis of the experimental and composite fluorescence spectra was performed based on the redshift of the main peak position, the fluorescence intensity distance, and the generalized included angle cosine, while correlation analysis was used to establish the relationship between the different fluorescence spectral parameters and the American Petroleum Institute gravity and viscosity of the oil species. The fluorescence spectra recorded for heavy oil samples indicated a reduction in the fluorescence signal of fluorene series and an increase in the contribution of acenaphthene and pyrene series, indicating that the currently developed composition method by fluorescence spectroscopy combined with GC-MS can be used to distinguish and identify oil species in seawater samples.

Intraspecific discrimination of fish populations by fluorescence spectroscopy

This study used the visible fluorescence signal of scales from Astyanax lacustris fishes to differentiate ten populations of streams in Ivinhema River Basin, Upper Paraná Basin, Brazil. Scales were removed from the humeral region of each fish and the fluorescence spectroscopy was carried out with two excitation wavelengths: at 360 nm (UV-A) and 405 nm. The broad emission covers all visible regions and it is related to the organic fraction of scale, basically composed from type I collagen. By interpreting the experimental fluorescence spectra with multivariate statistical analysis, it was possible to discriminate the investigated populations. By exciting the inner face of scales at 405 nm, for instance, the obtained Wilk’s lambda was 0.143, and the ten sampled streams could be statistically differentiated with 85.2% of explanation. This fluorescence interpretation exhibits very good correlation with the diet composition, which was also investigated for the same fishes from which the scales were removed. The applied methodology was capable to analyze the scales of A. lacustris, and to provide meaningful and enlightening results for the differentiation of populations. This methodology is very important for aquatic environmental study, mainly because small fishes, non-migratory or with small migration rate, can exhibit differences among habitats, as response to genetic isolation and adjustment to local conditions.

Theoretical study of lumichrome, 1-methyl-lumichrome and lumiflavin binding ability with thymine

Abstract Gas-phase geometry and electronic structure of lumichrome, 1-methyl-lumichrome and lumiflavin in the electronic ground state and their excited states were investigated using the Density Functional Theory. Their binding ability with thymine was estimated for model van der Waals dimers with two intermolecular hydrogen bonds. The influence of hydrogen bonds on their photophysical properties was analyzed. Obtained theoretical data were compared with available experimental absorption and fluorescence spectra.

Fluorescence band exchange narrowing in a series of squaraine oligomers: energetic vs. structural disorder.

The influence of oligosquaraine chain length on the energies and shape of absorption and emission bands and the exciton coherence length is studied in CHCl3 where the oligomers adopt a random coil structure. From the observed fluorescence band narrowing an effective coherence length of Ncoh = 2.5 was estimated for the nonamer. Applying a theoretical Frenkel exciton model the absorption and emission spectra were simulated which confirmed the experimental results. From the relative amplitude of the 00 peak to the vibronic shoulder the coherence length was estimated which yields a somewhat higher saturation value of Ncoh≈ 3 for the nonamer, which is in very good agreement with the theoretical amplitude ratio. The coherence length is much smaller than the geometrical length because the electronic delocalisation is reduced by structural disorder. Taking into account the energetic (diagonal) and structural (off-diagonal) disorder we observed a different influence on the absorption and fluorescence spectra. For the emission spectra, exciton delocalisation leads to a narrowing of the band caused by averaging over energetic disorder, but for the absorption band the spectra are broadened by excitonic splitting and structural disorder.

Assessment of long-range corrected density functional theory on the absorption and vibrationally resolved fluorescence spectrum of carbon nanobelts.

Time-dependent (TD) density functional theory (DFT) and Franck-Condon Hertzberg-Teller (FCHT) calculations of various DFT functionals [B3LYP, CAM-B3LYP, ωB97XD, and optimally tuned (OT) long-range corrected (LC)-BLYP] were performed to examine how well DFT functionals can predict the experimental absorption and fluorescence spectra of a 12-carbon nanobelt (CNB). OT-LC-BLYP reproduced the experimental absorption spectrum well in terms of the peak position and intensity in the case of using a basis set with a diffuse function, such as 6-31+G(d,p) and 6-311+G(d,p), whereas B3LYP showed a red-shift in the peak positions and CAM-B3LYP and ωB97XD, which have a long-range HF exchange, showed blue shifts. Regarding the fluorescence spectrum calculations with FCHT using 6-311+G(d,p), the OT-LC-BLYP reproduced both the peak intensities and positions closest to the experimental spectrum. B3LYP, however, showed red-shifted peaks, and ωB97XD showed blue-shifted peaks. CAM-B3LYP provided less blue-shifted peaks, but the relative peak intensities mismatched the experimental ones. Furthermore, calculations of the absorption and vibrationally resolved fluorescence spectra of 16-CNB and 24-CNB using OT-LC-BLYP/6-311+G(d,p) showed absorption and fluorescence spectra close to the experimental spectra with high accuracy. Moreover, the application of a polarizable continuum model (dichloromethane) produced a red shift in the peak positions of the absorption spectrum with increasing intensity but an increase in the peak intensities of the fluorescence calculations without shifting the peak position.

Extremely solvent-enhanced absorbance and fluorescence of carbazole interpreted using a damped Franck-Condon simulation.

Extremely solvent-enhanced absorption and fluorescence spectra of carbazole were investigated by performing a generalized multi-set damped Franck-Condon spectral simulation. Experimental absorption and fluorescence spectra of carbazole in the gas phase were first well reproduced by performing an un-damped Franck-Condon simulation, but a one-set scaling damped Franck-Condon simulation severely underestimated the intensities of the peaks of experimental absorption and fluorescence spectra of carbazole in n-hexane. Then, a multi-set scaling damped Franck-Condon simulation was proposed and carried out for simulating the extremely solvent-enhanced absorbance and fluorescence, and here, the simulated spectra agreed well with the experimental ones. Five (four) representative solvent-enhanced normal modes corresponding to the combination of ring stretching and ring breathing vibrational motions were determined to be responsible for enhanced absorbance (fluorescence) in n-hexane solution. Furthermore, different scalings were applied to the ground and first-excited states, resulting in different enhancement of absorbance and fluorescence, and this analysis revealed atoms in the carbazole interacting with n-hexane solvent molecules and, hence, leading to different normal-mode vibrational vector patterns in the ground and first-excited states, respectively. Basically, the same conclusion was drawn from a simulation with HF-CIS and the three functionals (TD)B3LYP, (TD)B3LYP-35, and (TD)BHandHLYP. The present multi-set scaling damped Franck-Condon simulation scheme was demonstrated to successfully interpret extremely solvent-enhanced absorbance and fluorescence of carbazole in n-hexane-solvent.

Quantum Mechanics/Molecular Mechanics Density Functional Theory Simulations of the Optical Properties Fingerprinting the Ligand-Binding of Pentameric Formyl Thiophene Acetic Acid in Amyloid-β(1-42).

The binding pocket proposed by König [ Chem. Commun. 2018 , 54 , 3030 - 3033 ] for the biomarker pentameric formyl thiophene acetic acid (p-FTAA) in the fibrillar structure of amyloid-β(1-42) has been put to the test by the comparison of theoretical and experimental optical absorption and fluorescence spectra obtained in a water environment and inside the protein scaffold. The optical absorption/emission properties of this luminescent conjugated oligothiophene were studied by means of classical force field molecular dynamics simulations to account for the sampling of configuration space in conjunction with polarizable embedding time-dependent density functional theory calculations of spectra. The nuclear motions of residues in the β-sheet were found to be modest, and the time dependence of embedding parameters was shown to be negligible so that a time-independent parameter set could be derived and used for all 300 snapshots considered in the spectrum averaging. In regard to linear absorption spectra, the calculated red shift due to protein binding for the dominant S1 ← S0 transition in p-FTAA was found to be equal to 23 nm (0.17 eV), which is in excellent agreement with the corresponding experimental result of 18 nm and taken as corroborating evidence for having correctly identified the binding pocket of p-FTAA in the amyloid. The underlying mechanisms for the calculated red shift were disentangled, and it is shown that some 20 nm (0.15 eV) of the total 23 nm (0.17 eV) is associated with increased planarity of p-FTAA in the binding pocket, whereas a mere 3 nm (0.02 eV) is associated with changes in the environment. In regard to emission spectra, we demonstrate that intersystem crossing from the excited S1 state to the triplet manifold of states is a less likely event for p-FTAA in the binding pocket as compared to in the aqueous solution, and we thereby partly explain the much higher quantum yield of fluorescence for the more rigid p-FTAA in the binding pocket. Two-photon absorption in p-FTAA is shown to predominantly occur to an overall symmetric excited state and be more than twice as strong for the biomarker in the binding pocket as compared to in water. The corresponding red shift, on the other hand, is very small. Earlier experimental two-photon fluorescence imaging using p-FTAA is shown not to target the dominant two-photon state, and ways to reach a higher image quality (lower signal-to-noise ratio) are proposed in terms of tuning the laser wavelength toward the region of 600 nm or the synthesis of asymmetric ligands with S1 states that are both one- and two-photon allowed.

The specific binding of a new 1,2,3-triazole to three blood proteins and it's appended rhodamine complex for selective detection of Hg2.

A synthesized compound, ethyl 2,5-diphenyl-2H-1,2,3-triazole-4- carboxylate (EDTC) was investigated on its physiochemical parameters and structural properties by using the quantum-chemical method. The results on the theoretical spectrum of EDTC were line with experimental fluorescence and absorption spectrum in large degree. Then EDTC was successfully synthesized to a novel rhodamine-based fluorescent probe (REDTC), which showed a distinct fluorescence enhancement upon the presence of Hg2+ in dimethyl formamide-water (DMF-H2O) buffer solution (pH 7.4). Meanwhile, the triazole appended colorless compound turns to pink upon complex formation with Hg2+ ions as 1:2 molar ratios and enables naked-eye detection. The chromogenic mechanism was determined by using spectroscopic measurements and TD DFT calculation. The fluorescence imaging experiments of Hg2+ in HeLa cell revealed that the probe REDTC could be labeled and it could be used in biological systems. Also, the intermediate EDTC was developed as a sensitive fluorescent probe for specific studies on the interactions to three kinds of blood proteins including human serum albumin (HSA), human immunoglobulin (HIg) and bovine hemoglobin (BHb) by using a series of spectroscopic methods and molecular docking under the simulative physiological conditions. The interactions between EDTC and these proteins led to the distinct fluorescence enhancement. The thermodynamic measured results further suggested that hydrophobic forces play a dominating role in stabilizing the complexes, which are in correspondence with the results from molecular docking. The UV-visible, synchronous, and three-dimensional (3D) fluorescence measurements demonstrated that EDTC influences the conformational of proteins and the microenvironment surrounding HSA, HIg, or BHb in aqueous solution.

Twisted intramolecular charge transfer: A time-dependent density functional theory study on the sensing mechanism of a Schiff base sensor for fluoride

The fluoride-sensing mechanism of a Schiff-base type sensor (Dyes Pigments, 2015, 123, 166) has been investigated by time-dependent density functional theory. The experimental ultraviolet and fluorescence spectra of the sensor before and after fluoride addition were well reproduced. The theoretical results showed that sensor molecules had distinctly different geometries in the ground state and first singlet excited state, which corresponded with the proposed twisted intramolecular charge transfer process and explained how the sensor fluorescence quenched. Thus, the sensor analysis of the fluoride anion by fluorescent spectroscopy was explained.

Analytical and computational investigation on host-guest interaction of cyclohexyl based thiosemicarbazones: Construction of molecular logic gates using multi-ion detection

Two novel cyclohexyl based thiosemicarbazones, H2L1 and H3L2, are synthesized and characterized. The anion and cation sensing properties of the two receptors has been unveiled as an effective ratiometric and colorimetric sensor for selective and rapid detection of fluoride, copper and cobalt ions. The H2L1 shows selective sensing towards F- and Cu2+ at 429 and 393 nm, whereas, H3L2 can detect F-, Cu2+ and Co2+ at 350, 393 and 408 nm respectively. The fluoride-sensing mechanism of the receptors has been investigated by means of the DFT and TD-DFT methods. The experimental UV-vis and fluorescence spectra are well reproduced by the calculated vertical excitation energies in the ground state and the first singlet excited state. The present theoretical study indicates that the deportation was taken from the 'NH' proton which is closer to the imine group, which has been confirmed by natural bond orbital (NBO) analysis and the potential energy curve (PES) of ground state for the function of NH bond. The absorption and emission response for receptors with and without F-, Co2+ and Cu2+ ions can mimic multiple logic gate such as NOR, XNOR, OR and TRANSFER gates.

Exploring the optoelectronic and charge transport properties of Pechmann dyes as efficient OLED materials

The structural, optoelectronic, and charge transport properties of dimethyl 2,3-bis((4-(bis(4-methoxyphenyl)amino)phenyl)ethynyl)fumarate (parent compound; E-1) and its acid-induced double lactonization Pechmann dyes, i.e., (E)-5,5′-bis(4-(bis(4-methoxyphenyl)amino)phenyl)-2H,2′H-[3,3′ bifuranylidene]-2,2′-dione (P55), and 3,7-bis(4-(bis(4-methoxyphenyl)amino)phenyl)pyrano[4,3-c]pyran-1,5-dione (P66) were investigated by DFT and TD-DFT calculations for potential use as efficient materials for organic light-emitting diodes (OLEDs). The charge transfer behaviour of these dyes has also been explored by shedding light on the frontier molecular orbitals, vertical ionization potential, reorganization energy, excitation energies, transfer integrals and intrinsic mobility for holes and electrons. The experimental absorption and fluorescence spectra were successfully reproduced by TD-BMK/6-31+G(d,p) level with the conductor-like polarizable continuum model (CPCM) in toluene. Additionally, calculated hole intrinsic mobility of P66 was observed greater than the electron one revealing this compound as p-type material that is rational to experimental data. Moreover, charge transfer nature (p-type or n-type) of E-1 and P55 has been probed on the bases of reorganization energy, transfer integrals and intrinsic mobility which showed that both dyes would be better p-type materials.

First-principles study of electronic properties of Cu doped Ag2S

Using first-principles calculations based on density functional theory, electronic properties of Ag2S and Cu doped Ag2S were investigated. The calculated results show that Ag2S crystal is semiconductor with a band gap of 0.92 eV which is consistent with previous PBE calculation. Three possible Cu doping configurations are investigated: Cu substitution of Ag_I, Cu substitution of Ag_II, and interstitial Cu. It is found that interstitial Cu doping reduces the band gap as the Cu concentration increases, while for Ag_I and Ag_II substitution doping the band gap is not sensitive to the impurity concentration. The band gap reduction can mainly be attributed to the downward shift of the bottom of conduction band upon Cu interstitial doping. The reduction of the band gap for Ag2S with interstitial Cu doping is consistent with experimental absorption and fluorescence spectra, where a significant red-shift after Cu doping in Ag2S crystal is observed.

Detection of iron atoms by emission spectroscopy and laser-induced fluorescence in solid propellant flames.

Planar laser-induced fluorescence on atomic iron is investigated in this paper, and a measurement strategy is proposed to monitor the fluorescence of iron atoms with good sensitivity. A model is proposed to fit the experimental fluorescence spectra, and good agreement is found between simulated and experimental spectra. Emission and laser-induced fluorescence measurements are performed in the flames of ammonium perchlorate composite propellants containing iron-based catalysts. A fluorescence signal from iron atoms after excitation at 248nm is observed for the first time in propellant flames. Images of the spatial distribution of iron atoms are recorded in the flame in which turbulent structures are generated. Iron fluorescence is detected up to 1.0MPa, which opens the way to application in propellant combustion.

A theoretical investigation on excited-state single or double proton transfer process for aloesaponarin I

The excited-state proton transfer (ESPT) dynamical behavior of aloesaponarin I (ASI) was studied using density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Our calculated vertical excitation energies based on TDDFT reproduced the experimental absorption and fluorescence spectra well [Nagaoka et al. J. Phys. Chem. B, 117, 4347 (2013)]. Two intramolecular hydrogen bonds were confirmed to be strengthened in the S1 state, which makes ESPT possible. Herein, the ESPT process is more likely to happen, along with one hydrogen bond (O1–H2⋯O3). Qualitative analyses about charge distribution further demonstrate that the ESPT process could occur because of the intramolecular charge transfer. Our constructed potential energy surfaces of both S0 and S1 states show that a single proton transfer reactive is more reasonable along with the intramolecular hydrogen bond (O1–H2⋯O3) rather than O4–H5⋯O6 in the S1 stated potential energy surface. Then, ASI-SPT* decays to the ground state with a 640 nm fluorescence; subsequently, the ASI-SPT form shows that reverse ground state single-proton transfer back to the ASI structure occurs. Particularly, dependent on relatively accurate potential energy barriers among these excited-state stable structures, we confirmed the excited-state single proton transfer process rather than using the controversial nodal plane model.