Long-wavelength Band Research Articles

The effect of packing density on luminescence of amorphous SiO2 nanoparticles

Photoluminescence of amorphous SiO2 nanoparticles compressed in the form of tablets is studied under exposure to UV radiation. The observed luminescence spectrum is a broad band extending from the excitation wavelength to 700 nm and with a maximum at ~470 nm. The spectrum can be decomposed into two Gaussian components with maxima at ~460 and ~530 nm. As the pressure applied for sample preparation increases, the integrated intensities of these bands change in opposite directions—the intensity of the short-wavelength band increases, while that of the long-wavelength band decreases. It is concluded that these bands are due to different luminescence centers of silicon dioxide located on the surface and in the bulk of SiO2 nanoparticles.

Local SDSS galaxies in the Herschel Stripe 82 survey: a critical assessment of optically derived star formation rates

We study a set of 3319 galaxies in the redshift interval 0.04 < z < 0.15 with far-infrared (FIR) coverage from the Herschel Stripe 82 survey (HerS), and emission-line measurements, redshifts, stellar masses and star-formation rates (SFRs) from the SDSS (DR7) MPA/JHU database. About 40% of the sample are detected in the Herschel/SPIRE 250 micron band. Total infrared (TIR) luminosities derived from HerS and ALLWISE photometry allow us to compare infrared and optical estimates of SFR with unprecedented statistics for diverse classes of galaxies. We find excellent agreement between TIR-derived and emission line-based SFRs for H II galaxies. Other classes, such as active galaxies and evolved galaxies, exhibit systematic discrepancies between optical and TIR SFRs. We demonstrate that these offsets are attributable primarily to survey biases and the large intrinsic uncertainties of the D4000- and colour-based optical calibrations used to estimate the SDSS SFRs of these galaxies. Using a classification scheme which expands upon popular emission-line methods, we demonstrate that emission-line galaxies with uncertain classifications include a population of massive, dusty, metal-rich star-forming systems that are frequently neglected in existing studies. We also study the capabilities of infrared selection of star-forming galaxies. FIR selection reveals a substantial population of galaxies dominated by cold dust which are missed by the long-wavelength WISE bands. Our results demonstrate that Herschel large-area surveys offer the means to construct large, relatively complete samples of local star-forming galaxies with accurate estimates of SFR that can be used to study the interplay between nuclear activity and star-formation.

A Group Theoretical and Quantum Chemical Study of Electronic Absorption and Fluorescence, Vibrational Spectra, and Conformations of Trimethine Cyanine Dye Molecules

The energetic structures and conformations of trimethine cyanine dye molecules were investigated. For research, group theoretical and quantum chemical calculation methods were used. The theoretical group analysis of electronic and vibrational structure of molecules was carried out. Also, the energetic structures and conformations of the molecule of this dye were studied. Research shows that the investigated molecule may reside in three different conformational states, one of which is highly symmetric (symmetry C2v) and the other two with low symmetry. The third conformer is characterized by lowering of binding energy of the electronic system by 0.23 eV, and the long-wavelength absorption band is shifted to lower energies. Also the group theoretical analysis of the trimethine cyanine molecule had allowed systematizing the vibrational and electronic quantum transitions and identifying the bands in the absorption spectra. It is shown that the excitation of the molecule in S1-state causes trans-cis-isomerization. The presence of the barrier of ~0.1 eV allows the fluorescence process to compete with isomerization process, but isomerization causes a decrease in the fluorescence quantum yield of the dye.

Effects of Strong Electronic Coupling in Chlorin and Bacteriochlorin Dyads.

Achieving tunable, intense near-infrared absorption in molecular architectures with properties suitable for solar light harvesting and biomedical studies is of fundamental interest. Herein, we report the photophysical, redox, and molecular-orbital characteristics of nine hydroporphyrin dyads and associated benchmark monomers that have been designed and synthesized to attain enhanced light harvesting. Each dyad contains two identical hydroporphyrins (chlorin or bacteriochlorin) connected by a linker (ethynyl or butadiynyl) at the macrocycle β-pyrrole (3- or 13-) or meso (15-) positions. The strong electronic communication between constituent chromophores is indicated by the doubling of prominent absorption features, split redox waves, and paired linear combinations of frontier molecular orbitals. Relative to the benchmarks, the chlorin dyads in toluene show substantial bathochromic shifts of the long-wavelength absorption band (17-31 nm), modestly reduced singlet excited-state lifetimes (τS = 3.6-6.2 ns vs 8.8-12.3 ns), and increased fluorescence quantum yields (Φf = 0.37-0.57 vs 0.34-0.39). The bacteriochlorin dyads in toluene show significant bathochromic shifts (25-57 nm) and modestly reduced τS (1.6-3.4 ns vs 3.5-5.3 ns) and Φf (0.09-0.19 vs 0.17-0.21) values. The τS and Φf values for the bacteriochlorin dyads are reduced substantially (up to ∼20-fold) in benzonitrile. The quenching is due primarily to the increased S1 → S0 internal conversion that is likely induced by increased contribution of charge-resonance configurations to the S1 excited state in the polar medium. The fundamental insights gained into the physicochemical properties of the strongly coupled hydroporphyrin dyads may aid their utilization in solar-energy conversion and photomedicine.

Effective refractive index of a quasi-two-dimensional polydomain film of a conjugated polymer

The relation between the effective ordinary refractive index n* = (none)1/2 of a quasi-two-dimensional polydomain uniaxial film of a conjugated polymer F8BT in the visible transparency region and the refractive indices (no,e) of uniaxial domains with the optical axes randomly oriented in the plane of the film has been confirmed experimentally. The permissible interval of variations in n* has been established and a strong spectral dispersion of this interval near the long-wavelength electronic absorption band of the film has been demonstrated.

Spectral and fluorescent properties of cross-conjugated ω,ω′-bisaminopolyenes containing pyran or dihydropyridine cycle with acceptor groups of different structures

The spectral and fluorescent properties of cross-conjugated bichromophoric ω,ω′-aminopolyenes containing the pyran or dihydropyridine cycle with acceptor groups of different structures have been studied. According to the two-dimensional 1H NMR spectroscopy (NOESY and ROESY) data obtained earlier, chromophores are arranged at an acute or obtuse angle in compounds with the pyran or the dihydropyridine moiety, respectively, thereby leading to significant differences in the absorption spectra of these compounds. The absorption spectra have been considered on the basis of the theory of interaction of chromophores. Since the long-wavelength bands of the absorption spectra of the compounds with the dihydropyridine cycle are broad and poorly resolved, we used decomposition of the absorption spectra of these compounds into Gaussian components. The angles between the chromophores, estimated from the ratio of the intensities of the absorption bands, were found to comply with the NMR data. Fluorescence quantum yields of the compounds studied have been also determined. In the case of the dyes with carbonyl, dinitrile, or indandione acceptors, the fluorescence quantum yields were found to be significantly higher for the compounds with the pyran rather than the dihydropyridine cycle.

Elaboration of an unexplored substitution site in synthetic bacteriochlorins

The ability to introduce substituents at designated sites about the perimeter of synthetic bacteriochlorins – analogs of bacteriochlorophylls of bacterial photosynthesis – remains a subject of ongoing study. Here, the self-condensation of a dihydrodipyrrin-dioxolane affords a 5-[2-(trimethylsiloxy)ethoxy]bacteriochlorin. Like a 5-methoxybacteriochlorin, the latter undergoes regioselective bromination at the 15-position, directed by the distal 5-alkoxy group. On the other hand, attempted bromination of a bacteriochlorin bearing a 5-(2-hydroxyethoxy) group resulted in intramolecular ether formation with the adjacent β-pyrroline position to give an annulated dioxepine ring (confirmed by single-crystal X-ray structural analysis). The hydroxyethoxy group at the 5-position can be derivatized by acylation. In addition, the installation of auxochromes (methoxycarbonyl, phenylethynyl) at the β-pyrrole rings causes a substantial bathochromic shift of the long-wavelength absorption band (812 nm) and companion fluorescence emission band (821 nm). Taken together, the modification of the 5-substituent complements existing methods for installing a single substituent on the bacteriochlorin macrocycle.

Structural and spectral investigations of the recently synthesized chalcone (E)-3-mesityl-1-(naphthalen-2-yl) prop-2-en-1-one, a potential chemotherapeutic agent.

BackgroundChalcones (1,3-diaryl-2-propen-1-ones, represent an important subgroup of the polyphenolic family, which have shown a wide spectrum of medical and industrial application. Due to their redundancy in plants and ease of preparation, this category of molecules has inspired considerable attention for potential therapeutic uses. They are also effective in vivo as anti-tumor promoting, cell proliferating inhibitors and chemo preventing agents.ResultsSynthesis and molecular structure investigation of (E)-3-mesityl-1-(naphthalen-2-yl) prop-2-en-1-one (3) is reported. The structure of the title compound 3 is confirmed by X-ray crystallography. The optimized molecular structure of the studied compound is calculated using DFT B3LYP/6-311G (d,p) method. The calculated geometric parameters are in good agreement with the experimental data obtained from our reported X-ay structure. The calculated IR fundamental bands were assigned and compared with the experimental data. The electronic spectra of the studied compound have been calculated using the time dependant density functional theory (TD-DFT). The longest wavelength band is due to H → L (79 %) electronic transition which belongs to π-π* excitation. The 1H- and 13C-NMR chemical shifts were calculated using gauge independent atomic orbitals (GIAO) method, which showed good correlations with the experimental data (R2 = 0.9911–0.9965). The natural bond orbital (NBO) calculations were performed to predict the natural atomic charges at different atomic sites. The molecular electrostatic potential (MEP) was used to visualize the charge distribution on the molecule. Molecular docking results suggest that the compound might exhibit inhibitory activity against GPb and may act as potential anti-diabetic compound.Conclusions(E)-3-Mesityl-1-(naphthalen-2-yl) prop-2-en-1-one single crystal is grown and characterized by single crystal X-ray diffraction, FT-IR, UV–vis, DFT and optimized geometrical parameters are close to the experimental bond lengths and angles. Molecular stability was successfully analyzed using NBO and electron delocalization is confirmed by MEP. Prediction of Activity Spectra Analysis of the title compound, predicts anti-diabetic activity with probability to have an active value of 0.348.Graphical (E)-3-Mesityl-1-(naphthalen-2-yl) prop-2-en-1-one: a crystal structure and computational studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13065-015-0112-5) contains supplementary material, which is available to authorized users.

Binuclear platinated 2-phenylbenzothiazole complexes with bridging 2-mercapto derivatives of thiazoline, 1-methylimidazole, and pyrimidine: Structures and optical and electrochemical properties

The structures of complexes [Pt(Bt)(μ-(N^S))]2 with platinated 2-phenylbenzothiazole (Bt) and bridging 2-mercapto derivatives (N∧S) of thiazoline, 1-methylimidazole, and pyrimidine in the crystalline state and in a CDCl3 solution are studied by X-ray diffraction analysis and 1H, 13C, and 195Pt NMR spectroscopy. Complexes [Pt(Bt)(μ-(N^S))]2 have the cis-N(Bt),S(N^S) structure with the Pt-Pt chemical bond (2.89–2.93 A) and antisymmetrical position of two cycloplatinated and two bridging ligands (CCDC nos. 1001204 (I), 1027021 (II), and 993566 (III)). The long-wavelength absorption bands (410–540 nm), phosphorescence bands with λmax = 685 nm, and two-electron electroreduction (E p = −(2.00–2.27) V) and oxidation (E p = 0.07–0.20 V) processes are assigned to photo- and electrostimulated processes involving the LUMO and HOMO predominantly localized on the π* orbitals of {Pt(Bt)} and on the σ* orbitals of the metal-metal chemical bond.

Spectral and Luminescent Characteristics of a Hexaphenyltetraazachlorin Zinc Complex

In continuation of previous studies on the photophysics of phenyl-substituted tetraazachlorins, we determined the spectral and luminescent characteristics of a tetramethylhexaphenyltetraazachlorin zinc complex at 293 and 77 K. Absorption, fluorescence, and fluorescence excitation spectra; the fluorescence quantum yield and lifetime; and the quantum yield for singlet oxygen generation were measured at room temperature. Fluorescence, fluorescence excitation, and fluorescence polarization spectra were measured at liquid nitrogen temperature. Fluorescence spectra indicated that the zinc complex rearranged in the excited electronic state S1 at both temperatures. A high quantum yield for singlet oxygen generation (0.91) was obtained for a toluene solution. Zn-tetramethylhexaphenyl tetraazachlorin was proposed as a photosensitizer for photodynamic therapy because the long-wavelength band at 707 nm was located in the transparent region of biological tissues.

Effect of Salt Ions on the Proton-Transfer Rate in 3-Hydroxyflavone

The effects of lithium and chloride ions on the spectral characteristics of the two-band fluorescence of 3-hydroxyflavone solutions were studied. The obtained absorption, emission, and fluorescence excitation spectra showed that the salt ions effectively modulated intramolecular proton transfer in the excited state, which led to increases in the shortwavelength band intensity and the fluorescence quantum yield. Thus, the quantum yield for 3-hydroxyflavone in acetonitrile with salt concentrations 0.005, 0.01, and 0.02 M increased by 1.5, 2.0, and 3.0 times, respectively, with standard excitation in the principal absorption band. The intensity ratio of the short-wavelength and longwavelength bands also increased as the salt concentration increased. The increase was so significant that the color change of the fluorescence was easily noticed visually. The good sensitivity of the fluorescence-band intensity ratio to the salt concentration could provide a basis for solving the inverse problem, i.e., determining the salt concentration in solutions and biological objects. An explanation allowing the obtained changes in the fluorescence spectral properties after adding LiCl to the solution to be interpreted was proposed.

Temperature-tunable lasing in negative dielectric chiral nematic liquid crystal**Project supported by the National Natural Science Foundation of China (Grant No. 61378042), the Outstanding Young Scholars Growth Plans of Colleges and Universities in Liaoning Province, China (Grant No. LJQ2013022), the Science and Technology Research of Liaoning Province, China (Grant No. L2010465), the Open Funds of Liaoning Province Key Laboratory of Laser

In this work, negative dielectric nematic liquid crystal SLC12V620-400, chiral dopant S811, and laser dye DCM are used to prepare dye-doped chiral nematic liquid crystal laser sample. In order to investigate temperature-tunable lasing in negative dielectric chiral nematic liquid crystal, we measure the transmission and lasing spectrum of this sample. The photonic band gap (PBG) is observed to red shift with its width reducing from 71.2 nm to 40.2 nm, and its short-wavelength band edge moves 55.3 nm while the long-wavelength band edge only moves 24.9 nm. The wavelength of output laser is found to red shift from 614.4 nm at 20 °C to 662.8 nm at 67 °C, which is very different from the previous experimental phenomena. The refractive indices, parallel and perpendicular to the director in chiral nematic liquid crystal have different dependencies on temperature. The experiment shows that the pitch of this chiral nematic liquid crystal increases with the increase of temperature. The decrease in the PBG width, different shifts of band edges, and the red shift of laser wavelength are the results of refractive indices change and pitch thermal elongation.

Ultrashort stretched-pulse L-band laser using carbon-nanotube saturable absorber.

In the paper, a passively mode-locked erbium-doped fiber ring laser in the long-wavelength band (L-band) is presented by using a single-wall nanotube saturable absorber (SWNT-SA). The optical properties of the SWNT-SA are compared with those in the C-band in view of the absorbance spectrum and the power-dependent transmittance of the SWNT-SA film. The effects of the net cavity dispersion and the length of the erbium-doped fiber (EDF) on L-band stretched pulse generation are discussed. The designed stretched-pulse L-band laser has a net dispersion of 0.017-ps2 and generates ultrashort (110 fs), broad-spectrum (41 nm) pulses with a signal-to-noise ratio over 70 dB.

Electronic absorption spectroscopic behavior and acidity constants of some new dinitrophenylhydrazone derivatives

In the present study, UV–visible electronic spectra of three new 2,4-dinitrophenylhydrazone derivatives (C1, C2 and C3) have been studied. Different bands observed have been assigned to the proper electronic transitions. The solvatochromic behaviors of these compounds were investigated by studying their electronic spectra in several organic solvents with different polarities. The longer wavelength band is assigned to an intermolecular charge transfer transition. The solvated H-bonding complexes formed between dimethylformamide and 2,4-dinitrophenylhydrazone derivatives were also investigated. ΔG, and the Kf values of the molecular complexes formed in solution have been determined. Effects of temperature increase and concentration changes on the longer spectroscopic wavelength band of the studied compounds were investigated. In this work, the behavior of acidity constants of these compounds in different pH values is studied by a multiwavelength spectrophotometric method too.

Spectra of divalent samarium in LaF3 crystals

The optical spectra and electrical conductivity of LaF3 crystals containing Sm2+ ions are studied. Groups of emission lines at 560–620, 650–690, and 680–770 nm at 7.9 K are produced by transitions from states 5 D 2, 5 D 1, and 5 D 0 to states 7 F j of Sm2+ ions. Radiative transitions from state 5 D 0 are characterized by a decay time of 8.9 ms and temperature quenching in the range of 70–160 K. A linear dependence of the crystals’ electrical conductivity on the magnitude of absorption bands of Sm2+ ions is observed, due the presence of anionic vacancies that compensate for the low charge of Sm2+ ions. The long-wavelength absorption band at 600 nm that is not observed in the excitation spectra is produced by the transition from 4f Sm2+ to the 1s level of anion vacancies. Absorption bands with wavelengths below 520 nm are due to 4f-5d transitions in the Sm2+ ions.

Spectral properties of BADAN in solutions with different polarities

Spectral characteristics (absorption spectra, excitation and emission spectra of solvatochromic dye 6-bromo-acetyl-2-dimethylamino-naphtalene (BADAN) were studied in solvents with different polarities. Comparison of BADAN fluorescence excitation spectra corrected for the primary inner filter effect and absorption spectra of this dye allowed to conclude that the long-wavelength absorption band of BADAN is determined by the superposition of two BADAN tautomeric forms having different conformation (planar and non-planar) and different distribution of electronic density. The analysis of BADAN excitation and emission spectra has shown that in non-polar solvents (hexane) fluoresces only one dye form which absorbs in more short-wave part of the spectrum than other conformer. In polar solvents (acetonitrile, mixture of acetonitrile/water) both forms fluoresce. It is concluded that the fluorescence of the dye in hexane and short-wavelength component of BADAN fluorescence at excitation in short-wavelength region of absorption spectrum are due to the locally excited state of the planar BADAN molecule. Fluorescence of BADAN in acetonitrile at excitation in long-wavelength part of long-wavelength absorption band and long-wavelength component of BADAN fluorescence spectrum in acetonitrile at excitation in short-wavelength region of absorption spectrum are due to non-planar BADAN conformers with internal charge transfer state.

Solvatochromism of 9,10-phenanthrenequinone: an electronic and resonance Raman spectroscopic study.

Solvent effects play a vital role in various chemical, physical, and biological processes. To gain a fundamental understanding of the solute-solvent interactions and their implications on the energy level re-ordering and structure, UV-VIS absorption, resonance Raman spectroscopic, and density functional theory calculation studies on 9,10-phenanthrenequinone (PQ) in different solvents of diverse solvent polarity has been carried out. The solvatochromic analysis of the absorption spectra of PQ in protic dipolar solvents suggests that the longest (1n-π(1)*; S1 state) and the shorter (1π-π(1)*; S2 state) wavelength band undergoes a hypsochromic and bathochromic shift due to intermolecular hydrogen bond weakening and strengthening, respectively. It also indicates that hydrogen bonding plays a major role in the differential solvation of the S2 state relative to the ground state. Raman excitation profiles of PQ (400-1800 cm(-1)) in various solvents followed their corresponding absorption spectra therefore the enhancements on resonant excitation are from single-state rather than mixed states. The hyperchromism of the longer wavelength band is attributed to intensity borrowing from the nearby allowed electronic transition through vibronic coupling. Computational calculation with C2ν symmetry constraint on the S2 state resulted in an imaginary frequency along the low-frequency out-of-plane torsional modes involving the C=O site and therefore, we hypothesize that this mode could be involved in the vibronic coupling.

Iridium(III) and Platinum(II) complexes with metallated and chelating benzothiazole derivatives: Structural, optical, and electrochemical properties

The structures of the Ir(III) and Pt(II) complexes with metallated 2-phenylbenzothiazole (Bt) and chelating 2-(2-hydroxo)phenylbenzothiazole (Hbt) in the crystalline state and in a CDCl3 solution are studied by X-ray diffraction analysis and 1H NMR spectroscopy. The structures of the complexes are shown to be cis-C,C-[Ir(Bt)2(HBt)] (I) and trans-N,N-[Pt(Bt)(HBt)] (II) (CIF files CCDC 996857 (I) and 995845 (II)). Based on the results of absorption and emission electron spectroscopy, the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) determining the character of long-wavelength optical bands and electrochemical processes are assigned to the orbitals predominantly localized on the {Ir(Bt)} fragment for complex I, whereas for complex II the LUMO is localized on {Pt(Bt)} and the HOMO is localized on the {Pt(HBt)} fragment.

Absorption and Emission Sensitivity of 2-(2'-Hydroxyphenyl)benzoxazole to Solvents and Impurities.

2-(2'-Hydroxyphenyl)benzoxazole (HBO) is known for undergoing intramolecular proton transfer in the excited state to result in the emission of its tautomer. A minor long-wavelength absorption band in the range 370-420 nm has been reported in highly polar solvents such as dimethylsulfoxide (DMSO). However, the nature of this species has not been entirely clarified. In this work, we provide evidence that this long-wavelength absorption band might have been caused by base or metal salt impurities that are introduced into the spectral sample during solvent transport using glass Pasteur pipettes. The contamination by base or metal salt could be avoided by using borosilicate glass syringes or nonglass pipettes in sample handling. Quantum chemical calculations conclude that solvent-mediated deprotonation is too energetically costly to occur without the aid of a base of an adequate strength. In the presence of such a base, the deprotonation of HBO and its effect on emission are investigated in dichloromethane and DMSO, the latter of which facilitates deprotonation much more readily than the former. Finally, the absorption and emission spectra of HBO in 13 solvents are reported, from which it is concluded that ESIPT is hindered in polar solvents that are also strong hydrogen bond acceptors.

Spectral Properties of Dyes with Interfragmental Charge Transfer: Solvatochromism and Solvatofluorochromism of 2-(3-Coumaroyl)-benzopyrylium Perchlorates

The paper deals with the spectral properties of dyes with interfragmental charge transfer, in particular, derivatives of 2-(3-coumaroyl)benzopyrylium (CBP) perchlorates. The positions of long-wavelength absorption and emission bands, quantum yields, and lifetimes of fluorescence were measured, mostly in aprotic solvents. Regression analysis of the relationship between the spectral characteristics of CBP and the main solvent parameters (polarity, polarisability, nucleophilicity, and electrophilicity) was carried out. It was found that the characteristics of CBP depend mainly on two solvent parameters—polarity and/or nucleophilicity. An increase in these parameters results in a hypsochromic shift of absorption bands and a decrease of lifetimes and fluorescence intensity. The positions of the emission bands can demonstrate either hypsochromism or bathochromism, depending on the nature of the substituents. The solvatofluorochromic effects are not as strong as the solvatochromic ones. We believe that the spectral behaviour of CBP can be explained by cation depolarisation and by a decrease in the stability of nucleophilic complexes with solvent molecules that is associated with interfragmental charge transfer following excitation, relaxation, and radiative deactivation of the excited state.