Long-wave Band Research Articles

(Invited) Stand-Alone Photoreduction of Carbon Dioxide on Copper Oxide Nanowires Powered By WO3/Dye Dual Absorber

A photoelectrochemical cell, composed of WO3/dye-sensitized solar cell (WO3/DSSC) and copper oxide (CuxO, where x = 1 and 2) nanowires as a dual absorber photoanode and cathode, respectively, is demonstrated as a stand-alone device for CO2 photoreduction to CO, H2 and formate. The single-absorber cell of a WO3 photoanode and CuxO nanowire cathode couple (WO3-CuxO) required the minimum overpotential of ~0.7 V to drive CO2 photoreduction. For the unassisted or stand-alone CO2 photoreduction, a DSSC was coupled to the WO3-CuxO system to construct a dual-absorber cell (WO3/DSSC-CuxO). In the dual-absorber cell, the long-wave band (λ > ca. 500 nm) passed through the semi-transparent WO3 film was absorbed by the dye-sensitized TiO2 electrode of DSSC. The WO3/DSSC-CuxO showed a potential gain of ~0.7 V, which resulted in the CO2 photoreduction successfully without supply of any external potential. In this stand-alone system, the primary CO2 conversion product is CO with solar-to-chemical energy efficiency of ~2.5% while H2 and formate are obtained with the energy efficiencies of 0.7% and 0.25%, respectively, in 5 h.

Stand-alone photoconversion of carbon dioxide on copper oxide wire arrays powered by tungsten trioxide/dye-sensitized solar cell dual absorbers

A photoelectrochemical (PEC) cell composed of a WO3/dye-sensitized solar cell (WO3/DSSC) and copper oxide (CuxO, where x=1 and 2) wire arrays as a dual-absorber photoanode and cathode, respectively, is demonstrated as a stand-alone, durable device for CO2 photoconversion. The CuxO wire arrays, which have high surface-to-volume ratios, exhibit promising electrocatalytic activity for CO2 conversion to CO at Faradaic efficiencies of ~80% and ~60% at E=−0.2 and −0.4V vs. RHE, respectively, and H2 production is minimized at a Faradaic efficiency <~20% in the potential range between −0.2 and −1.0V vs. RHE. The single-absorber cell of a WO3 photoanode and CuxO wire array cathode couple (WO3-CuxO) requires a minimum overpotential of ~0.7V to drive CO2 conversion. For stand-alone CO2 conversion, a DSSC is coupled to the WO3-CuxO system. In the dual-absorber cell (WO3/DSSC-CuxO), the long-wave band (λ >ca. 450nm) passed through the semitransparent WO3 film is absorbed by the dye-sensitized TiO2 electrode of the DSSC. The WO3/DSSC-CuxO shows a potential gain of ~0.7V and is able to successfully drive CO2 conversion on CuxO and simultaneously oxidize water on WO3 without an external power supply. In this stand-alone system, the primary CO2 conversion product is CO, with a solar-to-chemical energy efficiency of ~2.5%; H2 and formate are obtained with energy efficiencies of 0.7% and 0.25%, respectively, in 5h (overall efficiency ~3.45%). Neither CO2 conversion product nor H2 is found using the single-absorber system.

(Invited) Unassisted CO2 Photoconversion at Copper Oxide Electrodes

Artificial photosynthesis of value-added chemicals from CO2 and water has received renewed attention and diverse technical solutions for high efficiency and durability systems have been explored. The photoelectrochemical (PEC) systems have been demonstrated to be technically viable with a number of semiconductor photoanodes (e.g., WO3, BiVO4, etc.) coupled to metal (Cu, Au, Ag, etc.) or metal oxide electrodes (CuO and Cu2O), as well as photocathodes (Si, Cu2O, CuO2, CuFeO2, etc.) coupled to metal/metal oxide anodes for CO2 photoconversion. A photoelectrochemical cell, composed of WO3/dye-sensitized solar cell and copper oxide wire arrays, is demonstrated as an unassisted, durable device for CO2 photoconversion. The high surface-to-volume copper oxide wire exhibits a promising electrocatalytic activity of CO2 reduction reaction at faradaic efficiencies of ~80% and ~60% at E = -0.2 and -0.4 V vs. RHE, respectively. The single-absorber cell of a WO3 photoanode and copper oxide wire cathode couple requires the minimum overpotential (h) of 0.7 V to drive CO2 conversion. In the unassisted cell, the long-wave band (l > ~450 nm) passes through the semi-transparent WO3 film is absorbed by dye. The unassisted cell shows a potential gain of ~0.7 V, successfully driving the CO2 conversion without any external power supply.

Preliminary Inter-Comparison between AHI, VIIRS and MODIS Clear-Sky Ocean Radiances for Accurate SST Retrievals

Clear-sky brightness temperatures (BT) in five bands of the Advanced Himawari Imager (AHI; flown onboard Himawari-8 satellite) centered at 3.9, 8.6, 10.4, 11.2, and 12.3 µm (denoted by IR37, IR86, IR10, IR11, and IR12, respectively) are used in the NOAA Advanced Clear-Sky Processor for Oceans (ACSPO) sea surface temperature (SST) retrieval system. Here, AHI BTs are preliminarily evaluated for stability and consistency with the corresponding VIIRS and MODIS BTs, using the sensor observation minus model simulation (O-M) biases and corresponding double differences. The objective is to ensure accurate and consistent SST products from the polar and geo sensors, and to prepare for the launch of the GOES-R satellite in 2016. All five AHI SST bands are found to be largely in-family with their polar counterparts, but biased low relative to the VIIRS and MODIS (which, in turn, were found to be stable and consistent, except for Terra IR86, which is biased high by 1.5 K). The negative biases are larger in IR37 and IR12 (up to ~−0.5 K), followed by the three remaining longwave IR bands IR86, IR10, and IR11 (from −0.3 to −0.4 K). These negative biases may be in part due to the uncertainties in AHI calibration and characterization, although uncertainties in the coefficients of the Community Radiative Transfer Model (CRTM, used to generate the “M” term) may also contribute. Work is underway to add AHI analyses in the NOAA Monitoring of IR Clear-Sky Radiances over Oceans for SST (MICROS) system and improve AHI BTs by collaborating with the sensor calibration and CRTM teams. The Advanced Baseline Imager (ABI) analyses will be also added in MICROS when GOES-R is launched in late 2016 and the ABI IR data become available.

Ice water content vertical profiles of high-level clouds: classification and impact on radiative fluxes

Abstract. In this article, we discuss the shape of ice water content (IWC) vertical profiles in high ice clouds and its effect on their radiative properties, both in short- and in long-wave bands (SW and LW). Based on the analysis of collocated satellite data, we propose a minimal set of primitive shapes (rectangular, isosceles trapezoid, lower and upper triangle), which represents the IWC profiles sufficiently well. About 75 % of all high-level ice clouds (P &lt; 440 hPa) have an ice water path (IWP) smaller than 100 g m−2, with a 10 % smaller contribution from single layer clouds. Most IWC profiles (80 %) can be represented by a rectangular or isosceles trapezoid shape. However, with increasing IWP, the number of lower triangle profiles (IWC rises towards cloud base) increases, reaching up to 40 % for IWP values greater than 300 g m−2. The number of upper triangle profiles (IWC rises towards cloud top) is in general small and decreases with IWP, with the maximum occurrence of 15 % in cases of IWP less than 10 g m−2. We propose a statistical classification of the IWC shapes using IWP as a single parameter. We have estimated the radiative effects of clouds with the same IWP and with different IWC profile shapes for five typical atmospheric scenarios and over a broad range of IWP, cloud height, cloud vertical extent, and effective ice crystal diameter (De). We explain changes in outgoing LW fluxes at the top of the atmosphere (TOA) by the cloud thermal radiance while differences in TOA SW fluxes relate to the De vertical profile within the cloud. Absolute differences in net TOA and surface fluxes associated with these parameterized IWC profiles instead of assuming constant IWC profiles are in general of the order of 1–2 W m−2: they are negligible for clouds with IWP &lt; 30 g m−2, but may reach 2 W m−2 for clouds with IWP &gt; 300 W m−2.

Effects of Sn Ion on Photocatalytic Performances of Titanium Dioxide Thin Film

In order to improve the photocatalytic efficiency of TiO2, through adding different concentration of Sn ion, the photocatalytic performances of TiO2 thin films are changed. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) spectrum of TiO2 thin films before and after doping Sn ion are compared, and the transmission spectrum and optical absorption spectrum of TiO2 thin film are analyzed. The results show that: after the implantation of Sn ion, there is a new compound Ti1-xSnxO2 on the TiO2 film’s surface, which has a higher photocatalytic activity than pure TiO2. In addition, Sn/TiO2 film has broaden the scope of its light response after ion implantation, so that it can be more effectively in using light source to send out the photons of longer waveband, and makes the photocatalytic activity of Sn/TiO2 thin films increase.

Oxygen Vacancy Effect on Photoluminescence Properties of Self-Activated Yttrium Tungstate

A series of single-phase yttrium tungstate powders were synthesized through solid-state reaction under air or argon atmosphere. All powders showed broad band emission in the visible light region, and the argon-calcined samples presented strong near-infrared luminescence. Moreover, the long-wave excitation bands peaking at 340, 378, 380, 490, and 523 nm depended critically on the calcination atmosphere and temperature. The emergence of these new excitation bands was ascribed to different oxygen vacancy concentrations with the analysis of the first-principle calculation, Raman and X-ray absorption fine structure spectra. The oxygen vacancies caused the reduction of the average coordination number of tungsten, and the position of the localized energy band changed with the oxygen vacancy concentration. Finally, a schematic photoluminescence excitation model was proposed via anion and cation charge transfer. The obtained results promise to be very useful in interpreting self-activated tungstate luminescence mechanism. They can also serve as guide line for tuning the luminescence performance of yttrium tungstate and related materials.

Theoretical study of relationships between structural, optical, energetic, and magnetic properties and reactivity parameters of benzidine and its oxidized forms.

Structural, topological, optical, energetic, and magnetic properties and reactivity parameters of benzidine, its radical cation, and its dication as well as molecular complexes of the benzidine dication with the F(-), Cl(-), Br(-), I(-), NO3(-), HSO4(-), and H2PO4(-) anions were calculated at the B3LYP/6-311++G(2d,2p) level of theory in the CH2Cl2 medium. The CAM-B3LYP functional (as the most reliable one) and the 6-311++G(3df,3pd) basis set were used for the UV-vis absorption spectra prediction. The obtained spectral results are in a good agreement with available experimental data. A number of the calculated global and local molecular properties, including several recently developed ones, (in general, more than 20 parameters), namely, λmax, the bond lengths and orders (l and LA,B), adiabatic ionization energy (IEad), global electrophilicity index (ω), condensed electrophilic Fukui functions (f(+)) and dual descriptor (ΔfA), van der Waals molecular volume, nuclear independent chemical shifts (NICS) and QTAIM topological parameters were estimated in the critical points of the C(1)-C(1'), C(2)-C(3), and C(4)-N bonds as well as at the ring critical point. These quantities were found to be in a strong linear dependence (R(2) > 0.99 in most cases) with the number of detached electrons (Nel) from the benzidine molecule up to formation of the dication (Nel = 2). On one hand, a position of the long-wave absorption band (λCT) corresponding to the anion-to-cation charge transfer in the neutral complexes of the benzidine dication with anions, correlates with the Mulliken electronegativity of the anion (R(2) = 0.8646) and its adiabatic ionization energy (R(2) = 0.8054). On the other hand, the correlations with the anion charge in the complexes and the anion isotropic polarizability are rather poor (R(2) = 0.6392 and 0.3470, respectively). On the ground of the obtained strong relationships, one may recommend the calculated molecular properties as potentially preferable descriptors for the benzidine-based compounds in terms of the QSAR methodology.

Thermal radiation heat transfer: Including wavelength dependence into modelling

Thermal radiation heat transfer is receiving increased attention from the field of energy-efficient building. Well known is the enhanced greenhouse effect that results from an imbalance between incoming short-wave (SW) solar radiation and outgoing long-wave (LW) radiation from earth. Likewise, passive cooling can be achieved if outgoing radiation is not balanced by incoming radiation through another wavelength band. This paper reports on simulating thermal radiation from a building space using a double-glazed window with the option of having a participating gas like CO2 filling the inter-glazing space. The infrared spectrum is sectioned into four bands: SW < 4 μm, and three LW bands 4–8 μm, 8–14 μm (the atmospheric window) and >14 μm, respectively, and the relative importance of thermal radiation in the various bandwidths is assessed. The effect of changing the transmittance of the double-glazed gas-filled window on heat transfer is analysed for both day-time and night-time for air, CO2 and HFC-125. For distinguishing SW and LW thermal radiation through the atmosphere measurement data obtained with a pyranometer and a pyrgeometer is used. The results demonstrate that the calculation tool allows for designing double-glass window systems towards the minimisation of energy requirements for cooling or heating. It is found that expanding the wavelength range for window material transmittance increases heat fluxes through the system while using participating gases gives an insulation effect. For HFC-125 the effect is significant while for CO2 it is much smaller.

Evaluation of the NIR-SWIR atmospheric correction algorithm for MODIS-Aqua over the Eastern China Seas

The performance of the near-infrared (NIR) and short-wave infrared (SWIR) combined atmospheric correction algorithm (NIR-SWIR) for Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua over the Eastern China Seas (ECS) was evaluated. The in situ data set for evaluation in this study was collected during 2005 and 2012 through eight cruises in the ECS, wherein 49 in situ observation points were successfully matched with MODIS-Aqua data. The remote-sensing reflectance derived from MODIS-Aqua data using the NIR-SWIR algorithm and the NIR algorithm were compared to the in situ measurements in the matched-up data set, which included ocean bands (412, 443, 488, 531, 547, 667, and 678 nm) and land bands (469, 555, and 645 nm). The results show that the performance of the NIR-SWIR algorithm has been improved in turbid waters, and the effect at the short-wave bands (blue and green bands) is more significant than that at the long-wave bands (red bands). In addition, MODIS-Aqua data at the land bands (469, 555, and 645 nm) show a similar performance to those of nearby ocean bands. However, the lower estimation accuracy is still a remarkable question at bands 412, 645, 667, 678 nm. The results from both the NIR-SWIR and NIR algorithms were applied to the images of MODIS-Aqua in the ECS and they indicate that the extent to which the quality of the derived remote-sensing reflectance using the NIR-SWIR algorithm can be improved shows major differences for different seasons. The minimum area is in summer, and the maximum area in winter. The NIR-SWIR algorithm should be used for the whole of the Bohai Sea in winter.

Spectral signatures for swash on reflective, intermediate and dissipative beaches

In this paper we synthesise a large data set gathered from a wide variety of field deployments and integrate it with previously published results to identify the spectral signatures of swash from contrasting beach types. The field data set includes the full range of micro-tidal beach types (reflective, intermediate and dissipative), with beach gradients ranging from approximately 1:6 to 1:60 exposed to offshore significant wave heights of 0.5-3.0. m. The ratio of swash energy in the short-wave (f > 0.05. Hz) to long-wave (f < 0.05. Hz) frequency bands is found to be significantly different between the three beach types. Swash energy at short-wave frequencies is dominant on reflective and intermediate beaches and swash at long-wave frequencies is dominant on dissipative beaches; consistent with previously reported spectral signatures for the surf zone on these beach types. The available swash spectra were classified using an automated algorithm (CLARA) into five different classes. The ordered classes represent an evolution in the spectrum shape, described by a frequency downshifting of the energy peak from the short-wave into the long-wave frequency band and an increase in the long-wave swash energy level compared to a relatively minor variation in the short-wave swash energy level. A universally common feature of spectra from all beach-states was an f-4energy roll-off in the short-wave frequency band. In contrast to the broadly uniform appearance of the short-wave frequency band, the appearance of the long wave frequency band was highly variable across the beach-states. We incorporate the results presented here and previously published observations into the morphodynamic beach-state model, and propose an ordered sequence of swash spectra under increasing and decreasing incident wave energy level. This extension of the beach-state model to include the swash zone leads to the following propositions for morphodynamic controls on the nature of the swash spectrum. (1) The short-wave part of the swash spectrum is relatively constant in form across all beach-states (f-4 energy roll-off) and the energy density per unit frequency is controlled by the beach face gradient alone. (2) The spectral bandwidth of the energy roll-off varies directly with offshore wave energy level and inversely with beach face gradient (or beach-state), in a manner consistent with the non-linear wave breaking criterion. (3) The infragravity part of the swash spectrum is highly variable in form across all beach-states and the energy level is related to the offshore wave energy level and surf zone morphology.

Aerosol's optical and physical characteristics and direct radiative forcing during a shamal dust storm, a case study

Abstract. Dust aerosols are analyzed for their optical and physical properties during an episode of a dust storm that blew over Kuwait on 26 March 2003 when the military Operation Iraqi Freedom was in full swing. The intensity of the dust storm was such that it left a thick suspension of dust throughout the following day, 27 March. The synoptic sequence leading to the dust storm and the associated wind fields are discussed. Ground-based measurements of aerosol optical thickness reached 3.617 and 4.17 on 26 and 27 March respectively while the Ångstrom coefficient, α870/440, dropped to −0.0234 and −0.0318. Particulate matter concentration of 10 μm diameter or less, PM10, peaked at 4800 μg m−3 during dust storm hours of 26 March. Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved aerosol optical depth (AOD) by Deep Blue algorithm and Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) exhibited high values. Latitude–longitude maps of AOD and AI were used to deduce source regions of dust transport over Kuwait. The vertical profile of the dust layer was simulated using the SKIRON atmospheric model. Instantaneous net direct radiative forcing is calculated at top of atmosphere (TOA) and surface level. The thick dust layer of 26 March resulted in cooling the TOA by −60 Wm−2 and surface level by −175 Wm−2 for a surface albedo of 0.35. Slightly higher values were obtained for 27 March due to the increase in aerosol optical thickness. Radiative heating/cooling rates in the shortwave and longwave bands were also examined. Shortwave heating rate reached a maximum value of 2 K day−1 between 3 and 5 km, dropped to 1.5 K day−1 at 6 km and diminished at 8 km. Longwave radiation initially heated the lower atmosphere by a maximum value of 0.2 K day−1 at surface level, declined sharply at increasing altitude and diminished at 4 km. Above 4 km longwave radiation started to cool the atmosphere slightly reaching a maximum rate of −0.1 K day−1 at 6 km.

Optical absorption spectra as a useful tool to find parameters of deep impurity centers in semiconductors.

We analyze physical models accounting for deep-level conduction band transitions to describe impurity absorption spectra in tetrahedral-structured semiconductors. The investigations were carried out for ZnSe crystals doped with transition metals (Ti, V, Cr, Mn, Fe, Co, Ni) from a vapor phase. It was shown that the impurities provide acceptor centers with ground state energy offset by 0.3-0.6 eV from the edge of the conduction band, forming long-wave bands in the absorption spectra of the materials studied.

Effects of cobalt doping concentration on properties of zinc oxide films prepared by sol-gel

The cobalt doped zinc oxide thin films were synthesised on quartz glass substrates by sol-gel method. Through the analysis of XRD, FTIR, SEM, two dimensional Fourier transform and UV-VIS, it shows that, as the cobalt doping concentrations are less than 2 at%, the films have the c-axis preferred orientation with hexagonal wurtzite structure, smooth surface, compact structure and the average transmittance are more than 87% in the visible region. The photoluminescence (PL) emission spectra indicates the Blu-ray peaks move to the direction of long-wave band by cobalt doping; the research also shows that, with the further increasing of the cobalt doping concentration, the (002) of XRD peak and the intensity of PL gradually disappear, the films no longer have typical hexagonal wurtzite structure, meanwhile, SEM and two dimensional Fourier transform images indicate the surface of films become rougher, moreover, the optical band gap and the optical transmittance in the ultraviolet band significantly become smaller.

Photostimulated transformations in nanosized MoO3 films

Irradiation of MoO3 films (with a thickness d = 5–54 nm) with light (λ = 320 nm, I = (1.5–7) × 1015 quantum cm−2 s−1) led to the formation of an absorption band at λ = 870 nm along with the shift of the edge of the absorption band to the short-wave region of the spectrum. Further irradiation of the samples with light at λ = 870 nm caused diffusion of the long-wave absorption band. The conversion of MoO3 films increased when the incident light intensity and irradiation time increased and the film thickness decreased under the atmospheric conditions. A mechanism of the photochemical transformation of MoO3 films was suggested. It involves the generation of electron-hole pairs, recombination of some nonequilibrium charge carriers, formation of [(e(Va)++e] centers, and isolation of photolysis products.

Suomi‐NPP CrIS radiometric calibration uncertainty

AbstractThe Cross‐track Infrared Sounder (CrIS) is the high spectral resolution spectroradiometer on the Suomi National Polar‐Orbiting Partnership (NPP) satellite, providing operational observations of top‐of‐atmosphere thermal infrared radiance spectra for weather and climate applications. This paper describes the CrIS radiometric calibration uncertainty based on prelaunch and on‐orbit efforts to estimate calibration parameter uncertainties, and provides example results of recent postlaunch validation efforts to assess the predicted uncertainty. Prelaunch radiometric uncertainty (RU) estimates computed for the laboratory test environment are less than ~0.2 K 3 sigma for blackbody scene temperatures above 250 K, with primary uncertainty contributions from the calibration blackbody temperature, calibration blackbody reflected radiance terms, and detector nonlinearity. Variability of the prelaunch RU among the longwave band detectors and midwave band detectors is due to different levels of detector nonlinearity. A methodology for on‐orbit adjustment of nonlinearity correction parameters to reduce the overall contribution to RU and to reduce field of view (FOV)‐to‐FOV variability is described. The resulting on‐orbit RU estimates for Earth view spectra are less than 0.2 K 3 sigma in the midwave and shortwave bands, and less than 0.3 K 3 sigma in the longwave band. Postlaunch validation efforts to assess the radiometric calibration of CrIS are underway; validation results to date indicate that the on‐orbit RU estimates are representative. CrIS radiance products are expected to reach “Validated” status in early 2014.

Luminescence of the SrCl2:Pr crystals under high-energy excitation

The present research was carried out in order to elucidate the mechanisms of energy transfer from the crystal lattice to Pr3+ ions in SrCl2. The luminescence excitation and emission spectra as well as luminescence kinetics of the SrCl2:Pr single crystals containing 0.2mol% Pr were investigated at 300 and 10K using the vacuum ultraviolet (VUV) synchrotron radiation. The X-ray excited luminescence spectra of the SrCl2:Pr (CPr=0.2 and 0.5mol%) and SrCl2:Pr, K (CPr=1.5mol%; CK=1.5mol%) crystals were studied at 294 and 80K. Under optical excitation of the samples in the Pr3+ absorption bands, there were observed five fast ultraviolet emissions assigned to the 4f15d→4f2 transitions, and two long-wave bands corresponding to the f–f transitions. Furthermore, the intrinsic emission bands of SrCl2 were observed at 10K. The X-ray excited luminescence spectrum of the SrCl2:Pr crystal containing 0.2mol% Pr, besides intrinsic emission band near 400nm, has got a long-wave band at about 490nm of the Pr3+ centers. There were not observed any emission bands of the Pr3+ centers corresponding to the 4f15d–4f2 transitions in the X-ray excited luminescence spectrum of the SrCl2:Pr crystal. The possible mechanisms of energy transfer from the SrCl2 matrix to the Pr3+ centers are discussed.

Cyclometalated rhodium complexes of phenyl- and diphenyl-substituted oxazole and thiazole luminophores

Cyclometaleted rhodium complexes of oxazole and thiazole luminophores [Rh(C∧N)2En]Cl [(C∧N)−, deprotonated forms of 2,5-diphenyloxazole, 2-phenylbenzothiazole, 2-(biphenyl-4-yl)-6-phenylbenzoxazole, and 2-(biphenyl-4-yl)-5-phenyloxazole; En — ethylenediamine] were obtained and characterized by the methods of 1H NMR, IR, and electron absorption and emission spectroscopy. Two cyclometallated ligands in the inner sphere of the complexes are in the cis-C,C positions. Cyclometallating of the luminophores results both in a red shift of intraligand π-π*-optical transitions (Δν ∼1.2 kK) as compared to free luminophores and in the appearance of a long-wave band (λmax 376–392 nm) of a mixed nature: metal-ligand charge transfer/intraligand transition. Alongside with the internal conversion to a low-energy state of the metal-ligand charge transfer/ intraligand transition, the emission degradation of photoexcitation energy results in the intraligand π-π*-fluorescence of the complexes (λmax 390–423 nm) at room temperature.

Cyanine-Like and Polyenic Relaxation Paths of Merocyanine Derivatives of Malonodinitrile in the Excited State Detecting by Low Temperature Time-Resolved Fluorescence

The combined quantum-chemical and spectral study of features of the electron transitions in merocyanines is carried out. It is established that the two lowest transitions are split and involve both donor levels, similarly to symmetric cyanines. The long-wave absorption band has high intensity, while the second transition manifests itself only in the fluorescence excitation anisotropy spectra. In contrast to the ground state, the MO splitting in the excited state leads to the instability. The analysis of the results of theoretical and experimental studies enables us to propose that there are two paths of the relaxation in the excited state: a) cyanine-like one with equalizing the bond lengths; b) polyenic one with the considerable bond length alternation. This assumption is confirmed by the existence of two components in the time-resolved fluorescence spectra measured at low temperatures.

Molecular Structure and Interactions of Nucleic Acid Components in Nanoparticles: Ab Initio Calculations

Self-associates of nucleic acid components (stacking trimers and tetramers of the base pairs of nucleic acids) and short fragments of nucleic acids are nanoparticles (linear sizes of these particles are more than 10 Å). Modern quantum-mechanical methods and softwares allow one to perform ab initio calculations of the systems consisting of 150–200 atoms with enough large basis sets (for example, 6-31G*). The aim of this work is to reveal the peculiarities of molecular and electronic structures, as well as the energy features of nanoparticles of nucleic acid components. We had carried out ab initio calculations of the molecular structure and interactions in the stacking dimer, trimer, and tetramer of nucleic base pairs and in the stacking (TpG)(ApC) dimer and (TpGpC) (ApCpG) trimer of nucleotides, which are small DNA fragments. The performed calculations of molecular structures of dimers and trimers of nucleotide pairs showed that the interplanar distance in the structures studied is equal to 3.2 Å on average, and the helical angle in a trimer is approximately equal to 30º. The distance between phosphor atoms in neighboring chains is 13.1 Å. For dimers and trimers under study, we calculated the horizontal interaction energies. The analysis of interplanar distances and angles between nucleic bases and their pairs in the calculated short oligomers of nucleic acid base pairs (stacking dimer, trimer, and tetramer) has been carried out. Studies of interactions in the calculated short oligomers showed a considerable role of the cross interaction in the stabilization of the structures. The contribution of cross interactions to the horizontal interactions grows with the length of an oligomer. Nanoparticle components get electric charges in nanoparticles. Longwave low-intensity bands can appear in the electron spectra of nanoparticles.