S1 Spectra Research Articles

Photochemical reactions of chlorophyll tetramer in water-soluble chlorophyll-binding protein BoWSCP

The absorption dynamics of chlorophyll a in a symmetric tetrameric complex of the water-soluble chlorophyll-binding protein BoWSCP was measured by the broadband femtosecond laser pump-probe spectroscopy within the range from 400 to 780 nm with a time resolution of 20 f-200 ps. When BoWSCP was excited in the region of the Soret band at a wavelength of 430 nm, a nonradiative intramolecular conversion S3 → S1 was observed with a characteristic time of 83 ± 9 fs. When the complex was excited in the region of the Qy band at a wavelength of 670 nm, a relaxation transition between two excitonic states of the chlorophyll dimer was observed with a time of 105 ± 10 fs. Absorption spectra of excited singlet states S1 and S3 of chlorophyll a were obtained. It has been demonstrated that the delocalization of the excited state between exciton-coupled Chl molecules in the BoWSCP tetramer changes in time and depends on the excitation energy. Upon excitation of BoWSCP, an ultrafast photochemical reaction is observed in the Soret region, apparently due to the reduction of tryptophan in the vicinity of chlorophyll.

Performance evaluation of phosphor-based luminescent bricks using different coating methods

This study investigates the luminescence and durability properties of SrAl2O4: Eu/Dy phosphor (SP) coated bricks incorporating different coating materials, such as glaze powders (Fx200 and TranspG) and epoxy resin. The luminescent brick specimens were differentiated by materials and methods used for coating, including only SP (S1), SP with low content of glaze powders (S2), SP with high content of glaze powder (S3), and SP with epoxy resin (S4). The performance of specimens was evaluated through surface brightness, spectral analysis, decay characteristics, UV-VIS diffuse absorbance spectral (DAS) analysis, solar light aging resistance, and freeze-thaw resistance. The results revealed that S1, S2, and S4 exhibit the highest surface brightness and radiate slowly for more than 45 s after exciting specimens for 2 min. The peak excitation spectra of S1, S2, S3, and S4 exist between 517.5 nm and 519.5 nm, representing the electron transition between 4d and 5f in Eu2+. The decay characteristics and UV-VIS DAS analysis revealed that all specimens can absorb incident light energy and emit it for a longer time, and the capability of absorbing light energy and afterglow duration of S1 and S4 outperformed that of S2 and S3. Moreover, S1 and S4 exhibit high resistance against solar light aging and freeze-thaw cycles. However, such bricks may lead to a cost increase of 38–75 % compared to conventional bricks, which can be offset by energy conservation. This study suggests that luminescent bricks can be used as a multi-functional building material and contribute towards sustainable development goals.

Photoinduced Dynamics of 13,13'-Diphenylpropyl-β-carotene.

Carotenoids are ubiquitous pigment systems in nature which are relevant to a range of processes, such as photosynthesis, but the detailed influence of substitutions at the polyene backbone on their photophysics is still underexplored. Here, we present a detailed experimental and theoretical investigation of the carotenoid 13,13'-diphenylpropyl-β-carotene using ultrafast transient absorption spectroscopy and steady-state absorption experiments in n-hexane and n-hexadecane, complemented by DFT/TDDFT calculations. In spite of their bulkiness and their potential capability to "fold back" onto the polyene system, which could result in π-stacking effects, the phenylpropyl residues have only a minor impact on the photophysical properties compared with the parent compound β-carotene. Ultrafast spectroscopy finds lifetimes of 200-300 fs for the S2 state and 8.3-9.5 ps for the S1 state. Intramolecular vibrational redistribution with time constants in the range 0.6-1.4 ps is observed in terms of a spectral narrowing of the S1 spectrum over time. We also find clear indications of the presence of vibrationally hot molecules in the ground electronic state (S0*). The DFT/TDDFT calculations confirm that the propyl spacer electronically decouples the phenyl and polyene π-systems and that the substituents in the 13 and 13' positions point away from the polyene system.

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.

Chemical Characterization for the Detection of Impurities in Tainted and Natural Curcuma longa from India Using LIBS Coupled with PCA

The present manuscript explores a spectroscopic technique to select turmeric powder, free from impurities, and has compounds of medicinal importance among the tainted and natural turmeric. Six Curcuma longa (turmeric powder) samples, named S1, S2, S3, S4, S5, and S6, were analyzed to discriminate between tainted and natural turmeric using the LIBS and multivariate technique. Other techniques such as UV–Vis, FTIR, and EDX are also used to ascertain the elements/compounds showing the medicinal properties of C. longa. Spectral lines of carbon, sodium, potassium, magnesium, calcium, iron, strontium, barium, and electronic bands of CN molecules were observed in the LIBS spectra of turmeric samples. Spectral signatures of toxic elements such as lead and chromium are also observed in the LIBS spectra of all samples except S6. Adulteration of metanil yellow, a toxic azo dye, is used to increase the appearance of curcumin when the actual curcumin content is low. The presence of spectral lines of lead and chromium in the LIBS spectra of S1 to S5 suggested that it may be adulterated with lead chromate which is used for coloring turmeric. Further, the presence of sulfur in EDX analysis of sample S5 indicates that it may also have been adulterated with metanil (C18H14N3NaO3S). The concentration of samples’ constituents was evaluated using CF-LIBS, and EDX was used to verify the results obtained by CF-LIBS. The principal component analysis applied to the LIBS data of the turmeric samples has been used for instant discrimination between the sample based on their constituents. We also analyzed antioxidant activity and total phenolic and flavonoid content of different turmeric samples and found a negative Pearson correlation with heavy metals. The presence of curcumin in turmeric is confirmed using LIBS and UV–Vis, which have medicinal properties.

Preparation and characterization of SnO nanoflowers with controllable thicknesses using imidazolium-based ionic liquids as green media: Visible light photocatalytic degradation of Acid Blue 19

SnO nanoflowers with controllable thicknesses were prepared using a nonhydrothermal approach in mild conditions. Imidazolium-based ionic liquids, ILs, containing 1-butyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium bromide, and 1-octyl-3-methylimidazolium bromide, were applied during the preparation process as proper templates. The SnO nanoflowers with high purity and quality were prepared using 1:4:4 M ratios of SnCl2/NaOH/IL using simple reflux method at ambient pressure. The samples were analyzed by IR, XRD, SEM, EDX and DRS methods. The FT-IR spectrum obtained during the analysis confirmed the preparation of pure SnO. It should be noted that none of the ionic liquid functional groups were present in the samples and ILs only served as templates. Also, X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed high crystalline levels of as synthesized Romarchite SnO nanoparticles with thicknesses ranging from 48 to 88 nm. Furthermore, EDX analysis showed no traces of SnCl2 and IL in the sample which indicated high purity. The results indicated that the alkyl moiety variations of the ionic liquids affected the nanoflower sizes; therefore, reducing the alkyl chain length caused a decrease in the thicknesses of the SnO nanosheets. The results, moreover, illustrated that using diverse ionic liquids not only produced nanosheets with different thicknesses but also had a direct effect on the band gaps of the sheets. The UV–Vis diffuse reflectance spectrum of S1 (SnO nanosheets prepared in [bmim][Br]) with minimum thickness, has a band gap of 2.6 eV. Photodegradation in the aqueous solution showed 94.39% by the first-order kinetic model for Fast Acid Blue R (Acid Blue 19) by S1.

Reversible On-Off Switching of Excitation-Wavelength-Dependent Emission of a Phosphorescent Soft Salt Based on Platinum(II) Complexes.

Excitation-wavelength-dependent (Ex-De) emission materials show excellent potential in diverse advanced photonic areas. Of significant importance is the on-demand regulation of the Ex-De luminescence behavior of these materials, which is previously unprecedented. In this study, we report on a platinum(II) complex-based phosphorescent soft salt S1 ([Pt(tpp)(ed)]+[Pt(ftpp)(CN)2]- (where ttp = 2-(4-(trifluoromethyl)phenyl)pyridine, ed = ethane-1,2-diamine, and ftpp = 2-(4-fluoro-3-(trifluoromethyl)phenyl)pyridine)) with Ex-De photoluminescence (PL) property. UV-visible absorption and PL spectra of S1 were recorded in DMSO-H2O mixture (1 × 10-3 M) with various H2O fractions to investigate its ground and excited states. Interestingly, the PL spectra of S1 powder show that its maximum emission peak is red-shifted from 595 to 644 nm upon excitation at different wavelengths from 360 to 520 nm, accompanied by an obvious emission color change from yellow-orange to red. Furthermore, confocal laser scanning fluorescence microscopy was employed to determine the PL property of self-assembled uniform S1 nanostructure, and the result shows that the Ex-De emission behavior is absent. On the basis of these results, we conclude the various Pt(II)···Pt(II) distances that exist are the major factor responsible for the properties of the Ex-De PL of S1 powder. Thus, for the first time, reversible on-off switching of Ex-De PL of S1 was achieved by manipulating its Pt(II)···Pt(II) distances through mechanical stress and vapor fuming. Finally, we demonstrate the high-level anticounterfeiting applications via on-demand multicolor displays.

Effect of oxidants and dopant on morphology, crystallinity and optical absorbance of nano structural polyindole

We prepared the nanostructural polyindoles S1, S2, S3 and S4 (Pinds) by chemical oxidative route using anhydrous Iron (III) chloride (ferric chloride - FeCl3) and (NH4)2S2O8 (ammonium persulfate - APS) as oxidants and H2O2 (Hydrogen peroxide) as a dopant. The Pind samples are characterized by FTIR, UV–vis and XRD spectroscopy. The morphology of said samples has been examined by electron microscopy, SEM and TEM. The FTIR spectrographs enriched with bands show various bond absorptions which give the identity of Pind. The UV–vis spectra of S1 shows the absorption peaks in both regions, UV and visible. Using an oxidant as APS, the sample S2 spectra show the absence of an absorption peak in the visible region. The use of APS as oxidant gives the bathochromic and hyperchromic shift for UV absorption peak in case of S2 compare to S1, and also on the spectra of S2 there is bathochromic and hyperchromic shift in IR region which may be effect of APS as oxidant while polymerization. Hypsochromic shift is observed for samples S3 and S4, at both π - π* band and n- π* band with the use of dopants while synthesizing. Decrease in particle size (<100 nm) of S2 compared with S1 examined by SEM images (surface morphology). Small sized particles are observed in sample S3 compared to sample S1 with the use of H2O2 as dopant. The SEM image of S4 shows the presence of aggregation of particles up to some extent so that sheet- like structure is observed. Presence of Cl- in polymer matrix ensured by 4.64 wt% Cl on EDAX of S1, presence of SO2 - or SO3 - or SO4 - in polymer matrix ensured by 13.1 wt% oxygen and 2.89 wt% sulphur on EDAX of S2. Presence of Cl- in the polymer matrix is confirmed by EDAX of S3 and presence of SO2 - or SO3 - or SO4 - in the polymer matrix is confirmed by EDAX of S4. Increase in crystalline nature, formation of nano crystallites and removal of nanowires structure revealed by the XRD pattern of S2 due to APS as an oxidant. Nanoparticles surrounded by polymer nanowires are shown by the TEM image of S1. Nano crystallites embed spherical particles (>100 nm) as shown by the TEM image of S2. Small sized particles are observed in sample S3 (Pind/FeCl3/H2O2) compared to sample S1. In the present study we tried to find how the nature of oxidant affects the morphology, crystallinity and optical absorbance of Pind.

Rotationally resolved electronic S1 spectra of tryptoline and oxindole: Reversal of the 1La and 1Lb state character

Rotationally resolved S1←S0 fluorescence excitation spectra of the lowest electronic transitions (origin bands) of tryptoline (TRY) and oxindole (OXI) have been recorded and analyzed. A higher vibronic band of OXI has also been observed and assigned. The derived inertial parameters from the fits provide detailed information about their conformational or tautomeric structures in both the ground and excited electronic states. These molecules exhibit significantly different transition dipole moment orientations relative to the parent reference frame of indole that signify S1 state characters having principal parentage in a 1La state for OXI and a 1Lb state for TRY.

A new CBD-CC-E spectral similarity scale for optimizing computer-simulated UV–vis spectra

A new CBD-CC-E spectral similarity scale is proposed to optimize computer-simulated UV–vis spectra. The scale was tested using the S1←S0 spectrum of the dithienyl-diketopyrrolopyrrole molecule (DPP2T), an important building block for manufacturing materials for optoelectronic applications. Our results indicate that the spectrum calculated at M06/6-311++G(d,p) level was the one that best reproduced the intensity and shape features of the experimental spectrum, while CAM-B3LYP/6-311++G(d,p) was the one that best reproduced the energy. The CBD-CC-E scale makes the comparison between computer-simulated and experimental spectra statistically based, allowing a systematic and automated choice of the theory level whose calculated spectrum best reproduces the shape, intensity or energy of the experimental UV–vis spectrum.

The longer timescale excited state dynamics of isolated benzene.

The excited state photodynamics of isolated benzene have been studied in the nanosecond range by two-step photoionization through various vibrations of the lowest singlet state, with imaging photoelectron spectroscopy detection. Photoelectron spectra are measured as a function of pump-probe delay time, and their time evolution is successfully compared to a biexponential decay function without regard to a particular kinetic model. The only reasonable kinetic model with only two exponentials is the one that involves an intersystem crossing from S1 to T1, although that model has previously been called into question by high-resolution studies that failed to find any singlet-triplet perturbations in Zeeman studies of the S1 spectrum. That contradiction remains unresolved.

Identification of separate isoenergetic routes for vibrational energy flow in p-fluorotoluene.

A deceptively simple feature in the S1 ← S0 spectrum of p-fluorotoluene (pFT), 1013 cm-1 above the origin, is studied using both zero-electron-kinetic-energy (ZEKE) and two-dimensional laser-induced fluorescence (2D-LIF) spectroscopy. It is found to consist of a cornucopia of overlapped transitions to eigenstates that arise from numerous interacting levels. A significant variation in the activity is seen employing both the ZEKE and 2D-LIF techniques. Detailed insight into the complicated spectra can be achieved, owing to the large number of vibrational wavenumbers that have been previously determined for the S0, S1, and D0 + states, summarized herein. It is found that the activity is dominated by two overtones, which are individually interacting with other levels, so providing largely independent routes for vibrational energy flow at the same internal energy. Additionally, other weak features located 900-1050 cm-1 above the origin are examined.

Excited-state vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-ethylcytosine.

The S1 excited-state lifetime of jet-cooled 1-ethylcytosine (1ECyt) is ∼1 ns, one of the longest lifetimes for cytosine derivatives to date. Here, we analyze its S0 → S1 vibronic spectrum using two-color resonant two-photon ionization and UV/UV holeburning spectroscopy. Compared to cytosine and 1-methylcytosine, the S0 → S1 spectrum of 1ECyt shows a progression in the out-of-plane "butterfly" mode ν1 ', identified by spin-component scaled-second-order coupled-cluster method ab initio calculations. We also report time-resolved S1 state nonradiative dynamics at ∼20 ps resolution by the pump/delayed ionization technique. The S1 lifetime increases with the number of ν1 ' quanta from τ = 930 ps at v1 '=0 to 1030 ps at v1 '=2, decreasing to 14 ps at 710 cm-1 vibrational energy. We measured the rate constants for S1 ⇝ S0 internal conversion and S1 ⇝ T1 intersystem crossing (ISC): At the v' = 0 level, kIC is 8 × 108 s-1 or three times smaller than 1-methylcytosine. The ISC rate constant from v' = 0 to the T1(3ππ*) state is kISC = 2.4 × 108 s-1, 10 times smaller than the ISC rate constants of cytosine, but similar to that of 1-methylcytosine. Based on the calculated S1(1ππ*) state radiative lifetime τrad = 12 ns, the fluorescence quantum yield of 1ECyt is Φfl ∼ 7% and the intersystem crossing yield is ΦISC ∼ 20%. We measured the adiabatic ionization energy of 1-ethylcytosine via excitation of the S1 state as 8.353 ± 0.008 eV, which is 0.38 eV lower than that of amino-keto cytosine. Measurement of the ionization energy of the long-lived T1(ππ*) state formed via ISC reveals that it lies 3.2-3.4 eV above the S0 ground state.

Detection and Classification of Abnormities of First Heart Sound Using Empirical Wavelet Transform

It is expected that an automatic detection and classification algorithm for the abnormities of first heart sound (S1) can realize computer artificial intelligence diagnosis of some relative cardiovascular disease. Few studies have focused on the detection and classification of the abnormities of S1 and given out in detail the essential differences between abnormal and normal S1. This work applied Empirical Wavelet Transform (EWT) to decompose S1 and extracted the instantaneous frequency (IF) of mitral component (M1) and tricuspid component (T1) by using Hilbert Transform. Firstly, the heart sound signal is preprocessed following these processes: filtering, resampling, normalization and segmentation. Secondly, S1 is decomposed into several modes based on EWT. First two maximal points with a distance greater than 20Hz in Fourier Spectrum of S1 are selected and the nearest minimal points on both sides of the maximal points are found out as the boundaries for segmentation of the spectrum. S1 is decomposed into 5 modes and every mode’s IF are calculated through Hilbert transformation. At last, a k-mean cluster algorithm is applied to cluster the IF of different modes. TD and $A_{peak\_{}ratio}$ are calculated for decision tree classifier and S1s are divided into three categories: normal S1, S1 with abnormal split and S1with abnormal amplitude change. When the proposed method is applied to detect normal S1, Se=94.6%, Pp=98.6% and Oa=93.3%; When it is applied to detect S1 with abnormal split, Se=92.6%, Pp=96.9% and Oa=90%; When it is applied to detect S1 with abnormal amplitude change, Se=94.4%, Pp=95.7% and Oa=90.6%; Comparison experiments are carried out between the proposed method and HVD method. The results show Oa of the proposed method is higher than HVD method when detecting the three different S1s.

Fabrication, mechanism, formic acid−tuned degradation and photocatalytic hydrogen production of novel modified ZnO spheres by L−TA−DMF assisted hydrothermal method

Many ZnO microspheres were fabricated by hydrothermal method using l−TA and DMF as double capping agents. These spheres possess many novel nanostructures and exhibit unique and flexible self−assemblies and building units. For example, diverse pattern−like spheres, core/shell spheres, and semispheres were obtained. FTIR spectra of S1−S9 show TA and HCOOH modified ZnO spheres, which agree with those of XPS analysis. PL spectra show that violet, blue, green, yellow and orange emissions generated simultaneously can be tuned. Eg and ε are influenced by c. TA and DMF lead to diverse and novel ZnO growth, while DMF can tune the number of surface active sites of exposed (002) facet of ZnO, which determines final photocatalytic efficiency. TOC results show most of MB are mineralized rather than being partially degraded. The photocatalytic H2 generation rate is 4.15 ml h−1g−1 under simulated sunlight irradiation. In addition, DMF−induced photocatalytic mechanisms and two self−assemblies were proposed.

Chirality effects in the structures of jet-cooled bichromophoric dipeptides

Diastereomer cyclic dipeptides built on a diketopiperazine (DKP) ring and phenylalanine residues of either identical or opposite chirality have been studied in jet-cooled conditions by combining conformer-specific IR-UV laser spectroscopy. Comparison between the IR-UV double resonance experiments and anharmonic calculations shows the presence of only one conformer of cyclo Phe-Phe, with one aromatic ring folded on the dipeptide DKP ring and the other one extended. This allows weak NH…π and CH…π interactions to take place, which are slightly different in cyclo SPhe-SPhe and cyclo SPhe-RPhe. In both diastereomers, comparison between the S0 and S1 spectra of the all 12C species and that containing one 13C indicates that the electronic excitation is localized on one aromatic ring. This study has been extended to linear SPhe-SPhe and linear SPhe-RPhe, already studied by Abo-Riziq (2005).

Rotamer-Specific Photoisomerization of Difluorostilbenes from Transient Absorption and Transient Raman Spectroscopy.

Photoisomerization of 2,2'-, 3,3'-, and 4,4'-difluorostilbene (F2, F3, F4, respectively) in n-hexane, perfluoro-n-hexane, and acetonitrile is studied with broadband transient absorption (TA) and femtosecond stimulated Raman (FSR) spectroscopy and by DFT/TDDFT calculations. F2 and F3 possess three rotamers (rotational isomers) each, while F4 has one single conformation only. These differences are reflected in TA and FSR spectra. Thus F4 reveals a monoexponential decay of TA with τ1 = 172 ps in n-hexane, as expected for a single species. For F2 and F3, the decays are biexponential in all solvents, corresponding to two distinctly discerned rotamers or rotamer fractions. Specifically, for F2 in n-hexane, τ1 = 357 ps (83%) and τ2 = 62 ps (17%), and for F3 in the same solvent, τ1 = 222 ps (57%), and τ2 = 81 ps (43%). The weights in brackets agree with theoretically estimated ground-state abundances of the rotamers. Furthermore, a global fit of the TA and FSR data allows us to extract the spectra of the pure rotamers. The Raman spectra of S0 and S1 are in qualitative agreement with calculations.

Vibration and vibration-torsion levels of the S1 state of para-fluorotoluene in the 580-830 cm-1 range: Interactions and coincidences.

A study of the vibration and vibration-torsion levels of para-fluorotoluene in the 580-830 cm-1 region is presented, where a number of features are located whose identity is complicated by interactions and overlap. We examine this region with a view to ascertaining the assignments of the bands; in particular, identifying those that arise from interactions involving various zero-order states (ZOSs) involving both vibrations and torsions. Resonance-enhanced multiphoton ionization (REMPI) is employed to identify the wavenumbers of the relevant transitions, and subsequently zero-kinetic-energy (ZEKE) spectra are recorded to assign the various eigenstates. In some cases, a set of ZEKE spectra are recorded across the wavenumber range of a REMPI feature, and we construct what we term a two-dimensional ZEKE (2D-ZEKE) spectrum, which allows the changing ZOS contributions to the eigenstates to be ascertained. Assignment of the observed bands is aided by quantum chemical calculations and all b1 and a2 symmetry vibrational wavenumbers are now determined in the S1 state and cation, as well as those of the D10 vibration. We also compare to the activity seen in the corresponding S1 ← S0 spectrum of para-difluorobenzene.

Planarizing cytosine: The S1 state structure, vibrations, and nonradiative dynamics of jet-cooled 5,6-trimethylenecytosine.

We measure the S0 → S1 spectrum and time-resolved S1 state nonradiative dynamics of the "clamped" cytosine derivative 5,6-trimethylenecytosine (TMCyt) in a supersonic jet, using two-color resonant two-photon ionization (R2PI), UV/UV holeburning, and ns time-resolved pump/delayed ionization. The experiments are complemented with spin-component scaled second-order approximate coupled cluster (SCS-CC2), time-dependent density functional theory, and multi-state second-order perturbation-theory (MS-CASPT2) ab initio calculations. While the R2PI spectrum of cytosine breaks off ∼500 cm-1 above its 000 band, that of TMCyt extends up to +4400 cm-1 higher, with over a hundred resolved vibronic bands. Thus, clamping the cytosine C5-C6 bond allows us to explore the S1 state vibrations and S0 → S1 geometry changes in detail. The TMCyt S1 state out-of-plane vibrations ν1', ν3', and ν5' lie below 420 cm-1, and the in-plane ν11', ν12', and ν23' vibrational fundamentals appear at 450, 470, and 944 cm-1. S0 → S1 vibronic simulations based on SCS-CC2 calculations agree well with experiment if the calculated ν1', ν3', and ν5' frequencies are reduced by a factor of 2-3. MS-CASPT2 calculations predict that the ethylene-type S1 ⇝ S0 conical intersection (CI) increases from +366 cm-1 in cytosine to >6000 cm-1 in TMCyt, explaining the long lifetime and extended S0 → S1 spectrum. The lowest-energy S1 ⇝ S0 CI of TMCyt is the "amino out-of-plane" (OPX) intersection, calculated at +4190 cm-1. The experimental S1 ⇝ S0 internal conversion rate constant at the S1(v'=0) level is kIC=0.98-2.2⋅108 s-1, which is ∼10 times smaller than in 1-methylcytosine and cytosine. The S1(v'=0) level relaxes into the T1(3ππ*) state by intersystem crossing with kISC=0.41-1.6⋅108 s-1. The T1 state energy is measured to lie 24 580±560 cm-1 above the S0 state. The S1(v'=0) lifetime is τ=2.9 ns, resulting in an estimated fluorescence quantum yield of Φfl=24%. Intense two-color R2PI spectra of the TMCyt amino-enol tautomers appear above 36 000 cm-1. A sharp S1 ionization threshold is observed for amino-keto TMCyt, yielding an adiabatic ionization energy of 8.114±0.002 eV.

Preparation of ZnO from 2 D nanosheets to diverse 1 D nanorods and their structure, surface area, photocurrent, optical and photocatalytic properties by simple hydrothermal synthesis

Two–dimensional (2 D) ZnO nanosheets and one–dimensional (1 D) bud−like, grenade−like, prism−like, bamboo−like, brush−like, arrow−like, pencil−like, drip pipe−like, baseball bat−like, gear−like, walking stick−like, taper−like, shuttle−like, and/or hollow tower−like ZnO nanorods (nanotubes) with various tips were synthesized by a simple hydrothermal route from the system of CO(NH2)2N2H4. All the samples exhibit the wurtzite structure of ZnO. With the increase of the amount of N2H4 or decrease of CO(NH2)2, the interplanar spacing of different planes of ZnO increases or decreases simultaneously. FTIR shows that except the nanosheets of S1, all other samples are pure. The average reflectance of S8 reaches about 85% in the wavelengths ranging from 450 to 550 nm, and the reflectance of S3 is about 75%. The Eg values of ZnO from S1–S8 are 3.234, 3.215, 3.223, 3.215, 3.230, 3.243, 3.230 and 3.234 eV respectively. Raman spectra of S1 and S2 are obviously different from those of S3–S8. PL spectra of the ZnO samples exhibit a dominant UV luminescence peak of S1–S7, especially that of S1, S2 and S4. The addition of N2H4 can suppress the defects on the ZnO surface. However, the decrease of CO(NH2)2 introduces the defect. The BET surface area shows that except S1 (55.3 m2/g), S5 is a center of symmetric distribution of surface areas of S2–S8. From above discussion, the density, PL intensity of UV emission, and BET surface area of the ZnO nanorods can be easily tuned by controlling the concentrations of N2H4 and CO(NH2)2. The average values of photocurrent density of S1−S8 are 0.059, 0.170, 0.137, 0.184, 0.215, 0.091, 0.465 and 0.152 μA/cm2, respectively. S4, S2 and S7 possess the rapid photocatalytic activities and decompose 65%, 55% and 50% of MB within 50 min respectively. The order of the average diameters of S3, S4, S5, S6, and S7 agrees with that of photocatalytic efficiency, indicating that the polar (002) plane and/or the nanorod tips affect the photocatalytic activity. The decrease of the amount of CO(NH2)2 introduces the defects, which affects the photocatalytic activity of S8.