- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Electronic State and Photophysics of 2-Ethylhexyl-4-methoxycinnamate as UV-B Sunscreen under Jet-Cooled Condition
摘要： The title compound, 2-ethylhexyl-4-methoxycinnamate (2EH4MC), is known as a typical ingredient of sunscreen cosmetics that effectively converts the absorbed UV-B light to thermal energy. This energy conversion process includes the nonradiative decay (NRD): trans?cis isomerization and finally going back to the original structure with a release of thermal energy. In this study, we performed UV spectroscopy for jet-cooled 2EH4MC to investigate the electronic/geometrical structures as well as the NRD mechanism. Laser-induced-fluorescence (LIF) spectroscopy gave the well-resolved vibronic structure of the S1?S0 transition; UV?UV hole-burning (HB) spectroscopy and density functional theory (DFT) calculations revealed the presence of syn and anti isomers, where the methoxy (?OCH3) groups orient in opposite directions to each other. Picosecond UV?UV pump?probe spectroscopy revealed the NRD process from the excited singlet (S1 (1ππ*)) state occurs at a rate constant of ～1010?1011 s?1, attributed to internal conversion (IC) to the 1nπ* state. Nanosecond UV?deep UV (DUV) pump?probe spectroscopy identified a transient triplet (T1 (3ππ*)) state, whose energy (from S0) and lifetime are 18 400 cm?1 and 20 ns, respectively. These results demonstrate that the photoisomerization of 2EH4MC includes multistep internal conversions and intersystem crossings, described as "S1 (trans, 1ππ*) → 1nπ* → T1 (3ππ*) → S0 (cis)".
关键词： nonradiative decay,photophysics,DFT calculations,trans?cis isomerization,jet-cooled spectroscopy,2-ethylhexyl-4-methoxycinnamate,UV-B sunscreen
更新于2025-09-19 17:13:59
-
High-performance hydrogen evolution of MoSe2-Mo2C seamless heterojunction enabled by efficient charge transfer
摘要： A novel heterojunction consisted of Mo2C and MoSe2 is synthesized through CVD as high-performance electrocatalyst for HER in both acidic and basic media. The enhanced conductivity and the large surface area of as-prepared Mo2C/MoSe2 contribute to the efficient HER. Further DFT calculations can prove that in the interface region of Mo2C and MoSe2, there are MIGS which could benefit the fast charge transfer, boosting the hydrogen evolution.
关键词： DFT calculations,HER,Mo2C,heterojunction,CVD,MoSe2,electrocatalyst,MIGS
更新于2025-09-19 17:13:59
-
Development of Novel Mixed Halide/Superhalide Tin-Based Perovskites for Mesoscopic Carbon-Based Solar Cells
摘要： Tin perovskites suffer from poor stability and a self-doping effect. To solve this problem, we synthesized novel tin perovskites based on superhalide with varied ratios of tetrafluoroborate to iodide and implemented them into solar cells based on a mesoscopic carbon-electrode architecture because the film formation was an issue to apply this material for a planar heterojunction device structure. We undertook quantum-chemical calculations based on plane-wave density-functional-theory (DFT) methods and explored the structural and electronic properties of tin perovskites FASnI3-x(BF4)x in the series x = 0, 1, 2 and 3. We found that only the x = 2 case, FASnI(BF4)2, was successfully produced, beyond the standard FASnI3. The electrochemical impedance and X-ray photoelectron spectra indicate that the addition of tin tetrafluoroborate instead of SnI2 suppressed the trap-assisted recombination through decreasing the Sn4+ content. The efficiency of power conversion of the FASnI(BF4)2 device with FAI and Sn(BF4)2 in equimolar ratio improved 72 % relative to a standard FASnI3 solar cell, with satisfactory photostability under ambient air conditions.
关键词： DFT calculations,photostability,superhalide,tetrafluoroborate,solar cells,tin perovskites
更新于2025-09-19 17:13:59
-
Insights into the formation of N doped 3D-Graphene Quantum Dots. Spectroscopic and Computational Approach
摘要： In this work, we utilize a top-down approach to synthesize nitrogen doped graphene quantum dots from a 3D-graphene precursor via an eco-friendly hydrothermal method. The nanoparticles obtained showed a 2-3 nm diameter and well dispersion behavior in aqueous media. The reaction mechanism of insertion of nitrogen from polyvinylpolypyrrolidone onto the 3D-graphene structure, via an esterification reaction, was studied by the density functional theory, in addition, the kinetic and thermodynamic magnitudes of the reaction was analyzed with the help of Eyring's transition state theory and statistical thermodynamics. After analysis by ss-NMR and XPS spectroscopies, the functional groups involved in this process were characterized, and N was found mainly as amide / amine groups. Fluorescence emission, which exhibited a red shift (552 nm) and an emission maximum at 512 nm when excited at 480 nm, demonstrated a low stoke shift (Δλ =32 nm), explained by the proposed structural model.
关键词： XPS,solid-state NMR,Nitrogen doped graphene quantum dots,DFT calculations
更新于2025-09-12 10:27:22
-
Enhanced Incorporation of Guanidinium in Formamidinium‐Based Perovskites for Efficient and Stable Photovoltaics: The Role of Cs and Br
摘要： Recently, incorporating guanidium (GA) cations into organolead halide perovskites is shown to effectively improve the stability and performance of the solar cells. However, the underlying mechanisms that govern the GA incorporation have remained unclear. Here, FAPbI3 is used as a basic framework to investigate experimentally and theoretically the role of cesium (Cs) and bromine (Br) substitutions in GA+ incorporation. It is found that simultaneous introduction of the small-size Cs+ and Br– in the FAPbI3 lattice is critical to create sufficient space for the large GA+ and that the presence of the Cs+ prevents the formation of a GA-contained low-dimensional phase, which both assist GA+ incorporation. Upon entering the perovskite lattice, the GA+ can stabilize the lattice structure via forming strong hydrogen bonds with their neighboring halide ions. Such structure modification suppresses halide vacancy formation, thus leading to improved material properties. Compared to the GA-free perovskite reference samples, the optimal system GA0.05Cs0.15FA0.8Pb(I0.85Br0.15)3 exhibits substantially improved thermal and photothermal stability, as well as increased photocarrier lifetime. Solar cells fabricated with the optimal material system show an excellent photovoltaic performance, with the champion device reaching a power conversion efficiency of 21.3% and an open circuit voltage of 1.229 V.
关键词： DFT calculations,methylammonium-free,guanidium incorporation,hysteresis
更新于2025-09-11 14:15:04
-
Halogenated Antimonene: One‐Step Synthesis, Structural Simulation, Tunable Electronic and Photoresponse Property
摘要： Surface functionalization is considered to be an effective and versatile strategy to tailor intrinsic electronic and optoelectronic properties of 2D materials. In this work, surface-decorated few-layer antimonene is synthesized by a one-step electrochemical exfoliation and synchronous halogenation method in halogen-containing an ionic liquid–based electrolyte at room temperature. The prepared halogenated antimonene nanosheets are composed of oxygen- and halogen-decorated amorphous and crystalline domains. The structural reconstructions and evolutions of halogenated antimonene are further revealed by ab initio molecular dynamics simulations and first-principles calculations. The band structures and optical properties of antimonene can be tailored after amorphization and surface functionalization, depending on the reactivity of different halogens. The photoresponse performance of the halogenated antimonene is further evaluated by photoelectrochemical measurement. Exhibiting self-powered photoresponse behavior, their photocurrent density increases with the increases of external bias potential and light intensity. This work proposes a new idea of tuning the optoelectronic properties of 2D materials by synchronous halogenation in the facile one-step electrochemical synthesis process. Benefiting from this facile synthesis procedure, the halogenation of antimonene may shed light on chemical functionalization of other 2D materials for electronic and optoelectronic applications.
关键词： photoresponse performance,halogenation,antimonene,DFT calculations,2D materials
更新于2025-09-11 14:15:04
-
Orthorhombic WP co-catalyst coupled with electron transfer bridge UiO-66 for efficient visible-light-driven H2 evolution
摘要： The abundant transition metal phosphides co-catalysts on the earth can satisfy the sustainable and clean solar H2 production through photocatalytic water splitting, which is promising to replace the rare precious metals, such as Pt, Au, Pd, Ru and so on. In this paper, we use the temperature-programmed solid phase method to prepare WP nanoparticles. Based on the Density Functional Theory (DFT) calculations, we demonstrate that the WP nanoparticles possess outstanding electrical conductivity and excellent capability to transport electrons. WP nanoparticles are loaded onto the surface of UiO-66 via the ultrasound-assisted impregnation method to induce a highly efficient visible-light photocatalytic H2 production activity of 384 mmol in 5 h, which is 10.67 times than that of pure UiO-66. The catalytic performance is attributed to the excellent metallic conductivity and the favourable Fermi level position of WP nanoparticles. Further studies of PL, TRPL and Mott-Schottky curves, we can not only know that the modification of WP nanoparticles do improve the electron transfer ability, but also that the matched work functions between the EY and UiO-66 provides a feasible thermodynamic path for the transmission of electrons. Our work demonstrates that the earth-abundant transition metal phosphides material have the potential to construct cheaper and high catalytic performance photocatalysts.
关键词： WP,DFT calculations,H2 production,UiO-66,Metallic characteristics
更新于2025-09-11 14:15:04
-
Similarity and Specificity of Chlorophyll <i>b</i> Triplet State in Comparison to Chlorophyll <i>a</i> , as Revealed by EPR/ENDOR and DFT Calculations.
摘要： An investigation of the photoexcited triplet state of chlorophyll (Chl) b has been carried out by means of Electron Nuclear Double Resonance (ENDOR), both in frozen organic solvent and in protein environment provided by the Water-Soluble Chlorophyll Protein of Lepidium virginicum. Density functional theory (DFT) calculations have allowed the complete assignment of the observed hyperfine couplings corresponding to the methine protons and the methyl groups, leading to a complete picture of the spin density distribution of the triplet state in the tetrapyrrole macrocycle. The triplet state properties of Chl b were found to be similar in many respects to those previously reported for Chl a, although some specificities have been highlighted. Concerning the spin density distribution, the differences are manly localized on the carbon atoms close to the formyl group which, in Chl b, replaces the methyl group of Chl a.
关键词： EPR/ENDOR,triplet state,DFT calculations,Chlorophyll b,spin density distribution
更新于2025-09-11 14:15:04
-
Electronic Structures and Catalytic Activities of Niobium Oxides as Electrocatalysts in Liquid Junction Photovoltaic Devices
摘要： Two types of nanosized niobium oxides and their composite: pseudo-hexagonal Nb2O5 (TT-Nb2O5), monoclinic NbO2 (M-NbO2) and the coexistence of TT-Nb2O5 and M-NbO2 (TT-Nb2O5/M-NbO2) are successfully synthesized through the urea-metal chloride route, and they exhibit excellent catalytic activity and photovoltaic performance in dye-sensitized solar cells (DSSCs). First-principles density function theory (DFT) calculations show that their catalytic activity is significantly influenced by their intrinsic electronic structures and properties. The lone-pair 4d1 electrons of Nb4+ in M-NbO2 enhance the Nb-I interaction and promote the electron transfer from the M-NbO2 counter electrode (CE) to I, and thus resulting in superior catalytic properties in M-NbO2 based DSSCs. In addition, the adsorption energy of I on the M-NbO2 surface is in the optimal energy range of 0.3?1.2 eV, and the Fermi level of M-NbO2 is 0.6 eV, which is higher than the I3? reduction reaction (IRR) potential and I3? can be spontaneously reduced to 3I?. This work provides a general strategy for understanding the electronic structures and catalytic activities of transition metal compounds as CE catalysts for DSSCs.
关键词： electrocatalytic activity,counter electrodes,first-principles DFT calculations,dye-sensitized solar cells,niobium oxides
更新于2025-09-11 14:15:04
-
Molecular Packing and Solid-state Fluorescence of Conjugated Compounds of Carbazole-acrylonitrile Derivatives
摘要： In this review paper, have been investigated three novel crystal structures of three molecules with carbazole substituents as the electron-donor group. These molecules, 2-(phenyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile (I), 2-(3''-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile (II), and 2-(4-pyridyl)-3-(N-ethyl-(3′-carbazolyl))acrylonitrile (III) in their structure, possess the electron-donor carbazole moiety, a -CN group attached to the double bond, and a phenyl or a pyridine function at the meta- or para-position. It was revealed with the help of single crystal diffraction X-ray analysis that there exists no difference in the crystal system, because all the compounds were crystallized in monoclinic system with space group P21/c. For determining the effect of the position of the nitrogen atom substitution on the crystal properties, has been analyzed and contrasted the molecular packing in a single crystal with that of other previously reported carbazole derivatives. The double bond bearing N-ethylcarbazole,–CN, phenyl or pyridine groups was observed to impart sufficient polarity in order to show slipped π-stacking aggregation in the solid state, affecting the compounds in the solid state and consequently affecting their fluorescence properties. The substitution at the para position was reported to exhibit more multiple C-H...π interactions as well as an interesting and unexpected short contact distance between adjacent N...N molecules those brought a conformational change resulting in an edge-to-face alignment in the molecules and affecting the best relative photoluminescence efficiency of the sample.
关键词： crystal structures,aggregation,cyano-substituted,Acrylonitrile derivatives,N-carbazole-acrylonitriles photophysical properties,TD-DFT calculations,pyridine derivatives
更新于2025-09-11 14:12:44