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Spin density encodes intramolecular singlet exciton fission in pentacene dimers
摘要： The formation of two triplet excitons at the cost of one photon via singlet exciton fission in organic semiconductors can potentially enhance the photocurrent in photovoltaic devices. However, the role of spin density distribution in driving this photophysical process has been unclear until now. Here we present the significance of electronic spin density distribution in facilitating efficient intramolecular singlet exciton fission (iSEF) in π-bridged pentacene dimers. We synthetically modulate the spin density distribution in a series of pentacene dimers using phenyl-, thienyl- and selenyl- flanked diketopyrrolopyrrole (DPP) derivatives as π-bridges. Using femtosecond transient absorption spectroscopy, we find that efficient iSEF is only observed for the phenyl-derivative in ~2.4 ps while absent in the other two dimers. Electronic structure calculations reveal that phenyl-DPP bridge localizes α- and β-spin densities on distinct terminal pentacenes. Upon photoexcitation, a spin exchange mechanism enables iSEF from a singlet state which has an innate triplet pair character.
关键词： spin density,pentacene dimers,charge resonance,intramolecular,singlet exciton fission
更新于2025-09-23 15:23:52
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Electronic and Magnetic Properties of Transition-Metal-Doped WS? Monolayer; First-Principles Investigations
摘要： The electronic structures and magnetic properties of the transition-metal (TM)-doped WS2 monolayers are investigated by using the first-principles calculations within the density functional theory. The W atoms of the pristine WS2 monolayer are partially replaced by the 3d TMs of Mn, Fe, Co, and Cu with the impurity concentration of about 4%. For the uniformly distributed doping, the ferromagnetic phases are found to be stabilized with the total spin magnetic moments of 1.00, 2.00, 3.00, and 1.00 μB for the Mn-, Fe-, Co-, and Cu-doping, respectively, where not only the spin moments of the TM dopants but also the induced spin moments of the W and S atoms contribute significantly depending on the dopant type as well as on the relaxation. All systems are found to be half-metallic with the spin gap of 0.10–0.53 eV. Among them, the biggest spin gap is found for the doping of Co which is the ingredient of the well-known half-metallic Heusler alloys. When the TM dopants were brought closer keeping the same impurity concentration, the preference of the substitutional doping site and the magnetic phase is changed sensitively depending on the type of doping and the interatomic distance between the TM dopants.
关键词： spin density,transition-metal (TM) dopant,Magnetic state,WS2 monolayer.
更新于2025-09-23 15:22:29
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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
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Electronic Structures of Hydrogen Functionalized Fullerenes: Density Functional Theory (DFT) Study
摘要： In this work, the electronic structures and formation mechanism of hydrogen-functionalized fullerene were investigated by means of density functional theory. The mechanism of the addition of a hydrogen atom to the fullerene surface was mainly investigated. Both pure and boron-nitrogen-substituted fullerenes (denoted by C60 and BNC58, respectively) were examined. We found that the addition of hydrogen atom to B (boron atom) and C (carbon atom) sites of BNC58 proceeded without an activation barrier, whereas the hydrogenation of N (nitrogen atom) sites required activation energy. The electronic states of hydrogen-functionalized C60 and BNC58 are discussed on the basis of these theoretical results.
关键词： Potential Energy Curve,BN-Fullerene,Hyperfine Coupling Constant,Spin Density,Interstellar Reaction
更新于2025-09-04 15:30:14