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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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Enhancement of attosecond pulse in water window region by using pump-probe approach
摘要： An effective scheme to enhance the harmonic yield and the attosecond (as) pulse signal from H+2 has been proposed by using the pump-probe laser field. It is found that with the help of the multi-cycle pump pulse, H+2 can be steered into the resonance ionization regions, where the ionization probability can be remarkably enhanced. Thus, the harmonic yield can be remarkably enhanced when a sequential mid-infrared probe pulse is added. Further, by modulating the phase of the probe pulse and by adding a controlling pulse, the harmonic cutoff can be extended up to the water window region. Finally, by the Fourier transformation of the selected harmonics on the harmonic supercontinuum, the water window attosecond pulses as short as 25 as can be obtained.
关键词： High-order harmonic generation,pump-probe pulse,charge resonance enhanced ionization,single attosecond pulse,harmonic enhancement
更新于2025-09-23 15:21:21
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Aromatic Charge Resonance Interaction Probed by Infrared Spectroscopy
摘要： Charge resonance is a strong attractive intermolecular force in aromatic dimer radical ions. For cations, this stabilization arises from sharing a positive charge between two identical or different molecules (A2 + or AB+) with comparable ionization energies within the π-stacked dimer. Despite its importance, this fundamental interaction has not been characterized at high resolution by spectroscopy of isolated dimers. Herein, we employ vibrational infrared spectroscopy of cold aromatic pyrrole dimer cations to precisely probe the charge distribution by measuring the frequency of the isolated NH stretch mode (νNH). We observe a linear correlation between νNH and the partial charge q on the pyrrole molecule in different environments. Subtle effects of symmetry reduction, such as substitution of functional groups (here pyrrole → N-methylpyrrole) or asymmetric solvation (here by an inert N2 ligand), sensitively shifts the charge distribution toward the moiety with lower ionization energy. This general approach provides a precise experimental probe of the asymmetry of the charge distribution in such aromatic homo- and heterodimer cations.
关键词： charge resonance,IR spectroscopy,cations,structure elucidation,arenes
更新于2025-09-10 09:29:36