Franck-Condon processes in pentacene monolayers revealed in resonance Raman scattering

He, Rui; Tassi, Nancy G.; Blanchet, Graciela B.; Pinczuk, A.

doi:10.1103/physrevb.83.115452

Cited by 13 publications

(3 citation statements)

References 24 publications

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“…In this case, the quantum process associated with the creation (or destruction) of quanta of vibrational energy is not considered explicitly [10]. The semiclassical model has been very useful to explain Raman intensities in molecules [13,14], and provides the most common picture to represent the Raman scattering process.…”

Section: Discussionmentioning

confidence: 99%

Raman excitation profile of theGband in single-chirality carbon nanotubes

et al. 2014

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We present in this work measurements of the Raman excitation profile of the high-energy phonons (G band) in single-chirality (n,m) semiconducting single-wall carbon nanotubes using more than 70 laser excitation energies, and a theoretical description based on the third-order quantum model for Raman scattering. We show that the observed asymmetry in the G band Raman excitation profile is rigorously explained by considering all physical elements associated with Raman scattering in (n,m) carbon nanotubes, such as the existence of van Hove singularities in the electronic density of states and wave-vector dependence of the matrix elements of the Raman process. We conclude that the proposed violation of the Condon approximation is not a fundamental principle underlying the nanotube photophysics.

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Section: Discussionmentioning

confidence: 99%

Raman excitation profile of theGband in single-chirality carbon nanotubes

et al. 2014

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“…This resonance Raman scattering creates an important avenue to studies of band/excitonic excitations in diverse nanomaterials. [34][35][36][37] It also offers unique insight into multiphonon process due to the relaxation of selection rules and a huge amplification of Raman intensity under the resonance condition. Fortunately, the direct gaps of all the above MX 2 bulk crystals and few-layer flakes ($1.5 eV-2.5 eV) 38 overlap the photon energies of visible light, which enables our studies of resonance Raman scattering in these materials by using visible laser excitations.…”

Section: Introductionmentioning

confidence: 99%

Resonance Raman scattering in bulk 2H-MX₂ (M = Mo, W; X = S, Se) and monolayer MoS₂

Fan¹,

Gao

Zhang

et al. 2014

Journal of Applied Physics

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We have performed a comparative study of resonance Raman scattering in transition-metal dichalcogenides 2H-MX 2 semiconductors (M ¼ Mo, W; X ¼ S, Se) and single-layer MoS 2. Raman spectra were collected using excitation wavelengths 633 nm (1.96 eV), 594 nm (2.09 eV), 532 nm (2.33 eV), 514 nm (2.41 eV), and 488 nm (2.54 eV). In bulk-MoS 2 and WS 2 , the resonant energies appear to coincide with their exciton excitations. The resonance can be fine tuned by varying sample temperatures, which confirms its excitonic origin in both MoS 2 and WS 2. Temperature dependence of Raman intensities is analyzed in the context of resonance Raman theory, which agrees well with the existing absorption data. While in WSe 2 , the resonance has been observed in a wider range of excitations from 633 to 514 nm, which cannot be explained with its excitonic energies of 1.6 and 2.0 eV. It is considered that additional excitonic bands induced by band splitting are involved in the inter-band transitions and substantially extend the resonance energy range. The Raman resonance energy range remains unchanged in single-layer MoS 2 compared with that in the bulk sample. However, most phonon modes in single-layer MoS 2 are significantly broadened or strongly suppressed under resonance conditions. This change could be related to the modification of acoustic modes by the substrate. V

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“…The second lowest energy exciton state (S 2 ) is calculated to be 0.15 eV higher in energy and is optically dark (with zero oscillator strength). Therefore, when the Raman pump is tuned to the red edge of the lowest energy exciton, only one electronic potential energy surface dictates the motion of the vibrational wavepacket and interference effects which have been shown to arise due to overlapping electronic resonances may be negligible Figure indicates that the manifold of closely spaced exciton states (S n ) blue of the lowest energy exciton (S 1 ) accounts for the lack of mirror image symmetry of the absorption and emission.…”

Section: Resultsmentioning

confidence: 99%

Resonance Raman Characterization of Tetracene Monomer and Nanocrystals: Excited State Lattice Distortions With Implications For Efficient Singlet Fission

et al. 2019

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The characterization of specific phonon modes and exciton states that lead to efficient singlet fission (SF) may be instrumental in the design of the next generation of highefficiency photovoltaic devices. To this end, we analyze the absolute resonance Raman (RR) cross sections for tetracene (Tc) both as a monomer in solution and as a crystalline solid in an aqueous suspension of nanocrystals. For both systems, a time-dependent wavepacket model is developed that is consistent with the absolute RR cross sections, the magnitude of the absorption cross sections, and the vibronic line shapes of the fluorescence. In the monomer, the intramolecular reorganization energy is between 1500 and 1800 cm −1 and the solvent reorganization energy is 70 cm −1 . In nanocrystals, the total reorganization is diminished to less than 600 cm −1 . The lowest energy exciton has an estimated intramolecular reorganization energy between 300 and 500 cm −1 while intermolecular librational phonons have a reorganization energy of about 130 cm −1 . The diminished reorganization energy of the nanocrystal is interpreted in the context of the delocalization of the band-edge exciton onto about ∼7 molecules. When electron and electron−hole correlations are included within many-body perturbation theory, the polarized absorption spectra of crystalline Tc are calculated and found to be in agreement with experiment. The low-lying exciton states and optically active phonons that contribute to the polarized crystal absorption are identified. The likely role of coherent exciton phonon evolution in the SF process is discussed.

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Franck-Condon processes in pentacene monolayers revealed in resonance Raman scattering

Cited by 13 publications

References 24 publications

Raman excitation profile of theGband in single-chirality carbon nanotubes

Raman excitation profile of theGband in single-chirality carbon nanotubes

Resonance Raman scattering in bulk 2H-MX₂ (M = Mo, W; X = S, Se) and monolayer MoS₂

Resonance Raman Characterization of Tetracene Monomer and Nanocrystals: Excited State Lattice Distortions With Implications For Efficient Singlet Fission

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Franck-Condon processes in pentacene monolayers revealed in resonance Raman scattering

Cited by 13 publications

References 24 publications

Raman excitation profile of theGband in single-chirality carbon nanotubes

Raman excitation profile of theGband in single-chirality carbon nanotubes

Resonance Raman scattering in bulk 2H-MX2 (M = Mo, W; X = S, Se) and monolayer MoS2

Resonance Raman Characterization of Tetracene Monomer and Nanocrystals: Excited State Lattice Distortions With Implications For Efficient Singlet Fission

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Product

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Resonance Raman scattering in bulk 2H-MX₂ (M = Mo, W; X = S, Se) and monolayer MoS₂