Optical Properties and Charge-Transfer Excitations in Edge-Functionalized All-Graphene Nanojunctions

Cocchi, Caterina; Prezzi, Deborah; Ruini, Alice; Caldas, M. J.; Molinari, Elisa

doi:10.1021/jz200472a

Cited by 50 publications

(60 citation statements)

References 37 publications

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“…Minor effects on the excitation energies and oscillator strengths in line with previous works [36][37][38] are discussed in the Supporting Information (see Figure S6 and Table S1). The character and spatial distribution of the electron-hole pairs are obtained from the analysis of the hole and electron densities, which for the λ th excitation are defined as 39,40…”

Section: Theoretical Background and Computational Detailsmentioning

confidence: 99%

Electronic and Optical Properties of Oligothiophene-F4TCNQ Charge-Transfer Complexes: The Role of the Donor Conjugation Length

Valencia

Cocchi

2019

J. Phys. Chem. C

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We investigate from first-principles many-body theory the role of the donor conjugation length in doped organic semiconductors forming charge-transfer complexes (CTCs) exhibiting partial charge transfer. We consider oligothiophenes (nT) with an even number of rings ranging from four to ten, doped by the strong acceptor 2,3,5,6tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ). The decrease of the electronic gaps upon increasing nT size is driven by the reduction of the ionization energy with the electron affinity remaining almost constant. The optical gaps exhibit a different trend, being at approximately the same energy regardless of the donor length. The first excitation retains the same oscillator strength and Frenkel-like character in all systems. While in 4T-F4TCNQ also higher-energy excitations preserve this nature, in CTCs with longer nT oligomers charge-transfer excitations and Frenkel excitons localized on the donor appear above the absorption onset. Our results offer important insight into the structure-property relations of CTCs, thus contributing to a deeper understanding of doped organic semiconductors.

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Section: Theoretical Background and Computational Detailsmentioning

confidence: 99%

Electronic and Optical Properties of Oligothiophene-F4TCNQ Charge-Transfer Complexes: The Role of the Donor Conjugation Length

Valencia

Cocchi

2019

J. Phys. Chem. C

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“…While further studies would be needed to clarify this point, we note that in these cases the Br is replaced with chains and dyes. Both Br and the chosen dyes have an electron-withdrawing character, and the dyes present electronic states close to the GNR gap and vibrational states in the same energy region: all of this can impact the intrinsic electronic and optical properties of the ribbon itself [30,76,77] and influence the coupling with vibrations in resonant regime. Moreover, the random functionalization pattern can induce localization of the electronic states further influencing the coupling with the vibrations.…”

Section: G Peak Dispersionmentioning

confidence: 99%

Multiwavelength Raman spectroscopy of ultranarrow nanoribbons made by solution-mediated bottom-up approach

et al. 2019

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Here we present a combined experimental and theoretical study of graphene nanoribbons (GNRs), where detailed multi-wavelength Raman measurements are integrated by accurate ab initio simulations. Our study covers several ultra-narrow GNRs, obtained by means of solution-based bottom-up synthetic approach, allowing to rationalize the effect of edge morphology, position and type of functional groups as well as the length on the GNR Raman spectrum. We show that the low-energy region, especially in presence of bulky functional groups is populated by several modes, and a single radial breathing-like mode cannot be identified. In the Raman optical region, we find that, except for the fully-brominated case, all GNRs functionalized at the edges with different side groups show a characteristic dispersion of the D peak (8-22 cm −1 /eV). This has been attributed to the internal degrees of freedom of these functional groups, which act as dispersion-activating defects. The G peak shows small to negligible dispersion in most of the cases, with larger values only in presence of poor control of the edges functionalization, exceeding the values reported for highly defected graphene. In conclusion, we have shown that the characteristic dispersion of the G and D peaks offer further insight on the GNR structure and functionalization, by making Raman spectroscopy an important tool for the characterization of GNRs. PACS numbers: 73.22.Pr, 78.30.Ly, 71.15.Mb

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“…Graphene edges have been studied intensively since the first interest in graphitic nanomaterials and graphene [1][2][3][4][5][6][7][8][9] . As recently shown, the precise edge termination of graphene nanoribbons and flakes has a significant effect on the material properties [10][11][12][13] . The graphene honeycomb lattice can be cut along two primary directions, the <1100> and the <2110>, creating so-called armchair and zigzag/Klein edges respectively (see Fig.1).…”

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confidence: 94%

Stable hydrogenated graphene edge types: Normal and reconstructed Klein edges

et al. 2013

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International audienceHydrogenated graphene edges are assumed to be either armchair, zigzag or a combination of the two. We show that the zigzag is not the most stable fully hydrogenated structure along the <2-1-10> direction. Instead hydrogenated Klein and reconstructed Klein based edges are found to be energetically more favourable, with stabilities approaching that of armchair edges. These new structures "unify" graphene edge topology, the most stable flat hydrogenated graphene edges always consisting of pairwise bonded C2H4 edge groups, irrespective the edge orientation. When edge rippling is included, CH3 edge groups are most stable. These new fundamental hydrogen terminated edges have important implications for graphene edge imaging and spectroscopy, as well as mechanisms for graphene growth, nanotube cutting, and nanoribbon formation and behaviour

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Optical Properties and Charge-Transfer Excitations in Edge-Functionalized All-Graphene Nanojunctions

Cited by 50 publications

References 37 publications

Electronic and Optical Properties of Oligothiophene-F4TCNQ Charge-Transfer Complexes: The Role of the Donor Conjugation Length

Electronic and Optical Properties of Oligothiophene-F4TCNQ Charge-Transfer Complexes: The Role of the Donor Conjugation Length

Multiwavelength Raman spectroscopy of ultranarrow nanoribbons made by solution-mediated bottom-up approach

Stable hydrogenated graphene edge types: Normal and reconstructed Klein edges

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