Tuning the edge states in X-type carbon based molecules for applications in nonlinear optics

Abstract

Novel carbon based “X-type” graphene nanoribbons (GNRs) with azulenes were designed for applications in nonlinear optics in the present work, and the second order nonlinear optical (NLO) properties of those...

BN-Doped Carbon Nanotubes and Nanoribbons as Nonlinear-Optical Functional Materials for Application in Second-Order Nonlinear Optics

“…The sum-over-states (SOS) model , is used for calculation of the NLO properties including static first hyperpolarizability (⟨β 0 ⟩) and 2D second-order NLO spectra (only the electronic contribution), and the advantage of such a model is interpretation of the NLO properties in terms of contributions from electron excitations. The consistency of the predicted NLO properties with other methods or models, e.g., finite field, − random-phase approximation, , and couple-perturbed models, gives confidence in the NLO property predictions of those carbon-based molecules using the SOS model. In the present work, the orientation-averaged first hyperpolarizabilities (⟨β⟩) in eq are predicted through ⟨β⟩ = (β x r x + β y r y + β z r z )/( r x 2 + r y 2 + r z 2 ) 1/2 and β i = β iii + [β ijj + β jij + β jji + β ikk + β kik + β kki ]/3 ( i , j , k ∈ [ x , y , z ]) using the LinSOSProNLO program , based on the SOS model.…”

Electronic Structure Modulation of Nanographenes for Second Order Nonlinear Optical Molecular Materials

“…[82] Such enhancement of the < β 0 > could be attributed to the significant CT based excitation in the electron excitations from 3.50 eV to 5.00 eV in compound 15 c in comparison with that in compound 15 b, in which NH 2 acts an electron donating group while NO 2 group functions as an electron withdrawing group and participate in the π-electron conjugation of high-lying unoccupied molecular orbitals involved in the CT based electron excitations. [82] The two-dimensional second order NLO spectra of those NGs, e. g. electronic SFG and DFG, confers these azulene-based NGs promising potential applications in studying molecular structure and charging at interfaces, light modulation and nonlinear nanophotonic devices. [99] The structural manipulation of Y-type and X-type NGs presents an opportunity to obtain novel multi-dendritic NLO molecular materials.…”

“…In addition to solely incorporating topologic defects or heteroatoms, introducing heteroatoms into azulene-based NGs offers an effective strategy to further enhance the second order NLO responses. [18,82,86,88,89] Functional group introduced at the end of azulene of NGs can enhance the second order NLO responses of NGs. For instance, a cyano group (À CN) is introduced as an electron withdrawing group locating at one end of azulene in compound 2 (compound 2-CN in Figure 9a), which not only breaks the degeneracy of the two-fold degenerate electron excitations but also lowers the excitation energy of one electron excitation with a dominant contribution to the < β 0 > of compound 2-CN, and eliminates the negative contribution of one of the degenerate electron excitations to the NLO response thus leading to much larger < β 0 > /N in compound 2-CN (Figure 9b).…”

“…Electronic spectra analyses of these B,N-doped NGs demonstrate a significant redshift of the lowest dipole-allowed electron excitation and decrease of the HOMO-LUMO energy gap compared with compound 17. [89] It is also found that the replacement of the C atoms in coronene and azulene moieties of compound 17 with B and N has a conspicuous impact on the second order NLO responses, and this could be ascribed to the [18,82] (b) Evolution of the static first hyperpolarizability (< β 0 >) with the electron excitation in compounds 2 and 2-CN, and the transition nature of the electron excitation with major contributions to the < β 0 > of compound 2-CN. [18] (c) Frontier MOs (H: HOMO; L: LUMO) of compounds 3 and 15 a.…”

“…[18] The remove or reverse of the negative contribution to < β 0 > of one of the two-fold degenerate electron excitations through symmetry breaking and charge polarization is very important for enhancing the second order NLO properties of those Y-type systems. [18] For X-type molecules, compound 3 (Figure 3) has narrowed HOMO-LUMO energy gap and spin-polarized edge states at the zigzag edges, [82] and such localized edge states in zigzag edged NGs possibly obstruct its synthesis, isolation, and application. [84] The elimination or stabilization of the edge states in ZNGs is imperative.…”