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

Abstract

Pure carbon-based nanomaterials with good π conjugation and thermal stability, e.g., nanotubes and nanoribbons, have long served as promising conjugated materials for application in second-order nonlinear-optical (NLO) devices but suffer from two inherent structural problems: weak polarity (or even nonpolarity) and high chemical reactivity ascribed to zigzag edge states. In the present work, boron nitride (BN) chains are used to divide carbon nanotubes and nanoribbons, forming a functional block to tune the electronic structure, and thus induce charge redistribution or modify the molecular energy gap for second-order NLO materials or integrated electronic materials. A balance between the electronic kinetic stability and second-order NLO properties is established by structural manipulation. The strong second-order NLO responses in the visible and near-infrared regions make these hybridized carbon-based molecules potential NLO materials for applications in biological nonlinear optics. The application of BN to tune the electronic structure of carbon nanomaterials paves a path for fabricating nanoelectronic and nano-NLO devices.

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

“…[98] Recently, BN-chains are utilized as a novel form to separate the π conjugation of carbon nanotubes and nanoribbons (Figure 7a) with the expectation to achieve strong NLO response by forming multiple individual functional NLO modules. [87] The insertion of BN-chains into carbon nanotubes and nanoribbons leads to large HOMO-LUMO energy gap and induces charge redistribution as compared with their pristine carbon counterparts. The electronic spectra of these BN-chains doped systems have low-lying dipole-allowed electron excitation in the visible region.…”

“…[87] Remarkably, some MOs involved in the major electron excitations indicate that the BN-chains in armchair systems serve as potential valley to separate and form independent carbon π-conjugations (Figure 8), and then the partial π-conjugation of BN-chains with their connected C atoms generates a synergistic effect to bring about large < β 0 > /N in compounds 13 a and 13 b. [87] In zigzag systems, the BNchains serve to separate the carbon π-conjugations, resulting in significantly polarized carbon π-conjugations localized at one end of carbon nanotubes and nanoribbons, and the conspicuous CT based excitations from one end to the other end of nanotube and nanoribbon (e. g. from the HOMO to the LUMO in Figure 8) lead to the strong second order NLO responses of compounds 14 a and 14 b. [87] In summary, different doping patterns of BN in NGs (such as h-BN nanoribbons, BN-chains, B 3 N 3 , N!B dative bond, B/N atoms, NBN and BNB) have diverse influences on the NLO properties of those doped molecules.…”

“…[87] In zigzag systems, the BNchains serve to separate the carbon π-conjugations, resulting in significantly polarized carbon π-conjugations localized at one end of carbon nanotubes and nanoribbons, and the conspicuous CT based excitations from one end to the other end of nanotube and nanoribbon (e. g. from the HOMO to the LUMO in Figure 8) lead to the strong second order NLO responses of compounds 14 a and 14 b. [87] In summary, different doping patterns of BN in NGs (such as h-BN nanoribbons, BN-chains, B 3 N 3 , N!B dative bond, B/N atoms, NBN and BNB) have diverse influences on the NLO properties of those doped molecules. Besides serving as inherent electronic structure modulator (e. g., inducing polarity or charge redistribution), B/N/NBN/BNB can be utilized as spin eliminator, and BN-chains act as electro-potential trench separating the carbon π-conjugation.…”

“…[18] The incorporation of carbonyl (CO) group at the edges of compound 15 a produces a relatively large HOMO-LUMO energy gap as well as enhanced polarity (Figure 5a and Table 1). [82] CO groups also stabilize or eliminate the edge states resulting in good π-electron conjugation as observed in the HOMO of compound 15 a and maintaining strong second order [87] with the permission from American Chemical Society. Black is carbon, magenta is boron, and green is nitrogen atom.…”

“… (a) Structures of B or (and) N‐doped triangulenes, carbon nanotubes and graphene nanoribbons [25b,87] . (b) The natural atomic spin distributions, and proposed doping sites (marked by red dots) for spin elimination in TG7 through a combination of configurations analyzed by using the Clar rule [25b] .…”