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Push–pull π-conjugated molecules are one of the paradigms of second order nonlinear optical (NLO) materials and have been extensively explored. However, high-performance second order NLO materials with an optimum electron donor (D), π-bridge (π) and acceptor (A) under this paradigm are still the most sought-after. In the present work, D–π–A molecules with optimal D, π and A combination for strong second order NLO properties are proposed based on molecular orbital theories. The optimal D–π–A push–pull molecule achieves an unprecedentedly strong NLO response under the D–π–A paradigm, i.e., the static first hyperpolarizability reaches −453.92 × 10−30 esu per heavy atom using azulene as part of the π-bridge and acceptor to synergistically reinforce the strength of the acceptor. The protocols of D–π–A NLO molecule design through frontier molecular orbital matching of D, π and A with optimal combination of electron donating and accepting strengths shed light on future molecular NLO materials exploration. The simulated two-dimensional second order spectra provide useful information (e.g., sum frequency generation) on the applications of those D–π–A push–pull molecules in nonlinear optics. [ABSTRACT FROM AUTHOR]

Abstract: The electronic properties and second-order nonlinear optical (NLO) responses of B/N-doped zigzag graphene nanoribbon (ZGNR) have been investigated using quantum chemistry methods. The electron-deficient B atoms prefer to form [...]

From the same piece of finite size graphene (F-graphene) sheet through different directions (zigzag edge or armchair edge), (4, 4) and (8, 0) carbon nanotube clips form. The electronic properties of the intermediate structures in the two rolling processes 44 (zigzag) and 80 (armchair) have been investigated using quantum chemistry method. The magnetism of the F-graphene sheet disappears with the rolling operation in 44, while it is maintained throughout the whole rolling operation in 80. Furthermore, the highest occupied molecular orbital (HOMO) α and HOMO β gradually extend to the whole framework from the zigzag edges with the rolling operation in 44, and they gradually localize to the lower and upper half of the framework in 80. Oxygen passivation along the opening of the intermediate structures effectively improves the nonlinear optical (NLO) response of the intermediate structures in both the zigzag and the armchair processes. Oxygen passivation along the armchair opening in 80 enhances the [β.sub.tot] value, yet does not bring essential changes to the electron transitions contributed to the NLO response. Oxygen passivation along the zigzag opening in 44 is able not only to enhance the [β.sub.tot] value but also to change the transition nature of electron excitations with a major contribution to the NLO response. Key words: rolling graphene to carbon nanotube, electronic properties, magnetic properties, nonlinear optical responses. Resume : Un meme feuillet de graphene de taille finie (graphene F) s'enroule dans differents sens (bordures de type << zigzag >> ou de type << fauteuil >>) pour former un nanotube de carbone soit de structure (4,4) ou de structure (8,0). Nous avons etudie au moyen d'une methode quantique les proprietes electroniques des structures intermediaires au cours des deux processus d'enroulement, soit le processus 44 (zigzag) et le processus 80 (fauteuil). Le magnetisme du feuillet de graphene F disparait lors du processus d'enroulement 44, alors qu'il se maintient pendant tout le processus d'enroulement 80. Par ailleurs, lors du processus d'enroulement 44, les orbitales moleculaires les plus hautes occupees HOMO α et HOMO β s'etendent progressivement a toute la structure a partir des bordures en zigzag, tandis que lors du processus 80, elles se localisent progressivement dans les moities inferieure et superieure de la structure. Le long de la bordure ouverte des structures intermediaires, la passivation par l'oxygene ameliore efficacement la reponse optique non lineaire de celles-ci lors des deux processus d'enroulement (en zigzag et en fauteuil). Lors du processus d'enroulement 80, la passivation par l'oxygene le long de la bordure ouverte de configuration de type fauteuil fait augmenter la valeur [β.sub.tot], sans toutefois occasionner de variations importantes des transitions electroniques qui contribuent a la reponse optique non lineaire. Lors du processus d'enroulement 44, la passivation par l'oxygene le long de la bordure ouverte de configuration zigzag non seulement fait augmenter la valeur [β.sub.tot], mais modifie aussi la nature de la transition des excitations electroniques qui contribuent largement fi la reponse optique non lineaire. [Traduit par la Redaction] Mots-cles : enroulement du graphene en nanotube de carbone, proprietes electroniques, proprietes magnetiques, reponses optiques non lineaires., Introduction Because of its exotic electrical properties and chemical tunability, graphene has been the object of extensive scientific research in both experiments and theory. (1-3) Theoretically, graphene is the starting [...]

Based on the successful achievement of graphene-C60 single-molecule transistors in experiments, a series of double-layered GNR-C60, X/GNR-C60 (GNR = graphene nanoribbon; X = H, O, S, passivated edge atoms) devices were designed and their transport properties investigated by means of density functional theory (DFT) and nonequilibrium Green's function (NEGF) methods. The overall conductivity followed the sequence: H/GNR-C60 > S/GNR-C60 > O/GNR-C60, exactly opposite to the electronegativity order of O > S > H. All the X/GNR-C60 (X = H, O, S) devices presented a multiple negative differential resistance (NDR) feature within the considered bias range of 0.0–1.4 V. The magnitude, position, and number of NDR peaks were remarkably influenced by the passivated edges, electrode linkages, interactions between the upper and lower GNRs, and applied voltage. C60, as a medium, had a blocking action at low bias for all H/GNR-C60 devices, and the NDR character originated from the crossing of the frontier molecular orbitals (FMOs), while it behaved as a conductor at high bias, and the NDR behavior was still derived from the change in FMO distributions along the scatter region. C60 always acted as a blocking body in both O/GNR-C60 and S/GNR-C60 devices at any applied voltage, and their NDR peaks also stemmed from the crossing of the FMOs. In addition, which channel to be mainly used depended on the synergistic effect of the applied bias and connecting positions of the electrodes. All these fascinating properties suggest the materials potential applications in the field of nano-electronic devices. [ABSTRACT FROM AUTHOR]