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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 [...]

Abstract: The electronic structures and the one- and two-photon absorption (TPA) properties of two series of the olefin-linked paracyclophane (pCp) oligomers have been studied using AM1 and ZINDO-SOS methods. The [...]

The absorption and emission spectra for a series of substituted 1,3-diphenyl-5-pyrene-2-yl-4,5-dihydro-1H-pyrazole (DPPyP) molecules are computed by TDDFT methods. The solvent effect is modeled using the self-consistent reaction field (SCRF) method with Tomasi's polarized continuum model (PCM). The ground-state geometries were optimized by the Hartree-Fock method with the 6-31G basis set (and also with 3-21G * for molecule A) (HF/6-31G), and the lowest singlet excited-state geometries were optimized at the ab initio CIS level with the 6-31G basis set (CIS/6-31G). The calculated results indicate that the TDDFT method can reproduce the experimental values. We consider the effects of different basis sets on the optimization of the ground-state geometries. Specially, some insights on the differences observed for these compounds in changing the substituted donors (H, C[H.sub.3], and N[H.sub.2]) and acceptor group (CN) are given; the results indicate that introduction of the donor groups will lead emission to be red-shifted, while introduction of the acceptor will induce the emission to be blue-shifted, which provides useful information for modulating light-emitting material colors. Key words: absorption and emission, TDDFT, CIS, SCRF-PCM.

The one-photon and two-photon absorption properties of donor-acceptor substituted dehydrobenzo[18]annulenes were determined by using density functional theory and ZINDO methods. The macrocycle containing [C.sub.2v] symmetry exhibited the largest TPA cross-section value of 3376 x [10.sup.-50] [cm.sup.4] s/photon. The calculated results indicate that the TPA response in the whole molecule comes from the contribution of that in the every side in the trigon. It is notable that the magnitudes of the transition dipole moment from the virtual intermediate state to the TPA final state and the dipole moment difference between the ground state and the virtual intermediate state play important roles in increasing the TPA cross-section value. This series of molecules can circumvent the trade-off between efficiency and transparency, and they provide a promising direction for the further development of novel two-dimensional molecules with such properties. Key words: two-photon absorption, ZINDO, sum-over-states, dehydrobenzo[18] annulenes, transparency. Faisant appel a la theorie de la densite fonctionnelle ainsi qu'a. des methodes ZINDO, on a determine les proprietes d'absorption monophotonique et biphotonique de dehydrobenzo[18]annulenes substitues, des donneurs-accepteurs. Le macrocycle comportant une symetrie [C.sub.2v] exhibe la valeur la plus elevee de section droite de << TPA >>, 3376 x [10.sup.-50] [cm.sup.4] s/photon. Les resultats calcules indiquent que la reponse de TPA dans une molecule complete provient de la contribution de ce qu'on retrouve dans l'aire trigonale. Il est a noter que les amplitudes de la transition du moment dipolaire de l'etat intermediaire virtuel a l'etat final de TPA ainsi que la difference de moment dipolaire entre l'etat fondamental et l'etat intermediaire virtuel jouent des roles importants dans l'augmentation de la valeur de la section droite de la TPA. Les molecules de cette serie permettent de contourner le compromis entre l'efficacite et la transparence et elles s'averent etre une direction de choix pour le developpement ulterieur de nouvelles molecules bidimensionnelles ayant de telles proprietes. Mots cles : absorption biphotonique, ZINDO, somme sur l'ensemble des etats, dehydrobenzo[18]annulenes, transparence. [Traduit par la Redaction]

The one-photon absorption (OPA) properties of tetrabenzoporphyrins (TBPs) and phthalocyanines (Pcs) were studied using the semiempirical ZINDO method and time-dependent density functional theory (TDDFT), respectively. The compared results confirmed that the semiempirical ZINDO method was reasonably reliable when calculating the OPA of tetrabenzoporphyrins and phthalocyanines. On the basis of the OPA properties obtained from the ZINDO method, two-photon absorption (TPA) properties of two series of molecules were investigated, using ZINDO and sum-over-states (SOS) methods. The results showed that the TPA cross-sections of all molecules were in the range of 220.6 x [10.sup.-50] - 345.9 x [10.sup.-50] [cm.sup.4]*s*[photon.sup.-1] which were in the same order of magnitude as the values reported in the literature. The relatively larger [delta]([omega]) value for Pcs with respect to that for corresponding TBPs originates from larger intramolecular charge transfer, which can be characterized by the difference of dipole moment between [S.sub.0] and [S.sub.1] and the transition dipole moment between [S.sub.1] and [S.sub.5]. Key words: two-photon absorption, ZINDO, sum-over-states, tetrabenzoporphyrin, phthalocyanines. On a etudie les proprietes d'absorption monophotoniques ([??] OPA [??]) de tetrabenzoporphyrines (TBPs) et de phtalocyanines (Pcs) a l'aide de la methode semi-empirique ZINDO et de la theorie fonctionnelle de la densite dependante du temps ([??] TDDFT [??]). Une comparaison des resultats confirme que pour le calcul des [??] OPA [??] des tetrabenzoporphyrines et des phtalocyanines, la methode semi-empirique ZINDO donne des valeurs raisonnablement fiables. Sur la base des " OPA " obtenus par la methode ZINDO, on a etudie les proprietes d'absorption biphotoniques ([??] TPA [??]) de deux series de molecules ont ete etudiees a l'aide des methodes ZINDO et de la somme de tous les etats ([??] SOS [??]). Les resultats montrent que les sections droites des " TPA " de routes les molecules se situent dans la fourchette 220,6 x [10.sup.-50] a 345,9 x [10.sup.-50] [cm.sup.4]*s*[photon.sup.-1], valeurs qui sont du meme ordre de grandeur que celles rapportees dans la litterature. La valeur de [delta]([omega]) relativement plus elevee pour les Pcs par rapport aux THBs resulte d'un plus grand transfert de charge qui peut etre caracterise par la difference entre les moments dipolaires [S.sub.0] et [S.sub.1] et le moment dipolaire de transition entre [S.sub.1] et [S.sub.5]. Mots cles : absorption biphotonique, ZINDO, somme de tous les etats, tetrabenzoporphyrine, phtalocyanine. [Traduit par la Redaction]