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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 π-conjugation with the C atoms nearby along the B-doped zigzag edge. On the other hand, the electron-rich N atoms with radical characteristics weaken the conjugated bonding effects in the N-doped ZGNR. The NLO response of the ZGNR is enhanced by doping only one zigzag edge with B or N atoms. The conjugated B-doped zigzag edge takes the role of electron donor, while the N-doped zigzag edge serves as electron acceptor, giving rise to the discordant impact on the second-order NLO response of the BN-doped ZGNR.

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 βtot 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 βtot value but also to change the transition nature of electron excitations with a major contribution to the NLO response.

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 relationship between the TPA cross sections and the molecular chain length is obtained. The maximum TPA cross section increases in proportion to Nα (N denotes the number of repeat units) and the values of α depend on different molecular structures. The olefin-linked pCp oligomers, which have good transparency and large TPA cross sections, are promising candidates for TPA materials.Key words: two-photon properties, paracyclophane oligomer, AM1, ZINDO-SOS.

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, CH3, and NH2) 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 C2v symmetry exhibited the largest TPA cross-section value of 3376 × 10–50 cm4 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.

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 × 10–50 – 345.9 × 10–50 cm4·s·photon–1, which were in the same order of magnitude as the values reported in the literature. The relatively larger δ(ω) 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 S0 and S1 and the transition dipole moment between S1 and S5.Key words: two-photon absorption, ZINDO, sum-over-states, tetrabenzoporphyrin, phthalocyanines.

The semiempirical INDO calculations were carried out to investigate the charge-transfer interaction and to evaluate the second-order nonlinear susceptibilities for a series of fulleropyrrolidine–tetrathiafulvalene(C60PY–TTF) dyads, C60PY, and C60PY-(CH=CH)n-TTF (n = 0–6). The equilibrium geometries, electronic structures, and UV–vis spectra of these C60PY–TTFs D–B–A dyads were determined by using ZINDO methods. On the basis of electronic spectra, we calculated the β for the dyads using the ZINDO-SOS expression, and found that these dyads have relatively large β. The calculated values of β are 48.78, 62.34, 97.90, 123.24, 183.78, 189.43, 193.45, 195.82 × 10–30 esu for C60PY and C60PY-(CH=CH)n-TTF (n = 0–6), respectively, which shows the enhancing effect when TTF is introduced. The β significantly increases as n increases from 0–3; and it tends to be saturated in the end.Key words: ZINDO-SOS, CI, structure, spectra, C60PY–TTF.