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In this work, novel alternative graphene-like hybrids covalent with porphyrin (porphyrin-graphene-like hybrids) are designed, named TPP-gra(n)-a and TPP-gra(n)-b (n = 1–5), respectively. Moreover, the differences in their electronic structures, one-photon absorption (OPA) and two-photon absorption (TPA) properties are revealed by theoretical chemistry calculations. Our study shows that the rearrangement of carbon-atom layers of the hybrids can effectively enhance electronic delocalization, bringing about outstanding TPA properties. In addition to the increase of the graphene-like size, substituting porphyrin into different active-carbon of graphene-like molecules can cause better polarization of TPP-gra(n)-b series than TPP-gra(n)-a series, resulting in TPP-gra(n)-b series possess relatively higher TPA cross sections ( δ TPA ) than that of corresponding TPP-gra(n)-a compounds, such as TPP-gra3-b, TPP-gra4-b and TPP-gra5-b, whose δ TPA can be as large as 5686.2–19496.6 GM ranging from 535.8 to 579.4 nm. The carbon-based materials possessing relatively high δ TPA values have a great potential for applications in optoelectronic devices and optical limiting fields. Consequently, we expect the calculations can provide a theoretical perspective for further studies on TPA materials based on graphene.

Density functional theory (DFT) and time-dependent DFT (TD-DFT) were used to calculate the properties of the carbazole dyes TYZ-1 to TYZ-5, which differed in their π-spacers. The carbazole dyes TYZ-6 and TYZ-7 were then designed; these were based on TYZ-3 (which had 2,2′:5′,2″-terthiophene as its π-spacer) but had more strongly electron-withdrawing second acceptor groups than TYZ-3. All of these dyes except for TYZ-5 presented quasi-planar conformations, and the calculated energies of their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) molecular orbitals as well as their HOMO-LUMO gaps (Eg) suggest that these dyes are suitable for use as sensitizers. Lengthening the π-spacer and increasing its degree of conjugation were found to cause the absorption spectrum of the dye to redshift and to facilitate hole injection. The Eg values of TYZ-6 and TYZ-7 were calculated to be smaller than that of TYZ-3 due to the weaker electron-withdrawing power of the second acceptor group in TYZ-3, and the dyes TYZ-2, TYZ-3, TYZ-6, and TYZ-7 presented the smallest Eg values. Local electron excitations following UV-vis absorption led to electronic transitions, particularly HOMO to LUMO transitions (> 94.3% of all transitions). The excited states of these dyes were found to have quasi-planar conformations, although their dihedral angles were smaller than those in the corresponding ground states. The Stokes Shifts calculated for the seven dyes (which ranged from 51.9 to 98.1 nm) suggested that self-absorption was unlikely to occur. Overall, the calculations indicated that the dyes TYZ-2, TYZ-3, TYZ-6, and TYZ-7 are promising candidates for use in dye-sensitized solar cells.

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 photophysical properties of six isomeric Ir(III) complexes with different N-heterocyclic naphthyridine ligands were investigated by density functional theory (DFT) and time dependent DFT (TD-DFT) approach. The radiative transition rates (kr) were determined through calculated the spin–orbital coupling (SOC) matrix elements T m H SOC S n and the energy levels (ESn and ETm). The non-radiative transition rates (knr) were estimated through analysis of the structural distortions, the d-orbital splittings and the energy differences between the S0 and T1 states ΔE(T1 − S0). As the results, the ESn, the ETm and the energy splittings Δ E S 1 - T m and Δ E T m - T m - 1 can be regulated by the position of two nitrogen atoms in naphthyridine ring for studied complexes. Moreover, Ir(III) complex inclusive of quinoxaline heterocyclic ring presents large kr and knr, so its phosphorescence quantum efficiency is difficult up to be 100%. While two Ir(III) complexes bound to quinazoline heterocyclic ring show weakly emissive because of large knr. Notably, the presence of the cinnoline heterocyclic ring in the Ir(III) complex makes singlet–triplet intersystem (ISC) rate and kr fast but knr slow, then leads to its high phosphorescence quantum efficiency.

From the same piece of graphene sheet, (3, 3) and (6, 0) carbon nanotube clips were obtained on the basis of the different manners of rolling. The nature of the electronic state varies differently with different manners of rolling and is significantly affected by zigzag edges. The intermediate structures formed during the rolling process were functionalized with fluorine and oxygen atoms to investigate the electronic states and nonlinear optical (NLO) responses. Passivation of the intermediate structures with fluorine neither changes the nature of electronic states and nor improves the NLO responses. In constrast, passivation with oxygen enhances the NLO properties and changes the electronic states of the structures upon passivating at the open zigzag edges.

Intracellular pH plays critical roles in cell, enzyme, and tissue activities, including proliferation and ion transport, and muscle contraction. Some pH fluorescent probes have been reported, but most of them are one-photon fluorescent probes, investigations on two-photon fluorescent probes are very rare. In this work, we thoroughly study two latest two-photon pH fluorescent probes and design two excellent two-photon pH fluorescent probes. One-photon properties of these pH fluorescent probes have been theoretically studied by using density functional theory (DFT) method. Their two-photon absorption (TPA) properties are calculated by using the DALTON program. The calculated results indicate that the designed CAE-CN can serve as a proper Photoinduced Charge Transfer two-photon pH fluorescent probe and the designed AP1 can serve as a proper Photoinduced Electron Transfer two-photon pH fluorescent probe.

Transition metal acetylide compounds have attracted enormous attention because of the extraordinary photophysical properties arising from the electronic interaction between the transition metal and the organic molecular fragment. In this study, the geometrical structure, electronic structure, one-photon absorption (OPA) and two-photon absorption (TPA) properties of a series of D – π′ – A – π – [Pt] – π – A – π′ – D type and A′ – π′ – A – π – [Pt] – π – A – π′ – A′ type platinum(II) acetylides were studied theoretically by using density functional theory (DFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods for getting TPA materials possessing large TPA cross-section. Our analysis suggests that intramolecular charge transfer between center metal and π-conjugated organic fragment dominates in TPA transitions, in which metal center increases conjugation length in the direction of long ligand. This contribution provides detailed theoretical analysis of one- and two-photon absorption property of Platinum (II) acetylide compounds and an effective way for designing of platinum (II)/nickel (II) acetylide compounds possessing large TPA cross-section.

A direct dynamics study was carried out at the CCSD(T)/aug-cc-pvtz//B3LYP/6-31G(d,p) level for the multichannel degradation reaction of perfluoropropionic acid (PFPA, CF 3 CF 2 COOH). It is shown that the main pathway of the CF 3 CF 2 COOH degradation reaction can give the main product P2 (CO + CF 3 CO), while the minor product is P1 (C 2 H 4 ). Due to the energetically intermediates and transition states involved in the dominant paths, the reaction is expected to occur rapidly, which is consistent with the experimental data. The present theoretical studies may provide useful information on the issues of the reaction mechanism and product distributions.

Recently, the covalently linked porphyrin–graphene composite materials with excellent nonlinear optical (NLO) properties and solubility have been experimentally studied, but their two-photon absorption (TPA) properties have not been reported yet. In this work, a series of novel graphene-like molecules and their corresponding hybrids with porphyrin have been designed to study their one-photon absorption (OPA) and TPA properties, as well as the structure–property relationships by employing quantum-chemical calculations. The maximum TPA cross sections (δmax) calculated by the ZINDO method, combined with the FTRNLO-JLU program compiled by our group, are as large as ∼913.0–3904.3 GM. Moreover, both molecular size and porphyrin result in a significant increase of the δmax values. Furthermore, the hybrid molecules possess a higher TPA response resulting from intramolecular charge transfer, compared with their counterparts without a porphyrin. The calculated results support the experimentally observed trends, as well as indicate that the designed compounds with large TPA cross-sections have potential for applications involving optical limiting and two-photon fluorescence microscopy (TPFM). We expect that this study will provide a theoretical perspective for designing novel TPA materials based on graphene for further applications in the future.

A series of alkali metal doped carbon bowls have been designed to optimize the nonlinear optical (NLO) contrast and achieve rapid transformation between ON and OFF states in NLO switch. Transformation among metal doped conformations can be achieved by migration of alkali metal on the bowl surface and bowl-to-bowl inversion. The type of doping agent and doping site on the curved carbon surface significantly influences the amplitude of the first hyperpolarizability of those metal doped systems. Large difference in charge transfer and interaction between the metal and buckybowl is responsible for the large hyperpolarizability contrast among alkali metal doped isomers.

A two-photon fluorescent probe has become a critical tool in biology and medicine owing to its capability of imaging intact tissue for a long period of time, such as in two-photon fluorescence microscopy (TPM). In this context, a series of Salen-based zinc-ion bioimaging reagents that were designed based on an intramolecular charge-transfer mechanism were studied through the quantum-chemical method. The increase of one-photon absorption and fluorescence emission wavelength and the reduction of the oscillator strength upon coordination with a zinc ion reveal that they are fluorescent bioimaging reagents used for ratiometric detection. When the Salen ligand is incorporated with Zn(2+), the value of the two-photon absorption (TPA) cross-section (δmax) will decrease, and most of the ligands and complexes exhibit a TPA peak in the near-infrared spectral region. That is, a substituent at the end of the ligand can influence the luminescence property, besides increasing solubility. In addition, the effect of an end-substituted position on the TPA property was considered, such as ortho and meta substitution. The detailed investigations will provide a theoretical basis to synthesize zinc-ion-responsive two-photon fluorescent bioimaging reagents as powerful tools for TPM and biological detection in vivo.

Triazatruxene derivatives and heterofluorenes have drawn increasing attention in the applications of OLED devices due to their particular electronic structures and optical properties. To improve on the thermal and morphological stability and enhance electroluminescent (EL) efficiency, six series of star-shaped triazatruxene/heterofluorene co-polymers have been designed. To reveal structure property relationships of the novel functional materials, an in-depth theoretical investigation was elaborated using the density functional theory (OFT) and time-dependent density functional theory (TDDFT) methods. The results HOMOs, LUMOs, A(H-L), E-g, as well as some other electronic structures and IPs, EAs, lambda, tau, the absorption and emission spectra can be tuned by the introduction of heterofluorenes into the triazatruxene core. The various properties of these co-polymers were obtained by extrapolating those of the co-oligomers to infinite chain length. It was concluded that these triazatruxene/heterofluorene co-polymers are interesting optoelectronic functional materials, which have great potential for the application in OLEDs. (C) 2012 Elsevier Ltd. All rights reserved.

A new way has been investigated for tuning the optical and electronic performance of cyclometalated iridium(III) phosphors by simple tailoring of the phenyl ring of ppy (Hppy = 2-phenylpyridine) with various main group moieties in [Ir(ppy-X)2(acac)] (X = POPh2, SO2Ph, GePh3, OPh, OPh(CF3)3, SOPh). The geometric and electronic structures of the complexes in the ground state are studied with time-dependent density functional theory (TD-DFT) and Hartree–Fock method, whereas the lowest singlet and triplet excited states are optimized by the configuration interaction singles method. At the TD-DFT level, absorptions and phosphorescence properties of the studied molecules were calculated on the basis of the optimized ground- and excited-state geometries, respectively. The various main group moieties produce a remarkable influence on their optoelectronic properties. The calculated data reveal that the studied molecules have improved charge transfer rate and balance and can be used as hole and electron transport materials in organic light-emitting devices. In particular, the work can provide valuable insight toward future design of new and relatively rare luminescent materials with enhanced electron-injection and electron-transporting features. Copyright © 2012 John Wiley & Sons, Ltd.

An elaborated theoretical investigation on the optical and electronic properties of three fluorene-based platinum(II) and iridium(III) cyclometalated complexes Pt-a, Ir-a and Ir-b is reported. The geometric and electronic structures of the complexes in the ground state are studied with density functional theory and Hartree Fock approaches, while the lowest triplet excited states are optimized by singles configuration interaction (CIS) methods. At the time-dependent density functional theory (TD-DFT) level, molecular absorption and emission properties were calculated on the basis of optimized ground- and excited-state geometries, respectively. The computational results show that the appearance of triphenylamino (TPA) moiety at the 9-position of fluorene ring favors the hole-creation and leads to red-shifts of absorption and emission spectra. Moreover, Pt-a and Ir-b are nice hole-transporting materials whereas Ir-a has good charge-transfer balance, which render them useful for the realization of efficient OLEDs (Organic Light-Emitting Diodes).

A theoretical investigation of the unique electronic transport properties of the junctions composed of boron nitride atomic chains bridging symmetric graphene electrodes with point-contacts is executed through non-equilibrium Green’s function technique in combination with density functional theory. Compared with carbon atomic chains, the boron nitride atomic chains have an alternative arrangement of polar covalent B-N bonds and different contacts coupling electrodes, showing some unusual properties in functional atomic electronic devices. Remarkably, they have an extraordinary odd-even behavior of conductivity with the length increase. The rectification character and negative differential resistance of nonlinear current-voltage characteristics can be achieved by manipulating the type of contacts between boron nitride atomic chains bridges and electrodes. The junctions with asymmetric contacts have an intrinsic rectification, caused by stronger coupling in the C-N contact than the C-B contact. On the other hand, for symmetric contact junctions, it is confirmed that the transport properties of the junctions primarily depend on the nature of contacts. The junctions with symmetric C-N contacts have higher conductivity than their C-B contacts counterparts. Furthermore, the negative differential resistances of the junctions with only C-N contacts is very conspicuous and can be achieved at lower bias.

The electronic transport properties of carbohelicenes and heterohelicenes absorbed between two metal electrodes have been investigated by using the nonequilibrium Green's function in combination with the density function theory. The transport properties of the molecular junctions are mainly dependent on the nature of spiral molecules. The detailed analyses of the transmission spectra, the energy levels as well as the spatial distribution of molecular projected self-consistent Hamiltonian explain how the geometry of molecules affects the intra-molecular electronic coupling. The spiral current in the configurations can be achieved by tuning the outer edge states of spiral-shaped molecules. Furthermore, the symmetric current–voltage characteristics are investigated with the bias changing for all devices as well as an negative differential resistance behavior is observed.

This contribution reports the geometries, electronic structures, linear and nonlinear optical properties of a series of macrocyclic thiophene derivatives with different connecting π-bridge and ring size in theory. It provides great optical properties that both OPA and TPA peaks shift red as Ne increases and in different window, which don't superimpose on each other, and the values of δ (1) max and δ (2) max enlarge, while the largest δ (2) max for C[6T_A_E] 3 observed at long wavelength (725.9 nm) is 23 times larger than that of the unit C[6T_A_E] . Besides connecting bridge and ring size, several key parameters essentially influencing on NLO property were highlighted, including M 0 k , M kn , ƒ 0 k × ƒ kn and Ne . In addition, ICT impacting on the values of δ (2) max was analyzed by contour surfaces of the frontier orbitals and Δ Q of thiophene and bridge. More particularly, large negative value of Reγ indicates their self-defocusing, implying it can be applied in self-defocusing optical power limiting materials.

We have theoretically investigated two series of cyclometalated Pt(II) complexes, a series [Pt (C, N, N) Cl] and b series [Pt (C, N, Npyrazolyl) Cl]. The geometrical and electronic structures are calculated at the ECP60MWB//6-31G*(H, C, Cl, N, S) basis set level using DFT method; one-photon absorption (OPA) properties are calculated by using both TDDFT and ZINDO methods and two-photon absorption (TPA) properties are obtained with the ZINDO/SOS method. The resonance integrals parameters ( β sp and β d) for Pt are adjusted to -1 and -28.5 eV, respectively, to make max OPA wavelength calculated by ZINDO closest to the experimental data and TDDFT results. The calculated results indicate the molecule 2b ([Pt (Cnaphthyl, N, Npyrazolyl) Cl]) has the biggest potential as outstanding TPA materials because (i) the TPA properties of b series are more outstanding in IR wavelength range, the molecules in b series have good transparencies and possess 1-pyrazolyl-NH that is also available for another metal coordination (e.g., dimerization) and chemical interactions; (ii) when C is Cnaphthyl in the C, N, N ligand of cyclometalated Pt(II) complexes, the molecules have the best conjugation effect and the best TPA properties.

The geometrical and electronic structures, and one- and two-photon absorption properties of macrocyclic thiophenes possessing push-pull groups were investigated. It shows that λ (1) max s appear red-shift for the designed macrocycles with strong donor/acceptor (D/A) substituents, and the red-shifts enlarge as increasing the number of D/A pair. As a result, their two-photon absorption cross-section ( δ max )s get larger, and the configurations with donor and acceptor location on the opposite site can result in larger δ max , which is ascribed to the enlargement of the stronger intramolecular charge transfer (ICT) between D and A or the inside of the whole ring skeleton. Taking SII series of molecules as an example, the enlargement of the net charge change (Δ Q ) is one factor for the increase of δ max . Moreover, transition dipole moments ( M 0 k and M kn ) play important roles on the increase of δ max . And the product of oscillator strengths ( f 0 k × f kn ) is in proportion to δ max .

Exploring the relationship between electronic structure and electroluminescent property has great significance to design some desirable OLED materials. A series of dithienylbenzothiazole derivatives were studied with Density Functional Theory method in this work. The results show that the hole injection/transporting ability of the compound is significantly increased by electron donors ( triphenylamine and 9-phenylcarbazole ). Introducing the cyano group apparently enhances the electron-injection ability of the compound but reduces its hole-injection ability. The dimethyl-chromene-malononitrile ( DCM ) group greatly enhances the electron injection/transporting ability of the molecule but has almost no effect on its hole injection/transporting ability. Both the electron reorganization energies and LUMO energy levels of the resulting molecules decrease with increasing electronegativities of the substituents. Extending the π-conjugation length between electron donors and acceptors not only increases the hole/electron injection ability of the molecule, but improves its carrier transport balance.