Shuixing Wu

Theoretical discussions on electron transport properties of perylene bisimide derivatives with different molecular packings and intermolecular interactions

Seven perylene bisimide derivatives with different molecular packings and intermolecular interactions were investigated in detail within Marcus-Levich-Jortner formalism at the level of density functional theory (DFT). In theory, we further proved the report that different halogen substitutions in the core position of perylene bisimide lead to different molecular packings in their single crystals and thus obviously different electron transport properties. Here, insight into the geometries, the character of the frontier molecular orbitals, the decompositions of reorganization energies and transfer integrals in different directions was provided to shed light on the relationship between structures and properties. The molecular dynamics (MD) simulations and band structures calculations were also employed to give a multiscale understanding of their transport properties. The results show that there are small discrepancies of the intramolecular electron reorganization energies among these compounds and the transfer integrals determine their electron transport properties. Compounds 1a, 3a and 3b, with typical “brick” packing, π-stacked face-to-face packing and “herringbone” packing, respectively, have larger electron mobilities among these systems and possess different transport dimensionalities. Moreover, we also find there is close relationship between the intermolecular interaction energy and the transfer integral.

Theoretical Characterization of a Typical Hole/Exciton-Blocking Material Bathocuproine and Its Analogues

The structural, electronic, and carrier transport properties of bathocuproine (BCP), which is a typical hole/exciton-blocking material applied in organic light-emitting diodes (OLEDs), have been investigated based on density functional theory (DFT) and ab initio HF method. The detail characterizations of frontier electronic structure and lowest-energy optical transitions have been studied by means of time-dependent density functional theory (TD-DFT). Five BCP analogues, o-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-diphenyl-1,10-phenanthroline (3), 4,7-diphenyl-1,10-phenanthroline (4), and 2,9-bis(trifluoromethyl)-1,10-phenanthroline (5) have also been studied in order to select more suitable candidates of efficient hole-blocking materials. The calculated results showed that rigid planar structures, conjugate degrees, and substitute groups play crucial roles in the hole/exciton-blocking and electron-transport properties of these materials. The calculated geometries, ionization energies (IP), and energy gap between the singlet ground state and triplet excited state (E(T1)) were well in agreement with the experimental results. On the basis of the incoherent transport model, the calculated electron mobility of BCP is 1.79 x 10(-2) cm(2)/(V s), which is comparable to experimental results of 1.1 x 10(-3) cm(2)/(V s). The electron mobilities for compounds 1, 4, and 5 are 3.45 x 10(-2), 2.90 x 10(-2), and 1.40 x 10(-2) cm(2)/(V s), respectively. The calculated results indicated that compounds 1, 4, and 5 may be more effective hole/exciton-blocking materials than BCP.

Theoretical Study on a Novel Series of Fullerene-Containing Organometallics Fe(η5-C55X5)2 (X = CH, N, B) and Their Large Third-Order Nonlinear Optical Properties

Geometry structures, electronic spectra, and third-order nonlinear optical (NLO) properties of Fe(eta (5)-C 55X 5) 2 (X = CH, N, B) have first been investigated by time-dependent density functional theory. We analyzed the intramolecular interactions between ferrocene and the C 50 moiety. The calculated electronic absorption spectrum indicates that the short wavelength transitions are ascribed to the C 50 moiety mixed charge transfer transition of ferrocene itself, while the low energy excitation transitions are ascribed to the unique charge transfer transition from ferrocene to C 50 moiety in these systems. The third-order polarizability gamma values based on sum of states (SOS) method show that this class of ferrocene/fullerene hybrid molecule possesses a remarkably large third-order NLO response, especially for Fe(eta (5)-C 55B 5) 2 with the static third-order polarizability (gamma av) computed to be -10410 x 10 (-36) esu and the intrinsic second hypepolarizability to be 0.250. Thus, these complexes have the potential to be used for excellent third-order nonlinear optical materials. Analysis of the major contributions to the gamma av value suggest that the charge transfer from ferrocene to C 50 moiety along the z-axis (through Fe atom and the centers of two hybrid fullerenes) play the key role in the NLO response. Furthermore, boron substitution is an effective way of enhancing the optical nonlinearity compared to CH and N substitution, owing to smaller energy gap and better conjugation through the whole molecule.

Carbonyl amine/Schiff base ligands in manganese complexes: theoretical study on the mechanism, capability of NO release.

A compound having the capability of releasing NO upon exposure to visible or near-infrared (vis or NIR) light could be a potential candidate for photodynamic therapy (PDT), which is significant for humans. Here, we investigated a series of Mn(II) complexes (a-d) based on density functional theory (DFT) to illuminate the mechanism of their behavior of releasing NO. Their structural, spectroscopic, and photodissociable properties were calculated by quantum theoretical methods to give a detailed and warranted explanation of the performance of releasing NO. The results indicate that, for a-d, releasing NO was attributed to the electron transfer from d(yz)/d(xz)(Mn) orbitals to π*(NO) orbitals at the second excited triplet state (T(2)). Importantly, we confirmed the finding in the experiment that d could release NO upon exposure to the NIR region and, thus, may be a best candidate for PDT in a-d. Therefore, to take d for example, the analyses of the potential energy curves (PECs) of difference states and electron density difference between the T(2) and the ground state (S(0)) were performed to further provide evidence of ligand dissociation and release of NO at the T(2) state. Finally, we hope that our discussion can provide assistance to understand the behavior of the release of NO and design novel photodissociable transition metal nitrosyls for PDT applications.

The origin of the unusual broad and intense visible absorption of tetrathiafulvalene-annulated zinc porphyrazine: a density functional theory study.

The vertical excitation energies of tetrathiafulvalene (TTF)-annulated zinc porphyrazine (ZnPzTTF) were investigated using time-dependent density functional theory (TDDFT) calculations and compared to the experimental UV-vis spectra. To examine the effects of the aza substitutions and TTF groups on the molecular properties, zinc complexes of porphyrin (ZnP), porphyrazine (ZnPz) and tetraTTF-annulated porphyrin (ZnPTTF) were also selected for comparison. It was shown that numerous electronic transitions with TTF-to-porphyrin or porphyrazine charge transfer character exist and the Q band of ZnPzTTF is dominated by TTF-to-porphyrazine charge transfer transition mixed with porphyrazine core unit itself except for classic porphyrazine π→π* transitions. The Q band of ZnPzTTF mixes with other configurations, which breaks down the Goutermans classic four-orbital model for the spectral interpretation. The data suggest that TDDFT/SAOP performs best for Q and B bands of ZnPzTTF with the maximum error in excitation energy being 0.17 eV. The CAM-B3LYP, ωB97XD and M06-2X calculations qualitatively predict that the low-lying electronic transitions of ZnPzTTF with TTF-to-porphyrazine charge transfer character located below the Q band. The broad and intense red-shifted Q band suggests that ZnPzTTF can be a candidate for dye-sensitized solar cells.

Quantum Chemical Insight into the LiF Interlayer Effects in Organic Electronics: Reactions between Al Atom and LiF Clusters.

It is well known that the aluminum cathode performs dramatically better when a thin lithium fluoride (LiF) layer inserted in organic electronic devices. The doping effect induced by the librated Li atom via the chemical reactions producing AlF3 as byproduct was previously proposed as one of possible mechanisms. However, the underlying mechanism discussion is quite complicated and not fully understood so far, although the LiF interlayer is widely used. In this paper, we perform theoretical calculations to consider the reactions between an aluminum atom and distinct LiF clusters. The reaction pathways of the Al-(LiF)n (n = 2, 4, 16) systems were discovered and the energetics were theoretically evaluated. The release of Li atom and the formation of AlF3 were found in two different chemical reaction routes. The undissociated Al-(LiF)n systems have chances to change to some structures with loosely bound electrons. Our findings about the interacted Al-(LiF)n systems reveal new insights into the LiF interlayer effects in organic electronics applications.

Can a linear metal–metal bonded array of tetravanadium be stabilized between two dicyclopenta[a,e]pentalene ligands? A theoretical investigation

The 14-π cross-linked annulene dicyclopenta[a,e]pentalene (dcpp) is suggested for the first time to function as a sandwich ligand. According to density functional theory (DFT) calculations, upon being sandwiched between two dcpp ligands, the tetravanadium chain, without the support of auxiliary ligands, has two unpaired electrons and has a tendency for deformation to gain extra stability through multicenter bondings in the ground state. The one-electron ligand chlorine can lead to two types of structures, one with two chlorine atoms connecting to the two central vanadium atoms and the other one with two chlorine atoms connecting to the two terminal vanadium atoms, both of which are energetically more favorable in the triplet state. In the carbonyl end-capping complex, the tetravanadium is stable as a linear metal–metal bonded array with alternating single and double bonds and all electrons paired for bonding, although a triplet state conformer exists with two extra carbonyl ligands bound to the two central vanadium atoms which is more energy favorable by 15.1 kcal mol−1. Bonding features within the tetravanadium moiety were obtained based on electron density analyses. We hope these discussions are helpful for the design of new extended metal atom chain (EMAC) systems and for the pursuit of effective catalysts based on the dcpp sandwich complexes.