Fe3O4@SiO2@HPW (12-tungstophosphoric acid) nanoparticles have been successfully obtained by a simple solvothermal and impregnation process. The as-obtained products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectrum (FT-IR), inductively coupled plasma (ICP) and MPM5-XL-5 superconducting quantum interference device (SQUID). The results revealed that the heteropolyacids were successfully grown on the Fe3O4@SiO2 nanoparticles. The photocatalytic studies suggested that the Fe3O4@SiO2@HPW nanoparticles show excellent photocatalytic efficiency for the degradation of Rhodamine B (RB) under UV light irradiation. More importantly, the obtained nanoparticles (Fe3O4@SiO2@HPW) could be effectively separated for reuse by simply applying an external magnetic field. Furthermore, the synthesized nanoparticles could keep their efficiency till four cycles.

•A D–A copolymer of indacenodithiophene and fluorinated benzotriazole, PIDT-FBTA, was synthesized.•PIDT-FBTA showed deeper HOMO energy level due to the strong electron-withdrawing difluorine substitution.•The PSCs based on PIDT-FBTA:PC70BM (1:3) exhibited a high Voc of 0.92 V and a power conversion efficiency of 4.90%.A medium band gap D–A copolymer of indacenodithiophene (IDT) and fluorinated dithienylbenzotriazole (FBTA), PIDT-FBTA, was synthesized for the application as donor material in polymer solar cells (PSCs). PIDT-FBTA showed deeper highest occupied molecular orbital (HOMO) energy level due to the strong electron-withdrawing difluorine substitution on benzotriazole acceptor unit in the D–A copolymer. The PSCs based on PIDT-FBTA:PC70BM (1:3) exhibited a high Voc of 0.90 V and a power conversion efficiency (PCE) of 3.62% under the illumination of AM 1.5G, 100 mW cm−2. The device performance was further improved by methanol treatment with PCE increased to 4.90% and Voc increased to 0.92 V.

•Three dyes with different electron donors derived from C219 for DSSC were designed.•A set of key parameters affecting the efficiency of the cell have been discussed.•Dye 3 with Coumarin donor shows higher Voc and Jsc than that of champion dye C219.Dye sensitized solar cell sensitized by organic dye C219 (Chem. Mater, 2010, 22, 1915–1925) has reached the record efficiency (η) of 10.1% with comparable short-circuit current density (Jsc) but relatively lower open-circuit photovoltage (Voc) as compared to that of ruthenium-based cells. With the motivation of further enhancing Voc, we designed three dyes 1–3 with different electron donors, i.e. carbazole, indoline and coumarin. Based on the theoretical analysis of the conduction band energy shift of TiO2, electron injection rate and electron lifetime, the three designed dyes all show larger Voc than that of C219. On the other hand, 3 should also have larger Jsc compared with that of C219 due to its red-shifted spectrum and higher light harvesting efficiency. Thus we expect that the cell sensitized by 3 could exhibit both larger Voc and Jsc in comparison to the champion C219-based cells.A theoretically designed coumarin dye shows both higher Voc and Jsc potential compared with champion dye C219 through the reliable DFT/TDDFT calculations on semiconductor/sensitizer/electrolyte interfacial interaction.

In this work, density functional theory (DFT) combined with the finite field (FF) method has been adopted to analyze the second-order nonlinear optical (NLO) properties of the triarylborane (TAB) derivatives obtained by introducing different inductive electron groups into the phenylene ring of the TAB (RTAB, where R=2-C6H5-C2B10H10(1), R=F(2), R=Me(3), R=NO2(4), R=NH2(5)). The static first hyperpolarizabilities (βtot) of the RTAB molecules can be switched by binding one F− to the boron center (RTAB′) or one-electron reduction (RTAB″). The DFT-FF calculations show that the βtot values of 2′, 3′ and 5′ decrease while those of 1′ and 4′ increase compared with the values of their neutral molecules, which was attributed to the fact that the charge transfers of 3 and 5 become smaller and those of 1 and 4 become larger by binding one F− ion to the boron center, according to time-domain DFT (TD-DFT) analysis. However, the incorporation of one electron enhances the second-order NLO properties of the RTAB molecules remarkably, especially for system 1. It is notable that the βtot value of reduced form 1″ is 508.69×10−30 esu, i.e. abou 578 times larger than that of system 1. Frontier molecular orbital (FMO) and natural bond orbital (NBO) analyses suggest that the reversal of the charge distribution between the neutral molecules and their reduced forms leads to low HOMO-LUMO energy gaps (E0) and thus large βtot values for the reduced forms.

The electronic absorption spectra of group 12 bis-metal (II) complexes of [26]hexaphyrin(1.1.1.1.1.1) were systematically investigated using the localized density matrix (LDM) method and the time-dependent density functional theory (TD-DFT). The results show that the LDM method is a reliable approach for determining the electronic transition properties of the complexes and substantially reduces the computational cost. By analyzing the changes in energy and frontier molecular orbitals, this study found that bis-Hg (II) hexaphyrin forms rectangle-shaped complexes easily whereas bis-Zn (II) hexaphyrin and bis-Cd (II) hexaphyrin are more likely to form dumbbell-shaped complexes. In the R-shaped complexes, the absorption characteristics mostly represent Q-like bands from intra-ligand charge transfer transitions of the 26π macrocycle conjugate system, whereas in the D-shaped complexes, the absorption characteristics exhibit B-like bands from ligand-to-metal charge transfer and ligand-to-ligand charge transfer transitions. In addition, the introduction of group 12 transition metals (II) leads to red shifts in the R-shaped complexes and blue shifts in the D-shaped complexes in the spectra of these metal complexes. Moreover, the transition properties of the D-shaped complexes show that the contribution from segmental phenyl rings is even more important at the B-like bands compared with those of the R-shaped complexes in the meso-carbons.Graphical abstractBy analyzing the changes in energy and frontier molecular orbitals, this study found that bis-Hg (II) hexaphyrin forms rectangle-shaped (R-shaped) complexes easily whereas bis-Zn (II) hexaphyrin and bis-Cd (II) hexaphyrin are more likely to form dumbbell-shaped (D-shaped) complexes. The transition properties of dumbbell-shape complexes show that contribution from segmental phenyl rings is even more important at the B-like band compared with those of rectangle-shape in meso-carbons.Highlights► Electronic absorption spectra of bis-metal complexes of hexaphyrin were modeled. ► Geometrical structure and electronic structures were investigated. ► Absorption wavelengths and transition properties computed with TD-DFT and LDM. ► LDM theory explain the mutual effects of the atomic. ► Contributions of the phenyl rings in meso-carbons are quite important.

Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculation were adopted to study the structures and properties of metal-free and magnesium tetrathieno[2,3-b]porphyrazine (TTPPzH2 and TTPPzMg) using B3LYP method with the 6–31G(d) basis set. A comparison of the geometrical structures, atomic charges, molecular orbitals, UV-vis spectra and infrared (IR) spectra among tetrathieno[2,3-b]porphyrazine (TTPPzH2), phthalocyanine (H2Pc) and porphyrazine (H2Pz) compounds was performed. The substituent effect of the thiophene heterocycle for electron-donating on the structures and properties of these compounds has been discussed. Compared with other atoms, the charge distribution of Cβ atoms adjacent to the sulfur atom is significantly influenced by the thiophene heterocycle substituents. The enlargement of the HOMO-LUMO gaps from H2Pc and MgPc to TTPPzH2 and TTPPzMg is at the origin of the observed blue shift of the Q band when moving from H2Pc to TTPPzH2 compounds. Special emphasis has been devoted to the strongest B bands for TTPPzH2 compounds which show red shift due to the large destabilization of the lower lying occupied orbitals compared with the corresponding B bands of H2Pc compounds. With the assistance of animated pictures produced on the basis of the normal coordinates, the significant peaks and vibration modes in the IR spectra of all the compounds were assigned and analyzed.

The absorption spectra of 2-(2′-pyridyl)benzimidazole derivatives and their Be and B complexes were systematically investigated using a localized density matrix (LDM) method and a time-dependent density functional theory (TD-DFT). Comparing the absorption spectra and electronic transition properties obtained by LDM and TD-DFT with the experimental result, the LDM method gives a more reliable approach for determining the electronic spectra of the compounds under study. This method can also substantially reduce computational cost. For 2-(2′-pyridyl)benzimidazole derivatives, the absorption characteristics mostly originate from benzimidazolyl and pyridyl rings with a calculated absorption wavelength of about 300 nm. In addition, the B and Be complexes of 1,4-2-(′2-pyridyl)benzimidazole were studied. The absorption spectra undergo a red shift when B coordination metal ion is substituted by a Be metal ion. The first absorption peak of [Be(II)(4,4′-bis[2-(2′-pyridyl)benzimidazolyl)(benzene)4] clearly appears with the enhancement of oscillatory strength, unlike with [Be(II)(2-(2′-pyridyl)benzimidazolyl)(benzene)2]. The absorption wavelengths of the two Be complexes are both near 430 nm, indicating that their transition properties originate from the ligand-to-ligand charge transfer between phenyl and 2-(2′-pyridyl)benzimidazolyl.