Dye-sensitized solar cells (DSSCs) are the most promising low-cost photovoltaic devices. Whereas, the absorption bands of most organic sensitizers, the most vital component in DSSCs, are limited to a relatively narrow visible range. To obtain efficient sensitizer, a series of D–A−π–A metal-free dyes have been designed based on one of the best sensitizers WS-9 by modifying auxiliary acceptor and characterized theoretically. The results illustrate that introduction of auxiliary heterocycle acceptor is revealed to very narrow band gap (HOMO–LUMO), leading to an obvious red-shifted broad near-infrared absorption band in the range of 750–1950 nm compared to WS-9 (536 nm). The critical parameters in close connection with the short-circuit current density (J sc), open circuit voltage (V oc), including singlet excited state lifetime (τ), total dipole moments (μnormal), the conduction band of edge of the semiconductor substrate (ΔE CB), and regeneration driving forces (ΔG reg) are superior to those of WS-9. Therefore, these novel sensitizers would be a promising candidate for improving the performance of the DSSCs.

The electronic structures and absorption spectra for a series of acene-based organic dyes and the adsorption energy and optical properties for these dyes adsorbed on (TiO2)38 have been investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The effects of acene units and different substitution positions of electron donors on the optoelectronic properties of the acene-modified dyes are demonstrated. The photophysical properties of tetracene- and pentacene-based dyes are found to be tuned by changing the size of acene and the substitution position of the donor. The donor sites have a significant influence on the absorption wavelength mainly because of different molecular orbital (MO) contributions of the highest occupied molecular orbital (HOMO) on the bridging acene units, and the increasing MO contribution would lead to the red shift in the absorption spectra. Meanwhile, the donor is located close to the center of the π-conjugated bridge, and the absorption spectra are extended. The adsorption energy and optical properties of tetracene- and pentacene-based dyes adsorbed on (TiO2)38 suggest that acene-bridged dyes could be adsorbed on the TiO2 surface and inject electrons into semiconductors effectively. Then the results obtained from the hexacene-based dyes confirm the conclusions proposed from the tetracene- and pentence-based dyes. This study will provide a useful reference to the future design and optimization of acene dyes for dye-sensitized solar cell applications.

The hydrogen abstraction and addition reactions of OH radical with A·U base pair have been explored by using density functional theory (DFT) both in gas phase and in aqueous solution. Solvent effects were taken into consideration by using the polarized continuum model. All the reaction pathways are exothermic in energy, and the compounds in aqueous phase are more favorable than those in gas phase. The relative free energies of adducts in the addition reaction are lower than those obtained for products in hydrogen abstraction reaction. Among dehydrogenation reaction, the hydrogen abstractions from AC2·U and AN6·U sites are more favorable than those from AC8·U, A·UC5, and A·UC6 sites. In addition, hydroxylation at AC8·U, A·UC5, and A·UC6 sites are more probable than other investigated positions. The hydroxylation at AH8·U site is most favorable, and hydroxylation at A·UC5 site is more preference than that at A·UC6 site controlled by the kinetics factors. The data in both gas phase and water solution demonstrated that addition of OH radical to A·UC5 and A·UC6 sites are more thermodynamically and kinetically favorable than abstracting the hydrogen atom form A·UC5 and A·UC6 sites. The phenomena are in agreement with the experimental observations. Copyright © 2015 John Wiley & Sons, Ltd.

C. The hydroxylation reactions at G . C C5 and G C8.C sites appear to be barrierless, and the sequence of the barrier energy is G .C. The results indicate that hydroxylation at G C base pair. Considering the solvent effects by using the polarizable continuum model, the stabilities of all the compounds are increased significantly. Little change is taken place on the data of the reaction energies and barrier energies. Their sequences and the stability order follow the same trends like them in gas phase. The fluctuation of natural bond orbital charge further confirms that the hydroxylation reactions are exothermic. And transient spectra computed with the time-dependent density functional theory (TD-DFT) match well with the previous experimental and theoretical reports. Our deduced mechanism is in good agreement with the experimentally observed hydroxylated adducts.

To address problems such as aging, mutation, and cancer, it is of great importance to understand the damage mechanism of DNA induced by hydroxyl radical. In this study, the abstraction reaction mechanism of hydroxyl radical with guanine-cytosine (GC) base pair in aqueous phase under the polarized continuum model (PCM) has been explored by using density functional theory (DFT). The results indicated that all the abstraction reactions in GC base pair were thermodynamically exothermic, and the stability of dehydrogenation radicals decreased in the order of (H2b-GC) • >(GC-H4b) • >(GC-H6) • >(GC-H5) •~(H8-GC) •. The reaction energy of H2b abstraction pathway was the lowest among all investigated pathways, thus indicating that the reaction conversion of (H2b-GC) • was the highest. In the five hydrogen abstraction pathways, the local energy barriers with respect to the corresponding reactant complexes increased in the following order: H2b