Effect of Nitrogen Cation as "Electron Trap" at π-Linker on Properties for p-Type Photosensitizers: DFT Study.

On the basis of thieno(3,2-b)thiophene and dithieno[3,2-b:2',3'-d]thiophene (T2 and T3 moieties) as π-linker, the A, D and S series dyes were designed to investigate the effect of the introducing N+ as an "electron trap" into T2 and T3 on the properties of the dyes. The optimized structures, electronic and optical properties were investigated by the density functional theory (DFT) and time-dependent DFT (TD-DFT). The results show that the properties of the dyes are sensitive to the N+ position in π-linkers. D series dyes with electron-withdrawing units located near the donor have better properties than the corresponding A series with the electron-withdrawing units located near the acceptor. For A and D series, the N+ modified dye named T2N+1-d displays the largest red shift of the UV-vis absorption, the maximum integral values of the adsorption-wavelength curves over the visible light, the highest light harvesting efficiency (LHE, 0.996), and the strongest adsorption energy (-44.33 kcal/mol). T2N+1-d also has a large driving force of hole injection (ΔGinj, -0.74 eV), which results in a more efficient hole injection. Bearing a lengthier π-linker than T2N+1-d, the properties of T2N+1-s are further improved. T2N+1-d moiety or its increased conjugated derivatives may be a promising π-linker.

Design of high performance p-type sensitizers with pyridinium derivatives as the acceptor by theoretical calculations.

Based on triphenylamine as an electron donor and thiophene as a π-linker, Series P and A p-type sensitizers were designed to investigate the effects of the different acceptors on the properties of the sensitizers. The optimized molecular structures, electronic and optical properties were investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT). The results showed that the properties of the dyes can be tuned by the introduction of the different electron-withdrawing groups to the N atom in the pyridinium acceptor. Compared with the synthesized Series P dyes used in p-type sensitizers, the properties of Series A dyes, except for two dyes that cannot be used as p-type sensitizers, are improved by means of modifying pyridinium acceptors. Due to the suitable electron-withdrawing ability of the hexafluorodiacetylamino group in its acceptor, A6 has the narrowest energy gap (1.90 eV), the largest driving force of hole injection (ΔG inj, -0.68 eV), the high light harvesting efficiency (LHE, 0.9984) and the smallest internal reorganization energy (λ int, 5.05 kcal mol-1). Hence, A6 not only enhances electronic excitation, but also improves the reorganization energy. Importantly, A6 shows the largest red shift and the maximum integral values of the adsorption over the visible light, as well as the strongest adsorption energy (-74.80 kcal mol-1) on a NiO surface. Thus, A6 may be a promising sensitizer for the p-type dye-sensitized solar cells (DSSCs), and the acceptor of A6 may provide a new and easily accessible high performance acceptor for p-type sensitizers.

Theoretical study of nitrogen cation modified aromatics containing thiophene as π-linker for p-type photosensitizers.

On the basis of triphenylamine as an electron donor with attachment of two -COOH anchoring groups and dicyanovinyl as acceptor, ten dyes with D-π-A structures were designed to investigate the effects of different π-linker groups on the properties of the sensitizers, especially the influence of the π-linkers containing nitrogen cation (N+). The optimized structures and electronic and optical properties were investigated by the density functional theory (DFT) and time-dependent DFT (TD-DFT). The results show that all the investigated dyes can be used as dye sensitizers for the p-type dye-sensitized solar cells (DSSCs) except one dye which contains two N+. The N+ modified dye (named S3-PZL1C) has narrow energy gap (2.02 eV), the best light-harvesting efficiency (LHE, 0.9974), and the smallest internal reorganization energy (λint = 7.00 kcal/mol). Importantly, S3-PZL1C displays the largest red shift of the UV-vis absorption, the maximum integral values of the adsorption-wavelength curves over the visible light (400~800 nm), and the strongest adsorption energy (- 66.84 kcal/mol) on NiO surface. In addition, S3-PZL1C not only enhances the electronic excitation but also improves the reorganization energy and charge separation. The intramolecular charge transfer towards the acceptor is sensitive to the N+ position in π-linkers. Therefore, the suitable introduction of N+ in dyes can improve the performance of the dyes, and the PZL1C moiety may be a promising π-linker for p-type DSSCs. Graphical abstract.

Theoretical study on p-type D-π-A sensitizers with modified π-spacers for dye-sensitized solar cells.

Based on a prototype sensitizer W2, we designed triarylamine-based p-type sensitizers W2-1 to W2-7 that contain modified π-spacers (π'), a π-spacer and two anchors. For W2-1 to W2-4, instead of 2,1,3-benzothiadiazole in W2, thieno[3,4-b]-1,4-dioxin, thiophene, thieno[3,4-c][1,2,5]thiadizole, thiazolo[5,4-d]thiazole are π' and thiophene as π-spacer. For W2-5 to W2-8, π' and π are same, with 2,1,3-benzothiadiazole, thieno[3,4-b]-1,4-dioxin, thieno[3,4-c][1,2,5]thiadiazo, thiazolo[5,4-d]thiazole, respectively, as the π'-spacers. Structure optimization, electronic level and absorption characters were calculated with density functional theory (DFT) and time-dependent DFT (TDDFT) at the CAM-B3LYP/6-311G (d,p). The solvent effect was involved using a polarized continuum model in chloroform. The results showed that the highest occupied molecular orbital and the lowest unoccupied molecular orbital guarantee sufficient hole injection (lower than -0.2 eV), and dye regeneration (lower than -0.2 eV). W2-4 has higher light-harvesting efficiency (LHE) (0.994) and larger overlap with the visible light from 400 nm to 600 nm. Finally, the results suggest that the driving force of hole injection, dye regeneration and charge recombination (ΔGinj, ΔGreg and ΔGCR) of W2-4 are the best, with more negative ΔGinj (-4.33), ΔGreg (-1.74) and more positive ΔGCR (1.92). Replacing 2,1,3-benzothiadiazole with thiazolo[5,4-d]thiazole as π'-spacers is a effective way to improve the performance of the dyes. An introduction of thiazolo[5,4-d]thiazole group can improve the absorption ability and hinder charge recombination. Graphical abstract Absorption spectra of p-type D-π-A sensitizers with modified π-spacers.

Theoretical study on stabilization mechanisms of nitrate esters using aromatic amines as stabilizers.

The propellants of nitrate esters can be stabilized by some aromatic amines practically. To probe the mechanism of this phenomenon, we performed DFT calculations on: (1) The decompositions of nitrate esters (with and without the catalysis of NO2) and (2) the reaction between the stabilizers and the nitro dioxide (NO2 is released during the storage of nitrate esters). The structures on the reaction paths (reactants, intermediates and products) were optimized at the (U)B3LYP/6-31G** level. It was shown that NO2 lowers the activation energy barrier in the decomposition of nitrate ester by 11.82-17.86kJ/mol and efficiently catalyzes the rupture of ONO2 bond. However, the aromatic amines, typical stabilizers for nitrate esters, can easily eliminate NO2 with activation barriers as low as 27-113kJ/mol (with one exception of 128kJ/mol). These values are, for most cases, lower or much lower than the activation energy barriers for reactions between nitrate esters and NO2 (127-137kJ/mol). Consequently, the stabilizers can block the NO2 catalysis for the decompositions of nitrate esters.

Verapamil reverses cardiac iron overload in streptozocin-induced diabetic rats.

Accumulating evidence shows that iron overload is a new risk factor for diabetes mellitus. L-type Ca(2+) channel (LTCC) has been identified as an important mediator for ferrous iron uptake into cardiomyocytes. In this study, we aimed to examine the effects of verapamil, the LTCC blocker, on myocardial iron metabolism in diabetic rats. Diabetes was induced by intraperitoneal injection of streptozocin after intragastric administration of fat emulsion, and then treated by verapamil (5 mg · kg(-1) · day(-1)) for 1 week. The results showed that verapamil did not alter the blood glucose level of diabetic rats. However, elevated levels of superoxide dismutase, malonaldehyde, and serum ferritin in diabetic rats were decreased significantly by verapamil treatment. Moreover, serum, myocardial, and urine iron were elevated remarkably along with a decrease of hepatic iron in diabetic rats. After verapamil administration, serum and myocardial iron in diabetic rats were reduced significantly but urine and hepatic iron were increased. Furthermore, confocal microscopy demonstrated that intracellular-free iron concentration was elevated dramatically in cardiomyocytes of diabetic rats, which was markedly attenuated after verapamil treatment. In summary, our data demonstrated that verapamil prevented myocardial iron overload by inhibiting intracellular iron accumulation in diabetic cardiomyocytes.

Reciprocal regulation between M3 muscarinic acetylcholine receptor and protein kinase C-epsilon in ventricular myocytes during myocardial ischemia in rats.

We have studied the association between M(3) muscarinic acetylcholine receptors (M(3)-mAChR) and protein kinase C-epsilon (PKC-epsilon) during ischemic myocardial injury using Western blot analysis and immunoprecipitation technique. Myocardial ischemia (MI) induced PKC-epsilon translocation from cytosolic to membrane fractions. This translocation participated in the phosphorylation of M(3)-mAChR in membrane fractions, which could be abolished by the inhibitor of PKC, chelerythrine chloride. On the other hand, M(3)-mAChR could also regulate the expression of PKC-epsilon in ischemic myocardium. Choline (choline chloride, an M(3) receptor agonist, administered at 15 min before occlusion) strengthened the association between PKC-epsilon and M(3)-mAChR. However, blockade of M(3)-mAChR by 4-diphenylacetoxy-N-methylpiperidine methiodide (an M(3) receptor antagonist, administered at 20 min before occlusion) completely inhibited the effect of choline on the expression of PKC-epsilon. We conclude that the translocation of PKC-epsilon is required for the phosphorylation of M(3)-mAChR; moreover, increased PKC-epsilon activity is associated with M(3)-mAChR during MI. This reciprocal regulation is likely to play a role in heart signal transduction during ischemia between ventricular myocytes.