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ABSTRACT: A series of metal-free organic donor-π bridge-acceptor dyes are studied computationally using density functional theory (DFT) and time-dependent DFT (TDDFT) approaches to explore their potential performances in dye-sensitized solar cells (DSSCs). Taking triphenylamine (TPA) and cyanoacrylic acid moieties as donor and acceptor units, respectively, the effects of different substituents of the π linkers in the TPA-based dyes on the energy conversion efficiency of the DSSCs are theoretically evaluated through optimized geometries, charge distributions, electronic structures, simulated absorption spectra, and free energies of injection. The results show that the molecular orbital energy levels and electron-injection driving forces of the TPA dyes can be tuned by the introduction of substituents with different electron-withdrawing or -donating abilities. The electron-withdrawing substituent always lowers the energies of both frontier orbitals, while the electron-donating one heightens them simultaneously. The efficiency trend of these TPA derivatives as sensitizers in DSSCs is also predicted by analyzing the light-harvesting efficiencies and the free energies of injection. The following substituents are shown to increase the efficiency of the dye: OMe, OEt, OHe, and OH.
ChemPhysChem 07/2012; 13(14):3320-9. · 3.41 Impact Factor
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ABSTRACT: AbstractThe ground-state geometries, electronic structures, and electronic absorption spectra of symmetrical squaraine dyes SQ1–SQ4
were investigated using density functional theory and time-dependent DFT at the B3LYP level. The calculated geometries indicate
that strong conjugation effects occur in the dyes. The highest occupied molecular orbital energy levels were calculated to
be −4.95, −5.22, −5.09, and −5.06eV, and the lowest unoccupied molecular orbital energies were −2.72, −3.05, −2.80, and −2.80eV
for SQ1–SQ4, respectively. Taking the conduction band energy of TiO2 into account, these data reveal the sensitized mechanism: the interfacial electron transfer between the semiconductor TiO2 electrode and the dye sensitizers SQ1–SQ4 are electron-injection processes from excited dyes to the semiconductor conduction
band. The intense calculated absorption bands are assigned to π→π* transitions, which exhibit appreciable blue-shift compared
with the experimental absorption maxima due to the inherent approximations in the TD-DFT.
Graphical abstract
KeywordsDensity functional theory-Squaraine dyes-Dye-sensitized solar cells-Electronic structures-Absorption spectra
Monatshefte fuer Chemie/Chemical Monthly 05/2012; 141(5):549-555. · 1.53 Impact Factor
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ABSTRACT: The ability of the Weighted Holistic Invariant Molecular (WHIM) and GEometry, Topology, and Atom-Weights AssemblY (GETAWAY)
descriptors to represent the effect of molecular structure on the infinite dilution activity coefficients (γ
∞) of chlorinated organic compounds in aqueous solution was investigated. To this end, the dataset of 45 chlorinated organic
compounds was randomly divided into a training set (35) and a test set (10). The genetic algorithm was employed for descriptor
selection and model development. Afive-parameter correlation equation for ln(γ
∞) was obtained, with a squared correlation coefficient (R
2) of 0.9609 and a standard error of estimation (s) of 0.599 for the training set. The reliability of the proposed model was further illustrated by means of the leave-one-out
cross-validation procedure and validation through an external test set. All descriptors involved in the model can be derived
directly from the structures of the compounds, which makes it very useful in predicting γ
∞ of other chlorinated organic compounds not involved in the present dataset.
KeywordsQSPR-Infinite dilution activity coefficients-Chlorinated organic compounds-Genetic algorithm-WHIM descriptors-GETAWAY descriptors
Journal of Solution Chemistry 04/2012; 40(1):118-130. · 1.41 Impact Factor
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ABSTRACT: Thermal decomposition of poly(lactic acid) (PLA) has been studied using thermogravimetry coupled to Fourier transform infrared
spectroscopy (TGA-FTIR). FTIR analysis of the evolved decomposition products shows the release of lactide molecule, acetaldehyde,
carbon monoxide and carbon dioxide. Acetaldehyde and carbon dioxide exist until the end of the experiments, whereas carbon
monoxide gradually decreases above the peak temperature in that the higher temperature benefits from chain homolysis and the
production of carbon dioxide. A kinetic study of thermal degradation of PLA in nitrogen has been studied by means of thermogravimetry.
It is found that the thermal degradation kinetics of PLA can be interpreted in terms of multi-step degradation mechanisms.
The activation energies obtained by Ozawa–Flynn–Wall method and Friedman’s method are in good agreement with that obtained
by Kissinger’s method. The activation energies of PLA calculated by the three methods are 177.5kJmol−1, 183.6kJmol−1 and 181.1kJmol−1, respectively.
Journal of Thermal Analysis and Calorimetry 04/2012; 97(3):929-935. · 1.60 Impact Factor
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ABSTRACT: Crystallization, melting, hydrolytic degradation, and mechanical properties of poly(trimentylene terephthalate)/poly(lactic
acid) (PTT/PLA) blends have been investigated. The blends show a single and composition-dependent glass-transition temperature
(T
g) over the entire composition range, implying that these blends are fully miscible in the amorphous state. The observed T
g is found to increase with increasing PLA content and fitted well with the Gordon–Taylor equation, with the fitting parameter
k being 0.91. The cold-crystallization peak temperature increases, while the melt-crystallization peak decreases with increasing
the PLA content. Both the pure PTT and PTT/PLA blends cannot accomplish the crystallization during the cooling procedure and
the recrystallization occurs again on the second heating. Therefore, on the thermogram recorded, there is exothermal peak
followed by endothermal peak with a shoulder. However, to pure PLA, no crystallization takes place during cooling from the
melt, therefore, no melting endothermic peak is found on the second heating curve. WAXD analysis indicates PLA and PTT components
do not co-crystallize and the crystalline phase of the blends is that of their enriched pure component. With increasing PLA
content, the hydrolytic degradation of the blend films increases, while both the tensile strength and the elongation at break
of the blend films decrease. That is to say, the hydrolytic degradation of the PTT/PLA blends increases with the introduction
of PLA at the cost of the decrease of the flexibility of PTT.
Polymer Bulletin 04/2012; 64(5):471-481. · 1.53 Impact Factor
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ABSTRACT: The quantitative structure-property relationship (QSPR) studies were performed between molecular structures and impact sensitivity for a diverse set of nitro energetic compounds based on three-dimensional (3D) descriptors. The entire set of 156 compounds was divided into a training set of 127 compounds and a test set of 29 compounds according to Kennard and Stones algorithm. Multiple linear regression (MLR) analysis was employed to select the best subset of descriptors and to build linear models; while nonlinear models were developed by means of artificial neural network (ANN). The obtained models with ten descriptors involved show good predictive power for the test set: a squared correlation coefficient (R²) of 0.7222 and a standard error of estimation (s) of 0.177 were achieved by the MLR model; while by the ANN model, R² and s were 0.8658 and 0.130, respectively. Therefore, the proposed models can be used to predict the impact sensitivity of new nitro compounds for engineering.
Journal of molecular graphics & modelling 03/2012; 36:10-9. · 2.17 Impact Factor
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ABSTRACT: The molecular structures and absorption spectra of three tetrahydroquinoline dyes (C2–1, C1–1, and C1–5) with a tetrahydroquinoline moiety as the electron donor, a cyanoacrylic acid moiety as the electron acceptor, and different thiophene-containing electron spacers were investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT). The calculated geometries indicate that a strong conjugation is formed in the dyes and the conjugate length increases with the increase of spacer length. The interfacial charge transfer between the semiconductor electrode and the tetrahydroquinoline dyes are electron-injection processes from the excited dyes to the semiconductor conduction band. The simulated absorption bands are assigned to π–π* transitions, which exhibit appreciable red-shift with respect to the experimental bands owing to the lack of direct solute–solvent interaction and the inherent approximations in TD-DFT. Moreover, the effect of different spacers on the molecular structures, absorption spectra, and photovoltaic performance were comparatively discussed.
Canadian Journal of Chemistry 08/2011; 89(8):978-986. · 1.24 Impact Factor
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ABSTRACT: The molecular structures and absorption spectra of triphenylamine dyes containing different numbers of anchoring groups (S1-S3) were investigated by density functional theory (DFT) and time-dependent DFT. The calculated geometries indicate that strong conjugation is formed in the dyes. The interfacial charge transfer between the TiO(2) electrode and S1-S3 are electron injection processes from the excited dyes to the semiconductor conduction band. The simulated absorption bands are assigned to π → π* transitions according to the qualitative agreement between the experimental and calculated results. The effect of anchoring group number on the molecular structures, absorption spectra and photovoltaic performance were comparatively discussed.
Journal of Molecular Modeling 08/2011; 18(5):1767-77. · 1.80 Impact Factor
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ABSTRACT: A quantitative structure-property relationship (QSPR) study was performed for the prediction of the Setschenow constants (K(salt)) by sodium chloride of organic compounds. The entire set of 101 compounds was randomly divided into a training set of 71 compounds and a test set of 30 compounds. Multiple linear regression, artificial neural network (ANN), and support vector machine (SVM) were utilized to build the linear and nonlinear QSPR models, respectively. The obtained models with four descriptors involved show good predictive ability. The linear model fits the training set with R(2) = 0.8680, while ANN and SVM higher values of R(2) = 0.8898 and 0.9302, respectively. The validation results through the test set indicate that the proposed models are robust and satisfactory. The QSPR study suggests that the molecular lipophilicity is closely related to the Setschenow constants.
Journal of Computational Chemistry 08/2011; 32(15):3241-52. · 4.58 Impact Factor
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ABSTRACT: The thermal stability and thermal decomposition kinetics of poly(trimethylene-co-butylene terephthalate) (PTBT) copolymers in nitrogen were studied by means of thermogravimetry. The PTBT copolymers had good thermal stability in nitrogen and the introduction of copolymer component had a slight influence on the thermal stability of copolymers. The mass loss of PTBT copolymer was accomplished in one main mass loss stage and one small weight loss in the early stage of decomposition. The PTBT copolymers started to decompose at ≈350.0°C and completed decomposition at ≈440.0°C with the heating rate of 5°C/min. The characteristic degradation temperatures of PTBT copolymers shifted toward higher temperatures with increasing heating rates and poly(trimethylene terephthalate (PTT) content. Furthermore, various degradation methods, including the Ozawa–Flynn–Wall method, Friedman's method, and Kissinger's method, were used to determine the activation energies of copolymers. The three methods were applicable to the kinetic description of thermal degradation of PTBT copolymers. The thermal activation energies obtained by three methods were in satisfactory conformity. The thermal degradation kinetics of copolymers could be interpreted in terms of multi-step degradation mechanisms. It was shown that the thermal stability of PTBT copolymers increased with increase in PTT content. Copolymers with higher PTT content showed higher degradation temperature and thermal activation energy. A general activation energy range of 180–200 kJ/mol was suggested for the processing and use of PTBT copolymer fibers.
Journal of Macromolecular Science. 08/2011; Part B(Vol. 50):1559-1570.
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ABSTRACT: The non-covalent adsorption of the insensitive explosive TATB (1,3,5-triamino-2,4,6-trinitrobenzene) on the sidewalls of single-walled carbon nanotubes (CNTs) has been calculated using an ONIOM approach. It was found that TATB deformed remarkably when attached non-covalently on the surface of CNTs, especially on the inner wall of the nanotubes. The diameter of the nanotube determined the degree of distortion of the inner-adsorbed TATB, but had little effect on the deformation of the outer-attached TATB. The non-covalent combination of TATB with the nanotube is an exothermic process due to the negative adsorption energy. TATB adsorption on the inner wall of nanotubes was energetically more favorable than that on the outer wall of the nanotubes. In both cases, the adsorption became more stable with increasing diameter of the nanotube. Our theoretical results can be used as a guideline for the design of energetic nanocomposites based on CNTs and aromatic nitro-explosives.
Molecular Physics. 07/2011; 109(14):1841-1849.
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ABSTRACT: Chemical reactivity and molecular structure of energetic materials may be significantly changed when they are confined inside carbon nanotubes (CNTs). The ONIOM calculations were carried out to investigate the molecular structures and the N-N bond decomposition of nitramide (NA) and methylnitramine (MNA) confined inside armchair single-walled CNTs with different diameter. Results showed that confinement in CNT(6, 6) and CNT(7, 7) had no evident influence on the structure of NA and MNA. However, the structures of NA and MNA within CNT(5, 5) were altered significantly with respect to the structures of the isolated NA and MNA. Compared with NA, MNA showed stronger interaction with these CNTs studied. By analyzing the potential energy curve along the N-N bond, we found that the energy barriers of the N-N bond decomposition for the NA and MNA are decreased by 11.6 and 10.8 kcal/mol, respectively, due to the confinement of CNT(5, 5). Confinement in CNT(6, 6) resulted in a slight decrease in the activation energy. Confinement in CNT(7, 7) did not affect the thermal decomposition of NA and MNA. We conclude that the N-N bond dissociation of NA and MNA can be promoted by confinement in a CNT with small diameter.
Journal of Nanoscience and Nanotechnology 04/2011; 11(4):3298-305. · 1.56 Impact Factor
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ABSTRACT: The dissociation and isomerization reactions of methyl-nitramine(MNA) confined inside armchair CNT(5,5) single-walled carbon nanotube were investigated by using the ONIOM (B3LYP/6-311++G:UFF) method. The results showed that some geometries of the confined MNA were modified by the CNT(5,5) in comparison with the structure of the isolated MNA. By analyzing the relevant structures and energies involved in the dissociation and isomerization reactions, we found that the transition state structures of the isomerization reactions to form CH(3)NHONO (R1) and CH(3)NNOOH (R2) were modified by the confinement of CNT(5,5). However, this confinement does not evidently affect the transition state structure of the HONO elimination reaction (R3). In addition, no transition state was found for the N-N bond dissociation (R4) of the isolated MNA, but this dissociation process occurred via a transition state for the confined MNA. When MNA was confined inside CNT(5,5), the activation energies of R1, R2, and R4 were decreased obviously but the energy barrier of R3 was increased slightly. The order of activation energy for these four initial reactions was also changed by the confinement of CNT(5,5). Furthermore, it was found that the relative energies of the intermediates formed by the isomerization and dissociation of MNA were also modified by the confinement of CNT(5,5). These intermediates become more stable in the confined case than in the isolated case. It was concluded that the initial reactions of MNA could be modified evdiently by confinement within a carbon nanotube.
Journal of Molecular Modeling 01/2011; 17(11):2751-8. · 1.80 Impact Factor
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ABSTRACT: A quantitative structure–property relationship study was performed between descriptors representing the molecular structures and the absorption maxima (λmax) of organic dyes for dye-sensitised solar cells. The entire set of 70 dyes was divided into a training set of 53 dyes and a test set of 17 dyes according to Kennard and Stones algorithm. Seven descriptors were selected on the training set by genetic algorithm. Based on these seven descriptors, a nonlinear model with the squared correlation coefficient R 2 = 0.991 was developed by using artificial neural networks. The reliability of the proposed model was validated through the test set. All descriptors involved in the model were derived solely from the chemical structures of the dyes, which makes the model very useful to estimate the λmax of the dyes before they are actually synthesised.
Molecular Simulation 01/2011; 37(1):1-10. · 1.33 Impact Factor
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ABSTRACT: The molecular structures and absorption spectra of triphenylamine dyes containing variable thiophene units as the spacers (TPA1-TPA3) were investigated by density functional theory (DFT) and time-dependent DFT. The calculated results indicate that the strong conjugation is formed in the dyes and the length of conjugate bridge increases gradually with the increased thiophene spacers. The interfacial charge transfer between the TiO2 electrode and TPA1-TPA3 are electron injection processes from the excited dyes to the semiconductor conduction band. The simulated absorption bands are assigned to π→π* transitions, which exhibit appreciable red-shift with respect to the experimental bands due to the lack of direct solute-solvent interaction and the inherent approximations in TD-DFT. The effect of thiophene spacers on the molecular structures, absorption spectra and photovoltaic performance were comparatively discussed and points out that the choice of appropriate conjugate bridge is very important for the design of new dyes with improved performance.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 10/2010; 78(1):287-93. · 2.10 Impact Factor
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ABSTRACT: A quantitative structure-property relationship (QSPR) study was performed for the prediction of the absorption maxima (lambda(max)) of organic dyes for dye-sensitized solar cells (DSSCs). The entire set of 70 dyes was divided into a training set of 53 dyes and a test set of 17 dyes according to Kennard and Stones algorithm. Three-dimensional (3D) descriptors were calculated to represent the dye molecules. A ten-descriptor model, with a squared correlation coefficient (R(2)) of 0.9543 and a standard error of estimation (s) of 14.7 nm, was produced by using the stepwise multilinear regression analysis (MLRA) on the training set. The reliability of the proposed model was further illustrated using various evaluation techniques: leave-one-out cross-validation procedure, randomization tests, and validation through the external test set. All descriptors involved in the model were derived solely from the chemical structure of the dye molecules, which makes the model very useful to estimate the lambda(max) of dyes before they are actually synthesized.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 03/2010; 76(2):239-47. · 2.10 Impact Factor
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ABSTRACT: The quantitative structure–property relationship approach was performed to study the nematic transition temperatures (T N) in thermotropic liquid crystals. The multi-linear regression analysis (MLRA) and artificial neural networks (ANNs) were employed to develop linear and nonlinear models, respectively. The proposed linear model contains five descriptors, with the squared correlation coefficient R 2 of 0.9837 and the standard error of estimation s of 2.31. The mean relative errors (MREs) for the training and test sets are 3.15 and 5.21%, respectively. Better predictive results were obtained from the nonlinear model: the MREs for the training and test sets are 2.03% (R 2 = 0.9911 and s = 1.71) and 1.92% (R 2 = 0.9892), respectively.
Molecular Simulation 01/2010; 36(1):26-34. · 1.33 Impact Factor
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ABSTRACT: In this work, we carried out the hybrid density functional theory (DFT) calculations in order to understand the thermal trans-cis isomerization and initial thermal decomposition of 3,3'-diamino-4,4'-azofurazan (DAAzF), 3,3'-diamino-4,4'-azoxyfurazan (DAAF), 3,3'-dinitro-4,4'-azofurazan (DAAF) and 3,3'-dinitro-4,4'-azoxyfurazan (DAAzF). The relative energy between the trans- and cis-isomer was also calculated at the B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level of theory. We found that a negative correlation existed between the relative energy and the sensitivity for these energetic azofurazan and azoxyfurazan compounds, where the higher relative energy means the lower the sensitivity. It was also found that the oxidation of azo-group could cause the decreasing in the relative energy between the trans- and cis-isomer, as well as the alteration of the isomerization mechanism. An inversion mechanism operates for azofurazan compounds (DAAzF and DNAF) while a rotation mechanism works for azoxyfurazan compounds (DAAF and DNOAF). Compared with the thermal trans-cis isomerization, the homolytic cleavage of C-N bond needs to overcome a much higher energy barrier, which indicates that the energy of the external stimulus should firstly trigger the trans-cis isomerization, rather than the breakage of C-N bond. A self-desensitization effect caused by the reversible thermal trans-cis isomerization process was firstly proposed to explain that the azofurazan and azoxyfurazan compounds are class of energetic materials with lower sensitivity. This new concept (self-desensitization effect) is expected to be useful to design the novel high density, insensitive energetic material.
Journal of molecular graphics & modelling 05/2009; 28(2):81-7. · 2.17 Impact Factor
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Journal of Physical Organic Chemistry 03/2009; 22(9):888 - 896. · 1.96 Impact Factor
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ABSTRACT: Poly(trimethylene-co-butylene terephthalate) (PTBT) copolymers containing PTT and PBT components were synthesized with various compositions in order to blend their advantageous properties together into one polymer system and to improve further their disadvantageous properties. The non-isothermal crystallization of the copolymers at various cooling rates was investigated by DSC. PTBT copolymers develop their crystallization later and show lower melting temperatures than the homopolymer corresponding to the richest component. The non-isothermal crystallization of PTBT copolymers is fitted better by the modified Avrami analysis than the Ozawa analysis. The combined Avrami and Ozawa model (Mo model) is also found to describe the experimental data fairly well. The estimated Avrami exponent n varies in the range of 3-4, indicating that the non-isothermal crystallization follows the homogeneous nucleation and two to three dimensional growth mechanism. The crystallization rate is accelerated by increasing cooling rate but retarded by PTT units in the polymer backbones as a minor component. In addition, the activation energy of non-isothermal crystallization was estimated by the Kissinger approach. PTT and PBT homopolymers have relatively lower activation energy of crystallization than PTBT copolymers and in the crystallization process lower activation energy leads to more rapid crystallization rate.
Journal of Macromolecular Science®. 01/2009; 48(3):487-499.
