A mass of porphyrin sensitizers have been designed and synthesized for dye-sensitized solar cells in previous works, and almost all of them incorporated an electron-rich system as the π-spacer. We here adopted the electron-deficient pyrimidine as an effective π-spacer and combined a cyanoacrylic acid anchoring group, as such a design yields a more bathochromic shift of the spectral absorption of the dye and results in an improved spectral overlap with the solar spectrum and an enhanced light-harvesting efficiency. The result does tally with the performance of sensitizer adsorbing on a semiconductor. From the electron density difference plots of electron transitions, we found that not all electron transitions could make for the effective electron transfer from donor to acceptor groups, which means the sensitizer performance in dye-sensitized solar cells not only relies on the extrinsic spectral absorption intensity but also depends on the intrinsic character of electron movement related to electron excitation. Moreover, the introduction of electron-deficient pyrimidine could affect the energy levels of excited molecules in solution, further affecting the kinds of electron transfer processes. We presented several novel porphyrin sensitizers for comparison on how the π-spacer and anchoring group influence the optical absorption, electron transfer processes, and regeneration of the oxidized dyes, thereby gaining potential dye-sensitized solar cells with highly efficient photo-to-electric conversion performances.

A series of dyes based on a porphyrin donor and a cyanoacrylic acid anchor/acceptor group for solar cell application are investigated with regards to varied-length p-spacers affecting the photo-to-electric conversion efficiency (PCE). Investigations are firstly performed on three porphyrin sensitizers with 1-3 conjugated phenylethynyl (PE) units, which have experimentally proved that the efficiency of power conversion decreases systematically with increasing spacer length. The distances and amounts of charge transfer after photoexcitation are calculated. In the PE bridged porphyrin dyes, the calculated electron injection driving forces and the regeneration driving forces gradually decrease as the distance of the p-spacer increases. Our theoretical calculations can reproduce well the experimental conclusion, showing that the photo-to-electric efficiency has a strong distance dependence for the electron-rich phenyl spacer.Then we replace the phenyl group with a pyrimidyl (PM) group to uncover how the characteristics of the p-spacer affect the performance of optical absorption, charge separation, and the regeneration process, to further improve the power conversion. We find that the adoption of electron-deficient pyrimidyl can break and even remove the distance dependence of the p-spacer. Some integral factors affecting the dye performance, such as short-circuit photocurrent, open-circuit voltage and charge collection efficiency are analyzed. It would help to interpret what role the electron deficient p-spacers with varied lengths will play and how they are expected to behave in the performance of sensitizers. In this regard, this study presents us with a promising way to design novel functional dyes and to utilize the potential advantages of the lengthy spacer dyes.

High resolved absorption and fluorescence spectra of zinc complexes of phthalocyanine (ZnPc) and tetrabenzoporphyrin (ZnTBP) in the region of Q states were reported. Few theoretical investigations were performed to simulate the well-resolved spectra and assigned the vibrational bands of the large molecules, especially for high symmetrical characteristic molecules, on account of the difficulties to optimize the excited states and analyze a large number of final vibrational-normal modes. In the present work, the S(0) ↔ S(1) absorption and fluorescence spectra (that is, the Q band) of ZnPc and ZnTBP were simulated using time-dependent density functional theory with the inclusions of Duschinsky and Herzberg-Teller contributions to the electronic transition dipole moments. The theoretical results provide a good description of the optical spectra and are proved to be in excellent agreement with experimental spectra in inert-gas matrices or in supersonic expansion. This study focused attentions on the optical spectral similarities and contrasts between ZnPc and ZnTBP, in particular the noticeable Duschinsky and Herzberg-Teller effects on the high-resolved absorption and fluorescence spectra were considered. Substitution of meso-tetraaza on the porphyrin macrocycle framework could affect the ground state geometry and alter the electron density distributions, the orbital energies that accessible in the Q band region of the spectrum. The results were used to help interpret both the nature of the electronic transitions in Q band region, and the spectral discrepancies between phthalocyanine and porphyrin systems.

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For the synthesis of vinyl boronate esters, the direct catalytic H2-acceptorless dehydrogenative boration of alkenes is one of the promising strategies. In this paper, the density functional theory method was employed to investigate the reaction mechanism of dehydrogenative boration and transfer boration of alkenes catalyzed by a zirconium complex (Cp2ZrH2). There are two possible pathways for this reaction: the alkene insertion followed by the dehydrogenative boration (path A) and the alkene insertion after the dehydrogenative boration (path B). The calculated results showed that path A is more favorable than path B, and that the rate-determining step is the C–B coupling step with an energy barrier of 18.7 kcal/mol. The reaction modes of the C–B coupling assisted dehydrogenative boration and the alkene insertion were also discussed. These analyses reveal a novel hydrogen release behavior in dehydrogenative boration and the alkene insertion modes and sequences were proposed to be of importance in the chemoselectivity of this reaction. In addition, the X ligand effect (X = H, Cl) on the catalytic activity of the zirconium complex was explored, indicating that the H ligand could enhance the catalytic activity of the complex for styrene dehydrogenative boration.

The synthesis of 1,1-diborylalkanes from readily available alkenes is an appealing method. The density functional theory (DFT) method was employed to investigate the reaction mechanism of 1,1-diborylalkanes, which was synthesized from alkenes and a borane, and the reaction was catalyzed by a zirconium complex Cp2ZrCl2. The entire reaction is divided into two cycles: dehydrogenative boration to form vinyl boronate esters (VBEs) and hydroboration of VBEs. This article focuses on the hydroboration cycle and elaborates on the role of the reducing reagents in the equilibrium of self-contradictory reactivity (dehydrogenative boration and hydroboration). The H2 and HBpin pathways were investigated as the reducing reagents in the hydroboration process. The calculated results showed that it is more advantageous to use H2 as a reducing agent (path A). Furthermore, the σ-bond metathesis is the rate-determining step (RDS) with an energetic span of 21.4 kcal/mol. This is consistent with the self-contradictory reactivity balance proposed in the experiment. The reaction modes of the hydroboration process were also discussed. These analyses revealed the origin of selectivity in this boration reaction, in which the σ-bond metathesis of HBpin needs to overcome the strong interaction between HBpin and the Zr metal. Meanwhile, the origin of the selectivity of different positions of H2 is the interaction between the σ­(H1–H2) → σ*­(Zr1–C1) overlap and these findings have implications for catalyst design and application.