The electronic structures and excitation properties of three meso-pentafluorophenyl substituted zinc porphyrin–fullerene dyad

N Basicity of Substituted Fullero[60]/[70]pyrrolidines According to DFT/TD-DFT Calculations and Chemical Thermodynamics

The basicity thermodynamic parameters of pyridyl/imidazole-substituted fullero[60]/[70]pyrrolidines with respect to N heteroatoms in dichloromethane, which are necessary both to deepen insight into aromaticity "neque levia" and to create supramolecular chemical structures for application, are obtained and discussed in this work. Because of the presence of a chromophore in the molecules, the acid-base reactions of three C₆₀ derivatives functionalized in different ways and one C₇₀ derivative are studied using spectrophotometric titration with trifluoroacetic acid. The dependence of the pK values determined using the data on Hammett's acidity functions, H₀, for a binary nonaqueous solvent on the molecule's chemical structure is shown. Density functional theory (DFT) and time-dependent DFT (TD-DFT) at the B3LYP/6-311G(d,p) level were used for the optimization of the fullerene derivative structures and modeling of their UV-vis spectra. The pK_BH⁺ values of substituted fullero[60]/[70]pyrrolidines are predicted by quantum-chemical calculations.

Optoelectronic properties of diathiafulvalene-functionalized diketopyrrolopyrrole-fullerene molecular dyad

Single component molecular dyad donor-acceptor junction is an important type of organic solar cells. Understanding the optoelectronic properties of molecular dyad plays the critical role to develop active layer materials for such kind of solar cells. Here, diathiafulvalene-functionalized diketopyrrolopyrrole-fullerene (DFDPP-Ful) was selected as the representative system, and the geometries, electronic structures and excitation properties of DFDPP-Ful monomer and dimer were systematically investigated based on extensive quantum chemistry calculations. The transition configurations and molecular orbitals show that the effective electron donor and acceptor are DFDPP and fullerene moieties, respectively. It also found the light harvesting is dominated by local excitation in DFDPP moiety. Meanwhile, the hybridization and quasi-degeneration between charge transfer (CT) and local excitation exist. The dimer data suggest that the increased excited states contribute to the expanding of absorption spectra, and the excitations exhibit both the intermolecular and intra-molecular CTs. Also, the remarkable CT energy differences among the different dimer models for the lowest CT excited states support the strong interface and energy disorder in such system. Therefore, the suggestions for developing molecular dyad of single component organic solar cells would be the combination of increasing light absorption, enhancing CT and local excitation hybridization, as well as suppressing energy and interface disorder by the aid of molecular design.

Zinc porphyrin-anthraquinonylimidazole supramolecular dyads

In this work, the synthesis and spectroscopic characterization of new zinc porphyrin-anthraquinone dyads is proposed. In particular, electron donor units based on zinc meso-tetraphenylporphyrin (ZnTPP) and zinc octaethylporphyrin (ZnOEP) have been coupled with differently substituted anthraquinones as acceptors. The quinone moiety was properly functionalized with imidazole, thus ensuring porphyrin complexation through zinc ion coordination. Accordingly, absorption and emission measurements demonstrated that the coordination occurred, and calculated binding constants were in the range 6.6 [Formula: see text] 10[Formula: see text]–3.9 [Formula: see text] 10[Formula: see text] M[Formula: see text]. Transient absorption spectroscopy for ZnTPP and ZnOEP dyads demonstrated that the electron transfer occurred, with the formation of the corresponding charge separated state, ZnTPP[Formula: see text]-AQ. Moreover, in ZnOEP complexes, a strong correlation between the chain length and flexibility with the charge separated state lifetime was observed.

Fusing Thienyl with N-Annulated Perylene Dyes and Photovoltaic Parameters for Dye-Sensitized Solar Cells

Due to the role of dyes in dye-sensitized solar cells (DSSCs), designing novel dye sensitizers is an effective strategy to improve the power conversion efficiency. To this end, the fundamental issue is understanding the sensitizer's trilateral relationship among its molecular structure, optoelectronic properties, and photovoltaic performance. Considering the good performance of N-annulated perlyene dye sensitizers, the geometries, electronic structures, and excitations of the selected representative organic dye sensitizers C276, C277, and C278 as well as dyes adsorbed on TiO₂ clusters were calculated in order to investigate the relationship between molecular structures and properties. It was found that fusing thienyl to N-annulated perlyene can elevate the highest occupied molecular orbital (HOMO) energy, reduce the orbital energy gap, increase the density of states, expand the HOMO to the benzothiadiazole moiety, enhance the charge transfer excitation, elongate the fluorescence lifetime, amplify the light harvesting efficiency, and induce a red-shift of the absorption spectra. The transition configurations and molecular orbitals of the dye-adsorbed systems support that the electron injection in DSSCs based on these dyes is a fast mode. Based on extensive analysis of the electronic structures and excitation properties of these dye sensitizers and the dye-adsorbed systems, we present new quantities as open-circuit voltage and short-circuit current density descriptors that celebrate the quantitative bridge between the photovoltaic parameters and the electronic structure-related properties in order to expose the relationship between properties and performance. The results of this work are critical for the design of novel dye sensitizers for solar cells.