Rui-Huan Duan

Phosphonate-Stabilized Titanium-Oxo Clusters with Ferrocene Photosensitizer: Structures, Photophysical and Photoelectrochemical Properties, and DFT/TDDFT Calculations

The metal-to-core charge transfer (MCCT) transition in sensitized titanium-oxo clusters is an important process for photoinduced electron injection in photovoltaic conversion. This process resembles most closely the Type II photoinjection in dye-sensitized solar cells. Herein we report the synthesis and photophysical and photoelectrochemical (PEC) properties of the phosphonate-stabilized titanium-oxo clusters containing the ferrocenecarboxylate ligands. These ferrocene-containing clusters exhibit intense visible absorption extended up to 600 nm along with low optical band gaps of ∼2.2 eV. The low-energy transitions of these clusters were systematically investigated by UV-vis spectroscopy and DFT/TDDFT calculations. The combined experimental and computational studies suggest that the ferrocenecarboxylate-substituted titanium-oxo clusters form a donor-acceptor (D-A) system. The low-energy transition of these clusters primarily involves the MCCT from the iron center to TiO cluster core. The TiO core structure and phosphonate ligands both have great influence on the PEC properties of the clusters. This work provides valuable examples for the sensitized titanium-oxo clusters in which electron injection takes place via MCCT transition.

Ba6Li2CdSn4S16: lithium substitution simultaneously enhances band gap and SHG intensity

Herein, a new noncentrosymmetric (NCS) compound Ba6Li2CdSn4S16 (1) was discovered. As compared to its isostructural Ba6Ag2CdSn4S16 (2), compound 1 with Li substitution exhibited enlarged band gap (1: 3.02 eV vs.2: 2.70 eV) as well as enhanced second harmonic generation intensity (SHG, 1: 7.6 vs.2: 5.3 × AgGaS2 at 2.05 μm laser radiation). This is rare because the band gap of an NLO compound is usually inversely related to the SHG intensity. Both structures were chararcterized by single crystal X-ray diffraction techniques. The three-dimensional (3D) frameworks are constructed by corner-sharing SnS4 and (Li/Cd)S4 or (Ag/Cd)S4 tetrahedra with Ba2+ as counter cations. Density functional theory calculations (DFT) have confirmed that Li+ plays a significant role in the widening of the band gap and enhancement of the SHG response due to its strong ionicity. Because Li has small electronegativity and strong ionic bond nature, in comparison with that of 2, the top of the VB in 1 is driven down to lower energy regions to widen Eg, and the non-bonding ingredients of S-3p states are increased in 1 to produce stronger SHG intensity. The calculated d23 for 1 and 2 are 27.81 and 17.30 pm V−1 respectively, that agree with the experimental observations.

Syntheses, structures, and properties of sulfides constructed by SbS4 teeter-totter polyhedra: Ba3La4Ga2Sb2S15 and BaLa3GaSb2S10

Two new pentanary sulfides Ba3La4Ga2Sb2S15 (1) and BaLa3GaSb2S10 (2) have been discovered by high temperature solid state reactions. Ba3La4Ga2Sb2S15 features a new zero-dimensional structure type, which consists of unique isolated Sb2S7 dimers and GaS4 tetrahedra. In contrast, with less GaS4 tetrahedra in the formula, BaLa3GaSb2S10 forms a one-dimensional structure which is constructed by teeter-totter (SbS4)n chains and isolated GaS4 tetrahedra. On the basis of UV/Vis spectroscopy, their band gaps are determined to be 2.42 and 2.15 eV, respectively, which are much wider than that of analogue La4FeSb2S10 (1.0 eV). In addition, theoretical studies illustrate the important role of Ga in expanding the band gaps with respect to Fe atoms. The calculated crystal orbital Hamilton population and electron localization function confirm that the long Sb–S bonds in Ba3La4Ga2Sb2S15 (2.932(2) A) and BaLa3GaSb2S10 (3.216(5) and 3.219(5) A) have weak but nonnegligible bonding interactions.