ABSTRACT
Detection of oxygen though color change is highly desirable for rapid qualitative analysis like the case of pH test papers. This work demonstrates 3O2-assisted photoinduced color change of a new photochromic coordination compound [Zn(4-aminopyridine)2Cl2] (ZnaPyCl), which represents the first photochromic compound with a selective 3O2 detection ability. The compound underwent photoinduced intraligand charge separation and formed a stable diradical-like triplet species in the solid state or in frozen solution, accompanied by conversion of triplet oxygen to singlet oxygen.
ABSTRACT
A new design strategy through the synergy of Mo(vi)-Mo(v) intervalence charge transfer and π(radical)-π(radical/cation) interactions is proposed to obtain semiconductors with photoresponsive ranges covering the whole UV-SWIR (ultraviolet-shortwave near-infrared; ca. 250-3000 nm) region. With this strategy, a viologen-based molybdate semiconductor with a UV-SWIR photoresponsive range was obtained through UV/X-ray irradiation or thermal annealing. The thermally annealed semiconductor has the highest conversion and the best photocurrent response in the range of 355-2400 nm.
ABSTRACT
Photoresponse ranges of commercially prevailing photoelectric semiconductors, typically Si and InGaAs, are far from fully covering the whole solar spectrum (â¼295-2500 nm), resulting in insufficient solar energy conversion or narrow wave bands for photoelectric detection. Recent studies have shown that infinite π-aggregation of viologen radicals can provide semiconductors with a photoelectric response range covering the solar spectrum. However, controlled assembly of an infinite π-aggregate is still a great challenge in material design. Through directional self-assembly of electron-transfer photoactive polycyclic ligands, two crystalline inorganic-organic hybrid photochromic viologen-based bismuth halide semiconductors, ((Me)3pytpy)[BiCl6]·2H2O [1; (Me)3pytpy = N,N',Nâ³-trimethyl-2,4,6-tris(4-pyridyl)pyridine] and ((Me)3pytpy)[Bi2Cl9]·H2O (2), have been synthesized. They represent the first series of pytpy-based photochromic compounds. After photoinduced coloration, the conductivities of both 1 and 2 increased. The radical products have electron absorption bands in the range of 200-1600 nm, exceeding that of Si. Both the conductivity and the photocurrent intensity of 2 are stronger than those of 1, due to better planarity, tighter π-stacking, and higher degrees of overlap of ((Me)3pytpy)3+ cations. This study not only provides a new design idea for synthesizing radical-based multispectral photoelectric semiconductors but also enriches the family of electron-transfer photochromic compounds.
ABSTRACT
The effects of strong interactions between Ti and ceria on the structures of Ti/CeO2(111) are systematically investigated by density functional theory calculation. To our best knowledge, the adsorption energy of a Ti atom at the hollow site of CeO2 is the highest value (-7.99 eV) reported in the literature compared with those of Au (-0.88--1.26 eV), Ag (-1.42 eV), Cu (-2.69 eV), Pd (-1.75 eV), Pt (-2.62 eV) and Sn (-3.68 eV). It is very interesting to find that Ti adatoms disperse at the hollow site of CeO2(111) to form surface TiOx species, instead of aggregating to form Ti metal clusters for the Ti-CeO2 interactions that are much stronger than those of Ti-Ti ones. Ti adatoms are completely oxidized to Ti4+ ions if they are monatomically dispersed on the next near hollow sites of CeO2(111) (xTi-NN-hollow); while Ti3+ ions are observed when they locate at the near hollow sites (xTi-N-hollow). Due to the electronic repulsive effects among Ti3+ ions, the adsorption energies of xTi-N-hollow are slightly weaker than those of xTi-NN-hollow. Simultaneously, the existence of unstable Ti3+ ions on xTi-N-hollow also leads to the restructuring of xTi-N-hollow by surface O atoms of ceria transferring to the top of Ti3+ ions, or oxidation by O2 adsorption and dissociation. Both processes improve the stability of the xTi/CeO2 system by Ti3+ oxidation. Correspondingly, surface TiO2-like species form. This work sheds light into the structures of metal/CeO2 catalysts with strong interactions between the metal and the ceria support.
