Organic-inorganic hybrid metal halide perovskites, an emerging class of solution processable photoactive materials, welcome a new member with a one-dimensional structure. Herein we report the synthesis, crystal structure and photophysical properties of one-dimensional organic lead bromide perovskites, C4N2H14PbBr4, in which the edge sharing octahedral lead bromide chains [PbBr4 2−]∞ are surrounded by the organic cations C4N2H14 2+ to form the bulk assembly of core-shell quantum wires. This unique one-dimensional structure enables strong quantum confinement with the formation of self-trapped excited states that give efficient bluish white-light emissions with photoluminescence quantum efficiencies of approximately 20% for the bulk single crystals and 12% for the microscale crystals. This work verifies once again that one-dimensional systems are favourable for exciton self-trapping to produce highly efficient below-gap broadband luminescence, and opens up a new route towards superior light emitters based on bulk quantum materials.

Single crystalline zero-dimensional organic metal halide hybrids have been developed.

Chromium(VI) sites homogeneously dispersed in a transparent silica xerogel matrix have been investigated to determine the coordination environment and rationalize the Raman spectra. X-ray absorption fine structure (EXAFS) analysis gives a structure that is consistent with Cr containing two terminal oxygens and is bound to the silica by two Cr-O-Si linkages. The structure was refined to an R factor of 1.28%. The terminal CrdO bonds were found to have a bond length of 1.60 Å and bridging Cr-O bonds of 1.80 Å. The Raman spectrum, collected with 785 nm excitation above the absorption edge of the chromium, shows a strong band at 986 cm -1 and a resolved shoulder at 1001 cm -1 . Isotopic labeling and polarization studies of low concentrations of Cr (0.5 mol %) indicate that the strong 986 cm -1 band is the totally symmetric Cr(dO) 2 mode; however, the isotopic shift and strong polarization of the 1001 cm -1 mode preclude it from being the antisymmetric component of the terminal dioxo stretch. At higher concentrations (e5.0 mol %) the high-energy shoulder becomes a resolved peak at 1004 cm -1 . While isotopic labeling shifts the peak to a position predicted for the antisymmetric stretch, the polarization ratio increases but does not reach a value that is unambiguous for an antisymmetric mode.

The detailed mechanism by which ethylene polymerization is initiated by the inorganic Phillips catalyst (Cr/SiO 2 ) without recourse to an alkylating co-catalyst remains one of the great unsolved mysteries of heterogeneous catalysis. Generation of the active catalyst starts with reduction of Cr VI ions dispersed on silica. A lower oxidation state, generally accepted to be Cr II , is required to activate ethylene to form an organoCr active site. In this work, a mesoporous, optically transparent monolith of Cr VI /SiO 2 was prepared using sol-gel chemistry in order to monitor the reduction process spectroscopically. Using in situ UV-vis spectroscopy, we observed a very clean, step-wise reduction by CO of Cr VI first to Cr IV , then to Cr II . Both the intermediate and final states show XANES consistent with these oxidation state assignments, and aspects of their coordination environments were deduced from Raman and UV-vis spectroscopies. The intermediate Cr IV sites are inactive towards ethylene at 80 °C. The Cr II sites, which have long been postulated as the endpoint of CO reduction, were observed directly by high-frequency/high-field EPR spectroscopy. They react quantitatively with ethylene to generate the organoCr III active sites, characterized by X-ray absorption and UV-vis spectroscopy, which initiate polymerization.