Controlling Phase Transitions in Two-Dimensional Perovskites through Organic Cation Alloying.

We demonstrate control over the phase transition temperature of Ruddlesden-Popper two-dimensional (2D) perovskites by alloying alkyl organic cations of varying lengths. By blending hexylammonium with pentylammonium or heptylammonium cations in different ratios, we continuously tune the phase transition temperature of 2D perovskites from approximately 40 to -80 °C in both crystalline powders and thin films. Correlating temperature-dependent grazing incidence wide-angle X-ray scattering and photoluminescence spectroscopy, we also demonstrate that the phase transition in the organic layer couples to the inorganic lattice, impacting PL intensity and wavelength.

Photoinduced umpolung addition of carbonyl compounds with α,β-unsaturated esters enables the polysubstituted γ-lactone formation.

We herein report the photoinduced intermolecular umpolung addition of aromatic ketones/aldehydes with α,β-unsaturated esters via ketyl radical intermediates. Following an intramolecular transesterification, a variety of γ-lactone derivatives are readily accessed. Mechanistic investigations demonstrate the significant role of Hantzsch ester, which serves both as the electron and proton donor.