“Old dog, new tricks”: the lone pair effect inducing divergent optical responses in lead cyanurates containing π-bonds

Abstract

The stereochemically active lone pair (SCALP) effect of Pb²⁺ plays a vital role in enhancing the nonlinear optical response and engineering the band gap of lead-based materials with intriguing properties. Herein, we combined SCALP Pb²⁺ cations and π-conjugated (HC₃N₃O₃)²⁻ anions into one structure to investigate the tunable optical properties. Two lead cyanurates, namely, Pb₃(HC₃N₃O₃)₂(OH)₂ (I) and its partly cadmium-substituted analog Pb₂Cd(HC₃N₃O₃)₂(OH)₂ (II) were grown by the mild hydrothermal method. They exhibited greatly narrowed bandgaps and enhanced optical anisotropy resulting from the SCALP effect. In addition, divergent optical responses induced from the involved Pb (6s²6p²) and Cd (4d¹⁰5s²) were elaborated by a combination of experimental and theoretical analyses.