Multinuclear Pd(II) oligomeric nanohoop complexes with 2,2′‐bipyridyl‐embedded cycloparaphenylenes ligands exhibiting ultrahigh third‐order nonlinear optical performance

Abstract

AbstractUnlike traditionally available linear frameworks, cyclic transition‐metal architectures with cycloparaphenylenes (CPPs) ligands provide new access to develop modern nonlinear optical (NLO) materials. In this work, a sequence of “staircase” Pd(II) oligomeric nanohoop complexes with the 2,2′‐bipyridyl‐embedded CPPs ligand unit through “series connection” mode and “Ω‐type” Pd(II) trimeric isomer have been systematically designed and investigated via density functional theory. Herein, we first report the dependence of third‐order NLO responses on the number of bipyridine CPP building ligands in a quantitative way. Impressively, the Pd(II) trimeric complexes possess ultrahigh third‐order NLO responses, which are ascribed to the large orbital delocalization and decreased energy gap. To our delight, the enlargement of the nanohoop size is beneficial to improving third‐order NLO responses for Pd(II) oligomeric nanohoop complexes, and the maximum absorption spikes show the blue shift tendency. The effect of size on the third‐order NLO responses becomes much larger with the addition of bipyridine CPPs ligand. Overall, we hope the current work will deliver a new quantitative structure–property relationship toward the design and synthesis of Pd(II) oligomeric nanohoop complexes with high third‐order NLO responses.