Different photochromic properties induced by lone pair–π interactions with varying strengths in two stereocontrolled self-assembly isomeric coordination polymers

Abstract

Two novel cadmium-based isomeric coordination polymers constructed from naphthalenediimide chromophoric components and aromatic dicarboxylic acids, [Cd(DPMNI)(m-BDC)]_n (1) and [Cd(DPMNI)(p-BDC)]_n (2) (DPMNI = N,N′-bis(4-pyridylmethyl)-1,4,5,8-naphthalenediimide, m-BDC²⁻ = isophthalate, p-BDC²⁻ = terephthalate) have been synthesized by solvothermal reactions and characterized systematically. Single-crystal X-ray diffraction analyses results indicate that compounds 1–2 possess the same basic building block, but show different 2D resultant constructions. The formation of non-covalent intermolecular interactions (CH–π, π–π, lone pair–π interactions) can not only generate 3D supramolecular structures, but also improve structural thermostabilities up to approximately 405 °C and 330 °C, according to their thermogravimetric analyses (TGA) results. Importantly, due to the stereocontrolled self-assembly of the isomeric coordination polymers, two kinds of lone pair–π interactions with varying strengths have been produced leading to different photochromic behaviors in 1–2. It is worth mentioning that the immediate photochromism of 1 is rare in NDI-based photochromic materials. Moreover, their photoluminescence properties have also been investigated to enrich the research on crystal photophysical properties.