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

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-, -, lone pair- interactions) can not only generate 3D supramolecular structures, but also improve structural thermostabilities up to approximately 405 degrees C and 330 degrees 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- 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.