Crystal structure and stimulus-responsive properties of three functional compounds containing 1-carboxyethyl-4,4′-bipyridine.

• Three compounds containing 1-carboxyethyl-4,4′-bipyridine have been synthesized. • Compounds 1 and 3 exhibit photochromism, while 2 reveals hydrochromism upon heating. • Photo-controlled fluorescence and ink-free erasable printing abilities are discussed. Herein, three compounds containing the neutral viologen derivative, 1-carboxyethyl-4,4′-bipyridine (CEbpy) have been synthesized, (CEbpy)·(H 2 TPDC)·2H 2 O (1) [Co(CEbpy)(TPDC)(H 2 O) 4 ]·3H 2 O (2) and [Cd 3 (CEbpy) 2 (TPDC) 3 ·7H 2 O] n (3) (H 2 TPDC = thiophene-2,5-dicarboxylic acid). Compound 1 is a supramolecular assembly, linked by non-covalent interactions to constitute the donor-acceptor (D-A) system. Compound 2 owns a zero-dimensional (0D) isolated structure in which metal ions are coordinated with CEbpy and fully deprotonated (TPDC)2- ligands. Compound 3 exhibits a three-dimensional (3D) framework of trinuclear metal clusters, where each metal atom forms its own distinct linear one-dimensional (1D) chain along a specific axis. Although the three compounds comprise the same bipyridinium moiety and aromatic acid, their chromic behaviors are different. Compounds 1 and 3 exhibit reversible photochromism, while 2 reveals hydrochromism upon heating. Additionally, photo-modulated fluorescence as well as their potential applications in inkless erasable printing have been studied. [Display omitted] [ABSTRACT FROM AUTHOR]