Azo-Label Heterometal-Organic Rhomboids Exhibiting Photoswitchable NIR Luminescence in Crystalline State

Solvent-Modulated Self-Assembly of Naphthalenediimide-Based Cd(II) Complexes and the Controllable Photochromism via Conformational Isomerization

Rational regulation of the properties of photochromic materials is a challenging and meaningful work. In the present work, NDI-based complexes, namely, [Cd_0.5(NDI)(HBDC)]·H₂O (1) and a series of conformational isomers of {[Cd(NDI)_0.5(BDC)]·MeCN}_n (2), were synthesized by varying the solvent conditions (H₂BDC = terephthalic acid, NDI = N,N'-bis(3-pyridylcarbonylhydrazine)-1,4,5,8-naphthalene diimide). Complex 1 exhibits a 0D mononuclear structure without photochromic behavior due to the bad conjugation of the naphthalene diimide moiety. The conformational isomers of complex 2 manifest a 3D network, showing ultra-fast photo-induced intermolecular electron transfer photochromic behavior under X-ray, UV, and visible light. However, they show different photochromic rates and coloring contrast upon photoirradiation, which originates from their difference in the distances of lone pair(COO)···π(NDI). This was realized via controlling the solvent ratio in the reaction system. In addition, compared to UV/X-ray light, 2 exhibits greater sensitivity to visible light and is an organic-inorganic hybrid material with photomodulated luminescence. Based on the excellent performance, complex 2 can be applied to filter paper, showing potential applications as an inkless printing medium and selective perception of ammonia and amine vapors in the solid state via different visual color changes.

Unusual motion of the n-methoxypropyl moiety observed in the photochromic crystals of an organorhodium dithionite complex with n-methoxypropyltetramethylcyclopentadienyl ligands

The crystalline-state photochromism of a new organorhodium dinuclear complex having n-methoxypropyltetramethylcyclopentadienyl (η⁵-C₅Me₄n-C₃H₆OCH₃) and photoresponsive dithionite (μ-O₂SSO₂) ligands was investigated directly by performing single-crystal X-ray diffraction experiments; a reversible conformational change of the n-methoxypropyl moiety was intriguingly observed during the course of a thermal back-reaction.

Radical-Doped Crystalline Lanthanide-Based Photochromic Complexes: Self-Assembly Driven by Multiple Interactions and Photoswitchable Luminescence

Stimuli-responsive functional materials, especially the light stimulation color change and tunable fluorescent materials, have received considerable attention because of their broad applications in smart materials. Herein, a series of lanthanide-based [Ln = Nd(III) (1), Sm(III) (2), Eu(III) (3), Gd(III) (4), Tb(III) (5), Yb(III) (6), and Lu(III) (7)] crystalline complexes were attained by simply adding the aqueous lanthanide nitrate solution to the water-soluble naphthalenediimide derivative. The obtained lanthanide-based crystalline materials not only show significant photochromism but also possess reactive organic radicals under ambient conditions. Intriguingly, photoswitchable near-infrared (NIR) fluorescence was realized in the crystalline complex 1. The structures of these crystalline materials were systematically studied to clarify the weak interaction-assisted charge-transfer process. The underlying multiple-interaction-assisted supramolecular self-assembly, the radical-doped nature, and the corresponding photochromic mechanism were thoroughly unearthed by single-crystal X-ray diffraction, in situ solid-state UV-vis diffuse reflectance, and electron paramagnetic resonance spectrometric analysis.