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

Abstract

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-interactionassisted 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.

A new photochromic Mg(II)‐viologen complex with photoswitchable emission and its application in ink‐free printing

“…The photochromic process to generate colored radicals of complex 1 involves photoinduced electron‐transfer from the carboxyl group to the bipyridinium unit. The absorption peak of the colored radicals, by partly overlapping with their emission band, is self‐attenuated, resulting in the quenching of the fluorescence of complex 1 [67] …”

Modulation of magnetization dynamics of an Er(iii) coordination polymer by the conversion of a ligand to a radical using UV light

“…2a and b). 38,39 After irradiation with 365 nm light, EPR signals at g = 2.0037 and 2.0036 are observed for 1a and 1a@Y, respectively, indicative of the existence of light-generated radicals. These g values are very close to that of a free electron found at 2.003 in HACA and 2.004 in ACA − based complexes.…”

Dual Photo-/Electrochromic Pyromellitic Diimide-Based Coordination Polymer

“…Stimuli-responsive chromic materials are a class of important smart materials, which exhibit a reversible transformation between two color forms in response to external physical or chemical stimuli, such as light, − electricity, − pressure, − heat, , pH, and organic amines. , Especially, bifunctional chromic materials with excellent photoelectric properties have been aroused great attention on account of their potential applications in smart windows, storage, energy conversion, gas sensing, camouflage, and cellular imaging. − Notably, the strategy of the development of bifunctional chromic materials, especially for the dual photo-/electrochromic coordination polymers (CPs), is an ingenious selection of redox organic ligands and assembles with the metal ions to regulate the local interactions . Although dual photo-/electrochromic behaviors have been observed in a series of CPs, it is restricted to the usage of a few species of ligands with strong electron-deficient characteristic and redox nature, such as viologen derivatives (V) and naphthalene diimide derivatives (NDIs). − However, the darker original colors of the most V-based and NDI-based CPs are not beneficial for the coloration contrast of photochromic and/or electrochromic materials. − Therefore, the development of novel organic ligands with suitable redox characteristics can not only enrich the species of bifunctional chromic materials but also endow them extraordinary photo-/electrochromic properties.…”