Multistimuli Responsive Solid-State Emission of a Zinc(II) Complex with Multicolour Switching

Abstract

The development of smart luminescent materials, especially those stimulus-responsive fluorescent materials that can switch between different colors repeatedly under external stimulation based on a single molecule, is of great significance but a challenge. In this work, a novel zinc(II)−Schiff base complex (ZnL 2 ) was obtained and characterized. Upon exposure to the HCl and NH 3 vapors, it displayed remarkable tricolor acidochromic behavior with high contrast and rapid response under the ambient light as well as UV light (365 nm). The XPS analyses of ZnL 2 crystals before and after HCl/NH 3 fuming show that the acidochromism originates principally from the adsorption of vapor and the gas−solid reaction equilibrium on the crystal surface. The reddish-brown color of the HCl-fumigated ZnL 2 crystals could be attributed to the generation of HL at the surface of ZnL 2 , and red-shifted emission could be ascribed to the self-absorption effect. The single crystal X-ray diffraction data indicate that these processes cause slight changes in the molecular conformation and crystal packing. ZnL 2 shows reversible mechanochromic luminescence behavior between yellow and orange emission during the grinding−fuming/heating cycles due to the modulation between amorphous and crystalline states. Moreover, ZnL 2 was successfully made into test paper for the rapid detection of HCl/NH 3 vapors and mechanical stimuli.

Thermo-, Mechano-, and Vapochromic Dinuclear Cuprous-Emissive Complexes with a Switchable CH3CN–Cu Bond

“…Stimuli-responsive luminescent materials, especially those with high-contrast luminescence colors that are reversibly convertible to each other, have received considerable interest for their potential applications in optical sensor, data recording, bioimaging, and security system. − However, the dual- and multiple-stimuli-responsive systems, particularly those with multicolor luminescence, are quite limited relative to the single-stimulus responsive ones. − Stimuli-responsive luminescent materials based on metal complexes have become a research hotspot in recent years due to their advantages of easy modification of organic compounds and stability of inorganic compounds. − Most of them are the platinum-, gold-, silver-, and other precious-metal-based complexes. − Some copper- and zinc-based complexes also show good stimuli-responsive luminescence properties. − Cuprous complexes are attractive for developing low-cost stimuli-responsive luminescent materials because of their good luminescent properties and diverse structures and abundant Cu element. − However, it remains a challenge to precisely design multi-stimuli-responsive cuprous-emissive complexes that are easily synthesized and exhibit switchable multicolor luminescence.…”

Multistimuli-responsive materials based on a zinc(ii) complex with high-contrast and multicolor switching

“…The zinc( ii ) complex ( 1 ) was obtained through the self-assembly solvothermal synthesis of 3-(2-benzothiazolyl)-2-hydroxybenzaldehyde (HBT-CHO), 4-(1,2,2-triphenylethenyl)benzenamine (TPE-NH 2 ), zinc( ii ) acetate dihydrate, and acetic acid in ethanol (Scheme 1). In our previous study, 42 we obtained a mononuclear zinc complex with O (hydroxyl) and N (CN) involved in coordination. In this study, we added twice the amount of Zn(OAc) 2 relative to the other reactants and a small amount of acetic acid to allow the acetate group to participate in coordination.…”

“…However, our previously reported mononuclear complex synthesized using the same ligand (HL) only exhibited luminescence of each state between light-yellow and orange (578–608 nm). 42 To better compare and understand the MCL properties of these two complexes, we further explore their molecular structure features. Compared with the mononuclear complex, there are ethanol molecules in the lattice, and acetate groups participate in the coordination to form the one-dimensional chain polymer (complex 1 ).…”

“…The patterns of 1-HCl and 1-HCl-NH 3 still exhibit sharp and intense diffraction peaks consistent with 1 , and the sharp diffraction peak of the sample under multiple HCl/NH 3 vapor fumigation cycles ( 1-HCl-NH 3 -n ) at 2 θ = 32.16° corresponds to the peak of NH 4 Cl resulting from the reaction of adsorbed HCl with NH 3 . Based on our previous research, 42 we compared the UV-visible absorption spectra in the solid and solution states of ligand HL and complex 1 before and after HCl/NH 3 vapor fumigation. Fig.…”

Thermosalience coupled to abrupt spin crossover with dynamic ligand motion in an iron(ii) molecular crystal

“…On-demand control of a specific property in molecular materials by various stimuli such as heat, light, and force and utilizing these materials for future devices are ongoing challenging issues. Recently, numerous crystalline molecular materials that exhibit various stimuli-responsive switching properties such as electric, 1 magnetic, 2 photophysical, 3 and macroscopic mechanical properties 4 have been reported. Such stimuli-responsiveness and related switching properties can be designed primarily by the choices of the individual molecule and its structure, intermolecular interactions, and whole three-dimensional (3D) architecture (molecular packing); however, they are significantly affected by the flexibilities of molecules in a crystal lattice such as conformational change, 5 isomerization, 6 rotation, 7 and order–disorder transitions.…”