Dynamic Aggregation Triggering Reversible Spin-State Switching

Abstract

The manipulation of spin-state switching (SSS) under ambient conditions is of significant importance for the construction of molecular switches. Herein, we demonstrate that reversible SSS can be mediated by the aggregation state of a near-infrared (NIR)-sensitive ferrous complex. The ferrous complex was J-aggregated in a DMF suspension and with a low-spin (LS) state; however, with the addition of water, it changed to H-aggregation and reached a high-spin (HS) state, owing to the enhanced intramolecular charge transfer and metal-to-ligand charge transfer. Interestingly, the following NIR irradiation can restore the J-aggregation and LS states owing to the enhanced ligand-to-ligand charge transfer. More interestingly, the ferrous complex can be further incorporated into a hygroscopic sponge that was capable of capturing humidity effectively for all weather conditions, which displayed reversible SSS via alternating atmospheric humidity capture and NIR irradiation under ambient conditions in the sponge state. This study thus opens up a new avenue for the development of novel smart molecular switches at the device level.

Charge transfer-triggered reversible spin-state switching

“…The D–A type NIR-II fluorophores L -C 2 H 5 were synthesized via the Schiff Base reaction using 1,10-phenanthroline-5,6-dione and 4,7-bis(4-(diethylamino)phenyl)benzo[ c ] [1,2,5] thiadiazole-5,6-diamine (Scheme S1, ESI†). 48 The dissolution of L -C 2 H 5 in DMF solution has given birth to a green-colored transparent solution with only a slight Tyndall effect under light (Fig. 1a), and the precipitation has provided a green-colored powder (Fig.…”

“…36,38,44 In contrast, far fewer achievements have been made via the charge transfer (CT) to regulate the π-A/D features of ligands to trigger SSS. 45–48…”

Visible-Light-Responsive Photoreversible Color Switching of Oxygen-Deficient WO3–x Hierarchical Nanostructures for Long-Legible Rewritable Paper

“…Photoreversible color switching materials (PCSMs) that can reversibly change color under light stimulation have attracted increasing attention because of their potential applications in anticounterfeiting, − optical recording, − color displays, − smart windows, and sensors. , Specifically, PCSMs are successfully demonstrated for the application in ink-free light-printable rewritable paper (LPRP), which has potential environmental benefits including forest conservation, pollution reduction, and resource sustainability compared with current paper printing. − Great advances have been achieved in the development of photochromic molecules (e.g., azobenzenes, spiropyrans, diarylethenes, etc.) with impressive photoreversible color switching properties. − However, their practical applications are still impeded by several challenges, such as gradual molecular degradation under sustained UV light exposure and the use of toxic synthetic precursors.…”