UVC-to-NIR-II Ultra-Broadband Response Photochromism of Stilbene Enabled by Donor-Acceptor Complexation Strategy Through One-Step Mechanochemical Synthesis

Abstract

We introduce a supramolecular approach to substantially expand the response wavelength of photoswitchable stilbene(E) from UVC (274 nm) to NIR-II (1064 nm) region, which doesn't depend on E-to-Z photoisomerization. Stilbene(E) acts as an electron donor and is co-assembled with a matched acceptor (e.g., FxTCNQ, x = 1/2/4) to form a solid complex with a loose stack and broadband absorption of 250–1100 nm through one-step mechanochemical synthesis. Reversible green-to-yellow chromism is observed for the complex exposed to 808 nm-light irradiation/heating treatment, which corresponds to the disappearance/appearance of the absorption band of ∼550-1100 nm. This behavior is attributed to photo-induced ultrafast torsion (<0.23 ps) of the stilbene(E) skeleton and resulting destruction of donor-acceptor π-π stacking, and subsequent heating-induced recovery. Besides, the complex can also serve as a UV-excited fluorescence switch and NIR-photothermal material. Hence, donor-acceptor complexation effectively reduces the photo-activation energy of stilbene(E) by π-π interaction and provides a promising route to design a multi-functional photoswitch with ultra-broadband light response.