Dynamic Metal-ligand Coordination for Fluorescence Color Regulation of Hydrazone-based Bistable Photoswitches

Achieving effective manipulation of emission color in photoresponsive materials is crucial for various advanced photonic applications. In this study, we designed and synthesized a hydrazone compound 1, ethyl (Z)-2-(2-([2,2':6',2''-terpyridin]-4'-yl)hydrazineylidene)-2-(4-(diphenylamino)phenyl)acetate, which possesses a push-pull structure incorporating triphenylamine and terpyridine. The emission intensity of compound 1 can be repeatedly switched "off" and "on" by irradiation with visible light and UV light, which induces the isomerization transition between the Z and E forms. In addition, compound 1 is capable of changing its emission wavelength from 540 nm to 607 nm through coordination with different zinc salts in toluene/CH₂ Cl₂ mixture (v : v=1 : 1). Importantly, we have successfully achieved dynamic manipulation of fluorescence color and intensity by altering the counterions of zinc complexes and switching the isomer from Z to E. Moreover, both compound 1 and its zinc complexes demonstrate remarkable photoswitchable properties with different fluorescence colors in the thin films. Finally, these films with various fluorescence colors were used for the production of luminescent tags.