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.

Conformation-dependent dynamic organic phosphorescence through thermal energy driven molecular rotations.

Organic room-temperature phosphorescent (RTP) materials exhibiting reversible changes in optical properties upon exposure to external stimuli have shown great potential in diverse optoelectronic fields. Particularly, dynamic manipulation of response behaviors for such materials is of fundamental significance, but it remains a formidable challenge. Herein, a series of RTP polymers were prepared by incorporating phosphorescent rotors into polymer backbone, and these materials show color-tunable persistent luminescence upon excitation at different wavelengths. Experimental results and theoretical calculations revealed that the various molecular conformations of monomers are responsible for the excitation wavelength-dependent (Ex-De) RTP behavior. Impressively, after gaining insights into the underlying mechanism, dynamic control of Ex-De RTP behavior was achieved through thermal energy driven molecular rotations of monomers. Eventually, we demonstrate the practical applications of these amorphous polymers in anti-counterfeiting areas. These findings open new opportunities for the control of response behaviors of smart-responsive RTP materials through external stimuli rather than conventional covalent modification method.