Optical-switchable energy transfer controlled by multiple-responsive turn-on fluorescence: Via metal-ligand and host-guest interactions in diarylethene-based [2]pseudo-rotaxane polymers

Multi-responsive and optically-active diarylethene-based [2]pseudo-rotaxane polymers Zn2+-TC2/DS(OC) were synthesized and prepared via metal-ligand and host-guest interactions, where Zn2+ ion was coordinated with two ligands (TC) containing a macrocyclic dibenzo-24-crown-8 (DB24C8) linked to a terpyridyl terminus to form a symmetrical host (Zn2+-TC2) and diarylethene (DAE) bearing two terminal secondary ammonium salts to form a symmetrical guest (DS). Upon irradiation of UV-light (λ = 355 nm), the prominent photo-induced electron transfer (PET) off process to promote optical-switchable Förster resonance energy transfer (FRET) process from the emissive metal-coordination Zn2+-TC2 host to the fluorescent DS(C) guest (in the closed form of emissive DAE unit) was explored for the multiple-responsive turn-on ratiometric fluorescence in supramolecular polymer Zn2+-TC2/DS(C). Remarkably, endowed with the novel features of reversible chemical/chelation-stimuli responsive dis-assembly/re-assembly of non-covalent interactions in response to pH/chelation, the polymer can be used for the sensing of pH and cyclen. Accordingly, the "molecular wire and stimuli-responsive effects"of diarylethene-based [2]pseudo-rotaxane polymer Zn2+-TC2/DS(C) reveal significant supramolecular interactions to elucidate the turn-on fluorescence via the controllable FRET-ON process from Zn2+-TC2 host donor to PET-OFF DS(C) guest acceptor, which pave a promising route to elaborate optical-switchable supramolecular platforms for the future energy transfer applications.