Metal-induced self-assemble transition: Triple responses on photophysical, liquid crystalline and gel properties of Hg(II)-coordination tetraphenylene dimer

Abstract

The metal-coordination self-assemble system played an important role on constructing novel supramolecular smart-response materials. Although the single and double-response materials based on metal-induced self-assembly had been studied extensively, the triple responses for this kind of supramolecular material was seldom reported. In this work, the first metal-induced self-assemble system with triple responses on photophysical, liquid crystalline and gel properties was presented based on Hg2+-coordination tetraphenylene dimer (Bis-TPE). Bis-TPE was prepared by bridging two alkyl-substituted tetraphenylene with amido chain. It possessed the fluorescence response from the strong emission for Bis-TPE to the faint emission for Bis-TPE-Hg2+ complex. The self-assemble mechanism of Bis-TPE-Hg2+ was clarified as that Hg2+ was located in the cavity of the amido-ether chain of Bis-TPE. The Hg2+-induced mesomorphic transition was also observed from smectic mesophase for Bis-TPE to hexagonal columnar mesophase for Bis-TPE-Hg2+ complex. The unique Hg2+-induced gel transition was further distinguished from low-order spherical morphology for Bis-TPE to high-order fibrous morphology for Bis-TPE-Hg2+ complex. The maximum fluorescence wavelength exhibited the giant shift from 494 nm for Bis-TPE in gel to 606 nm for Bis-TPE-Hg2+ in gel. This kind of triple responses on photophysical, liquid crystalline and gel properties for metal-coordination self-assemble system was described for the first time, affording a new idea on design of new multiple-response materials with unique properties.