Tetraphenylethylene-based emissive supramolecular metallacages assembled by terpyridine ligands

Abstract

We report the preparation and emission properties of tetraphenylethylene (TPE)-based metallacages with aggregation-induced emission (AIE) activities through coordination-driven self-assembly. Two supramolecular cages, [Zn6LA3] and [Zn6LB3], were assembled via TPE-decorated terpyridine (tpy) ligands, LA and LB, respectively, with Zn(II) ions. We performed a subtle change by introducing extra alkyne connectivity into LB to increase the degree of conjugation and geometric constraint, compared with LA. As a result, we obtained a highly emissive cage, [Zn6LB3], even in a dilute solution. At a low temperature, the intramolecular rotation of TPE was further restricted, thus, resulting in a significant increase in fluorescence. Through mixing LA and LB, we obtained a series of hybrid cages, which also indicated that the emission was enhanced with highly abundant LB in the cages. Further, we studied the emission behaviors of the ligands and cages in solid state under external pressure. Upon gradual increase of the external pressure, the luminescence of [Zn6LB3] increased initially, due to further rotation restriction, which was followed by quenching under 6.32 Gpa, owing to the tight packing of the supramolecules. The subsequent release of the pressure resulted in cage recovery of the emission.