Amphiphilic Metallacycles with Aggregation-Induced Emission and Aggregation-Caused Quenching Luminogens for White-Light Emission and Bioimaging

Abstract

Discrete metallacycles exhibiting multicolor luminescence, especially white-light emissions, are rarely used in supramolecular assemblies; however, they are crucial for fabricating fluorescent materials. Herein, three amphiphilic rhomboidal metallacycles are synthesized through the metal-ligand interactions and self-assembly of diplatinum(II) acceptors bearing hydrophilic chains, and endohedral aniline and tetraphenylethene-functionalized dipyridyl donors. To investigate the effect of bond linking variation (single, double, or triple bonds) on the supramolecular coordination complexes, the connectivity between the aniline core and dipyridyl group is varied. As the structural framework consisted of both aggregation-induced emission luminogens and aggregation-caused quenching luminophores, photophysical studies are conducted with the fabricated materials. The synthesized metallacycles exhibite solvatochromic properties and bimodal emission in some solvents. The effects of molecular aggregation in the metallacycles are studied using a CHCl3/hexane mixture. The results show the emission properties of the metallacycles could be tuned by varying the degree of molecular aggregation. Particularly, in the CHCl3/hexane mixture (1/9, v/v), fluorescence emission peaks are observed in the entire visible region, and white-light emission of a single molecule (CIE chromaticity coordinate: 0.29, 0.35) is recorded. Moreover, rhomboidal metallacycles with peripheral hydrophilic chains can form spherical micelles via hydrophilic/hydrophobic and π-π stacking interactions. The sizes of the obtained micelles are measured by transmission electron microscopy and dynamic light scattering. These micelles exhibit good biocompatibility and can be employed as cell imaging agents with satisfactory visualization outcomes. Hence, these amphiphilic rhomboidal organoplatinum(II) metallacycles help achieve the tunable emission of single molecule upon molecular aggregation and can be used in fluorescent imaging.