Amphiphilic rhomboidal 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 were 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 was varied. As the structural framework consisted of both aggregation-induced emission luminogens and aggregation-caused quenching luminophores, photophysical studies were conducted with the fabricated materials. The synthesized metallacycles exhibited solvatochromic properties and bimodal emission in some solvents. The effects of molecular aggregation in the metallacycles were studied using a CHCl₃/hexane mixture. The results showed 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 were observed in the entire visible region, and white-light emission of a single molecule (CIE chromaticity coordinate: 0.29, 0.35) was recorded. Moreover, rhomboidal metallacycles with peripheral hydrophilic chains could form spherical micelles via hydrophilic/hydrophobic and π–π stacking interactions. The sizes of the obtained micelles were measured by transmission electron microscopy and dynamic light scattering. These micelles exhibited good biocompatibility and can be employed as cell imaging agents with satisfactory visualization outcomes. Hence, these amphiphilic rhomboidal organoplatinum(II) metallacycles helped achieve the tunable emission of a single molecule upon molecular aggregation and can be used in fluorescence imaging.