Light-Emitting Superstructures with Anion Effect: Coordination-Driven Self-Assembly of Pure Tetraphenylethylene Metallacycles and Metallacages

Herein, we describe the synthesis of tetraphenylethylene (TPE)-based di-Pt(II) acceptors as shown by X-ray analysis, which are subsequently used to construct pure TPE-based 2D hexagonal metallacycles and 3D drumlike metallacages with three different counteranions via coordination-driven self-assembly. The metallacycles possess alternating TPE donor and acceptor units that arrange 12 pendant phenyl rings along the outer perimeter that provide the basis for the observed aggregation-induced emission (AIE) behavior. The metallacages are similarly constructed from TPE-based building blocks, specifically two donors and four acceptors, resulting in eight freely rotating phenyl rings decorating the prismatic core. The fluorescence of these cages in dilute solution is intensified when hexane is added to CH₂Cl₂ solutions, indicative of aggregation-induced enhanced emission (AIEE). The influence of the counteranions on the photophysics of the assemblies was investigated. The molar absorption coefficients (ϵ), fluorescence emission intensities, and quantum yield (Φ_F) values of the SCCs with different counteranions in CH₂Cl₂ follow the order PF₆^- > OTf^- > NO₃^-. The same trend also applies to the AIE characteristics of the SCCs in the aggregated state. The metal-organic materials developed here not only enrich a newly emerging library of self-assembly AIE metallacycles and cages that are promising candidates for turn-on fluorescent sensors and advanced optical devices but also provide an understanding of how structural factors affect the photophysics of AIE-active SCCs.