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 (ΦF) 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.