Synthesis, structures and fluorescence properties of gem-linked cyclic tetraphenylethylenes and cyclic hexaphenylethylenes

Abstract

Rigid cyclic molecules are of great interest due to their intriguing structures and unique properties. Here, we report the facile synthesis of gem-linked cyclic tetraphenylethylenes and cyclic hexaphenylethylenes, namely [n]CTPEs and [n]CHPEs, via the Pt-mediated cyclization of diborylated tetraphenylethylene (TPE) derivatives and subsequent reductive elimination. The structure of [2]CTPE was revealed by X-ray single crystal analysis. The structures and the ring strain energies of all [n]CTPEs and [n]CHPEs obtained were calculated and compared with those of [n]cycloparaphenylenes. Most of the macrocycles showed enhanced aggregation-induced emission (AIE), which was comparable to that of the TPE monomer. By contrast, [2]CTPE exhibits distinctive dual-state emission properties and a long solid-state fluorescence lifetime, which may result from its highly strained rigid structure. This work provides a new direction for organic luminogens with prominent AIE characteristics and dual-state emission.