An assembly-induced-emission orthogonal supramolecular network with spirobifluorene, pillararene, and tetraphenylethylene units for efficient light harvesting

Abstract

Herein, we designed an assembly-induced-emission orthogonal supramolecular network (AOSN) as a novel biomimetic artificial light-harvesting system (ALHS) with high performance and good fabrication error tolerance. A tetratopic host (H) bearing a spirobifluorene core and four pillararene moieties was used to bind a ditopic guest bearing a tetraphenylethylene moiety (GG) to form an AOSN as a nanostructure in suspension. The energy harvesting and transfer capacities of the AOSN were probed using a ditopic conjugated guest (GY) as an energy acceptor. The antenna effect values of the H–GG–GY-crosslinked AOSN remained greater than 60 over a wide range of component ratios, reaching 72.4 in a H₂O/THF mixture as a new record for supramolecular ALHSs. The high performance of the AOSN was attributed to several synergistic factors, including (1) supramolecular polymer formation through interactions between the tetratopic host and ditopic guests, which suppressed the aggregation-caused quenching of GY by separating guests from each other and promoted the assembly-induced emission of GG by restricting guest motion; (2) permanent crosslinking sites provided by the tetratopic orthogonal unit of H, which ensured scaffold rigidity and thus promoted the assembly-induced emission of GG; (3) the molecular wire effect of the conjugated structures in H; and (4) nearly perfect overlap between the fluorescence spectrum of the donor (H–GG complex moiety) and the absorption spectrum of the acceptor (GY moiety).