Turning on the solid emission from non-emissive 2-aryl-3-cyanobenzofurans by tethering tetraphenylethene for green electroluminescence

Abstract

Three green-emitting compounds 1–3 based on 2-aryl-3-cyanobenzofuran fluorophore tethered with aggregation-induced emission active (AIE-active) tetraphenylethene (TPE) were designed and synthesized. p-Methoxyphenyl (PMP) was installed on the 5-, 6-, and 7-positions of 2-aryl-3-cyanobenzofuran for systematically investigating the substituent effect on their photophysical properties in solutions, nanoparticles, films, crystals, as well as powders. The aggregation-caused quenching (ACQ) problem arising from the π–π stacking between fluorophores was surmounted by covalently bonding the TPE unit. Thus, these compounds emitted green light in solids, and the film's quantum yield approached 50.1%. Red-shifted mechanochromism was observed for the crystalline state with a small crystal density. The best OLED performance was achieved using the compound with PMP occupied at the 6-position of 2-aryl-3-cyanobenzofuran, which possessed the longest efficient conjugation length.