Metal-Free One-Pot Access to Benzofuran Building Blocks Toward Efficient Narrowband Blue-Cyan Emitters

A metal-free amino-group-directed regioselective cyclization from α-diketone compounds and diarylamines is reported for the synthesis of benzofuran derivatives. The transformation proceeds through sequential intermolecular and intramolecular Friedel-Crafts-type processes under acidic conditions, enabling one-pot construction of fused benzofuran frameworks. The method shows good substrate scope, providing products in moderate yields and demonstrating gram-scale practicality. Based on this scaffold, two donor units are developed and incorporated into multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters, namely BNFFA and BNFFC. Both compounds exhibit narrowband emission (full with at half maximum = 20 and 25 nm) and decent delayed fluorescence. Organic light-emitting diodes based on these emitters achieved maximum external quantum efficiencies of 23.5% and 29.3%, with blue-cyan emissions suitable for emerging four-primary wide-color-gamut displays.