Double Electrophilic Borylative Cyclization of a Pyridine Core Enables a Narrowband Ultraviolet B/N/O MR-TADF Emitter

A pyridine-embedded boron/nitrogen/oxygen multiple-resonance emitter, tBuBOPy, was synthesized on gram scale via methoxy-directed tandem borylation at the pyridine C3 and C5 positions. The incorporation of pyridine blue-shifts the emission by preferentially stabilizing the highest occupied molecular orbital. It also modifies the excited-state character, reducing hole–electron overlap and lowering the singlet–triplet energy gap. As a result, tBuBOPy exhibits ultraviolet TADF at 383 nm, with an fwhm of 25 nm and a high PLQY of 89%.