A stable triplet diradical emitter

Abstract

Molecules with luminescence have been extensively investigated, but the luminescence of a stable molecule with a triplet ground state has not been observed. Synthesis of boron-containing radicals has attracted lots of interest because of their unique electronic structures and potential applications in organic semiconductors. Though some boron-based diradicals have been reported, neutral boron-containing diradicals with triplet ground states are rare. Herein two borocyclic diradicals with different substituents (<b>3</b> and <b>4</b>) have been isolated. Their electronic structures were investigated by EPR and UV spectroscopy, and SQUID magnetometry, in conjunction with DFT calculations. Both experiment and calculation suggest that <b>3</b> is an open shell singlet diradical while <b>4</b> is a triplet ground state diradical with a large singlet-triplet gap (0.25 kcal mol^-1). Both diradicals show multi fluorescence peaks (<b>3</b>: 414, 431, and 470 nm; <b>4</b>: 420, 433, and 495 nm). <b>3</b> displays multiple redox steps and is a potential material towards the design of high-density memory devices. <b>4</b> represents the first example of a neutral triplet boron-containing diradical with a strong ferromagnetic interaction, and also is the first stable triplet diradical emitter.