Photostable Triphenylmethyl-Based Diradicals with a Degenerate Singlet-Triplet Ground State and Strong Photoluminescence

Abstract

We present a new class of luminescent diradicals based on tris(trichlorophenyl)methyl (TTM) cores symmetrically bridged by indolocarbazole donors. These diradicals exhibit pure diradical character y₀ and unprecedented photoluminescence quantum yields ϕ of up to 18 %, addressing key challenges in the development of stable, emissive organic diradicals. Light emitting diradicals represent a formidable challenge for synthetic chemists; for applications as molecular color centers in quantum sensing and as emitters in optoelectronics. Unlike conventional approaches that require the conversion of closed-shell precursors, we directly couple brominated TTM radicals via Buchwald–Hartwig coupling. The magnetic and optical properties of the resulting molecules are comprehensively characterized by electron paramagnetic resonance EPR, UV–vis absorption, and photoluminescence spectroscopy. This work unites the robust photophysics of discrete TTM radicals with the electronic versatility of donor-bridged multi-spin systems, offering a promising design strategy for functional open-shell emitters.