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.