Anthra/Tetra/Pentaquinodimethane‐Supported Organoboranes with Blue‐to‐Red Emissions and Responsive Transformations to Dication Species and Open‐Shell Diradical States

Comprehensive Summary Structurally‐modified acenes with a linear fusion of π‐extended systems have shown highly attractive properties and promising applications in semiconductor materials, optoelectronic materials and others due to their unique electronic structures. We have accessed a series of anthra/tetra/pentaquinodimethane‐supported organoboranes, Mes*B‐A , Mes*B‐T and Mes*B‐P , with highly tunable emissions from blue to red (~680 nm) by controlling the number of fused benzene rings of the [ n ]acene core ( n = 3–5). Interestingly, these redox‐switchable quinoid systems have chemically and electrochemically enabled two‐electron oxidations, leading to dicationic anthracene, tetracene and pentacene segments ( Mes*B‐A 2+ , Mes*B‐T 2+ and Mes*B‐P 2+ ) as evidenced by new absorption bands in the UV−vis−NIR spectra and spectroelectrochemical studies. Meanwhile, all the molecules feature a π‐conjugated, overcrowded ethylene structure that allows for a spin‐state transition from closed‐shell to the open‐shell diradicals ( Mes*B‐A 2• , Mes*B‐T 2• and Mes*B‐P 2• ) under thermal conditions. This can further be confirmed by the variable‐temperature (VT) 1 H NMR and electron spin resonance (ESR) spectroscopy. These organoboranes also experienced an emission change in response to fluoride binding with electron‐deficient boron centers. Our current work demonstrates not only the synthetic contribution to [ n ]acene‐based luminescent materials, but also showcases multistate transformations for potential applications depending on well‐tuned electronic, magnetic, electron transfer and charge transport mechanisms.