Synthesis of Cyclobutadienoid-Fused Phenazines with Strongly Modulated Degrees of Antiaromaticity

The streamlined synthesis of a series of regioisomeric azaacene analogues containing fused phenazine and antiaromatic cyclobutadienoids (CBDs), using a catalytic arene–oxanorbornene annulation, followed by aromatization is reported. Controlling the fusion patterns allowed strong modulation of local antiaromaticity. Enhancing antiaromaticity in these regioisomeric azaacenes led to stabilized LUMO, reduced band gap, and quenched fluorescence. This synthetic strategy provides a facile means to fuse CBDs with variable degrees of antiaromaticity onto N-heteroarenes to tune their optoelectronic properties.