Synthesis, Structure, and Properties of a Nitrogen–Boron–Nitrogen-Embedded Polycyclic π-System Containing a Pleiaheptalene Framework

A novel polycyclic π-system (1) featuring both a pleiaheptalene framework (a three-fused heptagon system) and nitrogen–boron–nitrogen (NBN) unit was constructed by electrophilic borylation. A combined experimental and computational study demonstrated that 1has a highly twisted π-backbone with approximate C2symmetry, which can undergo conformational isomerization at room temperature in contrast to pleiaheptalene. It was also found that 1can bind the fluoride ion in the solution, which induces changes in the absorption and emission spectra.