Access tetracoordinate boron-doped polycyclic aromatic hydrocarbons with aggregation-induced emission under mild conditions

The boron-doped polycyclic aromatic hydrocarbons (PAHs) have attracted ongoing attention in the field of optoelectronic materials due to their unique optical and redox properties. To investigate the effect of tetracoordinate boron in PAHs bearing N-heterocycles (indole and carbazole), a facile approach to four-coordinate boron-doped PAHs was developed, which does not require elevated temperature and pre-synthesized functionalized boron reactants. Five tetracoordinate boron-doped PAHs (NBNN-1 – NBNN-5) were synthesized with different functional groups. Two of them (NBNN-1 and NBNN-2) could further undergo oxidative coupling reactions to form fused off-plane tetracoordinate boron-doped PAHs NBNN-1f and NBNN-2f. Compared to the three-coordinate boron-doped counterparts, the UV/Vis absorption and fluorescent emission are significantly red-shift. Unlike the distinct impact of coordination number of boron on optoelectronic properties, the difference of functional groups on the boron atom has negligible impact on their optical and electrochemical properties. The compounds NBNN-1f and NBNN-2f show aggregation-induced emission.