Synthesis and Properties of B N -Heteropentalenes Fused with Polycyclic Hydrocarbons.

Hybrid molecules of π-conjugated carbon rings and BN-heterocyclic rings (h-CBNs) fused with each other have been a rare class of compounds due to the limited availability of their synthetic methods. Here we report the synthesis of new h-CBNs featuring a B N -heteropentalene core and polycyclic aromatic hydrocarbon wings. Using 1,2-azaborinine derivatives as a building block, we developed a rational synthetic protocol that allows the formation of a B N ring in a stepwise manner, resulting in the fully fused ABA-type triblock molecules. Thus, three derivatives of 1 bearing naphthalene (1 ), anthracene (1 ), or phenanthrene (1 ) wings fused with the B N core were synthesized and characterized. Among them, 1 , which displays the highest triplet-state energy, was found to serve a host material for phosphorescent OLED devices, for which a maximum external quantum efficiency of 13.7 % was recorded. These findings may promote the synthesis of various types of h-CBNs aiming at new properties arising from the synergy of two different π-electronic systems.