Lighting up nonbenzenoid acepleiadylene with ultra-narrowband emission through aromaticity modulation

Nonbenzenoid polycyclic arenes have attracted great attention because of their unique topological structures and appealing properties; however, they are generally considered as poor luminescent materials due to the ring puckering behavior of the nonhexagons. Acepleiadylene (APD), a nonbenzenoid isomer of pyrene, has been demonstrated as an excellent building block for optoelectronic applications, but its poor photoluminescence quantum yield (PLQY) has hampered its application in luminescent materials. Considering that the ring puckering character can be suppressed by increasing the rigidity of the nonhexagon rings, herein, we propose a novel strategy for enhancing the aromaticity of the nonhexagons to improve the PLQYs of APD derivatives. Electron-withdrawing cyano groups are introduced on the five-membered ring of APD to enhance the charge-separated character and thus the aromaticity of the nonhexagons, endowing the cyano-substituted APDs (CNAPD and 2CNAPD) with better rigidity. Therefore, the cyano substitution successfully suppresses the nonradiative energy dissipation caused by the ring puckering, improving the PLQY from 2.4