Synthesis of luminescent dinaphthopentacene isomers and their application in OLEDs

Here we report the straightforward synthesis of a novel nanographene, syn-dinaphthopentacene. This new compound was prepared along with its isomer anti-dinaphthopentacene to compare how small structural differences may affect properties such as crystal packing, photostability, and device performance. syn-Dinaphthopentacene has a twisted, chiral structure, and assembles in enantiomerically pure π-stacked columns in the solid state, while the anti-isomer is rigid and planar and forms a slip-stacked packing structure. anti-Dinaphthopentacene quickly undergoes light-induced [4+2] cycloaddition with singlet oxygen when exposed to ambient light and air, but the twisted syn-dinaphthopentacene exhibits remarkable stability under the same conditions. The two isomers have notably different UV-Vis absorbance and emission profiles, and upon probing the efficacy of these compounds as OLED emitters, the anti-isomer was found to be the better fluorophore, achieving luminance values exceeding 2000 cd m⁻² at peak efficiencies of almost 1%, as compared to the syn-counterpart which only reached 250 cd m⁻².