Soluble Flavanthrone Derivatives: Synthesis, Characterization, and Application to Organic Light‐Emitting Diodes

Simple modification of benzo[ h ]benz[5,6]acridino[2,1,9,8‐ klmna ]acridine‐8,16‐dione, an old and almost‐forgotten vat dye, by reduction of its carbonyl groups and subsequent O ‐alkylation, yields solution‐processable, electroactive, conjugated compounds of the periazaacene type, suitable for the use in organic electronics. Their electrochemically determined ionization potential and electron affinity of about 5.2 and −3.2 eV, respectively, are essentially independent of the length of the alkoxyl substituent and in good agreement with DFT calculations. The crystal structure of 8,16‐dioctyloxybenzo[ h ]benz[5,6]acridino[2,1,9,8‐ klmna ]acridine ( FC‐8 ), the most promising compound, was solved. It crystallizes in space group P 1 ‾ and forms π‐stacked columns held together in the 3D structure by dispersion forces, mainly between interdigitated alkyl chains. Molecules of FC‐8 have a strong tendency to self‐organize in monolayers deposited on a highly oriented pyrolytic graphite surface, as observed by STM. 8,16‐Dialkoxybenzo[ h ]benz[5,6]acridino[2,1,9,8‐ klmna ]acridines are highly luminescent, and all have photoluminescence quantum yields of about 80 %. They show efficient electroluminescence, and can be used as guest molecules with a 4,4′‐bis( N ‐carbazolyl)‐1,1′‐biphenyl host in guest/host‐type organic light‐emitting diodes. The best fabricated diodes showed a luminance of about 1900 cd m −12 , a luminance efficiency of about 3 cd A −1 , and external quantum efficiencies exceeding 0.9 %.