Synthesis, physical properties and OLED performance of azatetracenes

Two novel azatetracenes: 5,7,8,9,10,12-hexaphenyl-2-azatetracene (2) and 1,4,6,11-tetraphenyl-2,3-diazatetracene (3), were synthesized and characterized. Comparing to Rubrene, 2 and 3 show blue-shifted absorptions. Interestingly, 2 displays stronger emission than rubrene in CH₂Cl₂, while the fluorescence of 3 is almost quenched. The electrochemical studies suggested that inserting sp² N atoms into the backbone of tetracene could decrease both HOMO and LUMO orbital energies and more sp² N atoms would result in lower HOMO orbital energy level. Since 2 has stronger fluorescence than rubrene, organic light emitting devices with 2 as emitters have been fabricated and the as-fabricated devices show a maximum current efficiency as high as 6.6 cd A^-1. Our results indicated that the number of sp² N atoms in the backbone of parent oligoacenes did have strong effect on the properties of as-resulted azaoligoacenes and this research could provide some guides to design and synthesize novel larger azaacenes. © 2014 Elsevier Ltd. All rights reserved.