Nine-ring angular fused biscarbazoloanthracene displaying a solid state based excimer emission suitable for OLED application

Abstract

A new biscarbazoloanthracene consisting of nine fused aromatic rings, including two pyrrole units, has been obtained in a straightforward and convergent synthesis. Computational chemistry and conformational analysis revealed that the semiconductor's molecule is not planar, the two carbazole moieties being helical twisted from the plane of the anthracene unit. Photophysical and electrochemical measurements showed that this angular fused heteroacene has a low lying HOMO energy level with a wide band gap despite its extended π--conjugated molecular framework. Based on its relatively low--lying HOMO level, the titled compound semiconductor promises a high environmental stability in comparison to other related linear fused acenes and heteroacenes. The biscarbazoloanthracene has been applied as the light emitting layer in a white light emitting diode (WOLED). It is proposed that the white OLED feature is due to dual light emission properties from the active semiconductor layer being based on both the molecular luminescence of the small molecule and a discrete excimer emission made possible by suitable aggregates in the solid state. Noteworthy, this is the first reported example of such a behavior observed in a small molecule heteroacene rather than an oligomer or a polymer.

Synthesis and Characterization of Azine‐[5]Helicene Hybrids

“…In accordance with the above strategy, we first synthesized ortho ‐halogen alkynylazines 1a – d via the Sonogashira reaction of commercially available 2,3‐dihaloazines (2,3‐dichloroquinoxaline and 2,3‐dichloropyrazine) with phenylacetylene and 4‐methoxyphenylacetylene using known[13o] procedure.…”

“…In all cases, the product yield exceeded 84 %. It should be noted that compounds 7 are derivatives of the little‐known heterocyclic systems naphtho[1,2‐ h ]quinoline,[16a] naphtho[2,1‐ f ]quinoxaline,[13o], [16b], [16c] naphtho[2,1‐ a ]phenazine. [13n], [16d], [16e], [16f], [16g] After reviewing these publications, the synthetic sequence described above seems to be the best method for constructing these heterosystems.…”

“…2‐(Naphthalen‐2‐yl)‐3‐(phenylethynyl)quinoxaline (2a): Method A . 2‐Chloro‐3‐(phenylethynyl)quinoxaline 1a [13o] (264 mg, 1.0 mmol), naphthalen‐2‐ylboronic acid (258 mg, 1.5 mmol), Pd(PPh 3 ) 4 (69 mg, 0.06 mmol), K 3 PO 4 (424 mg, 2.0 mmol) and dry THF (15 mL) were stirred and refluxed under argon for 24 h. The reaction mixture was then evaporated to dryness. The residue was treated with water (50 mL) and extracted with CH 2 Cl 2 (3 × 20 mL).…”

“…Most publications are related to [5]helicenes and tetrahydro[5]helicenes condensed with furan‐2,5‐dione or pyrrole‐2,5‐dione rings. There are single reports on [5]helicenes fused with pyranone,[15l] indole,[15m] phthalocyanine,[15n], [15o] triazatruxene,[15p] dihydroimidazole,[15q] pyrrolobenzimidazole,[15r] naphthopyrazine,[15s] phenanthropyrazine,[15s] hexahydroquinoxaline[15q] and pyridine[13i] core.…”

An optical and electrical study of full thermally activated delayed fluorescent white organic light-emitting diodes

“…With this in mind, multiple hybrid W-OLEDs implementing fluorescent 4 or phosphorescent 5–7 emitters, as well as exciplex 8 , excimer 9 , electroplex 10 , aggregated induced emission (AIE) 11, 12 or quantum dots 13 have been developed with various device structures.…”