Silke Koser

Dibenzobarrelene-Based Azaacenes: Emitters in Organic Light-Emitting Diodes

The synthesis of soluble dibenzobarrelene-substituted azaacenes either by condensation reactions in solution or, more effectively, in the solid state by using a ball mill is reported herein. We relate their optical properties in thin films to their packing in the solid state. The targets are characterized by cyclic voltammetry, X-ray crystallography and UV/Vis and fluorescence analysis. Three highly fluorescent, amorphous azaacenes were processed into organic light-emitting diodes, and their improved performance (luminance, efficiency and efficacy) was compared with that of structurally related iptycene-based azaacenes.

Bent N-Heteroarenes

The syntheses and optical, electronic, and structural properties of a series of bent N-heteroarenes are described. The targets were obtained by condensation reactions of substituted aromatic o-diamines with 1,2-naphthoquinone and 1,2-anthraquinone in yields between 34 and 94%; naphthoquione-based products are generally formed in higher yields.

Dibenzohexacene: Stabilization Through Additional Clar Sextets

Triphenylene units stabilize hexacenes as dibenzohexacenes. The hexacenes formed by a statistical Yamamoto coupling of dibromobenzene with dibromo-TIPS-pentacene or, alternatively, Stille coupling with dimethyldibenzostannole. UV/Vis spectroscopy and quantum chemical calculations show that despite the double benzannulation, the species have hexacene-type character, as evidenced by their redshifted absorption characteristics. The charge carrier mobility of dibenzohexacene 1 a was determined up to 0.2 cm2 /(Vs).

Alkyne-Substituted N-Heterophenes

The synthesis and characterization of novel S-shaped N-heterophenes is reported. The targets contain a central anthracene connected to two heterophenanthrene units. N-Heterophenes are synthesized by reacting Boldts 1,2,6,7-anthracenetetraone with different dialkynylated ortho-diaminobenzenes. The condensation yields range from 63 to 75 %; all of the N-heterophenes are stable and isolable.

A Golden Access to Acenopentalenes

By employing gold catalysis, starting from dialkynylated acenes a series of novel un-symmetrical aceno-annulated dibenzopentalenes has been prepared. The achieved yields range from 62-68 %. The fused systems contain naphthalene, anthracene, tetracene, and pentacene units. All new compounds are soluble and stable under standard conditions. The optical properties of the systems are dominated by the dibenzopentalene core for the smaller representatives, while for the anthracene-pentacene-based aceno-benzopentalenes the optical properties of the acene group dominates. Preliminary morphology tests on thin films showed a reverse trend between crystal size and molecule size.

Phenylene Bridged Cyclic Azaacenes: Dimers and Trimers

The synthesis and characterization of novel macrocyclic, phenylene-bridged azaacenes is reported. These species were obtained either by a conventional benzoin- diamine condensation, as shown for the case of the cyclotrimers, in which the azaacene units are separated by meta-connected phenylene bridges, or by a Buchwald-Hartwig-type Pd-catalyzed coupling, which employs 1,2,5,6-tetrabromodibenzocyclooctatetraene as the substrate and bis-TIPS-ethynylated diaminobenzene, -naphthalene or -anthracene as the coupling partner to give the double coupling products azaacene-annulated dibenzocyclooctatetraenes in moderate yields. The macrocycles show strong emission and light emitting diodes have been built with brightnesses exceeding 1600 cd m-2 . We evaluated the optical and electronic properties and the solid-state structures of the molecules and discuss their properties through comparison with their linear and tetrameric N-heteroacene counterparts.

Poly(para-phenyleneethynylene)s as Emitters in Polymer LEDs

11 different dialkoxy- and dialkyl-poly(para-phenyleneethynylene)s (PPEs) featuring novel branched and literature described linear and branched side chains were prepared using a Sonogashira coupling. The side chains were of different length and branching character. The degree of polymerization of the PPEs ranged from Pn = 44–343 with polydispersities ranging from 1.5–3.1. Fairly simple OLED-stacks with up to three layers (electron injection, emitter layer, and hole injection) were produced. Depending upon the PPEs’ structure and the stack architecture but particularly the thickness of the emitting PPE-layer, a large increase in brightness up to 2.2 × 103 cd m−2 was observed, a significant improvement over earlier reported values.

Azaacenes Bearing Five‐Membered Rings

We report the synthesis of processible (dihydro)pyracyclene- and acenaphthylene-substituted azaacenes using condensation reactions in solution. The targets are characterized via cyclic voltammetry, X-ray crystallography, UV/Vis, fluorescence spectroscopy and DFT/NICS calculations. Formal hydrogenation of the annulated five-membered ring surprisingly alters emission in the solid-state as a consequence of modulation of aromaticity and HOMO-LUMO overlap. Five highly fluorescent, crystalline azaacenes were investigated as emitters in organic light-emitting diodes, and their performance with respect to luminance and efficiency was compared to that of structurally related azaacenes.

Yamamoto Coupling for the Synthesis of Benzophenes and Acene-Based Cyclooctatetraenes

Two TIPS-ethynylated dibromoacenes were used in a shotgun Yamamoto-reaction with 1,2-dibromobenzene or 4,5-dibromoveratrol. Four soluble benzononaphenes/benzoundecaphenes were isolated in satisfactory yields. Examples of tetracene- and pentacene-fused tetrabenzocyclooctatetraenes also isolated from this reaction are reported. All compounds were characterized by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X-ray crystallography as well as DFT and NICS calculations.

Bromination Improves the Electron Mobility of Tetraazapentacene

A cyclocondensation of TIPS-ethynyl-substituted diaminoarenes with in situ obtained 4,5-dibromocyclohexa-3,5-diene-1,2-dione has led to the synthesis of tetrabromotetraazapentacene (BrTAP). BrTAP is easily reduced to its air-stable radical anion and electron mobilities >0.56 cm2  V-1  s-1 can be achieved in thin-film transistors.