Design, Synthesis, Self-assembly And OLED Devices Of Diazafluorene-based Organic Molecules And Polymers

Organic light-emitting diodes (OLEDs) have attracted increasing attentions for their application as flat-panel displays and solid-state lighting technology since the original works first reported by Tang and co-workers, due to their light weights, wide-viewing angles, high contrast, wide and cheap raw material source, self-emission properties, flexible large-area, fast response times, and so on. Many phosphorescent and fluorescent emitters based devices have been developed to meet the demands of full-color displays. The main approaches to adjust the photoelectric properties are classified into two general categories:one method to adjust the optoelectric properties is based on the modulation of different chemical structures, which was first reported by our group. The other promising approach that tunes the above properties is using supramolecular interactions, such as hydrogen bonding, π-π stacking interactions, coordination role. We try to combine these two different methods, in order to obtain more excellent performance of Organic/Polymeric Materials. In this paper, we designed and synthesized a series of diazafluorene-based organic molecules and polymers, and tuned their optoelectric properties by using supramolecular interactions.1. The synthesis, properties and self-assembly of diazafluorene-based organic semiconductorsA mild and effective method to prepare2,7-dibromo-4,5-diazafluoren-9-one (3) has been described involving tandem oxidation and rearrangement reactions. Diazafluorenone-based donor-acceptor molecules via stille coupling reactions exhibit solvent-dependent fluorescence and excellent selfassembly behaviors at the solideliquid interface according to the characterization of scanning tunneling microscopy (STM). The monolayer of compounds6is a large uniform and highly ordered assembly structure. The van der Waals forces play a significant role in the formation of the molecular monolayers. Based on that, a simple OFET device was fabricated.2. Synthesis and Characterization of Diazafluorene-based Oligofluorenes and Polyfluorenes4,5-Diazafluorene (DAF) has the similar configuration with fluorene unit except for the replaction of two carbon atoms with nitrogen atoms, offering an ideal model of supramolecular conjugated polymers to investigate the structure-property relationship. Herein, a series of DAF-based oligofluorenes and polyfluorenes, including NFF, NF2F, F2NF, PFO-NO, PFO-N5, PFO-N15and PFO-N50, have been synthesized by Suzuki and/or Yamamato polymerization. The DAF can cause to reduce lowest unoccupied molecular orbital (LUMO) levels with the increasement content. All dioctyldiazafluorene-based copolymers show a improved solubility, high quantum yields, and good thermal stability. The diazafluorenone (DAFone)-based oligomers exhibit solvent-dependent fluorescence and DAF-based copolymers show optical response with a large red-shift (ca.40-60nm) of the absorption peakwhen they were protonated with trifluoroacetic acid. Their photoluminescent properties couldalso obviously changed with the introduction of metal ions. DAF are useful building blocks for suprmaolecular polymer semiconductors and thin films.3. A Diazafluorene-containing Polyfluorene:Synthesis, Supramolecular Assembly and Their Optoelectronic PropertiesNitrogen heteroatomic fluorenes, diazafluorenes (DAFs), was incorporated into poly (9,9-dioctylfluorene)(PF8) to systematically investigate the effect of nitrogen heteroatomic substitution on supramolecular self-assembly property. As a result, the optical property of typical self-assembled aggregates, conjugated polymer gels (CPGs) and water-dispersible nanoparticles (CPNs), were significantly different to PF8for the C-H…N supramolecular interactions. Optical response of water-dispersible CPNs to proton acid provided new platform to explore theses nitrogen heterocyclic CPs in water or bio-system. Finally, for the stronger hydrogen-bonded-assisted energy transfer, the first DAF-containing polymer white light-emitting diode (WPLED) with CIE (0.26,0.30) was fabricated.4. Solution-processible Diazafluorene-based Oligomers as a single emitting-component for white electroluminescenceA pure white organic light-emitting diode (WOLED) with a simple device architecture of indium tin oxide (ITO)/poly-(3,4-ethylenedioxythiophene):poly-(styrenesuphonic acid)(PEDOT:PSS)/compound2a/1,3,5-tri(N-phenylbenzimidazol-2-yl)benzene (TPBI)/LiF/Al was realized by using a single small molecule, compound2a as the light-emitting material. The device emits almost pure white light with stable CIE coordinates under different driving voltages. The white emission comes from the combination of the blue emission originating from compound2a and the long-wavelength orange emission originating from the excimer of compound2a.