Polymeric Zinc-Bisquinoline Based Self-Assembled Light Emitting Diodes
- PDF / 558,860 Bytes
- 9 Pages / 414.72 x 648 pts Page_size
- 97 Downloads / 133 Views
The incorporation of polymers in light emitting devices (LEDs) is currently challenged by purity and processability issues. The ability to purify macromolecules devoid of defects requires tight control of side reactions.[8] Furthermore, when traditional thin-film spin or dip casting techniques are utilized to fabricate multilayer LEDs, interlayer solubility, thickness variations, and pinhole defects may commonly occur. Self-assembly of thin films has introduced ways to improve film uniformity and layer architecture at the molecular level. [9] Rubner et al.[ 10] have constructed pinhole-free poly(p-phenylenevinylene)-based LEDs as thin as 300 A. Although the versatility of a polycation/polyanion layering approach shows increasing promise as an alternative fabrication method, it is inapplicable for molecular-based devices which lack ionic functionalities, such as Alq 3 . Self assemblies of small molecules on glass and metal surfaces have been demonstrated in numerous motifs with alkanol and alkanoic acids,[1 1] alkylsilanes,[12] disulfides and thiols,[13] and isonitriles.[14] Zirconium phosphonates represent an interesting class of self assemblies. The aqueous or highly polar (e.g., dimethyl sulfoxide (DMSO)) solvents necessary for solubilizing the ZrOCI2 and the bifunctional phosphonic acid terminated organics result in heavily hydrated assemblies which develop pores upon drying, further compromising film quality.[15,16] Transition metal coordination with bifunctional isonitriles in polar solvents has also been used to fabricate multilayer self-assemblies.[14] Currently, only a limited number of coordinating transition metals have been suitable for multilayer fabrication, and the substantial film shrinkage upon drying (ca. 35%) are limiting factors in device fabrication. * To
whom correspondance should be addressed. 105 Mat. Res. Soc. Symp. Proc. Vol. 488 © 1998 Materials Research Society
The fabrication of polymer analogs of 8-hydroxyquinoline-based metal chelates (such as Alq 3 , etc.) for electroluminescence applications has been a challenging task. These metal chelate polymers are nontraditional polymers and are usually associated with considerable handling difficulties. Their major intricacy arises from complexation-decomplexation dynamics, which are very sensitive to the pH and ionic strength of the solute.[17] For linear metal chelate polymers, solubilization typically occurs only in polar aprotic solvents,[18] which are difficult to remove from spun films. The insoluble and intractable nature of these polymers makes them amenable to the self-assembly growth which is the subject of this paper. Single layer light emitting diodes of these polymers were constructed via alternative dipping of hydroxy-functionalized ITO substrates in solutions of bisquinoline and ZnEt2 separated each time by a washing step to remove excess reactants. EXPERIMENTAL
Monomer Synthesis: The synthesis of bisquinoline (I) was done following the method of Archer et al.[19] Prior to its use, (I) was purified by sublimation to yield a w
Data Loading...
