The fabrication of multilayer organic light-emitting diodes through solution processing presents challenges, especially regarding dissolution of the first layer during deposition of a second layer. One possible approach to this problem is to insolubilize the first layer using cross-linking. Cross-linking has also been used to control the morphological stability and aggregation phenomena of the active organic materials. In this short review, we discuss the alternative chemically, thermally, and photochemically promoted cross-linking chemistries that have been examined in the context of organic light-emitting diodes including: the hydrolysis of silicon compounds to form siloxanes; the polymerization of styrene, acrylate, and oxetane groups; and the dimerization of trifluorovinyl ethers, benzocyclobutenes, and cinnamates.

Polymethacrylates, polystyrenes, and polynorbornenes bearing 2-(3-(carbazol-9-yl)phenyl)-5-phenyl-1,3,4-oxadiazole, 2-(4-(carbazol-9-yl)phenyl)-5-phenyl-1,3,4-oxadiazole, 2-(3,5-di(carbazol-9-yl)phenyl)-5-phenyl-1,3,4-oxadiazole) groups linked to the polymer backbone through the 3-position of their terminal phenyl groups have been synthesized for use as solution-processable ambipolar hosts for phosphorescent light-emitting diodes. The polymers exhibit good thermal stabilities, with no weight loss below 350 °C, and have glass-transition temperatures in the range 118–209 °C. Spectroscopic, electrochemical, and quantum-chemical data for small-molecule model compounds suggest that the side chain groups are suitable hosts for a range of phosphors, including the green-emitter fac-tris(2-phenylpyridinato-N,C 2′)iridium (Ir(ppy)3). Light-emitting diodes were fabricated, each with a solution-processed photo-cross-linked hole-transport layer, a solution-processed emissive layer composed of a carbazole-oxadiazole-functionalized polymethacrylate doped with Ir(ppy)3, and an evaporated electron-transport layer. The polymer with 2-(3,5-(dicarbazol-9-yl)phenyl)-5-phenyl-1,3,4-oxadiazole units in the side chain exhibited the lowest turn-on voltage (6.0 V), and the highest efficiency (external quantum efficiency of 10.0%, current efficiency of 34.1 cd/A).

Copolymers with a triscarbazole hole-transport group and an oxetane or benzocyclobutene crosslinkable group can be readily thermally crosslinked on timescales of 30 min or less, with rapid thermal processing (RTP) being highly effective for this purpose. Devices with RTP-crosslinked hole-transport layers and spin-coated emissive layers exhibit high external quantum efficiencies of up to 15%.

ABSTRACT. Partially reduced graphene oxide (prGO) was covalently functionalized with an diazonium containing, imidazolium based, polyzwitterionic polymer to afford a composite material with excellent dispersibility and long-term stability in high salinity brines including standard API and Arab-D found in deep oil reservoirs. When heated at 90 °C, the dispersions remained stable in excess of 140 days. These results suggest the utility of imidazolium-based polymers for brine stabilization as well as the use of diazonium containing polymers for a 'grafting-to' approach to nanocarbon functionalization.

Two norbornene-functionalized tetradentate cyclometalated platinum(II) complexes were synthesized and copolymerized with a bis(carbazolyl)benzene-based comonomer using ring-opening metathesis polymerization (ROMP). The copolymers are soluble in common solvents and the molecular weights of these copolymers can be well controlled as a result of the living character of the ROMP. The photophysical and electrochemical properties of the copolymers were compared to their corresponding small molecules. The copolymers showed almost identical photophysical and electrochemical properties demonstrating the inertness of the polymer backbone toward the photophysical properties of the tethered platinum complexes. All complexes exhibit bright photoluminescence in the green region with lifetimes around 0.4 μs and solution phosphorescence quantum efficiencies as high as 0.56, which suggest that these materials could be interesting for OLED applications.