Orthogonally Processable Carbazole-Based Polymer Thin Films by Nitroxide-Mediated Polymerization.

Cross-linking of hole-transporting polymer thin films in organic light emitting diodes (OLEDs) has been shown to increase device efficacy when subsequent layers are deposited from solution. This improvement, due to resistance of the films to dissolution, could also be achieved by covalently grafting the polymer film to the substrate. Using nitroxide-mediated polymerization (NMP), we synthesized a novel poly(9-(4-vinylbenzyl)-9H-carbazole) (poly(VBK)) copolymer which can be cross-linked and also developed two simple methods for the grafting-to or grafting-from, also known as surface-initiated polymerization, of poly(VBK) to indium tin oxide (ITO) substrates. All three of these methods produced thin films that could be orthogonally processed; that is, they resisted dissolution when the spin-coating of a subsequent layer was simulated. Similar electrochemical behavior for the poly(VBK) films was observed regardless of the technique used, suggesting that all three techniques could be used in the engineering of organic electronic devices. We expect that all three methods would be worth investigating in the solution-based assembly of OLEDs and other organic electronic devices.