General photo-patterning of polyelectrolyte thin films via efficient ionic bis(fluorinated phenyl azide) photo-crosslinkers and their post-deposition modification

Abstract

We have extended the well known bisfluorinated(phenyl azide) (bisFPA) methodology to develop an ionic bisFPA process suitable for photo-crosslinking a wide variety of polyelectrolyte thin films. The crosslinking efficiencies (0.1-1.0 crosslink per photo-reaction) are sufficiently high for the gel fraction to exceed 80 % for crosslinker concentrations of only a few weight %. This method is based on the photo-induced formation of singlet nitrenes from FPAs and their insertion into unactivated C-H or other bonds, which thus general and not dependent on the presence of specific chemical functional groups. By derivatizing with ionic charge groups, we obtained ionic bisFPAs that can be properly dispersed into polyelectrolyte thin films. The, sorbed moisture always present in these films however severely limits the photo-crosslinking efficiency, apparently through nitrene protonation and intersystem crossing. This can be avoided by dehydration of the films, in some cases, to 130°C for 10 min in nitrogen before photo-exposure. We found that efficient photo-crosslinking can then be achieved for polyelectrolytes even when they have nucleophilic groups. These include poly(styrenesulfonic acid) and their salts, poly(acrylic acid) and their salts, poly(dimethyldiallylammonium salts), as well as the electrically-conducting poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonic acid) complex (PEDT:PSSH). We further demonstrate using this ionic bisFPA methodology both photo-patterning and post-deposition chemical modifications of polyelectrolyte thin films. This opens broad new possibilities in membrane, sensor and actuator technologies, as well as for organic semiconductor plastic electronics (such as field-effect transistors) and polyelectrolyte-based devices. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.