Elucidating the balance between metal ion complexation and polymer conformation in maleimide vinyl ether polymer multilayer structures

Abstract

We have grown layered assemblies of poly[4-(N-maleimido)azobenzene-co-diisopropyl (2-vinyloxy)ethylphosphonate], (poly(MAB-VEP)), where interlayer connections are made using zirconium bisphosphonate (ZP) ionic complexation chemistry. The linear optical response of the azobenzene chromophore side group shows constant layer density but a layer-dependent ratio of trans-to-cis isomers. Optical null ellipsometry data show a constant average layer thickness despite the change in conformer ratio. The change in conformer ratio with the growth of multiple polymer layers results from the steric constraints imposed on the polymer side groups by the formation of the ZP interlayer linkage. The driving force for metal ion complexation is greater than the isomerization barrier of S0 azobenzene. Once the layers are formed, the side-groups do not exhibit any changes in conformer ratio, even when exposed to UV for a prolonged period.