Materials with a ribbon- or ladder-type framework possess a two-dimensional geometry and are thus intermediate between linear and three-dimensional systems. The limited conformational freedom of ladder polymers is particularly relevant in the case of conjugated ladder-type materials since the steric inhibition of electron delocalization is drastically reduced.
Up until today two general routes have been used to prepare ladder-type materials: (1) the polymerisation of multifunctional monomers, in which both strands of the ladder structure are generated in a single reaction; and (2) the cyclisation of suitably functionalized open-chain (single-stranded) precursor polymers in a polymer-analogous process. Both strategies pre-suppose certain essentials to arrive at structurally defined ladder polymers, especially the exclusion of side-reactions and an almost quantitative conversion of the starting materials.
The main attention of this article is focused on an active physical function of ladder-type materials. Among others, ladder-type poly( p-phenylene)s (LPPPs) represent an outstanding class of ladder-type materials. They are characterized by an extraordinarily low concentration of active traps (topological defects, impurities) and display a set of attractive electronic properties (very intensive photo- and electroluminescence, high charge carrier mobilities). This unique performance has established the solution processable LPPPs as standard materials for organic polymer based light emitting diodes (LEDs) and optically pumped solid state lasers.
- This article is part of the themed collection: Functional Organic Materials for Devices