Ladder-type materials

Materials with a ribbon- or ladder-type framework possess a two-dimensional geometry and are thus intermediate between linear and three-dimensional sy stems. The limited conformational freedom of ladder polymers is particularl y 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 mat erials: (1) the polymerisation of multifunctional monomers, in which both s trands of the ladder structure are generated in a single reaction; and (2) the cyclisation of suitably functionalized open-chain (single-stranded) pre cursor polymers in a polymer-analogous process. Both strategies pre-suppose certain essentials to arrive at structurally defined ladder polymers, espe cially the exclusion of side-reactions and an almost quantitative conversio n of the starting materials. The main attention of this article is focused on an active physical functio n of ladder-type materials. Among others, ladder-type poly(p-phenylene)s (L PPPs) represent an outstanding class of ladder-type materials. They are cha racterized by an extraordinarily low concentration of active traps (topolog ical defects, impurities) and display a set of attractive electronic proper ties (very intensive photo- and electroluminescence, high charge carrier mo bilities). This unique performance has established the solution processable LPPPs as standard materials for organic polymer based light emitting diode s (LEDs) and optically pumped solid state lasers.