New Synthesis/Processing Routes to Materials Exhibiting Large Optical Nonlinearity

Synthesis/processing schemes for the preparation of optical quality thin films of π-electron containing organic and organometallic materials are discussed. Fabrication approaches range from preparation of molecular/polymer composites, to preparation of copolymers containing pendant electroactive moieties, to preparation of copolymers with electroactive units incorporated into the polymer backbone, to the preparation of polymer/polymer composites. Such fabrication methodologies (particularly the latter three approaches) have the advantage of facilitating control over polymer solubility and of avoiding aggregation of electroactive units. The synthetic schemes discussed here yield materials with well-defined electroactive units; thus, diffuse bandedges associated with a distribution of π-electron conjugation lengths are avoided. Degenerate four wave mixing (DFWM) measurements at 532, 579–600, and 1064 nm are used to determine third order susceptibilities. Investigation of the frequency dependence of χ(3)/α established that resonance contributions dominate non-linear optical activity near the π-iπ* bandedge. A variety of electroactive moieties have been investigated with the largest values of χ(3)/α (= 10−12 esu cm) being observed for triphenodioxazine, metal phthalocyanine, metal tetraazaannulene, 6,6′-dimethoxy-quinolidine cyanine units.