By optimizing electron delocalization and intramolecular charge transfer, polymers yielding third order nonlinear optical susceptibilities in excess of 10-9 esu have been prepared as thin (1 micron) films. Figures of merit as high as 104 have been obtained for pristine materials. Doping (intermolecular charge transfer) yields even larger values in some cases. Ladder and penylpolyene materials prepared in preliminary studies also exhibit doping-induced visual transparency, i.e., bleaching of the pi-pi* interband transition and accompanying appearance of intraband (polaron/bipolaron) transitions. Electron-donating and withdrawing substituents are observed to stabilize these mid-gap state species. The reactivity of delocalized pi electron systems with molecular oxygen has been investigated and the effect of interruption of electron delocalization upon nonlinear optical activity has been demonstrated. This research focues upon further development of polymers, copolyers, and composite materials for enhanced nonlinear optical activity. Particular attention is paid to the development of air-stable materials and to correlation of data obtained for model compounds (oligomers) and polymers. Copolymers and composites of linear and nonlinear optical materials will be developed. Components will be so chosen that indices of refraction are matched at low light intensities but are mismatched at high intensities.