Yanhou Geng

Glassy nematic conjugated oligomers: materials for organic light-emitting diodes

Conjugated organic molecules and polymers are of great interest for applications as the active element in new types of electroluminescent, photovoltaic, and electronic devices. Control of the molecular order of these materials can have a significant impact on their optical and electronic properties. In particular, alignment of conjugated organics that exhibit an intrinsic anisotropy in a dipole moment permits generation of thin films that emit linearly polarized light in an orientation specific to the alignment direction of the molecule. Polarized photoluminescence and electroluminescence from ordered conjugated oligomers and polymers has been demonstrated using many alignment methods, but particular success in integrating these materials into electrical devices has been achieved by utilizing conjugated materials that exhibit a glassy nematic liquid-crystalline phase. We report the status of our ongoing development of OLED devices based on glassy nematic oligofluorenes. These devices exhibit electroluminescent peak polarization ratios as high as 31:1 and color coordinates spanning the entire visible spectrum.

Implications of Delayed Luminescence for Conjugated Polymer Photophysics

We observe unusual decay dynamics of persistent luminescence in a model oligofluorene. Generation of interchain triplet polaron pairs can account for the dynamics but not the reduction of photoluminescence in films relative to dilute solution.