Spatial Patterning of the β-Phase in Poly (9,9-dioctylfluorene): A Metamaterials-Inspired Molecular Conformation Approach to the Fabrication of Polymer Semiconductor Optical Structures

Materials in which sub-wavelength physical structures, rather than variations in chemical composition, are used to modify the nature of their interaction with electromagnetic radiation form the promising new class of metamaterials. For molecular materials one has an intriguing alternative, namely structuring the conformation or physical geometry of the molecule. In order for this to be an effective methodology one needs the change in conformation i) to engender a significant change in electromagnetic properties and ii) to be spatially controllable to allow patterning of practical structures. In this paper the potential of such an approach is demonstrated through spatial patterning, via masked solvent vapor exposure, of the beta-phase conformation in poly (9,9-dioctylfluorene) (PFO). Significantly the conformation change approach preserves a planar film form format and is found not to negatively impact on optical gain properties, both very attractive features for optoelectronic and photonic lightwave circuit applications. As a specific demonstration the ability to spatially control the lasing wavelength for samples in which a beta-phase conformation is selectively patterned in a glassy PFO film spin coated atop a one-dimensional distributed-feedback grating etched into a spectrosil substrate is shown.