High Refractive Index Poly(thiophene) for Organic 3-D Photonic Crystals with a Complete Photonic Band Gap*

Photonic crystals (PC) with a complete 3-D photonic band gap (PBG) require materials with sufficient refractive index ($n)$ contrast to be in specific 3-D periodic structures on the length scale of light. Currently, only inorganics have an adequate $n$ to open a complete 3-D PBG. Poly(thiophene) (PT), a sulfur containing conjugated polymer, is predicted to have a sufficient $n$, but this has not been realized. By optimizing the electropolymerization of PT including reaction rates, temperatures, additives, and reactant concentrations, high quality PT films with an adequately high $n$ can be synthesized. Using a density differential colloidal crystallization technique, which allows the crystallization process to approach thermodynamic equilibrium, high quality templates were produced. A nano-mechanical annealing technique was developed to enable the further perfection of the entropy driven structures. The next step is to combine these to fabricate an organic 3-D PC with a complete PBG.