Dr. Robert Twieg: "Organic Materials with Novel Optical and Electronic Properties"

The research interests of the group headed by Dr. Twieg involve the synthetic chemistry of organic molecules and macromolecules that possess novel optical and electronic properties. This research is done in collaboration with numerous academic and industrial laboratories where the new materials are further characterized and implemented in devices. The Liquid Crystal Institute (LCI) on the Kent Campus and collaborators in the Advanced Liquid Crystalline Optical Materials (ALCOM) NSF Center are just two local examples of where collaborators are found. Students involved in this research not only have the opportunity to participate in the design and preparation of novel materials but also are able to follow through and exercise them.

In the area of liquid crystals efforts are underway to identify and prepare systems that have large linear optical anisotropy that leads to high birefringence. For example, a variety of specific conjugated molecules including tolane oligomers and methylenedihydropyridines (MDHP) are being examined. Other general approaches, including the implementation of lateral substituents and selective fluorination, are typical of the molecular engineering employed to imbue the molecules with the appropriate bulk properties. Such liquid crystals may be of use in reflecting or scattering polymer modified displays (PDLC and PSCT) and work is also in progress on the modification of the polymer network forming materials, such as a range of chiral monomers, for this class of displays. Additionally, unusual molecular structures are being examined to see if they can be successfully incorporated into mesogenic molecules.

In the area of nonlinear optical (NLO) materials organic and polymer systems with a range of properties are sought. For electro-optic (EO) applications chromophores with large first optical hyperpolarizabilities are required but the efforts do not stop there as special attention is also given to durability issues. Are the molecules thermally and photochemically stable? Can they be successfully mixed in a polymer or covalently bound to it in high concentration? Can sufficient bulk polar order be created and sustained in low-loss waveguides containing these materials? Again, only by working closely with groups actually building devices can meaningful evaluations be made and questions like these answered leading to a successful outcome.

Another area of current interest involves photorefractive (PR) polymers. These organic materials have a wide range of potentially valuable applications and much progress on the composition and understanding of the basic physical processes in these systems has occurred. We are looking for new chromophores and transport agents with special attention to the glass forming capabilities of the constituents so that high quality optical specimens can be fabricated. Here again, MDHP structures are a successful example. A general and pervasive long-term goal is to better understand and exploit such monomer and oligomer glasses as alternatives to glassy polymers in a range of applications including photoconduction (xerography) and electroluminescence (organic light emitting diodes, OLED).

Selected Publications
  1. Nishimura, S. Y., Lord, S. J., Klein, L. O., Willets, K. A., He, M., Lu, Z. K., Twieg, R. J. & Moerner, W. E. Diffusion of lipid-like single-molecule fluorophores in the cell membrane. Journal of Physical Chemistry B 110, 8151-8157 (2006).
  2. Getmanenko, Y. A., Twieg, R. J. & Ellman, B. D. 2,5-dibromopyridine as a key building block in the synthesis of 2,5-disubstituted pyridine-based liquid crystals. Liquid Crystals 33, 267-288 (2006).
  3. Duzhko, V., Semyonov, A., Twieg, R. J. & Singer, K. D. Correlated polaron transport in a quasi-one-dimensional liquid crystal. Physical Review B 73 (2006).