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).

Scholarly, Creative & Professional Activities

1. Lord, S. J., Conley, N. R., Lee, H.-l. D., Samuel, R., Liu, N., Twieg, R. J. & Moerner, W. E. A Photoactivatable Push-Pull Fluorophore for Single-Molecule Imaging in Live Cells. Journal of the American Chemical Society 130, 9204-9205 (2008).
2. Raymond, J. E., Ramakrishna, G., Twieg, R. J. & Goodson, T. Two-Photon Enhancement in Organic Nanorods. Journal of Physical Chemistry C 112, 7913-7921 (2008).
3. Getmanenko, Y. A. & Twieg, R. J. Unprecedented Negishi Coupling at C-Br in the Presence of a Stannyl Group as a Convenient Approach to Pyridinylstannanes and Their Application in Liquid Crystal Synthesis. Journal of Organic Chemistry 73, 830-839 (2008).
4. Bhaskar, A., Ramakrishna, G., Twieg, R. J. & Goodson, T., III. Zinc Sensing via Enhancement of Two-Photon Excited Fluorescence. Journal of Physical Chemistry C 111, 14607-14611 (2007).
5. Lord, S. J., Lu, Z., Wang, H., Willets, K. A., Schuck, P. J., Lee, H.-L. D., Nishimura, S. Y., Twieg, R. J. & Moerner, W. E. Photophysical Properties of Acene DCDHF Fluorophores: Long-Wavelength Single-Molecule Emitters Designed for Cellular Imaging. Journal of Physical Chemistry A 111, 8934-8941 (2007).
6. 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).
7. 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).
8. 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).
9. Willets, K. A., Nishimura, S. Y., Schuck, P. J., Twieg, R. J. & Moerner, W. E. Nonlinear optical chromophores as nanoscale emitters for single-molecule spectroscopy. Accounts of Chemical Research 38, 549-556 (2005).
10. Schuck, P. J., Willets, K. A., Fromm, D. P., Twieg, R. J. & Moerner, W. E. A novel fluorophore for two-photon-excited single-molecule fluorescence. Chemical Physics 318, 7-11 (2005).
11. Sanguinet, L., Twieg, R. J., Wiggers, G., Mao, G. L., Singer, K. D. & Petschek, R. G. Synthesis and spectral characterization of bisnaphthylmethyl and trinaphthylmethyl cations. Tetrahedron Letters 46, 5121-5125 (2005).
12. Lu, Z. & Twieg, R. J. Copper-catalyzed aryl amination in aqueous media with 2-dimethylaminoethanol ligand. Tetrahedron Letters 46, 2997-3001 (2005).
13. Kim, S. Y., Semyonov, A. N., Twieg, R. J., Horwich, A. L., Frydman, J. & Moerner, W. E. Probing the sequence of conformationally induced polarity changes in the molecular chaperonin GroEL with fluorescence spectroscopy. Journal of Physical Chemistry B 109, 24517-24525 (2005).
14. Hudson, K., Ellman, B., Gettwert, V., Getmanenko, Y. & Twieg, R. J. Radiation-induced trapping and charge transport in a smectic liquid crystal. Applied Physics Letters 87 (2005).