Faculty Research
Alphabetical · By research area

The interplay between molecular structure and function in organic materials and carbon-rich compounds is at the heart of my research program. Exploiting the versatility of organic synthesis and the most modern characterization techniques, our research concentrates on several prominent questions: (1) What are the fundamental electronic characteristics of non-traditional organic chromophores based on cross-conjugated architectures? (2) Can we realize conjugated compounds that have enhanced properties for use as nonlinear optical (NLO), liquid crystalline, and electroluminescent materials? and (3) can we direct and control the organization of materials at the molecular level?

Many of the molecules, oligomers, and polymers that we develop evolve from the cross-conjugated enyne framework of iso-polydiacetylenes (iso-PDAs, 1), a novel semi-conducting material that we have recently reported. The π-electronic system of iso-PDAs provides for high energy UV-Vis absorption and a greater transparency when compared to linearly-conjugated materials. This potentially useful property of iso-PDAs is being exploited to overcome a fundamental problem associated with the use of organic compounds as NLO materials - the so called transparency-efficiency trade off - where increasingly conjugated compounds are too highly absorptive to be useful for many optical applications. We are also using this design element to provide chiral oligomers and polymers, as well as materials with high-energy fluorescence that could be used to produce blue light in organic light emitting diodes (OLEDs).

On the way to oligomeric and polymeric materials, unique nanometer-sized objects are being created with useful properties, as well as unconventional and esthetically pleasing structures. Cyclic, cross-conjugated radialenes and similar macrocycles provide the opportunity to probe numerous concepts as to the physical organic nature of these new molecules. Analysis of trends by ¹H and ¹³C NMR, UV-Vis, and Raman spectroscopies, and X-ray crystallography define structure-function relationships and outline the fundamental electronic make-up of these compounds. Ultimately, our efforts have and will shed light on the subtle electronic characteristics of these compounds, such as homo-conjugation and aromaticity. Finally, the realization and study of molecular systems is being used to extrapolate the properties of larger, extended systems such as two- and three-dimensional carbon-rich networks that are similar in structure to nanotubes and fullerenes.

Related to radialenes, cross-conjugated macrocycles with directed functionality (e.g., 2) have been realized. The predictable and directional bonding of aromatic ligands, such as pyridine, allows for the design and preparation of a variety of supramolecular coordination complexes with extraordinary structures and functional properties. For example, orientation of the pyridine nitrogen(s) outward from the core allows for the preparation of a variety of hybrid metal-organic structures and organized, porous materials.

A plethora of uncommon, extended polyyne structures are now feasible based on our successful formation of alkylidene carbene/carbenoid species (3) and the subsequent rearrangement to the corresponding triyne. Prior to our work, alkyne migration in carbenes was unprecedented, and this method represents a major synthetic advance for modern acetylenic chemistry. The usefulness of this rearrangement is dramatically enhanced by the fact that several such rearrangements can be achieved in a single molecule, leading to the formation of extended polyyne systems that are very difficult or impossible to access with existing synthetic methods (e.g., decayne 4). A particularly interesting application of this method involves the synthesis of molecular carbon allotropes such as cyclo-C₂₀.

Selected Publications

S. Eisler, A.D. Slepkov, E. Elliott, T. Luu, R. McDonald, F.A. Hegmann, R.R. Tykwinski, "Polyynes as a Model for Carbyne: Synthesis, Physical Properties and Nonlinear Optical Response," J. Am. Chem. Soc. 2005, 127, 2666-2676.

Y. Zhao, A.D. Slepkov, C. Osei Akoto, R. McDonald, F.A. Hegmann, R.R. Tykwinski, "Synthesis, Structure, and Nonlinear Optical Properties of Cross-Conjugated Perphenylated iso-Polydiacetylene," Chem. Eur. J. 2005, 11, 321-329.

T. Luu, E. Elliott, A.D. Slepkov, S. Eisler, R. McDonald, F.A. Hegmann, R.R. Tykwinski, "Synthesis, Structure and Nonlinear Optical Properties of Diarylpolyynes," Org. Lett. 2005, 7, 51-54.

K. Campbell, C.A. Johnson II, R. McDonald, M.J. Ferguson, M.M. Haley, R.R. Tykwinski, "A Simple, One-step Procedure for the Formation of Chiral Metallomacrocycles," Angew. Chem. Int. Ed. 2004, 43, 5967-5971.

A.L.K. Shi Shun, R.R. Tykwinski, "Synthesis of Naturally Occurring Acetylenes via an Alkylidene Carbenoid Rearrangement," J. Org. Chem. 2003, 68, 1339-1347.