Dr. Petia Bobadova

Design of Carborane-Containing Conducting Polymers for Solar Cell Applications

Design of Fluorescent Dyes with Enhanced Photoluminescent Characteristics

Application of ONIOM for the Computational Modeling of Carbon Nanotubes

Our research group uses computer modeling to design and develop novel materials with industrial and medical applications. Theoretical models and calculations are able to answer questions that cannot be answered by experiment only. It is possible to explain the properties of different materials and get insights of the reasons for their unique behavior. Thus, it is possible to predict and design new materials with enhanced desired characteristics and propose their synthesis and practical applications.

We currently focus our research on three projects:

Design of Carborane-Containing Conducting Polymers for Solar Cell Applications

High demand for inexpensive and renewable energy resources has stimulated the design of efficient, low-cost conductive materials, most notably conductive organic polymers. Conductive polymers have already found important applications in photovoltaics, microelectronics, and medical sensing. These materials are flexible, malleable, elastic and have potential for roll-to-roll high throughput production. Although they have a lower cost of production than traditional silicon semiconductive materials, conductive polymers are susceptible to photodegredation after prolonged exposure to UV light and heat resulting in a short lifespan.

Fortunately, the most intriguing advantage of conductive polymers is the fact that their properties can be engineered with the use of different substituents on the polymer chain. Recent experiments demonstrated that the incorporation of substituents containing carboranyl groups dramatically increases its chemical, electrochemical and thermal stability, while keeping the conducting properties intact.

We model computationally a series polypyrroles and polythiophenes containing carborane-cage substituent groups, connected to the polymer backbone via variety of aliphatic and substituted or non-substituted aromatic spacers. We study the effect of different substituents and spacers on the conductivity of the polymer. This allows us to finely tune the properties of the material and suggest only the best candidates for actual experimental synthesis. The major advantage of computer modeling is the fact that vast variety of combinations of different substituents and spacers can be investigated in detail without the need of expensive synthesis of the real polymer. Thus, new, not even yet synthesized polymers can be examined and their properties predicted. Once the successful combinations of spacers and substituents are determined, the most promising candidates can be synthesized in the laboratory.

For the successful implementation of this project, we have established an active collaboration with the group of Prof. M. Graca H. Vicente from Louisiana State University (http://chemistry.lsu.edu/site/People/Faculty/Graca%20Vicente/item1107.html) The two groups work synergetically: our group generates candidates for polymers with enhanced conductive ability, and Dr. Vicente’s group performs the actual synthesis of the best candidates.

Design of Fluorescent Dyes with Enhanced Photoluminescent Characteristics

Borondipyrromethene (BODIPY) is a class of fluorescent dyes with exciting applications in fluorescence imaging, molecule sensors, biomedical indicators and photoelectric materials. Due to their favorable photophysical and optoelectronic properties that include high photostability, high extinction coefficients and high fluorescence quantum yields, BODIPYs have attracted special interest in drug discovery, biomedical imaging] and optical sensing.

Recently, a new class of reactions has been discovered for the synthesis of benzo-appended BODIPYs with enhanced photoluminescent characteristics. The synthesis has raised several puzzling questions. First, the use of different substituents results in dramatically different reactivities. Also, two synthetic routes have been proposed, showing different product yields. We model computationally the mechanisms of these reactions, following the two synthetic routes. We examine all intermediates and transition states in detail, linking step-by-step the reactants to the products. We use a series of different ligands and substituents and study their effect on the reaction energetic, aiming to explain why the reaction yield changes dramatically when different subsitutents are used. Our ultimate goal is to understand the reaction mechanism in detail. These insights will help us design and propose for synthesis new BODIPY’s with greater stability and higher yields, while keeping their excellent photoluminescent properties intact.

We work in close synergetic collaboration with the group of Prof. M. Graca H. Vicente from Louisiana State University who performs the synthesis of the series of BODIPYs (http://chemistry.lsu.edu/site/People/Faculty/Graca%20Vicente/item1107.html).

Application of ONIOM for the Computational Modeling of Carbon Nanotubes

Nowadays one of the major scientific focuses is the design of novel materials for industrial applications. Especially intriguing are all tasks related to a remarkable material called carbon nanotube. These are long, thin tubes made entirely from carbon. The diameter of the tube is only about 1 nm. Since their discovery, nanotubes have attracted the attention of many scientists and engineers around the world. The remarkable interest stems from their extraordinary strength, light weight, and outstanding application potential ranging from medicine and medical sensing to electronics and architecture. Pristine nanotubes are unfortunately insoluble in many liquids such as water, polymer resins, and most solvents. This complicates efforts to utilize the carbon nanotubes’ outstanding physical properties in the manufacture of composite materials, as well as in other practical applications which require preparation of uniform mixtures of carbon nanotubes with different organic, inorganic, and polymeric materials. In the recent years, reliable methods for the chemical functionalization of carbon nanotubes have been developed. This significantly extended the scope of the application spectrum while raising the interest in their characteristics.

Computer modeling of chemical compounds allows us to predict their properties and guides the synthesis of new materials with enhanced desired characteristics. Unfortunately, nanotubes have so many carbon atoms, that they are out of the reach of high-level, precise, computer modeling methods. The existing computer resources (even supercomputers) do not allow performing high-level calculations of large materials. Materials can be modeled with low-level methods that are computationally much less demanding. However, these cannot serve for precise prediction of material characteristics.

A more effective way of computational modeling for materials is applying hybrid methods like ONIOM (Our Own N-layered Integrated molecular Orbital and molecular Mechanics) methodology. ONIOM is a multi-level technique in which a large system is divided into layers (like an onion) and different computational methods are used for different parts of the system and combined to produce a consistent energy expression. The high-level calculation is performed on just a small part of the system and the effects of the surroundings are included at a low-level method. ONIOM has been successfully applied for a variety of systems. Applying ONIOM to nanotubes, however, requires careful selection of the high-level model system. The model system can be selected as a different-size patch, or even a ring. The figure to the left illustrates application of ONIOM model to carboxylated carbon nanotubes. Balls represent atoms treated at a high level of theory, whereas wire represents atoms treated at a low level of theory.

In our group, we study a series of functionalized nanotubes using patch and ring models that vary by conjugation, symmetry and size. We compare these models with target, high-level calculations to determine the best patch and ring selection. The results will help us draw a conclusion on whether patches or rings should be the method of choice for future ONIOM calculations. We will also come up with guidelines on how to select the patch and the ring in order to obtain reliable data.

This project runs in collaboration with Prof. Keiji Morokuma from Emory University (http://www.chemistry.emory.edu/faculty/morokuma.html), who is the developer of the ONIOM method.

Past research students:

Elizabeth Horn, graduated 2010
Gennie Stehn, graduated 2010
Joseph Varberg, graduated 2011 Stephanie Maschek, graduated 2011
James Riddel, graduated 2011

Current research students:

Peeyus Rai
Ethan Harak
Michael Cottam
Bridgette Pretz
James Thode

Undergraduate Research Awards

Spring 2011: Rockhurst Outstanding Research Seminar student: Joseph Varberg project: “Using Computer Modeling to Design Novel Conducting Polymers” featured at the Council on Undergraduate Research website (http://www.cur.org/urwevents.html#Rockhurst).
Spring 2010: Rockhurst Outstanding Research Seminar student: Elizabeth Horn project: “Computer Modeling of Carbon Nanotubes”

Undergraduate Research Students Presentations at Regional and National Conferences
  1. E. Harak, J. Varberg, M. G. H. Vicente, and P. Bobadova-Parvanova, “Band Gap Engineering of Carborane-Containing Conducting Polymers: A Computational Study”, 46th Midwest and 39th Great Lakes Joint Regional ACS Meeting, St. Louis, MO, October 2011 (poster). 
  2. J. Varberg, M. G. H. Vicente, and P. Bobadova-Parvanova, “Using First-Principle Calculations to Design Novel Carborane-Containing Conducting Polymers”, 241st ACS Annual National Meeting, Anaheim, CA, April 2011 (poster). 
  3. S. Maschek, T. Uppal, M. G. H. Vicente, and P. Bobadova-Parvanova, “Computational Insights on the Synthesis of Benzo-fused BODIPYs”, 241st ACS Annual National Meeting, Anaheim, CA, April 2011 (poster). 
  4. J. Varberg, M. G. H. Vicente, and P. Bobadova-Parvanova, “Computational Study of Novel Carborane-Containing Conjugated Polypyrroles”, 45th ACS Midwest Regional Meeting, Wichita, KS, October 2010 (oral presentation). 
  5. E. Horn, K. Morokuma, and P. Bobadova-Parvanova, “Computer Modeling of Large Materials: How to Select the Correct Model”, National Conference on Undergraduate Research, Missoula, MT, April 2010 (poster). 
  6. E. Horn, V. Parvanov, K. Morokuma, and P. Bobadova-Parvanova, “Selecting the Correct ONIOM Model for Computational Studies of Carbon Nanotubes”, ACS Midwest Regional Meeting, Iowa City, IA, October 2009 (poster).
Recent Publications
  1. T. Uppal, X. Hu, F. R. Fronczek, S. Maschek, P. Bobadova-Parvanova, and M. G. H. Vicente, “Synthesis, Computational Studies, Spectroscopic Properties and Biological Investigations of Benzo-appended BODIPYs“, Chemistry: A European Journal, in press. 
  2. Book chapter. D. G. Musaev, P. Bobadova-Parvanova, K. Morokuma, “Principles of Dinitrogen Hydrogenation: Computational Insights”, Chapter 4 in “Computational Modelling of Homogenous and Enzymatic Catalysis”, K. Morokuma and D. G. Musaev, Eds, Wiley-VCH, 2008. http://www.wiley.com/WileyCDA/WileyTitle/productCd-3527318437.html