Pak Laboratory Research

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Research Interests:Organic, Organometallic, Materials and Polymer Chemistry


    Research interests in Pak Lab consist of the preparation and study of non-natural nano- to meso-scale materials.  We develop and utilize modern synthetic methods for the preparation of novel organic, organometallic, inorganic, and organic-inorganic hybrid materials with technologically important properties.  Some of the desired properties are conductivity, photo- and electro-luminescence, and nonlinear optical (NLO) activities. Although the above properties seem quite different from each other, chemically, they are closely related and can be achieved in materials called “semi-conductors”.  The semi-conductors that we are interested in can be divided into three categories based on their compositions: Organic, Inorganic, and Organometallics.  Upon the preparation of these materials, we collaborate closely with other chemists, physicists, and engineers to design, construct and study the resulting devices.  We envision that the preparation and fundamental understanding of these materials will eventually contribute to the development of next generation solar cells, light emitting diodes, and opto-electric sensors.


1.    Organic Chemistry
    In our lab, we synthesize highly π-conjugated organic molecules such as polypyridines and heteroaromatics, which can be used as building blocks for metal coordination complexes, supramolecular self-assembly structures, and organic-inorganic hybrid polymers.  For example, highly conjugated 2,2’-bipyridines can be used to prepare Ru complexes like Ru(dcbpy)2L2+, which is an effective photosensitizer for Grätzel-type organic solar cells.  Other heterocycles such as crown ethers can be used to achieve suparmolecules with potentials in luminescence sensors.  In addition, by taking advantage of self-assembly between polypyridyl ligands and metal centers, linear complexes (oligomers and polymers) can also be prepared. When complexing ligands are highly conjugated, resulting materials may show interesting properties such as conductivity and non-linear optical (NLO) properties.  Similarly, star-shape self-assemblies (dendrimers) between polypyridyl ligands and metals can also be accomplished. Since we are using a divergent strategy, we can also introduce different metals at different generations of the dendrimer structure.

2.    Inorganic and Organometallic Chemistry
    We also prepare organometallic compounds, which can be used to prepare specific inorganic semi-conductors.  Currently, we are particularly interested in CuInS2 and their alloy systems.  Thin films and/or nanoparticles of CuInS2 are recognized as the next generation photovoltaic materials.  The challenges of this project are to find ways to prepare uniform CuInS2 thin films and particles without introducing significant amounts of defects in the nanometer range.  To control the growth of thin films, we employ various deposition techniques such as Radio Frequency Enhanced Chemical Vapor Deposition (RFE-CVD) and Super Critical CO2 Thermal Deposition (SC-CO2-TD) of molecular single source precursors.  To control the growth of nanoparticles, we employ microwave irradiation assisted decomposition of molecular single source precursors in the presence of organic thiol capping agents, including highly functionalized cavitands. 

3.    Educational Aspect
    The described projects are designed to accommodate the unique circumstances of undergraduate research, which can be difficult to carry out projects that are labor-intensive or time-consuming. With this in mind, the projects are divided into three sub-stages, which allow student researchers to spend shorter periods of time in the laboratory and still reach a definite goal and sense of accomplishment.  The first stage concentrates on synthesis of simple building blocks using short sequences of organic/organometallic procedures.  The second stage focuses on the preparation and characterization of complex materials.  The third involves probing the potential applications of the materials prepared.  Students who participate in these projects are expected to acquire skills that are essential to synthetic organic chemists.  They will be exposed to newly emerging concepts in materials and analytical chemistry.  A significant portion of their research time is spent exploring the interface between classic organic chemistry and rapidly expanding area of materials science, green chemistry, and chemical education.  While in my group, students learn to improve their writing and oral presentation skills.  Students are strongly encouraged and supported to present their work in regional and/or national meetings.

Publications 
 

1.         “Rapid and Size Control Synthesis of CuInS2 Nanoparticles via Microwave Irradiation.” Gardner, Joseph S.; Shurdha, Endrit; Lau, Lisa D.; Wang, Chongmin: Rodriguez, Rene G.; Pak, Joshua J. J. Nanoparticle Research, 2008, 10(4), 633-641.

 

2.         “Pulsed-Spray Radiofrequency PECVD of CuInS2 Thin Films.” Rodriguez, Rene G.; Pulsipher, Daniel J. V.; Lau, Lisa D.; Shurdha, Endrit; Pak, Joshua J.; Jin, Michael H.; Banger, Kublinder K.; Hepp, Aloysius F. Plasma Chemistry and Plasma Processing 2006, 26(2), 137-148.*

 

3.         “Facile synthesis of 4,4’,5,5’-tetraiododibenzo-24-crown-8 and its highly conjugated derivatives.” Endrit Shurdha, Jaime L. Mayo, and Joshua J. Pak, Tetrahedron Letters 2006, 47, 233-237.*

 

4.         “Synthesis and crystallographic characterization of a 'palladadehydrobenzo[19]annulene.”  Pak, Joshua J.; Darwish, Ossama S.; Weakley, Timothy J. R.; Haley, Michael M. J. Orgmet. Chem.  2003, 683(2), 430-434.*

 

5.         “Diastereoselective Self-Assembly of a Pentacoordinate Siliconate Tetraanionic Molecular Square. A Mechanistic Investigation.” Pak, Joshua J.; Greaves, John; McCord, Dianne J.; Shea, K. J., Organometallics, 2002, 21, 3552-3561.

 

6.         “Synthesis and Characterization of Annulene-Fused Pseudorotaxanes." J. J. Pak, T. J. R. Weakley, M. M. Haley, D. Y. K. Lee, and J. F. Stoddart, Synthesis 2002, 1256-1260.

 

7.         “Nonlinear Optical Properties of Dehydrobenzo[18]annulenes: Expanded Two-Dimensional Dipolar and Octupolar NLO Chromophores.” A. Sarkar, J. J. Pak, G. W. Rayfield, and M. M. Haley, J. Mater. Chem. 2001, 11, 2943-2945.

 

8.         “Carbon Networks Based on Dehydrobenzoannulenes.  2.  Synthesis of Expanded Graphdiyne Substructures” W. Brad Wan, Stephen C. Brand, Joshua J. Pak, and Michael M. Haley, Chem. Eur. J. 2000, 6, 2044-2052.

 

9.         “Stepwise Assembly of Site-Specifically Functionalized Dehydrobenzo[18]annulenes”  Joshua J. Pak, Timothy J. R. Weakley and Michael M. Haley, J. Am. Chem. Soc. 1999, 121, 8182-8192.

 

10.      “Macrocyclic Oligo(phenylacetylenes) and Oligo(phenyldiacetylenes).”  Michael M. Haley, Joshua J. Pak and Stephen C. Brand, Topics in Current Chemistry (Carbon-Rich Compounds II), Vol. 201, Armin de Meijere (Ed.), Springer-Verlag: Berlin, 1999, 81-130.

 

11.      “One-Pot Desilylation/Dimerization of Ethynyl– and Butadiynyltrimethylsilanes.  Synthesis of Tetrayne-Linked Dehydrobenzoannulenes.”  Michael M. Haley, Michael L. Bell, Stephen C. Brand, David B. Kimball, Joshua J. Pak and W. Brad Wan, Tetrahedron Lett. 1997, 38, 7483-7486.*

 

12.      “Synthesis and Crystallographic Characterization of a Platinadehydrobenzo[19]annulene.”  Joshua J. Pak, Timothy J. R. Weakley and Michael M. Haley, Organometallics 1997, 16, 4505-4507.

 

13.      “Carbon Networks Based on Dehydrobenzoannulenes:  Preparation of Substructures of Graphdiyne.”  Michael M. Haley, Stephen C. Brand and Joshua J. Pak, Angew. Chem., Int. Ed. Engl. 1997, 36, 836-838.

 

14.       “a,b–Unsaturated Nitriles:  An Effective Conjugate Addition with Potassium Phenyl Selenolate And Potassium Phenyl Sulfenylate.”  Fraser F. Fleming and Joshua J. Pak, J. Org. Chem. 1995, 60, 4299-4301.

*Undergraduate Co-Authors

Back row: From left, Dr. Pak, Josh Peterson (SEEDII), Andrew Baker (SEEDI), Richard Westover,
Front row: From left, Ian Kihara, Dom Denty, Jeff Hess, & Ben Donahoo. (Summer 2008)

Back row: From left, Jeff Hess, Dominic Denty, Tamara Shephard, Ben Donahoo, Ian Kihara, & Dr. Joseph Gardner.
Front row: From left, Josh Peterson (SEED), Stephanie Prichard, Bob Barnett, & Dr. Pak (& Eddie).(Summer 2007)

For more information about Pak Group Members and Pictures click here.
 

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Modified May 2008