MYJOHNSHOPKINS.EDU
John D. Tovar
Organic and Materials Chemistry
Johns Hopkins University
New Chemistry Building
3400 North Charles St.
Baltimore, MD 21218
Phone: 410.516.4358
Email: tovar@jhu.edu
Tovar Group Website
Ph.D. - Massachusetts Institute of Technology
Postdoctoral Fellow - Northwestern University
The Tovar group has broad interests in electrically-conductive plastics and other types of pi-conjugated organic electronic materials. We use molecular design as a tool to predict, control and seek a better understanding of charge mobility and conductivity through organic electronic materials to enable their employment in emerging applications ranging from inexpensive flexible circuitry to active biomedical materials. Current molecular targets incorporate unusual pi-conjugated systems and therefore provide extensive experience in organic synthesis (aromatic, polymer and peptide chemistries) along with optical and electrochemical characterization techniques. A few of the projects we are pursuing are described below:
Unusual aromaticity and charge transport. Cyclic pi-conjugated molecules have provided a wealth of information on the concept of aromaticity, yet relatively difficult chemical syntheses have limited their widespread evaluation and application in the context of advanced materials. We are interested in the synthesis and characterization of elaborate molecular and polymeric scaffolds with unusual electronic properties imparted by non-traditional aromatics such as 2 and 10 electron pi-systems and boron-based frameworks. Our recent studies with methano[10]annulene (below) revealed how unusual aromatic segments can facilitate charge injection into and transport through conducting organic polymers.
Photochromic conducting polymers. We recently initiated a program to study photochromic polymers that can attenuate electrical conductivity via indirect alterations of the conjugated polymer. To do so, we take advantage of well-known electrocyclic reactions triggered by light that lead to new electronic structures within the polymer backbone. In conjunction with this effort, we uncovered a remarkably regioselective aromatic halogenation reaction enabled by a conformational protecting group. This strategy allows us to construct highly complex pi-conjugated molecules in short order from readily available building blocks and minimizes the reliance on protecting or masking groups.
Self-assembling bioelectronic nanomaterials. Studies of organic electronic materials in solution often do not translate adequately to the solid state due to the dominating influence of chromophore aggregation and other non-specific interactions. These solution studies (as well as solution-processing for devices) are typically performed in organic solvents thus complicating possible extensions into biological applications. We designed and prepared water-soluble oligopeptides that incorporate pi-conjugated oligomers within the peptide main chain. Specific environmental influences trigger molecular self-assembly into well-defined nanostructures with strong intermolecular electronic communication due to the pi-staking enforced by the macromolecular architecture. In effect, this process as shown below results in the controlled aggregation of pi-conjugated organics yielding optoelectronic fibrils at size regimes (sub-10 nm) unattainable through polymer processing or current lithographic techniques. We are now exploring the possibilities for using the peptidic segments as insulating dielectrics while enabling cellular interactions that rely on oligopeptide epitope recognition. Current work investigates the bioactivity of these electronic nanomaterials and their potential for constructing novel hybrid materials.
Recent publications:
B. D. Wall, S. R. Diegelmann, S. Zhang, T. J. Dawidczyk, W. L. Wilson, H. E. Katz, H.-Q. Mao and J. D. Tovar, “Aligned macroscopic domains of optoelectronic nanostructures prepared via the shear flow assembly of peptide hydrogels,” cover article in Advanced Materials, 2011 (23) 5009-5014. (DOI: 10.1002/adma.20110296)
C. P. Harvey and J. D. Tovar, “Main chain photochromic conducting polymers,” in Polymer Chemistry, 2011 (2) 2600-2706. (DOI: 10.1039/C1PY00304F)
A. Caruso Jr., M. A. Siegler and J. D. Tovar, “Synthesis of functionalizable boron-containing pi-electron molecules that incorporate formally aromatic fused borepin rings,” in Angewandte Chemie International Edition, 2010 (49) 4213-4217 (DOI: 10.1002/anie.201000411)
G. S. Vadehra, B. D. Wall, S. R. Diegelmann and J. D. Tovar, “On-resin dimerization incorporates a diverse array of pi-conjugated functionality within aqueous self-assembling peptide backbones,” in Chemical Communications, 2010 (46) 3947-3949 (DOI: 10.1039/c0cc00301h)
A. M. Fraind and J. D. Tovar, “Comparative survey of conducting polymers containing benzene, naphthalene and anthracene cores: interplay of localized aromaticity and polymer electronic structures,” in the Journal of Physical Chemistry B, 2010 (114) 3104-3116. (doi:10.1021/jp9101459)
P. A. Peart and J. D. Tovar, “Expanding the realm of furan-based conducting polymers through conjugation with 1,6-methano[10]annulene,” in Macromolecules, 2009 (42) 4449-4455. (doi:10.1021/ma9006494)