As technology continues to shrink to the molecular scale, chemists are in a unique position to contribute.  The Jasti research group’s goal is to leverage state-of-the-art organic synthesis to address challenging problems in nanoscience and materials science. 

Over the last several years, we have developed scalable synthetic methods to prepare highly functionalized derivatives of the [n]cycloparaphenylenes ([n]CPPs), which we termed “carbon nanohoops.”  We found that these molecules display surprising size-dependent optical and electronic properties.  For instance, CPPs have narrowing HOMO-LUMO energy gaps and red-shifted emissions as the nanohoop size gets smaller, exactly opposite of what is observed in acyclic conjugated systems.  CPPs are extremely bright fluorophores with extinction coefficients as high as 1.4 x 105 M-1cm-1 and quantum yields exceeding 80% in some cases.  Accessing these unique oligomeric structures with atomistic control has inspired us to pursue a variety of new directions, as detailed below. 


Synthesis of curved aromatics
Carbon  nanotubes (CNTs) are fascinating materials that could lead to faster electronics, better sensors for detection of disease, and more efficient energy generation and storage.  Unfortunately, current CNT production methods result in heterogeneous mixtures that are insufficient for advanced applications.  We envision that short CNT fragments synthesized from the bottom up may serve as seeds for the growth of CNTs with predetermined size and chirality.  CPPs themselves are not robust enough to serve this purpose, so we are currently developing methods for the synthesis of aromatic belts.


Supramolecular chemistry
We have found that in addition to the dependence of nanohoop properties on their size, the properties of CPPs can also be tuned by the inclusion of heteroatoms and variations in linkage patterns.  For instance, the crystal packing of CPPs is dramatically altered by the incorporation of perfluorobenzene units in the hoop structure.  Pyridine- and bipyridine-containing CPPs have been shown to coordinate to metals, opening up possibilities for CPPs as ligands in metal organic frameworks, transition metal complexes, and enzyme-like catalysts.  We are investigating host-guest chemistry of CPPs as well as strategies for using supramolecular interactions as guides for the synthesis of interlocked molecules. 


Polymer and materials chemistry
The remarkable structure of CPPs among small molecules suggests that polymers composed of these curved motifs would offer interesting and perhaps unprecedented properties.  CPP-based monomers may offer benefits over non-cyclic repeating units in terms of increased solubility and decreased fluorescence self-quenching in the resultant polymers.  Additionally, conjugated CPP-containing polymers may display unique charge delocalization pathways.  We are pursuing strategies to prepare CPP-containing polymers for a variety of studies. 


Biological imaging
The design and optimization of biocompatible fluorescent molecules is of utmost importance for observing complex biological events in real time.  Most advances in small molecule dye technology today rely on structural modifications of scaffolds discovered over a century ago, whereas CPPs represent an unexplored fluorophore scaffold for biological imaging.  CPPs share an absorption maximum at 340 nm, suggesting that multiple sizes of CPPs could be used simultaneously for multi-channel imaging.  We have recently prepared the first aqueous-soluble CPP derivative and demonstrated its utility for imaging live cells.  We are currently exploring avenues for targeting these new fluorescent probes to various regions of a cell. 


We thank the following agencies and companies for generous funding support and graduate student fellowships: