Tag: Ramesh Jasti

Synthesis of 6,13-pentacene-incorporated [10]cycloparaphenylene

Presenter(s): Cyrus Waters − Biochemistry

Faculty Mentor(s): Ramesh Jasti, Brittany White

Poster 20

Research Area: Organic Chemistry

Funding: SAACS Summer Research Award

Cycloparaphenylenes (CPPs) have size-dependent optoelectronic properties: the HOMO/LUMO gap size increases as benzene subunits are added. This capacity to tune the band gap makes CPPs attractive for use in organic electronic devices. Similarly, pentacene shows promise as a component of photovoltaic cells because of its uniquely high capacity for singlet fission (SF), whereby one high-energy incident photon is harnessed to yield two lower-energy triplets. In devices sensitized to SF, two electrons can be pushed per photon, bypassing the Shockley-Queisser efficiency limit and doubling the photocurrent from specific wavelengths of absorbed light relative to traditional, silicon-based photovoltaics. Pentacene-incorporated CPPs combine the two structures in a fully-conjugated system, potentially allowing the size of the CPP to control the energy of light at which the pentacene undergoes SF. Here, the synthesis of 6,13-pentacene-incorporated [10]cycloparaphenylene was attempted. Suzuki coupling of selectively-linked curved precursors yielded a strained macrocyclic intermediate. Attempts at reductive aromatization of the macrocycle have successfully aromatized the CPP backbone but have failed to aromatize the pentacene unit, instead yielding either the insufficiently reduced diol or its overly reduced dihydrogen analogue.

Synthesis and Characterization of Ru(II) Cycloparaphenylene Complexes

Presenter(s): Shayan Louie − Biochemistry

Faculty Mentor(s): Ramesh Jasti, Jeff Van Raden

Poster 87

Research Area: Natural Science

Funding: Presidential Undergraduate Research Scholars

Ruthenium polypyridyl complexes undergo metal-to-ligand charge transfer (MLCT) in the presence of light, allowing energy from light to be captured in the form of an electron transfer. These molecules possess great potential as catalysts for efficient and clean chemical processes. To develop light-harvesting complexes that perform advanced functions, new ligands, or groups around metal ions, must be made. Cycloparaphenylenes (CPPs) are hoop-shaped photoactive molecules with virtually unexplored roles as ligands. They possess exceptional size-dependent optic and electric properties, and show potential as a new class of macrocycles for supramolecular chemistry, ultimately making them suitable for charge-transfer complexes. Through the incorporation of nitrogen atoms into the backbone of [8]CPP, we found that CPPs act as versatile ligands for a variety of metals including Ru(II). However, the effects of CPP diameter on the electric properties of Ru(II)-based light- harvesting complexes are unknown. We have recently synthesized CPP ligands of various sizes and coordinated them to ruthenium centers, which has allowed for the investigation of size/diameter on these properties.

The optic and electric properties of the complexes have been studied using UV-Vis spectroscopy and cyclic voltammetry. Here, we present our findings.

Synthesis of Alkyne Substituted Cycloparaphenylenes for Conjugated Polymers

Presenter(s): William Edgell − Biochemistry

Faculty Mentor(s): Ramesh Jasti

Poster 69

Research Area: Organic Synthetic Chemistry

Funding: Undergraduate Research Opportunities Program (UROP)

Conjugated polymers possess excellent conductive properties that could facilitate the construction of light weight flexible electronics. This potential application makes an efficient route to conjugated polymers synthetically desirable. The current barrier to large-scale synthesis of these molecules is an inversely proportional relationship between solubility and conductivity. The sought-after conductivity is due to charge transfer across a conjugated π system within the polymer. This affords the polymers with electronic properties atypical of organic molecules. Unfortunately, intermolecular stacking of these π systems leads to poor solubility. Cycloparaphenylenes(CPPs) offer a solution for this conflict between solubility and charge transfer. CPPs are large hoops of strained benzene rings which possess a conjugated π system without a clear avenue for π stacking. A CPP polymer would form a sort of molecular necklace; with large bulky hoops hanging off the polymer backbone, the potential polymers would not stack well with each other, thus reducing chance of aggregation. Utilization of the CPPs as monomers for polymer synthesis could produce a polymer chain with the ideal electrical properties without diminishing the solubility. To this end, this research project focuses on the synthesis of the CPP monomers to be used for the polymer reaction. Creating this highly strained hoop requires a series of reactions to form a string of benzene rings that will be coupled to a single alkyne functionalized benzene. Previous work shows challenges in the route that yields the eight ring CPP. Current work has yielded successful synthesis of functionalized six ring cycloparaphenylene.

A Novel Application of Carbon Nanohoops in Ion-Sensitive Devices: A Potential Story

Presenter(s): Patrick Fajardo

Faculty Mentor(s): Ramesh Jasti

Poster 17

Session: Sciences

Of the many types of ion-sensitive devices, one who’s potential has not been fully realized are chemically modified field effect transistors (CHEMFETs). These devices utilize ion receptors to detect specific target ions, commonly used to detect the presence of pollutants. One possible receptor is cycloparaphenylene (CPP), also called carbon nanohoops. In this research we determined the interaction between CPP and a variety of ions using CHEMFET devices, by measuring a change in output voltage at different ion concentrations. We expected CPPs to interact strongly with cations, as these molecules have an electron rich pore which has been applied as a chemical host in other systems. A preliminary screening showed an interaction between CPP and lithium, ammonium, and sodium cations. In addition control experiments established a baseline, in order to accurately quantify the interaction taking place. Further ion screenings, as well as ionic strength control studies, are future experiments that will be carried out to further characterize the interaction taking place.