Chemistry and Physics: Research / Projects
Research / Projects
Students conduct research at Dowling or with our collaborating partners such as Brookhaven National Laboratory, the National Park Service, U.S. Geological Survey, and other governmental, academic, civic and industrial partners. Undergraduates participate in research that integrates chemistry with computer science, environmental science, and biology. Students perform research at Dowling and/or with our partners in areas such as global climate change, environmental contaminants tracking, environmental monitoring and inventories, atmospheric science, energy, pharmaceuticals, forensics, and hydrology. The undergraduate program, along with active internships at EPA, USGS, BNL and other agencies, give Dowling chemistry students an excellent marketability level.
“Chemistry in Action” is a research program that brings Chemistry to life through investigations in areas of importance to society, such as new materials, new energy sources, and the environment. Ongoing projects include water quality monitoring, sediment analysis of heavy metals, wetland restoration and studies, and stream flow and tidal flushing measurements.
Recent presentations by students and faculty in the Chemistry and Physics Dept. include:
|• “Singlet, triplet, electron and hole transport along single polymer chains” Physical Chemistry of Interfaces and Nanomaterials XIV Conference of SPIE International Society for Optics and Photonics. San Diego, CA (3-19 Aug. 2015)• “Transport along conjugated polymer chains” Brookhaven National Laboratory. Upton, NY (March 2015)
• “Exciton diffusion lengths of 30-40 nm measured along single polyfluorene chains with end traps by transient absorption spectroscopy and steady state fluorescence.” Excitonic Photovoltaics Conference, Telluride Science Research Center, Colorado (13 Aug. 2014)
• “Polymers resist forming charge-transfer complexes” American Chemical Society 243rd National Meeting. San Diego, CA (28 March 2012)
• “Intramolecular electron transfer in polyfluorenes with electron acceptor endcaps” American Chemical Society 242nd National Meeting. Denver, CO (31 Aug. 2011)
• “Reduction of poly-2,7-(9,9-dihexylfluorene) molecular wires to form polyanions“ American Chemical Society 237th National Meeting: invited Sci-Mix & Physical Chemistry Division. Salt Lake City, UT (25 March 2009)
Recent publications by students and faculty in the Chemistry and Physics Dept. include:
|• Zaikowski, L.; Mauro, G.M.; Karten, B.; Asaoka, S.; Wu, Q.; Bird, M.J.; Cook, A.R.; Miller, J.R. (2015) “Charge transfer fluorescence and 34nm exciton diffusion length in polymers with electron acceptor end traps.” Journal of Physical Chemistry B 119(24) 7231-7241. dx.doi.org/10.1021/jp510095p• Zaikowski, L.; Kaur, P.; Gelfond, C.; Selvaggio, E.; Asaoka, S.; Wu, Q.; Hung-Cheng, C.; Takeda, N.; Cook, A.; Yang, A; Rosanelli, J.; Miller, J.R. (2012) “Polarons, bipolarons, and side-by-side polarons in reduction of oligofluorenes” Journal of American Chemical Society 134(26), 10852-10863.
• Zaikowski, L.; Friedrich, J.M.; Seidel, S.R. (Eds.) (2010) Chemical Evolution II: From Origins of Life to Modern Society. American Chemical Society Books #1025. New York: Oxford University Press. 430 pp.
|• Seidel, S.R.; Zaikowski, L. (2010). “Coordination-driven self-assembly”. In Zaikowski, L.; Friedrich, J.M.; Seidel, S.R. (Eds.) Chemical Evolution II: From Origins of Life to Modern Society. (pp. 249-268). American Chemical Society Books #1025. New York: Oxford University Press.|
Lori Zaikowski Research Projects
The National Academy of Engineering identified 14 Grand Challenges for the 21st Century. “Foremost among the challenges are… the need to develop new sources of energy, at the same time as preventing or reversing the degradation of the environment.” The #1 challenge is to make solar energy economical.
In addressing that grand challenge, my students and I collaborate with scientists at Brookhaven National Laboratory (BNL), conducting research both at Dowling and at BNL on electron transfer processes in molecules with important applications in modern society: photovoltaics (solar energy), light emitting diodes (LEDs), optical/electronic devices, energy storage, and energy transfer. Our research focuses on Molecular Wires and Charge Separation.
I. Molecular Wires
When most people think of a wire, they think of metals (like copper) that conduct electrons. Most organic molecules (like rubber or plastic) are insulators. However, organic molecules with conjugated systems of electrons act as “molecular wires” and have applications to energy harvesting, storage, and transfer. We study a variety of molecular wires, and four ongoing projects are described below.
A. Electron transfer and delocalization in molecular wires
Oligofluorene molecular wires are examined by UV-vis-near infrared spectroscopy and semiempirical calculations. We determine how many electrons can be captured by a series of oligofluorenes in the presence of sodium or NaK, and quantify the relative amounts of anion to dianion to trianion to tetraanion to pentaanion, etc. by conducting titrations with strong electron acceptors. We use pulsed radiolysis at the BNL Laser Electron Accelerator facility to provide a verification of anion identity and extinction coefficients. We perform semiempirical calculations to get theoretical electronic spectra, energies, geometries, and HOMO/LUMO orbitals. We also examine fluorescence spectra of each oligofluorene. Future explorations will include similar investigations on other polymers.
Zaikowski, L.; Kaur, P.; Gelfond, C.; Selvaggio, E.; Asaoka, S.; Wu, Q.; Hung-Cheng, C.; Takeda, N.; Cook, A.; Yang, A; Rosanelli, J.; Miller, J.R. (2012) “Polarons, bipolarons, and side-by-side polarons in reduction of oligofluorenes” Journal of American Chemical Society 134(26), 10852-10863.
B. Charge-transfer fluorescence and exciton movement in polymers
A principal problem in organic solar cells is transport of excitons (excited electrons) to junctions where they can split to form electrons and holes. Typical estimates of the diffusion length in films are around 3-10nm, although possibly as large as 20nm in crystalline domains. Attempts at measuring diffusion lengths along a single chain have suggested values of 7nm (P3HT with fullerene end traps) and 17nm (pF with fullerene end traps). The properties of conjugated molecules suggest the possibility of efficient transport over long distances along single continuous chains, and we ask how long exciton diffusion lengths can be. We use steady state fluorescence spectroscopy to examine long polyfluorene (pF) chains with naphthylimide (NI) and anthraquinone (AQ) electron acceptor “trap” groups at the ends to investigate charge-transfer complex energies, quantum yields, solvent reorganization energies, vibrational energies, and exciton diffusion lengths. Measurements on chains >100 repeat units indicate that end traps capture ∼50% of the excitons, and that the exciton diffusion length is LD = 34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains.
Zaikowski, L.; Mauro, G.M.; Karten, B.; Asaoka, S.; Wu, Q.; Bird, M.J.; Cook, A.R.; Miller, J.R. (2014) “Charge transfer fluorescence and 34nm exciton diffusion length in polymers with electron acceptor end traps.” Journal of Physical Chemistry B dx.doi.org/10.1021/jp510095p
C. Rates of exciton transport and exciton diffusion lengths in polymers using laser transient absorption spectroscopy
The average distance that an exciton can travel in its lifetime is an important parameter in organic solar cells. It has been observed recently that excitons can form significant numbers of charges in <100 femtoseconds, suggesting that the initial excitation may occupy a larger volume than the relaxed exciton and that this process is important in the most efficient solar cells. We perform transient absorption spectroscopy to gain insight into exciton transport along single polymer with end traps. Conjugated fluorene polymers (polyfluorenes) are among the organic semiconductors researched in solar cells today, and we utilize specially- synthesized polyfluorene derivatives having two different electron- accepting end traps, anthraquinone and naphthylimide to determine exciton transport rates. Read More.
D. Charge-Transfer Complexes in Oligomers and Polymers
We want to know the extent to which charge-transfer complexes (CTCs) versus full ions form upon reactions of polymer electron donors with strong electron acceptors. We react oligothiophenes (T3, T4, T6) and polythiophenes (pT) with electron acceptors such as dichlorodicyanoquinone (DDQ), tetracyanoethene (TCNE), and tetrachloroquinone (Cl4Q). We vary concentrations of donor-acceptor pairs in solvents of different polarity (dichloroethane, chloroform, carbon tetrachloride), and monitor CTC and ion pair formation by UV-vis-NIR absorption spectroscopy and conductivity. Equilibrium constants and extinction coefficients for the CTCs were calculated in each solvent, and the delocalization length of polythiophene cations was determined. CTC formation depends upon solvent polarity, redox potential of the electron acceptor, and donor molecule length. Read More.
II. Redox Potentials and Charge Separation
New organic materials with application to solar energy storage and transfer exist in a non-polar environment. Therefore, knowledge of redox potentials in non-polar solvents is essential to developing new organic materials with high energy storage and transfer capabilities. We study energetics of charge separation as a function of solvent polarity and electrolyte concentration utilizing UV-visible spectroscopy and electrochemical conductivity. We study quinone-metallocene redox pairs in organic solvents with and without electrolyte, and quantify “ion pair charge transfer complex” formation by measuring conductivity and comparing to spectroscopic data. Equilibrium constants and Gibbs Free Energies are calculated from absorptions and extinction coefficients using Beer’s Law. These values and redox potentials are compared as a function of solvent polarity, solute concentration, and electrolyte concentration. Future work will extend this to new quinone-metallocene pairs, and to analyses at the BNL Laser Electron Accelerator Facility. The overarching goal is to establish a mathematical relationship that enables chemists to determine redox potentials as a function of solvent polarity using the existing vast data of redox potentials that are reported in polar solvents. Read More.
III. Chemistry in Action Research Program:
Projects primarily examine water quality on tributaries of the South Shore Estuary, and quantify sediment contamination at stations on three South Shore Estuary tributaries: Patchogue River, Carman’s River, and Swan River. One research goal is to inform actions for practical land use improvements that may be implemented by governmental agencies in order to enhance water quality and the maritime economy. The program expanded to include natural products projects that involve extraction, purification, and identification of compounds with bioactivity: anti-bacterial, anti-fungal, allelopathy, etc. Natural products from terrestrial and marine plants, animals, fungi, and microorganisms are studied. Natural products projects offer many opportunities for integrating biological applications, such as using chemical structure to elucidate evolutionary relationships, identification of new herbal medicinals and natural pesticides. Read More.