Department of Chemistry, Columbia University
3000 Broadway, mail code 3119
New York, NY 10027
In my research group we view a photon both as a reagent (photon absorption) for initiating photoreactions and as a product (photon emission) which allows molecules to be imaged in space and time. Photons as reagents possess some outstanding properties, e.g., they may be used to selectively excite specific groups of atoms in a single molecule or a specific molecule in a mixture, because the light absorption depends on definite and unique electron energy gaps. This selectivity of photon absorption may be controlled and varied at will by use of lasers or by a monochrometer. The concentration of photons may be varied at will by controlling the light intensity. Photons can even be made optically active by the use of circularly polarized light. Finally, by use of lasers that can produce short pulses of light, high concentrations of photons can be injected into a system to trigger reactions in times as short as a trillionth of a second (a picosecond).
We study the structure and dynamics of a range of reactive intermediates such as carbenes, singlet oxygen, radicals, radical pairs, and biradicals. These species are produced by photochemical excitation. Their chemistry is investigated directly by a range of time-resolved techniques and then characterized in real time by UV-VIS, IR, ESRor NMR analysis.
Our group is developing a novel field termed "supramolecular photochemistry”, or photochemistry beyond the conventional intellectual and scientific constraints implied by the term "molecular photochemistry." In supramolecular processes, non-covalent bonds between molecules play a role analogous to that of covalent bonds between atoms of a molecule. Many of the supramolecular structures of interest may be considered as "guest@host" complexes, where the @ represents a non-covalent bond between guest and host. Among the host structures investigated are polymers (such as starburst dendrimers), porous solids (such as molecular sieve zeolites), and biological molecules (such as DNA and RNA). Photochemical and photophysical methods are employed to investigate the structure and dynamics of reactive intermediates produced by photolysis of guest@host complexes. Current projects include: the use of photoemission to track mRNA molecules in living cells with “molecules beacons” which are specifically designed to “light up” when they hybridize with their complimentary strand on the mRNA; an investigation of the mechanism of reversible oxidation of carbon nanotubes; the stereoselective addition of singlet oxygen to double bonds; the characterization of the surface of nanocrystals; and the mechanism of paramagnetic interconversion of electron and spin paired systems.
The research of students in my group is strongly interdisciplinary and collaborative. Typically, a student will be working together and actively with other research groups in the Chemistry Department, other departments at Columbia , or even departments in other universities. This approach familiarizes students with the advantages of teamwork in research, and allows students to be exposed to a range of intellectual and scientific methods to solve scientific problems and to be engaged in projects ranging from materials science, to environmental science, to chemical biology.
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“Aliphatic [beta]-Nitroalcohols for Therapeutic Corneoscleral Cross-linking: Chemical Mechanisms and Higher Order Nitroalcohols” David C. Paik, Marissa R. Solomon, Quan Wen, Nicholas J. Turro, Stephen L. Trokel, Invest. Ophthalmol. Vis. Sci. 51, 836-843 (2010)
“Some hydrogels having novel molecular structures” Jeremiah A. Johnson, Nicholas J. Turro, Jeffrey T. Koberstein, James E. Mark, Prog. Polym. Sci. 35, 332-337 (2010)
“Steady-State and Time-Resolved Studies of the Photocleavage of Lysozyme by Co(III) Complexes” Thota Jyotsna, Challa V. Kumar, Steffen Jockusch, Nicholas J. Turro, Langmuir 26, 1966-1972 (2010)
“Charge Transfer Chemical Doping of Few Layer Graphenes: Charge Distribution and Band Gap Formation” Naeyoung Jung, Namdong Kim, Steffen Jockusch, Nicholas J. Turro, Philip Kim, Louis Brus, Nano Letters 9, 4133-4137 (2009)
“Fundamental Study of Optical Threshold Layer Approach Towards Double Exposure Lithography” Xinyu Gu, Adam J. Berro, Younjin Cho, Kane Jen, Saul Lee, Tomoki Nagai, Toshiyuki Ogata, William J. Durand, Arunkumar Sundaresan, Jeffrey R. Lancaster, Steffen Jockusch, Paul Zimmerman, Nicholas J. Turro, C. Grant Willson, Proc. of SPIE 7273, 72731-C (2009)
“Mechanism for Oxygen-Enhanced Photoconductivity in Rubrene: Electron Transfer Doping” Ashok J. Maliakal, Judy Y.-C. Chen, Woo-Young So, Steffen Jockusch, Bumjung Kim, Maria Francesca Ottaviani, Alberto Modelli, Nicholas J. Turro, Colin Nuckolls, Arthur P. Ramirez, Chem. Mater. 21, 5519-5526 (2009)
“Mechanistic Studies of Photoinitiated Free Radical Polymerization Using a Bifunctional Thioxanthone Acetic Acid Derivative as Photoinitiator” Feyza Karasu, Nergis Arsu, Steffen Jockusch, Nicholas J. Turro, Macromolecules 42, 7318-7323 (2009)
“Optical Threshold Layer and Intermediate State Two-Photon PAG Approaches to Double Exposure Lithography” Adam J. Berro, Xinyu Gu, Naphtali O'Connor, Steffen Jockusch, Tomoki Nagai, Toshiyuki Ogata, Paul Zimmerman, Bryan J. Rice, Elizabeth Adolph, Travis Byargeon, Jose Gonzalez, Nicolas J. Turro, C. Grant Willson, Proc. of SPIE 7273, 72731-B (2009)
“Role of Environmental Factors on the Structure and Spectroscopic Response of 5'-DNA-Porphyrin Conjugates Caused by Changes in the Porphyrin-Porphyrin Interactions” A. Mammana, G. Pescitelli, T. Asakawa, S. Jockusch, A. G. Petrovic, R. R. Monaca, R. Purrello, N. J. Turro, K. Nakanishi, G. A. Ellestad, M. Balaz, N. Berova, Chem. Eur. J. 15, 11853-11866 (2009)
“Self Aggregation of Supramolecules of Nitroxides@Cucurbituril Revealed by EPR Spectra” Nithyanandhan Jayaraj, Mintu Porel, M. Francesca Ottaviani, Murthy V. S. N. Maddipatla, Alberto Modelli, Jose P. Da Silva, Balakrishna R. Bhogala, Burjor Captain, Steffen Jockusch, Nicholas J. Turro, V. Ramamurthy, Langmuir 25, 13820-13832 (2009)
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