Voice: 215-204-7703 Fax: 215-204-1532
B.S., 1994, National and Kapodistrian University of Athens, Greece;
Ph.D., 2000, The Ohio State University;
Postdoctoral fellow, 2000-2003, Johns Hopkins University.
2005 NSF CAREER Award
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Most chemical processes follow the Born-Oppenheimer
(adiabatic) approximation, in which the nuclei move on a single electronic
potential energy surface (PES). However there are important processes where
this approximation breaks down. These nonadiabatic events play an important
role in essential processes in nature such as photosynthesis, vision, charge
transfer and photochemistry. Nonadiabatic processes are facilitated by
the close proximity of two PES where radiationless transitions between
the surfaces can occur with higher probability. The efficiency for radiationless
transitions increases in the extreme case when two PES become degenerate
forming conical intersections. Thus many ultrafast nonradiative transitions
occur through conical intersections. Theoretical developments have enabled
the efficient study of conical intersections in small systems. The focus
of our group is to extend these studies to more complicated systems, particularly
of biological interest, in an effort to understand the underlying mechanisms
of photoinitiated nonadiabatic processes and their potential implications.
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| UV radiation and DNA |
The photophysical and photochemical behavior of the nucleobases is of
particular importance since they are the chromophores in DNA and RNA.
The excited states of the nucleobases are extremely short-lived,
having lifetimes of the order of femtoseconds or picoseconds.
This property has been associated with their photostability in ultraviolet (UV) radiation from the sun.
When UV radiation is absorbed by DNA photochemistry can occur which may lead to DNA damage and photocarcinogenesis. Efficient dissipation of the absorbed energy prevents extensive photodamage.
We are investigating the radiationless decay mechanisms that can explain
the ultrafast lifetimes and fluorescence quenching in these systems.
Two- and three-state conical intersections are present that can facilitate
nonadiabatic transitions between the different electronic states of these molecules.
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In order to be able to study the role of solvation into photophysical and photochemical
processes we have developed a combined quantum and classical mechanics (QM/MM) method.
A multireference configuration interaction (MRCI) method is used for the quantum mechanical
description and classical molecular dynamics simulations are used for the solvent.
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