Chemical Physics and Physical Chemistry

Talat Rahman, U. of Central Fl.; PChem Seminar

Thu, 2012-12-06 13:00 - 14:30
Location: 

Lynch Room

Title: "Selectivity and reactivity of metal-oxide surfaces and interfaces: insights from ab initio calculations"

Mark Johnson, Yale; Physical Seminar

Thu, 2012-11-29 13:00 - 14:30
Location: 

Lynch Room

Arnd Pralle, Buffalo; PChem Seminar

Thu, 2012-11-15 13:00 - 14:30
Location: 

Lynch Room

William Brennen

Photo: 
First Name: 
William
Last Name: 
Brennen
Official Title: 
Emeritus Professor of Chemistry
Contact Information
Office Location: 
Senior Faculty Suite
Email: 
brennen2@sas.upenn.edu

Hendrik Hameka

Photo: 
First Name: 
Hendrik
Last Name: 
Hameka
Official Title: 
Emeritus Professor of Chemistry

Physical Chemistry

Contact Information
Office Location: 
Senior Faculty Suite
Email: 
hameka@sas.upenn.edu

Mark Johnson, Yale; Physical Seminar - CANCELED

Thu, 2012-11-01 09:00 - 10:30

Location: Carolyn Hoff Lynch Room

Adam Wasserman, Purdue; Physical Seminar

Thu, 2012-10-11 09:00 - 10:30

Location: Carolyn Hoff Lynch Room

Connie Roth, Emory; Physical Seminar

Thu, 2012-10-04 09:00 - 10:30

Location: Carolyn Hoff Lynch Room

Michael R. Topp

Photo: 
First Name: 
Michael R.
Last Name: 
Topp
Official Title: 
Professor of Chemistry

Physical Chemistry 

Contact Information
Office Location: 
249 N, Lab: 240 N
Email: 
mrt@sas.upenn.edu
Phone: 
(215) 898-4859
Admin Support: 
Education: 
  • B.Sc. Sheffield University (1966) - Haworth Medal winner
  • Ph.D. University College London and the Royal Institution of Great Britain (1969)
  • Member of Technical Staff, Bell Labs, (1969-71)
  • IBM Research Fellow, Pembroke College, Oxford (1971-73)
Research Interests: 

Conformational Relaxation in Isolated Molecular Clusters

When molecules become electronically excited, the rearrangement of electronic charge can precipitate many types of relaxation processes. To probe details of such events, one can employ isolated molecular clusters consisting of only a few hydrogen-bonded molecules. One particularly interesting case is the cluster involving a Coumarin 151 molecule bonded to a water dimer. Two different structures have been identified in the ground state, as shown below.

 

 

Recent experiments have shown that the species shown on the left here is unstable in the excited state, and relaxes to that shown on the right on a picosecond or nanosecond time scale depending on the available energy. This corresponds to movement of the water dimer by ~10Å from one side of the molecule to another, following and yet the activation energy is only 60 cm-1. Such conformational changes have been studied by a combination of fluorescence and infrared double resonance techniques in conjunction with ionization and mass resolution.

 

Hydrogen-Bonded Molecular Dimers

 

Hydrogen-bonded dimers present important opportunities to study short-range intermolecular interactions, including modification of the electronic structure, and corelated proton or hydrogen atom transfer. Molecules such as the dimer of 4-Amino-N-methylphthalimide, shown here, reveal dramatic changes in their infrared spectra between the ground and excited states. The simple ground-state ground-state infrared spectrum reflects the high symmetry of the ground state. On the other hand, the much more complex excited-state spectrum shows evidence for a loss of symmetry resulting from changes in the acid-base properties of NH2 and >C=O groups, which may result in proton transfer across the intermolecular hydrogen bonds. These types of strongly bonded dimers are different from many other dimer systems studied so far, because both their electronic and vibrational spectra are highly structured, despite the large increase in binding energy upon electronic excitation. Femtosecond-domain experiments are planned, to follow in real time the changes in vibrational spectra, which will provide further insights into the reasons for their complexity in the excited state.

 

 

Ultrafast Electronic Relaxation of Hydrogen-Bonded Molecules Studied by Femtosecond Pump-Probe Spectroscopy

 

Femtosecond pump-probe experiments allow us to observe the time evolution of the first events following pulsed laser excitation, including motions in the first coordination shell of a hydrogen-bonded molecule in fluid solution. New pump-probe experiments involving the detection of ultrashort-lived fluorescence have explored spectroscopic changes of aminophthalimide molecules in hydrogen-bonding solvents on a time scale more than 10 times faster than existing data for fluorescence Stokes shifts. Both fluorescence upconversion and pump-probe methods are being used to investigate ultrafast energy transfer processes in complex molecules, in collaboration with the Regional Laser and Biomedical Technology Laboratories at Penn.

Joseph Subotnik

Photo: 
First Name: 
Joseph
Last Name: 
Subotnik
Official Title: 
Edmund J. and Louise W. Kahn Endowed Term Professor of Chemistry

Physical and Theoretical Chemistry

Contact Information
Office Location: 
268 Cret wing
Email: 
subotnik@sas.upenn.edu
Phone: 
215-746-7078
Admin Support: 
Education: 

B.A. Harvard University, 2000

Physics and Math (summa cum laude)


Ph.D.  UC Berkeley, 2006  Biophysics

 

NSF International Research Fellow (2007 -2009), Tel-Aviv

Postdoctoral Fellow, Northwestern University (2009-2010)

Research Interests: 

Research in the Subotnik group focuses on the intersection of static quantum chemistry methods (especially for excited states) with nonadiabatic dynamics methods (specifically surface hopping). The focus is quantifying electron transfer, energy transfer, and electronic relaxation. Applications are to almost all photo-induced processes!

Department of Chemistry

231 S. 34 Street, Philadelphia, PA 19104-6323

215.898.8317 voice | 215.573.2112 fax | web@chem.upenn.edu

Syndicate content