Electronic Coherence and Collective Optical Excitations of Conjugated Molecules
Shaul Mukamel,
*
Sergei Tretiak,
Thomas Wagersreiter,
Vladimir Chernyak
Optical spectroscopy of conjugated molecules is
described by using collective electronic coordinates, which represent
the joint dynamics of electron-hole pairs. The approach relates the optical signals directly to the dynamics of charges and bond orders (electronic coherences) induced by the radiation field and uses only
ground-state information, thus avoiding the explicit calculation of
excited molecular states. The resulting real-space picture is
reminiscent of the normal-mode analysis of molecular vibrations and
offers a unified framework for the treatment of other types of systems
including semiconductor nanostructures and biological complexes.
Spatial coherence displayed in two-dimensional plots of the five
electronic normal modes that dominate the optical response of
poly(p-phenylene vinylene) oligomers with up to 50 repeat units (398 carbon atoms) in the 1.5- to 8-electronvolt frequency
range suggests a saturation to bulk behavior at about five repeat
units.
The authors are in the Department of Chemistry and the Rochester
Theory Center for Optical Science and Engineering, University of
Rochester, Rochester, NY 14627, USA.
*
To whom correspondence should be addressed.
