Molecular Excited States
In order to be able to manipulate the photoresponse of
materials it is necessary to know and understand the
photochemical and photophysical properties of individual
molecules, and to investigate how these molecular
properties are influenced by the environment. One line of
research is therefore concerned with “high-resolution”
spectroscopic studies on molecular systems. In the
frequency domain, high-resolution studies are performed in
the gas phase on isolated molecules that range from simple
chromophores to large supramolecular systems such as
rotaxanes and catenanes in order to investigate their
electronic and geometric structure, how these are affected
by energy absorption, and - ultimately - how these are
related to their (photoactive) function. In the
time-domain, high-resolution studies are mainly performed
under non-isolated conditions with various femtosecond
laser spectroscopic techniques in order to answer the
question as to what the molecule does with the energy that
is absorbed in the form of photons, i.e., we “watch the
energy flow”. A second line of research is specifically
concentrated on the dynamics of (organic) molecules in
solution and/or solid state. Photoinduced electron transfer
is an important theme in this research. It is an elementary
chemical reaction that leads to important follow-up
processes from the charge-separated states prepared, such
as multistep electron transport, redox reactions, charge
transfer emission, photocatalysis and large-amplitude
molecular motions. A continuous effort is made to apply the
know-how gained to the development of photonic molecular
systems and materials with potential practical use. These
comprise luminescent optical probes, materials with
nonlinear optical properties, electroluminescent devices,
and molecular switches. Microphotochemistry and
microspectroscopy, including single-molecule detection,
have proven to be exciting new experimental approaches to
advance the research in these directions.