Chemistry Reference
In-Depth Information
flexible polymer chains, and nonradiative energy transfer due to dipole-dipole
interactions. All those processes affect the fluorescence characteristics. The ad-
vanced fluorescence measurements introduced about 40 years ago with a time
resolution corresponding to the rate of these processes (i.e., nanosecond and
subnanosecond time-resolved fluorescence measurements) almost immediately
opened a new field of study of fast processes at the molecular level.
As a result of enormous development in the technology and production of pulse
lasers, laser diodes, detector systems, and powerful computers in recent decades,
steady-state and time-resolved fluorometers now belong to the standard equipment
of biochemical and macromolecular laboratories. For example, there are appara-
tuses combined with microscopes that are suitable for time-resolved fluorescence
measurements of individual organelles in living cells. However, the widespread use
of fluorescence techniques generates certain danger, which is connected with their
routine use. We would like to point out that the fluorescence spectroscopy is an indi-
rect technique and that the interpretation of results needs great care and precaution.
It almost always requires additional information on the system.
When designing a fluorescence experiment and interpreting data, one more pos-
sible complication has to be kept in mind: Only a limited number of systems involve
intrinsic fluorophores and are inherently luminescent. Such systems (e.g., proteins
containing tryptophan) are very suitable for fluorescence studies and reliable in-
formation on the location, mobility, and accessibility of tryptophane residues can
be obtained in a relatively straightforward way. In other cases, an extrinsic fluores-
cence probe has to be added to the system. Its addition modifies the system, which
can be a problem (more or less severe) depending on the system studied and on
the fluorescence technique used. Because the fluorescence reports on the behavior
of the microenvironment of the probe, it does not yield information on the orig-
inal system, but only on its small perturbed part, even though the overwhelming
part of the system has not been altered at all and behaves as the system without
added fluorophore. It is obvious that an attempt to reduce the probe content in
the host system could partially suppress this problem, but would not eliminate it
entirely.
The aim of this feature article is to outline our application of fluorescence tech-
niques to polymer self-assembly studies. We do not intend to give a complete survey
of the use of fluorescence in polymer chemistry. We focus only on techniques that
we have been using within the POLYAMPHI network. We start with a description of
the principles of fluorescence phenomena and an explanation of the role of processes
that influence the rates of transition and the spectroscopic characteristics. Then we
discuss several examples of our experimental studies, in which we applied different
variants of time-resolved measurements. Finally, we show how computer modeling
can be used to support the interpretation of data on complex systems.
Search WWH ::
Custom Search