MSC Colloquium Frans C. De Schryver
|03 februari 2005||FWN-Building 5111.0080, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Prof.dr. F.C. De Schryver|
|Affiliation:||Department of Chemistry, Katholieke Universiteit Leuven , Celestijnenlaan 200F, 3001 Heverlee , Belgium|
|Title:||Single-molecule visualization and evaluation|
|Date:||Thu Feb 3, 2005|
|Start:||16.00 (Doors open and coffee available at 15.30)|
Chemist have since long been fascinated by the structure–property relations in molecules. Recent developments have allowed not only the visualization but also the interrogation and manipulation of single molecules and hence the probing of these properties at a real molecular and even sub-molecular level. This will be illustrated using confocal fluorescence and scanning probe microscopy.
The photophysical properties of in particular dendritic structures eventually containing either a single central chromophore or decorated with chromophores at the rim will be addressed and the complementarities between ensemble and single-molecule data will be stressed. The importance of the substitution pattern and the size of the dendrimer generation will be illustrated using these rigid dendrimer core scaffolds. The energy dissipation processes including annihilation, energy hopping, energy transfer and electron transfer at the ensemble and single-molecule level will be discussed. One of the most intriguing findings at the single-molecule level was the presence of collective on/off jumps in the fluorescence intensity traces of the dendrimers. This phenomenon can be explained by assuming both a radiative trap (energetic lowest chromophoric site) and a non-radiative trap (triplet state of one chromophore) within the individual dendrimers. It was shown that a similar scheme can explain the collective on/off jumps in the fluorescence intensity traces of polymers.
Photoinduced electron transfer in synthetic systems is of great importance not only in biological systems such as photosynthesis but also in many modern devices such as organic light emitting diodes. Evidence for intramolecular photo-induced electron transfer in synthetic systems consisting of a triphenylamine-perylenediimide donor-acceptor dendrimer or a triphenylamine-peryleneimide dendrimer at the ensemble and single-molecule level will be presented. Moreover, for the first time a direct observation of the forward as well as the backward electron transfer step is made in a single emitting entity. Fluctuations in the values of the rate constants for forward and backward electron transfer were observed, induced by the local environment as well as by conformational changes of the dendrimer itself. On the basis of the retrieved rate constants potential energy surfaces can be constructed.
The relation between structure and properties such as chirality or electron density of a physisorbed two-dimensional array at a surface studied by scanning tunneling microscopy will be addressed.
|Laatst gewijzigd:||22 oktober 2012 14:30|