Photoinduced Energy Transfer, Re-Edit, René M. Williams, UvA. Förster and Dexter mechanims. FRET. скачать в хорошем качестве

Photoinduced Energy Transfer, Re-Edit, René M. Williams, UvA. Förster and Dexter mechanims. FRET.

IMPROVED SHORTER VERSION, BETTER AUDIO. This is a lecture at the BSc/MSc level for chemistry students that are interested in molecular photochemistry. From Förster to Dexter to the GRORG and CISBIO. Learning objectives: • If we want to harvest light efficiently with molecular systems we need to chose multiple chromophoric units that can transfer the energy to the lowest state. • Intermolecular (or interchromophoric) interactions in the excited state can lead to electronic interactions enabling transfer processes. • There are two important theoretical frameworks that can be used for energy transfer: the Coulomb based Förster Resonance Energy Transfer (FRET) and the Exchange based Dexter mechanism. • FRET can be applied in biology for bio-assays on protein proximity. Thanks to Dr. Catharina Hippius and Prof. Dr. Frank Würthner for sharing their slides on the "GRORG project". Thanks to Iza, Paula Teeuwen and Yorrick Boeije for asking questions! EXTRA ADDITION, 9-12-2023: Regarding the distance dependence of energy transfer: If we plot the natural logarithm of the rate vs distance, we get al linear curve for the Dexter mechanisms. The slope is negative and gives the beta value. https://doi.org/10.1021/ja990044b The abscissa gives the fastest rate at close contact. Similar observations have been made for photo-induced electron transfer. https://doi.org/10.1021/ja00245a014 If we do the same for the Forster mechanism, the curve is not straight, but is curved. http://www.wiley-vch.de/contents/jc_2... The rate is proportional to 1/R^6 (see also video at 27:00) Only changing the distance in molecular systems, keeping all other parameters the same, is often not that easy. END OF NEW ADDITION. NOTE: The transition dipole moment is an electric dipole moment associated with the transition between two states and is a (complex) vector. As such it has an (arbitrary) direction relative to the Cartesian coordinates of the two molecules that are interacting. (This "direction" is a mathematical convenience). The direction of the vectors does not play a role in the kappa factor, only the angles between the vectors (so they can be displayed as double headed arrows!!). The strength (or size) of the vectors is related to the overlap integral in Förster resonance energy transfer. The basic theory of resonance energy transfer assumes the donor fluorophore can be treated as an oscillating dipole that can transfer energy to a similar dipole at a particular resonance frequency in a manner analogous to the behavior of coupled oscillators, such as a pair of tuning forks vibrating at the same frequency. The tuning forks can be oriented parallel or anti-parallel, the result is the same. (see "Pitfalls" paper below) For more information see: Principles of Fluorescence Spectroscopy, Joseph R. Lakowicz https://link.springer.com/book/10.100... Chapter 13 "Pitfalls and limitations in the practical use of Förster's theory of resonance energy transfer" https://doi.org/10.1039/B810620G For more complex mechanisms for e.g. lanthanides, have a look at Prof. P. A. Tanner's paper: "Misconceptions in electronic energy transfer: bridging the gap between chemistry and physics" https://doi.org/10.1039/C8CS00002F (different spin states can play a role here: Eu(III) has six unpaired electrons!! http://dx.doi.org/10.1021/acs.inorgch... This is the older, un-edited version:    • Photoinduced Energy Transfer, René M. Will...   Energy Transfer ReEdit 1