This is a recorded (re-edited) Zoom lecture at the MSc/PhD level for chemistry students and researchers that are interested in molecular photochemistry. The topic is: triplet formation by charge recombination, and it focuses on mechanistic aspects regarding the electron spin flip (not on the energetics).
The so-called SOCT-ISC mechanims is discussed, as well as the H-HFI mechanism.
If you want to grasp all details of this talk, you may want to look at these talks first:
• Molecular Photochemist...
Learning objectives:
Intermolecular (or inter-chromophoric) interactions in the excited state can lead to electron transfer processes that are succeeded by recombination processes.
Charge recombination to the triplet excited state is a complex process that can proceed by a slow and a fast mechanism. The fast one is the Spin Orbit Charge Transfer Inter System Crossing mechanism (SOCT-ISC). The slow one is H-HFI, the interaction of nuclear spin with electron spin through (proton) HyperFine Interactions, and can be described by spin de-phasing.
The orientation of chromophores that interact is very important. A 60 to 90 degree angle between the two pi systems is optimal for triplet formation by charge recombination.
Ultimately, the matrix element for spin orbit coupling limits the optimal charge recombination rate to the triplet, if the energetic conditions are optimal. These energetic conditions are described by the Marcus theory of electron transfer (see the other lectures on this topic).
This matrix element for spin orbit coupling can be determined with computational chemistry.
Thanks to Max Paradiz for slide number 12 on the Frustrated Lewis Pairs!
The presentation is based on this Open Access publication:
doi.org/10.103...
Some other reviews on this topic:
doi.org/10.103...
doi.org/10.103...
doi.org/10.103...
doi.org/10.103...
A more general reference on spin orbit coupling:
N. J. Turro , V. Ramamurthy and J. C. Scaiano , Principles of Molecular Photochemistry: An Introduction , University Science Books, 2009
www.uscibooks....
TCR edit 4