Abstract
The conformational dependence of the matrix element for spin–orbit coupling and of the electronic coupling for charge separation are determined for an electron donor–acceptor system containing a pyrene acceptor and a dimethylaniline donor. Different kinetic and energetic aspects that play a role in the spin–orbit charge transfer intersystem crossing (SOCT-ISC) mechanism are discussed. This includes parameters related to initial charge separation and the charge recombination pathways using the Classical Marcus Theory of electron transfer. The spin–orbit coupling, which plays a significant role in charge recombination to the triplet state, can be probed by (TD)-DFT, using the latter as a tool to understand and predict the SOCT-ISC mechanism. The matrix elements for spin–orbit coupling for acetone and 4-thio-thymine are used for benchmarking. (Time Dependent-) Density Functional Theory (DFT and TD-DFT) calculations are applied using the quantum chemical program Amsterdam Density Functional (ADF).
Highlights
Transitions between singlet and triplet states are forbidden in a non-relativistic framework; intersystem crossing from a singlet to a triplet state is possible in the presence of spin–orbit coupling
It is possible to gain more insight into the SOCME, because it is the result of the spin-operator expressed by its Hamiltonian [9,40]
This spin–orbit Hamiltonian describes the interaction between the spin and orbital motions of an electron and induces singlet and triplet excitations
Summary
Of electron transfer, and can occur in large bifunctional molecules containing an electron donor and an electron acceptor [7,8] This process, triplet charge recombination (TCR), plays a role in organic photovoltaic materials, heavy-atom-free photosensitizers, as well as in LEDs. Photosensitizers often contain transition metals [13] such as Ru, [14] Pd [15] and Pt [16,17] In these complexes, intersystem crossing (ISC) is efficient due to spin–orbit interactions, [18] a relativistic effect usually present in atoms with large nuclei, commonly called the heavy-atom effect. It is still difficult to design these structures with efficient ISC due to a lack of understanding of the relationship between ISC and the molecular structure
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