Title: Singlet Oxygen Photosensitization in Weakly Coupled Floppy Complexes
Speaker: Prof. Mario Barbatti, Aix Marseille University
Date: 2020-10-15 15:00
Location: Room B311, Zengchengkui Building (Online)
Abstract：
Singlet oxygen (1O2) is a chemically reactive species of great importance for biological and medical research. It is usually synthesized through triplet fusion, following the general internal conversion formula
1[3A + 3B] → 1[1A + 1B] (1)
where A + B is a molecular complex.
Triplet fusion treatment in a weakly-coupled floppy complex like PS-O2, where PS is a photosensitizer, poses a tremendous challenge for computational chemistry due to the process’s long time scales, the lack of a unique transition state, and the open-shell character of the ground state.
In the last years, Shuming Bai and I have worked out a research program to address these challenges, combining conventional quantum-chemical methods, software implementation for calculating spin-orbit couplings,1 model development for calculating kinetic rates for reaction 1,2 and proposition of proxies for efficient calculation of nonadiabatic and diabatic couplings.3 All this program has been specially tailored to deal with reaction 1 in weakly-coupled floppy complexes.
Taking thionucleobases and thionucleosides as prototypical PS, we have characterized their spectra,4 intersystem crossing dynamics,5 and decay of their triplet state.6 We have tackled the physical chemistry of reaction 1, for which we have determined singlet oxygen rates as a function of the incidence direction of the O2 on PS.7 We could explain the main features of the reaction and even propose heuristic rules to maximize or minimize the 1O2 yield, according to the application.8
Finally, we generalized the theory underlying triplet fusion, showing that it is a particular case of a broader class, the Spin-Exchange Internal Conversion, which includes other important reactions like singlet fission.3
1. Gao, X.; Bai, S.; Fazzi, D.; Niehaus, T.; Barbatti, M.; Thiel, W., J. Chem. Theory Comput. 2017, 13, 515-524.
2. Bai, S.; Barbatti, M., J. Chem. Theory Comput. 2017, 13, 5528-5538.
3. Bai, S.; Barbatti, M., J. Chem. Theory Comput. 2019, 15, 1503-1513.
4. Bai, S.; Barbatti, M., J. Phys. Chem. A 2016, 120, 6342-6350.
5. Mohamadzade, A.; Bai, S.; Barbatti, M.; Ullrich, S., Chem. Phys. 2018, 515, 572-579.
6. Bai, S.; Barbatti, M., Phys. Chem. Chem. Phys. 2017, 19, 12674-12682.
7. Bai, S.; Barbatti, M., J. Phys. Chem. Lett. 2017, 8, 5456-5460.
8. Bai, S.; Barbatti, M., Phys. Chem. Chem. Phys. 2018, 20, 16428-16436.
