From electronic coupling to exciton dynamics: Modeling photophysical processes in rubrene solids

PhD Program

Speaker

Aitor Diaz Andres

When

2025/12/19
10:30

Place

Salón de Grados, Faculty of Chemistry, EHU, Donostia/San Sebastián

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PhD Thesis defense by Aitor Diaz Andres

Supervisor: David Casanova (DIPC, Ikerbasque)

Quantum / Theoretical Chemistry and Computational Modelling

This Thesis studies the triplet-triplet annihilation process in the crystalline and amorphous solids of rubrene. Triplet annihilation is the process that converts two triplet excitons into a high-energy singlet exciton (twice the energy of the triplets). However, other processes are important to understand the dynamics of these excitons in solids, such as exciton transport, absorption, and emission. In this Thesis, I have focused my efforts on understanding the transport processes of singlet and triplet excitons as well as the interaction of two triplets to form the TT state and the subsequent formation of the singlet state. All these processes have been studied first for the crystalline solid rubrene, and later, thermal vibrations have been included as an approximation of the effect of temperature on solids. With these results, a computational protocol has been designed to calculate all the mentioned couplings, with special mention to the RASCI method to calculate the couplings in which the TT state is involved. Following this protocol, the triplet fusion process in the amorphous solid rubrene was studied. The results have shown that the triplet fusion process is impeded because triplet transport is not allowed. However, the triplet fusion coupling indicates that the process would be allowed in systems where triplet transport is possible.

The second part of the thesis focuses on simulating the processes involved in triplet fusion. For this purpose, I have developed SEDyn, a software for simulating photophysical processes in molecular organic solids. Simulations have been performed on the crystalline and amorphous solids of rubrene. In this thesis, in addition to the exciton transport simulations, the triplet fusion and singlet fission processes in the crystalline solid are simulated, including the effect of temperature. The results show that in this solid, the predominant process is singlet fission, coinciding with the experimental studies. This tells us that SEDyn is capable of simulating complex processes efficiently to help the scientific community discover molecular organic solids (crystalline or amorphous) that can perform the triplet annihilation process efficiently.