Triplet-triplet spin interactions: understanding magnetic field effects on organic excitons Miles I. Collins 1 , Francesco Campaioli 2 , Murad J. Y. Tayebjee 3 , Jared H. Cole 4 and Dane R. McCamey 1 1 School of Physics and ARC Centre of Excellence in Exciton Science, UNSW Sydney, Australia, 2 Padua Quantum Technologies Research Center, and Dipartimento di Fisica e Astronomia ‘G. Galilei’, Università degli Studi di Padova, Italy, 3 School of Photovoltaic and Renewable Energy Engineering, UNSW Sydney, Australia, 4 ARC Centre of Excellence in Exciton Science, School of Science, RMIT University, Australia Singlet fission and triplet-triplet annihilation (TTA) are photochemical energy conversion processes that occur with high efficiency in organic semiconductor materials. Singlet fission is the generation of two spin-correlated triplet excitons from a photo-generated singlet exciton, while TTA is the reverse - two triplet excitons can annihilate, via a spin-correlated pair-state, to create an emissive singlet exciton. Both processes have the potential to assist single-junction cells to exceed the thermodynamic limit in photovoltaics, and have other potential applications in nuclear hyper-polarisation, efficient blue LEDs, and optically addressable molecular qubits. The spin-interaction of the triplet exciton pair gives rise to many interesting phenomena, such as spin-2 'quintet' states formed from singlet fission, and magnetic field effects in the photoluminescence of TTA materials. Understanding these spin-interactions is an important step towards applying singlet fission and TTA in devices. Here we present recent theoretical and experimental results on the spin dynamics of triplet exciton pairs, including predictions about how time-varying exchange coupling between the triplet excitons can drive the formation of quintet states, and measurements of microscopic variation in the magnetic field effects in TTA-induced luminescence. References 1. Miles I Collins et al., Quintet formation, exchange fluctuations, and the role of stochastic resonance in singlet fission, Communications Physics, 6, 64, 2023.
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© The Author(s), 2023
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