Spin dynamics of photo-excited quintet state in a parallel oriented acene dimer towards the application to a room temperature qubit Wataru Ishii 1 , Masaaki Fuki 3 , Eman M Bu Ali 4 , Samara Medina 4 , Shunsuke Sato 5 , Bhavesh Parmar 1 , Reiya Yabuki 1 , Akio Yamauchi 1 , Yasuhiro Kobori 3 , Jenny Clark 4 , Go Watanabe 5 and Nobuhiro Yanai 1,2 1 School of Eng., Kyushu University, Japan, 2 JST FOREST, Japan, 3 Kobe University, Japan, 4 Sheffield University, UK, 5 Kitasato University, Japan Spin is one of the degrees of freedom with quantum properties and is a promising candidate for quantum bits (qubits). Electron spins in molecules have attracted particular attentions as qubits because the spin degrees of freedom can be modulated by molecular design. To achieve the quantum operations, the generation of the pure quantum state, which is called “initialization”, is required. The quintet excitons generated through singlet fission (SF) seem promising as novel qudits. Since quintets have been theoretically proved to be selectively distributed to specific sublevels by controlling parallel orientation between molecules 1 , they are expected to become optically addressable qudits. In this study, we synthesized a schiff base-bridged parallel-oriented pentacene dimer and evaluated the quintet excitons generated through SF. Single-crystal X-ray diffraction measurements revealed that the two pentacene units in the dimer was orientated in parallel (Fig.1) . Molecular dynamics (MD) simulation implied the parallel orientation of the pentacene dimer could be maintained even at room temperature. Then femtosecond transient absorption (fsTA) spectroscopy confirmed that SF occurred in the diluted pentacene dimer solution. Transient ESR (TRESR) were performed on the pentacene dimer dissolved in polystyrene at room temperature (Fig. 2) . It revealed the selective population among the quintet sublevels, which implies the potential of the pentacene dimer as room temperature qudit. The correlation between the orientation between two pentacene units and the population among the quintet sublevels revealed by the results of simulations will be discussed.
References 1. Smyser, K. E.; Eaves, J. D. Singlet fission for quantum information and quantum computing: the parallel JDE model. Scientific Reports 2020 , 10 (1)
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