Using Molecular Design to Enhance the Coherence Time of Quintet Multiexcitons Generated by Singlet Fission in Single Crystals

Abstract

Multiexciton quintet states, 5 (TT), photogenerated in organic semiconductors using singlet fission (SF), consist of four quantum entangled spins, promising to enable new applications in quantum information science. However, the factors that determine the spin coherence of these states remain underexplored. Here, we engineer the packing of tetracene molecules within single crystals of 5,12-bis(tricyclohexylsilylethynyl)tetracene (TCHS−tetracene) to demonstrate a 5 (TT) state that exhibits promising spin qubit properties, including a coherence time, T 2 , = 3 μs at 10 K, a population lifetime, T pop , = 130 μs at 5 K, and stability even at room temperature. The single-crystal platform also enables global alignment of the spins and, consequently, individual addressability of the spin-sublevel transitions. Decoherence mechanisms, including exciton diffusion, electronic dipolar coupling, and nuclear hyperfine interactions, are elucidated, providing design principles for increasing T 2 and the operational temperature of 5 (TT). By dynamically decoupling 5 (TT) from the surrounding spin bath, T 2 = 10 μs is achieved. These results demonstrate the viability of harnessing singlet fission to initiate multiple electron spins in a well-defined quantum state for next-generation molecular-based quantum technologies.

Singlet fission as a polarized spin generator for biological nuclear hyperpolarization

“…In the second quantum revolution, we explore the unique spin degree of freedom of SF for quantum technologies 17,18 . It has been revealed that the | TT ⟩ spin sublevel with a magnetic quantum number ms = 0 can be selectively populated among five quintet sublevels because the state immediately after photoexcitation is a spinless singlet state, and the transitions occur by preserving its total spin [13][14][15][16] .…”

“…To date, the spin aspect of SF has only been used to explain the microscopic mechanisms of SF. Because organic spin materials have advantages with their extremely small size, down to nanometers, and excellent bio-compatibility, it is worthwhile to research applications of the unique quintet state in quantum information science (QIS) and quantum biotechnologies 17,18 . Dynamic nuclear polarization (DNP) of biomolecules is one of the fields where polarized electron spins can play a pivotal role [19][20][21][22][23][24][25][26] .…”

Diphenyldihydropentalenediones: Potential Singlet Fission Materials with High Triplet Energy Levels

“…[6][7] Consequently, over the past several years, many experimental and theoretical investigations have been conducted to uncover new SF materials. [8][9][10][11][12][13][14][15][16][17][18][19][20] [21] To achieve the proper exergonicity for efficient SF, the singletexcited state energy level (ES, Fig. 1) of a substance must be higher than twice the energy level of its triplet-excited state (ET) (i.e., ES > 2ET).…”

Quintet formation and exchange fluctuations: The role of stochastic resonance in singlet fission

“…However, recent spectroscopic studies have revealed that the triplet-pair undergoes spin dynamics, forming triplet 3 (TT) and quintet 5 (TT) multiexcitons [20,21], before dissociating into uncorrelated triplet excitons. High-spin states such as quintets have fundamental implications for the use of SF in photovoltaics [21], and have also been considered for quantum information processing applications [22]; understanding how these high-spin states form in SF, and how material design can affect their formation, presents an important unanswered question in the field [22].…”