Entangled spin-polarized excitons from singlet fission in a rigid dimer

Abstract

Singlet fission, a process that splits a singlet exciton into a biexciton, has promise in quantum information. We report time-resolved electron paramagnetic resonance measurements on a conformationally well-defined acene dimer molecule, TIPS-BP1', designed to exhibit strongly state-selective relaxation to specific magnetic spin sublevels. The resulting optically pumped spin polarization is a nearly pure initial state from the ensemble. The long-lived spin coherences modulate the signal intrinsically, allowing a measurement scheme that substantially removes noise and uncertainty in the magnetic resonance spectra. A nonadiabatic transition theory with a minimal number of spectroscopic parameters allows the quantitative assignment and interpretation of the spectra. In this work, we show that the rigid dimer TIPS-BP1' supports persistent spin coherences at temperatures far higher than those used in conventional superconducting quantum hardware.

Anisotropic Multiexciton Quintet and Triplet Dynamics in Singlet Fission via Pulsed Electron Spin Resonance

“…This observation of transient 5 (TT) ±2 quintets in PT2 demonstrates that the spin dynamics of SF are more complex than a linear evolution from 1 (TT) 0 singlets to 5 (TT) 0 quintets to free triplets and raises the question of how these transient exciton populations evolve over time. Previous studies have investigated the kinetics of SF excitons by fitting kinetic-spectral models to transient cw-ESR data, but these multiparameter fits are rarely unambiguous and rely on correct kinetic models of the underlying dynamic populations.…”

“…Singlet fission (SF) is a fast, spin-conserving electronic process in which one high-energy singlet exciton decays into two low-energy triplet excitons. , SF has attracted interest as a way to improve the efficiency of photodetectors and photovoltaics , through energy downconversion and has also been investigated as a route to well-defined photogenerated spin states for use in quantum information , or dynamic nuclear polarization . SF can occur in a wide range of materials including solutions, − organic crystals, − and semiconducting polymers. , Molecular chromophore dimers ,− have emerged as key platforms for mechanistic studies of SF due to their well-described structures and tunable photophysical parameters. ,− …”

Preparation of a Rigid and Nearly Coplanar Bis-tetracene Dimer through an Application of the CANAL Reaction

“…Recently, it has been realized that dynamics at play in the initial steps of SF may have value well beyond solar technologies, reaching into quantum information sciences. − In that field, qubits (quantum bits) are needed for computation or sensing, requiring the initialization of quantum-mechanically pure states, commonly based on spin angular momentum . In order to avoid the need for exceedingly low temperatures for qubit initialization, there is great interest in identifying systems where optical excitation is coupled with spin selectivity in the dynamics, resulting in the generation of pure states. − The reason that SF becomes interesting in this context lies in opportunities to exploit spin dynamics in the multiexciton manifoldthat includes 1 TT but also states with 5 TT and 3 TT charactersto selectively focus excited-state population into specific magnetic sublevels such as the 5 TT 0 .…”

“…In order to avoid the need for exceedingly low temperatures for qubit initialization, there is great interest in identifying systems where optical excitation is coupled with spin selectivity in the dynamics, resulting in the generation of pure states. − The reason that SF becomes interesting in this context lies in opportunities to exploit spin dynamics in the multiexciton manifoldthat includes 1 TT but also states with 5 TT and 3 TT charactersto selectively focus excited-state population into specific magnetic sublevels such as the 5 TT 0 . We have recently shown this to be the case in a rigid norbornyl-bridged TIPS-pentacene dimer (TIPS-BP1′) at elevated temperature (90 K) and have demonstrated relatively long T 2 times reflecting coherence between 5 TT 0 and 5 TT ±1 states . More specifically tied to the synthetic goals in this paper, it has recently been predicted that when two chromophores share a common set of axes relative to an external magnetic fieldin other words, when they are parallelselection rules are imposed such that dynamics leading to the loss of the 5 TT 0 to other states in the manifold will be slowed .…”

“…19 We have recently shown this to be the case in a rigid norbornyl-bridged TIPS-pentacene dimer (TIPS-BP1′) at elevated temperature (90 K) and have demonstrated relatively long T 2 times reflecting coherence between 5 TT 0 and 5 TT ±1 states. 22 More specifically tied to the synthetic goals in this paper, it has recently been predicted that when two chromophores share a common set of axes relative to an external magnetic field�in other words, when they are parallel�selection rules are imposed such that dynamics leading to the loss of the 5 TT 0 to other states in the manifold will be slowed. 19 These are conditions that could increase the time needed to perform qubit operations.…”