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

Abstract

The quintet triplet-pair state may be generated upon singlet fission and is a critical intermediate that dictates the fate of excitons, which can be exploited for photovoltaics, information technologies, and biomedical imaging. In this report, we demonstrate that continuous-wave and pulsed electron spin resonance techniques such as phase-inverted echo-amplitude detected nutation (PEANUT), which have emerged as the primary tool for identifying the spin pathways in singlet fission, probe fundamentally different triplet-pair species. We directly observe that the generation rate of high-spin triplet pairs is dependent on the molecular orientation with respect to the static magnetic field. Moreover, we demonstrate that this observation can prevent incorrect analysis of continuous-wave electron spin resonance (cw-ESR) measurements and provide insight into the design of materials to target specific pathways that optimize exciton properties for specific applications.

Radiative pumping in a strongly coupled microcavity filled with a neat molecular film showing excimer emission

“…The rapid excimer formation would hinder the effect of strong coupling on spin evolution processes of triplet-pair intermediates which typically proceeds over nanoseconds timescale. 50,51 Therefore, properly controlling intermolecular interactions is necessary to exploit the enhancement under strong coupling.…”

Magnetic Field Effects in Triplet–Triplet Annihilation Upconversion: Revisiting Atkins and Evans’ Theory

“…The solutions for triplet and quintet multiplicity pair states provide the magnetic field dependence for the population of the optically dark states which can be studied experimentally using electron spin resonance (ESR) spectroscopy and time-resolved transient absorption spectroscopy. These approaches have been recently used to understand the pathways and intermediate states in singlet fission. − In principle, our approach can be adapted to compute relevant time- and field-dependent population results for these types of experiments.…”

Room-temperature quantum coherence of entangled multiexcitons in a metal-organic framework

“…To maximize the potential of these SF-derived 5 TT as qubits, it is crucial to generate quantum spin coherence in the quintet sublevels by microwave manipulation at room temperature. However, only a few cases of 5 TT quantum coherence have been observed so far, and these cases are limited to cryogenic temperatures of 75 K or lower ( 13 – 19 ). This poses a major challenge for the development of SF-derived 5 TT qubits.…”