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High-spin ground-state polyradicals are an important platform due to their potential applications in magnetic and spintronic devices. However, a low high-to-low spin energy gap limits the population of the high-spin state, precluding their application at room temperature. Also, design strategies delineating control of the ground electronic state from a closed-shell low-spin to open-shell polyradical character with a high-spin ground state are not well established. Here, we report indacenodinaphthothiophene isomers fused with a 6,6-dicyanofulvene group showing a high-spin quintet ground state. Density functional theory calculations indicate that the syn - and anti -configurations have a closed-shell low-spin singlet ground state. However, the linear -configuration displays a high-spin quintet ground state, with the energy difference between the high-spin quintet to the nearest low-spin excited states calculated to be as large as 0.24 eV (≈5.60 kcal mol −1 ), exhibiting an exclusive population of the high-spin quintet state at room temperature. These molecules are compelling synthetic targets for use in magnetic and spintronic applications.
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Exchange controlled triplet fusion in metal–organic frameworks
Abstract Triplet-fusion-based photon upconversion holds promise for a wide range of applications, from photovoltaics to bioimaging. The efficiency of triplet fusion, however, is fundamentally limited in conventional molecular and polymeric systems by its spin dependence. Here, we show that the inherent tailorability of metal–organic frameworks (MOFs), combined with their highly porous but ordered structure, minimizes intertriplet exchange coupling and engineers effective spin mixing between singlet and quintet triplet–triplet pair states. We demonstrate singlet–quintet coupling in a pyrene-based MOF, NU-1000. An anomalous magnetic field effect is observed from NU-1000 corresponding to an induced resonance between singlet and quintet states that yields an increased fusion rate at room temperature under a relatively low applied magnetic field of 0.14 T. Our results suggest that MOFs offer particular promise for engineering the spin dynamics of multiexcitonic processes and improving their upconversion performance.
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- Award ID(s):
- 2105495
- PAR ID:
- 10375859
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Materials
- Volume:
- 21
- Issue:
- 11
- ISSN:
- 1476-1122
- Page Range / eLocation ID:
- p. 1275-1281
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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