EPR and DEER Characterization of New Mixed Weakly Coupled Nitroxide Triradicals for Molecular Three-Spin Qubits

Spirocyclic Nitroxides as Versatile Tools in Modern Natural Sciences: From Synthesis to Applications. Part I. Old and New Synthetic Approaches to Spirocyclic Nitroxyl Radicals

“…After the oxidation of intermediate N -hydroxy derivatives to SNRs 251 , the latter are acylated by means of one or two residues of 4-alkoxybenzoic acids to form corresponding paramagnetic esters 252 (one of examples is shown in Scheme 44 ). Three mixed triradicals 254a–c with small exchange coupling parameters ( J ≪ A N ) are obtained on the basis of a coupling reaction between spirofused 2,5-dihydroimidazole–type monoradical 251 and two molar equivalent of carboxylic acid derivatives 253a–c of PROXYL-, TEMPO-, or 2,5-dihydro-1 H -pyrrol-type nitroxides [ 160 ]. In this case, compound 251 (R = H, X = 4-OH-C 6 H 4 ), carrying two phenolic groups with different acidity, serves as a convenient template for the assembly of heteropolyradicals ( Scheme 44 ).…”

Synthesis of mono-nitroxides and of bis-nitroxides with varying electronic through-bond communication

“…Towards understanding quantum coherence (QC) phenomena, proof-of-concept paramagnetic molecules have been designed and electronic communication has been studied via electron paramagnetic resonance (EPR) spectroscopy which allows direct measurement of the exchange energy between two singly occupied molecular orbitals. 2,3 In recent years pulse dipolar EPR spectroscopy (PDS) has also emerged to analyse such molecules for quantum information processing. 2,4,5 For example, three molecular assemblies with similar macromolecular structure and flexibility differing only in the degree of the electronic communication via π-conjugation were used as proof-of-principle compounds for demonstrating constructive QC where a four-fold increase of the exchange coupling ( J ) was found using two conjugated linkers rather than a single one, a value in accordance with the theoretical increase in conductance.…”

“…2,3 In recent years pulse dipolar EPR spectroscopy (PDS) has also emerged to analyse such molecules for quantum information processing. 2,4,5 For example, three molecular assemblies with similar macromolecular structure and flexibility differing only in the degree of the electronic communication via π-conjugation were used as proof-of-principle compounds for demonstrating constructive QC where a four-fold increase of the exchange coupling ( J ) was found using two conjugated linkers rather than a single one, a value in accordance with the theoretical increase in conductance. 4 Such experiments have been sparked by new methodologies for creating and analysing different magnitudes of weak exchange interactions and their distribution.…”