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We report relatively persistent, open‐shell thiophene‐based double helices, radical cations 1^•+‐TMS₁₂and 2^•+‐TMS₈. Closed‐shell neutral double helices, 1‐TMS₁₂and 2‐TMS₈, have nearly identical first oxidation potentials,E^+/0 ≈ +1.33 V, corresponding to reversible oxidation to their radical cations. The radical cations are generated, using tungsten hexachloride in dichloromethane (DCM) as an oxidant,E^+/0 ≈ +1.56 V. EPR spectra consist of a relatively sharp singlet peak with an unusually lowg‐value of 2.001–2.002, thus suggesting exclusive delocalization of spin density over π‐conjugated system consisting of carbon atoms only. DFT computations confirm these findings, as only negligible fraction of spin density is found on sulfur and silicon atoms and the spin density is delocalized over a single tetrathiophene moiety. For radical cation, 1^•+‐TMS₁₂, energy level of the singly occupied molecular orbital (SOMO) lies below the four highest occupied molecular orbitals (HOMOs), thus indicating the SOMO–HOMO inversion (SHI) and therefore, violating the Aufbau principle. 1^•+‐TMS₁₂has a half‐life of the order of only 5 min at room temperature. EPR peak intensity of 2^•+‐TMS₈, which does not show SHI, is practically unchanged over at least 2 h.

 

We demonstrate the possibility to evaporate Blatter radical derivatives in a controlled environment obtaining thin films that preserve the (poly)radical magnetic character. However, their thermal evaporation is challenging. We analyse the evaporation process and the thin film formation using thermodynamic concepts and describe the material properties also using first principles calculations. The presence of more than one radical site makes the radical more reactive, narrowing the windows left for evaporation, thus, favouring the assembly of molecules and island formation rather than two-dimensional growth. 

We demonstrate a host-guest molecular recognition approach to advance double electron-electron resonance (DEER) distance measurements of spin-labeled proteins. We synthesized an iodoacetamide (IA) derivative of 2,6-diazaadamantane nitroxide (DZD) spin label that could be doubly incorporated into T4 Lysozyme (T4L) by site-directed spin labeling (SDSL) with efficiency up to 50% per cysteine. The rigidity of the fused ring structure and absence of mobile methyl groups increase the spin echo dephasing time (Tm) at temperatures above 80 K. This enables DEER measurements of distances >4 nm in DZD labeled-T4L in glycerol/water at temperatures up to 150 K, with increased sensitivity compared to common spin label such as MTSL. Addition of β-cyclodextrin (β-CD) reduces the rotational correlation time of the label, slightly increases Tm, and most importantly, narrows (and slightly lengthens) the inter-spin distance distributions. The distance distributions are in good agreement with simulated distance distributions obtained by rotamer libraries. These results provide a foundation for developing supramolecular recognition to facilitate long-distance DEER measurements at near physiological temperatures.