We have characterized the temperature dependent transverse relaxation for 100 μM protonated and deuterated nitroxides in both protonated and deuterated o-terphenyl (OTP and dOTP) in distinct temperature regimes between 10 K and room temperature (RT). The choice of sample compositions allowed for a clear separation into slow and fast relaxation contributions based on a sum of two stretched exponential (SSE) parameterization between 10 and 60 K, and likewise at RT. The slow contribution is purely matrix dependent, while the fast process is determined by an interplay between a molecule and a matrix. Our systematic study of dynamical decoupling (DD) as a function of temperature (at 40, 80 K and RT), spin concentration, deuteration of nitroxide and/or OTP matrix and DD scheme for 1 to 5 refocusing pulses reveals that DD significantly prolongs phase memory times with respect to Hahn echo relaxation at 40 K, which we discuss in an SSE framework. At 80 K and RT, where (intra)molecular motions dominate relaxation, DD does not preserve electron spin coherence independent of the sample composition. Instead, we report a matrix nuclei dependent performance of the applied DD scheme at 40 K with Uhrig outperforming Carr-Purcell DD in OTP, and vice versa for a dOTP matrix.

A Zr-based MOF of the PIZOF type, which consists of two independent and mutually interpenetrating UiO-type frameworks with [ZrO(OH)(OC)] nodes, does not only form with a PEPEP dicarboxylic acid (P = phenylene, E = ethynylene). Also dicarboxylic acids with the shorter PPPP and PEPP spacers were found to give PIZOFs, denoted PPPP-PIZOF and PEPP-PIZOF, respectively. Reducing the spacer length even further to a PEEP segment caused a switchover to the formation of a UiO framework. The hysteresis in the Ar sorption curve of PEPP-PIZOF-1 and the slightly too large amount of combustion residue from PPPP-PIZOF-1 suggest structural defects. These hint at a mismatch between the requirement of the optimal linker length for PIZOF formation and the lengths of the PEPP and PPPP dicarboxylates. Nevertheless, these dicarboxylates prefer the formation of a PIZOF over the formation of a UiO structure. PEPEP-PIZOF-2, PPPP-PIZOF-1, and PEPP-PIZOF-1 are stable in air up to 325, 350, and 300 °C, respectively, and have BET surface areas of 2350, 2020, and 1650 m g, respectively. PEPEP-PIZOFs, even those with very hydrophilic oligo(ethylene glycol) side chains on the linkers, are very stable in water and also during drying from a water-wetted state. On the contrary, PEPP-PIZOF-1 and PPPP-PIZOF-1 that had been exposed to water required exchange of water for ethanol before drying to mostly preserve the framework. The results emphasize the importance of differentiating between framework damage caused through hydrolysis in water and through drying from a water-wetted state. The sensitivity of PEPP-PIZOF-1 and PPPP-PIZOF-1 against drying from a water-wetted state may be the consequence of defects. The drying stability of water-wetted PEPEP-PIZOFs lets us suggest that reversible bending of the linkers contributes to the stability of the PEPEP-PIZOFs.

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The synthesis and application of monodisperse oligo(para-phenyleneethynylene)s (oligoPPEs) with side chains that are adjustable to specific needs, such as water solubility, on a very late stage of the multistep synthesis are described. The adjustable side chains allow for circumventing problems associated with the isolation of highly hydrophilic compounds during early stages of a synthesis. Furthermore, these oligoPPEs can be stocked as adaptable advanced building blocks for rapid assembly of tailor-made spacers and rulers. A rapid growth synthesis provides oligoPPEs with alkyne termini protected with the orthogonal groups trimethylsilyl and 1-hydroxy-1-methylethyl (HOP) and with propargyloxy side chains protected with the triisopropylsilyl group. The three protecting groups allow independent modification of the two termini and the side chains. The HOP group not only acts as a protecting group but also as a polar tag for simple product isolation. We demonstrate one application of these oligoPPEs as spacers for the water-soluble Gd rulers of the type Gd-PyMTA-spacer-Gd-PyMTA with Gd-Gd distances of 2.1-10.9 nm. For this purpose, the terminal alkyne units were used for backbone assembly and attachment of the ligand PyMTA, and the porpargyloxy side chains were used to attach water solubilizing poly(ethylene glycol) chains through a click reaction after spacer assembly.

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