https://aurora.auburn.edu/handle/11200/44209 Tue, 07 Apr 2026 22:53:32 GMT 2026-04-07T22:53:32Z https://aurora.auburn.edu/handle/11200/50754 An Fe(II) Complex Detects Hydrogen Peroxide with 1H and 19F Magnetic Resonance Imaging Responses We report the fluorinated quinol-containing ligand, 1,8-bis(2,5-dihydroxy-4-fluorobenzyl)-1,4,8,11-tetraazacyclotetradecane (F2H4qp4), and its highly water- and air-stable Fe(II) complex. Upon oxidation by H2O2, the 19F MRI signal of the complex decays while its 1H MRI contrast increases; these spectroscopic responses enable the complex to ratiometrically detect H2O2. https://aurora.auburn.edu/handle/11200/50754 https://aurora.auburn.edu/handle/11200/50749 The Use of Intramolecular Quinol Redox Couples to Facilitate the Catalytic Transformation of O2 and O2-Derived Species The redox reactivity of transition metal centers can be augmented by nearby redox-active inorganic or organic moieties. In some cases, these functional groups can even allow a metal center to participate in reactions that were previously inaccessible to both the metal center and the functional group by themselves. Our research groups have been synthesizing and characterizing coordination complexes with polydentate quinol-containing ligands. Quinol is capable of being reversibly oxidized by either one or two electrons to semiquinone or para-quinone, respectively. Functionally, quinol behaves much differently than phenol, even though the pKa values of the first O-H bonds are nearly identical. The redox activity of the quinol in the polydentate ligand can augment the abilities of bound redox-active metals to catalyze the dismutation of O2-• and H2O2. These complexes can thereby act as high-performing functional mimics of superoxide dismutase (SOD) and catalase (CAT) enzymes, which exclusively use redox-active metals to transfer electrons to and from these reactive oxygen species (ROS). The quinols augment the activity of redox-active metals by stabilizing higher-valent metal species, providing alternative redox partners for the oxidation and reduction of reactive oxygen species, and protecting the catalyst from destructive side reactions. The covalently attached quinols can even enable redox-inactive Zn(II) to catalyze the degradation of ROS. With the Zn(II)-containing SOD and CAT mimics, the organic redox couple entirely substitutes for the inorganic redox couples used by the enzymes. The ligand structure modulates the antioxidant activity, and thus far, we have found that compounds that have poor or negligible SOD activity can nonetheless behave as efficient CAT mimics. Quinol-containing ligands have also been used to prepare electrocatalysts for dioxygen reduction, functionally mimicking the enzyme cytochrome c oxidase. The installation of quinols can boost electrocatalytic activity and even enable otherwise inactive ligand frameworks to support electrocatalysis. The quinols can also shift the product selectivity of O2 reduction from H2O2 to H2O without markedly increasing the effective overpotential. Distinct control of the coordination environment around the metal center allows the most successful of these catalysts to use economic and naturally abundant first-row transition metals such as iron and cobalt to selectively reduce O2 to H2O at low effective overpotentials. With iron, we have found that the electrocatalysts can enter the catalytic cycle as either an Fe(II) or Fe(III) species with no difference in turnover frequency. The entry point to the cycle, however, has a marked impact on the effective overpotential, with the Fe(III) species thus far being more efficient. https://aurora.auburn.edu/handle/11200/50749 https://aurora.auburn.edu/handle/11200/50746 Nickel(II) Complexes with Covalently Attached Quinols Rely on Ligand-Derived Redox Couples to Catalyze Superoxide Dismutation Although nickel is found in the active sites of a class of superoxide dismutase (SOD), nickel complexes with non-peptidic ligands normally do not catalyze superoxide degradation, and none has displayed activity comparable to those of the best manganese-containing SOD mimics. Here, we find that nickel complexes with polydentate quinol-containing ligands can exhibit catalytic activity comparable to those of the most efficient manganese-containing SOD mimics. The nickel complexes retain a significant portion of their activity in phosphate buffer and under operando conditions and rely on ligand-centered redox processes for catalysis. Although nickel SODs are known to cycle through Ni(II) and Ni(III) species during catalysis, cryo-mass spectrometry studies indicate that the nickel atoms in our catalysts remain the +2 oxidation state throughout SOD mimicry. https://aurora.auburn.edu/handle/11200/50746 https://aurora.auburn.edu/handle/11200/50716 Data for: Effect of local chain ordering on macroscopic charge mobility in chemically doped P3HT Charge carrier mobility is a key factor underlying the performance of conjugated polymers as conductive materials for flexible and lightweight electronics. Chemical doping is typically used to improve polymer conductivity by increasing the carrier density. However, doping consequently induces both morphological and electrostatic changes within the polymer that impact charge mobility, the extent to which remains unclear. Using regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) polymer films with tuned morphology and controlled ion-carrier distance, we investigated the influence of nanoscale chain ordering on the device-scale mobility of its chemically-induced carriers. Grazing-incidence x-ray diffraction measurements revealed that chemically doping the films resulted in a similar lamellar d-spacing of ~18.5 Å, despite differences in chain ordering within their nanocrystalline domains. Transient absorption (TA) spectroscopy was used to examine the relaxation of hole polarons excited with 0.62 eV (2000 nm) light to study their trapping behavior, and the results were compared with field-effect mobility measurements. Despite a 4-fold difference in hole mobility, the average relaxation times of the mobile and trapped polarons were identically ~0.1 ps and 17 ps, respectively, between the two films. The TA results only showed qualitative differences in the ratio of mobile to trapped polarons, indicating that ordered nanocrystalline domains facilitate the formation of free polarons, which enhance the hole mobility. The results from this study suggest that TA spectroscopy can be used as an electrode-free method of assessing the local mobility of doping-induced charge carriers, and that nanoscale chain ordering – and not just mesoscale structure or ion-carrier distance – is essential to control for improving the device-scale mobility of polarons. https://aurora.auburn.edu/handle/11200/50716