Dominic Vincent McGrath

Verdazyl radicals featuring thiomethyl groups at the 1 and 5 positions were synthesized employing modified conventional methodologies. Designed with appropriate anchoring groups for incorporation into molecular junctions, the verdazyl radicals were characterized using electron paramagnetic resonance (EPR) spectroscopy, UV-visible spectroscopy, cyclic voltammetry (CV) and high-resolution mass spectrometry (HRMS). We observed electrochemically reversible oxidation and reduction of these radicals in solution, and the correlation between gas-phase ionization and electron affinity modulations were considered by DFT calculations.

Stronger molecule–electrode coupling is associated with higher conductance in single‐molecule junctions. This has been taken to imply that more coordination—what will be referred to here as higher denticity—between the molecule and the electrode is expected to impart higher conductance to the overall junction. Herein, this assumption using a single molecule construct, a rigid N‐heterohexacene molecule with tetradentate ethyl sulfide (‐SEt) anchors, is examined. Thus, rather than comparing a series of molecules with different anchoring groups, it is investigated how variations in effective denticity arise naturally within one molecule. Using the nonequilibrium Green's function technique in conjunction with density functional theory and mechanically controlled break‐junction (MCBJ) experiments, it is found that increasing the denticity between the molecule and the electrode does not yield the expected higher conductance. Instead, simulated break‐junction traces reveal a strong correlation between conductance and the dihedral angle between the electrode and the molecular core, with changes to dihedral angles providing far more variation in conductance values than denticity alone. In fact, it is shown that counter to naïve expectations, different denticities cannot be distinguished by conductance, merging instead into a single conductance feature. This is supported by MCBJ experiments on this molecule, where only a single conductance state is identified, suggesting that the expected denticity‐dependent multistate conductance behavior is dominated by the effect of dihedral angles. By restricting dihedral angles to more favorable values by molecular design, the calculations show that significantly higher conductance values can still be achieved despite the limitations imposed by dihedral‐denticity coupling. The work demonstrates that mere denticity may not be sufficient to design highly conductive molecular junctions, and that the association of conductance features with different denticities should be treated with caution.

We disclose a four-step oxidize-condense-oxidize-condense synthesis pathway to prepare nonsymmetric pyrene-fused pyrazaacenes (PPAs) using our recently discovered oxidation conditions for 2,7-di-tert-butylpyrene. The new pathway results in marked improvements in yields and simplifies purification as compared with the sequential condensation strategy previously employed to make these compounds.

Dioxiranes are multi-tasking reagents with mild and selective oxygen transfer attributes. These oxidants are accessed from the reaction of ketones with an oxidant and are employed stoichiometrically or catalytically (in situ) for numerous transformations such as oxidations, epoxidations, C–H hydroxylation, etc. The oxidations involve a broad spectrum of substrates such as alcohols, amines, phenols, silanes, phosphines, etc. Similarly, the epoxidation of olefins, alkynes, allenes and arenes is achieved efficiently, where alkene epoxidation can be regioselective, chemoselective, stereoselective, and stereospecific. Furthermore, C–H hydroxylation using dioxiranes proceeds in both an inter- and intramolecular fashion producing a variety of potent molecules that are difficult to access using other means. Dioxiranes are used for the synthesis of various natural products, drugs, and biomolecules. This review covers all the aforementioned aspects of dioxirane chemistry along with the historical development, characteristics, and reaction mechanisms of dioxirane-mediated transformations established over the last five decades.