Gold Corroles as Near-IR Phosphors for Oxygen Sensing

The triplet state of gold­(III) corroles is exploited for optical oxygen sensing. We report intense phosphorescence for gold­(III) corroles in the near-IR, an optical window that is ideal for tissue transparency. Moreover, the triplet excited-state emission exhibits significant changes in intensity and lifetime over the 0–160 Torr O₂ pressure range. This renders these compounds sensitive at biologically relevant pressures and overcomes the spectral limitations of palladium and platinum porphyrins for oxygen sensing in biology

Photophysical Properties of β‑Substituted Free-Base Corroles

Corroles are an emergent class of fluorophores that are finding an application and reaction chemistry to rival their porphyrin analogues. Despite a growing interest in the synthesis, reactivity, and functionalization of these macrocycles, their excited-state chemistry remains undeveloped. A systematic study of the photophysical properties of β-substituted corroles was performed on a series of free-base β-brominated derivatives as well as a β-linked corrole dimer. The singlet and triplet electronic states of these compounds were examined with steady-state and time-resolved spectroscopic methods, which are complemented with density functional theory (DFT) and time-dependent DFT calculations to gain insight into the nature of the electronic structure. Selective bromination of a single molecular edge manifests in a splitting of the Soret band into <i>x</i> and <i>y</i> polarizations, which is a consequence of asymmetry of the molecular axes. A pronounced heavy atom effect is the primary determinant of the photophysical properties of these free-base corroles; bromination decreases the fluorescence quantum yield (from 15% to 0.47%) and lifetime (from 4 ns to 80 ps) by promoting enhanced intersystem crossing, as evidenced by a dramatic increase in <i>k</i>_nr with bromine substitution. The nonbrominated dimer exhibits absorption and emission features comparable to those of the tetrabrominated derivative, suggesting that oligomerization provides a means of red-shifting the spectral properties akin to bromination but without decreasing the fluorescence quantum yield

Halogen Photoelimination from Sb^V Dihalide Corroles

Main-group p-block metals are ideally suited for mediating two-electron reactions because they cycle between M^<i>n</i> and M^<i>n</i>+2 redox states, as the one-electron state is thermodynamically unstable. Here, we report the synthesis and structure of an Sb^III corrole and its Sb^VX₂ (X = Cl, Br) congeners. Sb^III sits above the corrole ring, whereas Sb^V resides in the corrole centroid. Electrochemistry suggests interconversion between the Sb^III and Sb^VX₂ species. TD-DFT calculations indicate a HOMO → LUMO+2 parentage for excited states in the Soret spectral region that have significant antibonding character with respect to the Sb–X fragment. The photochemistry of <b>2</b> and <b>3</b> in THF is consistent with the computational results, as steady-state photolysis at wavelengths coincident with the Soret absorption of Sb^VX₂ corrole lead to its clean conversion to the Sb^III corrole. This ability to photoactivate the Sb–X bond reflects the proclivity of the pnictogens to rely on the Pn^III/V couple to drive the two-electron photochemistry of M–X bond activation, an essential transformation needed to develop HX-splitting cycles

Ag(III)···Ag(III) Argentophilic Interaction in a Cofacial Corrole Dyad

Metallophilic interactions between closed-shell metal centers are exemplified by d10 ions, with Au(I) aurophilic interactions as the archetype. Such an interaction extends to d8 species, and examples involving Au(III) are prevalent. Conversely, Ag(III) argentophilic interactions are uncommon. Here, we identify argentophilic interactions in silver corroles, which are authentic Ag(III) species. The crystal structure of a monomeric silver corrole is a dimer in the solid state, and the macrocycle exhibits an atypical domed conformation. In order to evaluate whether this represents an authentic metallophilic interaction or a crystal-packing artifact, the analogous cofacial or “pacman” corrole was prepared. The conformation of the monomer was recapitulated in the silver pacman corrole, exhibiting a short 3.67 Å distance between metal centers and a significant compression of the xanthene backbone. Theoretical calculations support the presence of a rare Ag(III)···Ag(III) argentophilic interaction in the pacman complex

Solvent-Induced Spin-State Change in Copper Corroles

The electronic structure of copper corroles has been a topic of debate and revision since the advent of corrole chemistry. The ground state of these compounds is best described as an antiferromagnetically coupled Cu(II) corrole radical cation. In coordinating solvents, these molecules become paramagnetic, and this is often accompanied by a color change. The underlying chemistry of these solvent-induced properties is currently unknown. Here, we show that a coordinating solvent, such as pyridine, induces a change in the ground spin state from an antiferromagnetically coupled Cu(II) corrole radical cation to a ferromagnetically coupled triplet. Over time, the triplet reacts to produce a species with spectral signatures that are characteristic of the one-electron-reduced Cu(II) corrole. These observations account for the solvent-induced paramagnetism and the associated color changes that have been observed for copper corroles in coordinating solvents