Trisaminocyclopropenium Cations as Small-Molecule Organic Fluorophores: Design Guidelines and Bioimaging Applications.

The discovery of fluorescence two centuries ago ushered in, what is today, an illuminating field of science rooted in the rational design of photochromic molecules for task-specific bio-, material-, and medical-driven applications. Today, this includes applications in bioimaging and diagnosis, photodynamic therapy regimes, in addition to photovoltaic devices and solar cells, among a vast multitude of other usages. In furthering this indispensable area of daily life and modern-day scientific research, we report herein the synthesis of a class of trisaminocyclopropenium fluorophores along with a systematic investigation of their unique molecular and electronic dependent photophysical properties. Among these fluorophores, tris[N(naphthalen-2-ylmethyl)phenylamino] cyclopropenium chloride (TNTPC) displayed a strong photophysical profile including a 0.92 quantum yield ascribed to intramolecular charge transfer and intramolecular through-space conjugation. Moreover, this cyclopropenium-based fluorophore functions as a competent imaging agent for DNA visualization and nuclear counterstaining in cell culture. To facilitate the broader use of these compounds, design principles supported by density functional theory calculations for engineering analogs of this class of fluorophores are offered. Collectively, this study adds to the burgeoning interest in cyclopropenium compounds and their unique properties as fluorophores with uses in bioimaging applications.

Selective Aerobic Oxidation of Benzylic Alcohols Catalyzed by a Dicyclopropenylidene-Ag(I) Complex.

The unprecedented synthesis, single-crystal X-ray structure, and first catalytic application of a dicarbene-Ag(I) complex [Ag(BAC)2][CO2CF3] (BAC = bis(diisopropyl)aminocyclopropenylidene) is reported. This novel complex provides a versatile catalytic platform for selective aerobic oxidation of benzylic alcohols to aldehyde or ketone products in high yields. Ease of experimental execution coupled with the use of abundant atmospheric molecular oxygen as an oxidant and low catalyst loading are inherit strengths of these oxidations.

Bis(amino)cyclopropenium Trifluoroborates: Synthesis, Hydrolytic Stability Studies, and DFT Insights.

A simple and direct two-step synthesis of bis(amino)cyclopropenium trifluoroborate (BAC-BF3) derivatives from readily available reagents is reported. Hydrolysis studies revealed these BAC-BF3 derivatives were remarkably stable toward defluorination. Notably, this first study of BAC-BF3 adduct hydrolytic stability establishes the compounds reported herein possess half-lives ( t1/2) exceeding 0.23 × 106 min (∼160 days). Density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) calculations exploring the basis of this high stability are described.

Phase-Transfer Catalyzed O-Silyl Ether Deprotection Mediated by a Cyclopropenium Cation.

The use of a cyclopropenium cation as a phase-transfer catalyst for O-silyl ether deprotection is reported. Mechanistic insight into this deprotection methodology derived by linear free-energy relationships (LFER), quantum theory of atoms in molecules (QTAIM), and density functional theory (DFT) calculations are also provided.

A Au(I)-Precatalyst with a Cyclopropenium Counterion: An Unusual Ion Pair.

The synthesis and X-ray crystal structure of a novel Au(I)-precatalyst applied to intermolecular alkyne hydroamination is reported. Density functional theory (DFT) calculations revealed the cyclopropenium counterion of this Au(I)-precatalyst imparts stability through H-bonding and other noncovalent interactions.