The Olympicenyl Radical and Its Derivatives

Heteroatom-Doping Engineering of Fused Olympic Cations: Metal-Free Modular Syntheses and NIR-II Radicals with Mixed Aromatic/Antiaromatic Characters

Heteroatom-doping polycyclic aromatic hydrocarbons have attracted immense attention owing to their fascinating optoelectrical properties. However, precise heteroatom-doping engineering and fabricating charged polycyclic aromatic scaffolds remain challenging and far from satisfactory. Herein, a new family of nitrogen and sulfur/oxygen dual-doping fused Olympic heterocyclic cations (FPT/FPOs) are modularly synthesized employing an efficient and convenient metal-free protocol. Tunable optical and redox properties can be achieved by rational structural editing. Compared with their half-fused counterparts, FPTs and FPOs hold higher redox stability and can undergo single-electron reduction to form delocalized neutral radicals, exhibiting NIR-II absorptions around 1300-1400 nm and unexpected mixed aromatic/antiaromatic characters. It is anticipated that this line of research provides a new approach for heteroatom-doping engineering and constructing novel charged π-molecules, with deeper insights into their redox-amphoteric features and aromaticity manipulation.

Chiral Peropyrene by Selective Dimerization of Phenalenyl

Two aryl substituted phenalenyl derivatives were synthesized, providing an opportunity to study the steric effects on selectivity of phenalenyl dimerization. Owing to σ-dimerization serving as the decisive step in phenalenyl-peropyrene transformation, a chiral peropyrene compound was generated by dimerization of triarylphenalenyl, while tetraarylphenalenyl did not afford any dimerized product. The structure and properties of chiral peropyrene were elaborated. Our study showcases that phenalenyl dimerization could function as a useful tool to synthesize fascinating π-conjugated hydrocarbons.

Phenalenyl Chemistry Revisited: Stable and Bioactive Multisubstituted Phenalenyl Radicals Synthesized via a Protection-Oxidation-Protection Strategy

Phenalenyl chemistry has flourished for decades but currently faces bottlenecks related to synthetic challenges and stability issues. In this study, we introduced an iterative protection-oxidation-protection (POP) strategy to synthesize stabilized phenalenyl radicals (PRs) with multiple substitutions at the α-positions. The applicability of this POP strategy was verified using triisopropylsilylthyl and phenyl substituents to generate trisubstituted PR1 and hexasubstituted PR2. In particular, both oxidation and dimerization were observed during the synthesis involving phenyl substituents. Both PR1 and PR2 were bench-stable, with half-lives in solution of up to 46 d and thermal decomposition temperatures of up to 300 °C. X-ray crystallographic analysis revealed that PR1 existed as a distinct 12-center-2-electron π-dimer, whereas PR2 existed as a monomer. The properties associated with monomer-dimer equilibrium both in the solid state and in solution were systematically investigated via variable-temperature spectroscopy, and the results revealed a small singlet-triplet energy gap and concentration-dependent absorption and electrochemical behaviors. Remarkably, both PR1 and PR2 formed biocompatible nanoparticles, with the latter capable of depleting reactive oxygen species in liver cells. This study thus demonstrated the applicability of the POP strategy for the construction of stable, functionalized PR derivatives with practical applications as spin functional materials.

Achieving Olympicene Functionalization Three Ways

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives are of interest in many fields, from materials science to supramolecular chemistry. 6H-Benzo[cd]pyrene, or olympicene, is a PAH bearing a central sp3-carbon bridge. We sought methods to modify this center position while maintaining stable tetrahedral geometry. Here, we characterize reactivity patterns of three olympicene core starting materials, with two of the three leading to center functionalization of the olympicene core, including the first use of 5H-benzo[cd]pyren-5-one as an olympicene synthon.

1,1'-Biolympicenyl: A Stable Non-Kekulé Diradical with a Small Singlet and Triplet Energy Gap

Dimerization of delocalized polycyclic hydrocarbon radicals is a simple and versatile method to create diradicals with tailored electronic structures and accessible high-spin states. However, the synthesis is challenging, and the stability issue of the diradicals remains a concern. In this study, we present the synthesis of a stable non-Kekulé 1,1'-biolympicenyl diradical 1 using a protection-oxidation-protection strategy. Diradical 1 demonstrated exceptional stability, with a solution half-life time exceeding 3.5 years and a solid state thermal decomposition temperature above 300 °C. X-ray crystallographic analysis revealed its intersected molecular structure and tightly bound dimer configuration. A singlet ground state with a small singlet-triplet energy gap is consistently identified using electron paramagnetic resonance (EPR) and a superconducting quantum interference device (SQUID) in a rigid matrix, and the triplet state is thermally accessible at room temperature. The solution phase properties were systematically examined through EPR, absorption spectroscopy, and cyclic voltammetry, revealing a rotational motion in the slow-motion regime and multistage redox characteristics. This study presents an efficient synthetic and stabilization strategy for organic diradicals, enabling the development of various high-spin functional materials.