Chiral Peropyrene by Selective Dimerization of Phenalenyl

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.