Nanographene-Oxy Radical Stabilized by a Carbaporphyrin Framework
Haodan He, Jaehyeok Ryu, Zhaohui Zong, Jiyeon Lee, Tae Hun Heo, Juwon Oh, Jiwon Kim, Jonathan L. Sessler, Xian‐Sheng Ke
Abstract
Stable organic radicals are garnering increased attention due to the unusual properties of open-shell electronic systems. However, there are limitations associated with their preparation. For instance, hexa-peri-hexabenzocoronene (HBC), a representative nanographene, has armchair edges and shows good stability, reflecting the presence of Clar sextet rings. This renders HBC-based organic radicals challenging to prepare. Here, we report HBC-based organic radicals that are stabilized within a recently reported carbaporphyrin-like dipyrromethene-fused nanographene hybrid ( HBCP ). Using a straightforward process involving acetoxylation followed by hydrolysis, an inner-hydroxy-substituted HBCP, termed HBCP-OH, is obtained. Oxidation of HBCP-OH with MnO 2 gives the HBC-oxy radical HBCP-O . This radical is highly stable and is tolerant to air, moisture, and silica gel column chromatography. As prepared, HBCP-O displays organic π radical character, as confirmed by electron paramagnetic resonance (EPR) spectroscopy, cyclic voltammetry, femtosecond transient absorption measurements, and density functional theory (DFT) calculations. Furthermore, this HBC-oxy radical can act as a ligand to coordinate Cu(III) and Pd(II) as representative metal cations. The resulting Cu(III) ( HBCP-OCu ) and Pd(II) ( HBCP-OPd ) complexes show distinct electronic features. While the former is a closed-shell nonradical complex, the latter exists as an open-shell organic radical. The present study demonstrates a new way to access stable nanographene-based organic radicals that can be further functionalized through metal complexation.