Year: 2026
Type: preprint
Abstract: Direct modification of the carbon framework of cycloparaphenylenes (CPPs) remains challenging despite the substantial strain stored in these carbon nanorings. Here, we report two complementary chemical methods for inserting an oxygen atom into a C–C bond of pristine [n]CPPs and the methylene-bridged [6]CPP ([6]MCPP) to give the corresponding oxylene derivatives. Treatment with m-chloroperbenzoic acid and copper(II) acetylacetonate affords mono-oxygenated products from [6]–[9]CPP in modest yields. Photocatalytically generated singlet oxygen is more efficient for smaller, more strained nanorings: [6]MCPP is converted to [6]MCPP-oxylene in 58% yield within 0.5 h, whereas the reactivity decreases sharply with increasing CPP size. Density functional theory calculations reveal that oxygen-insertion enthalpies become progressively less exothermic with increasing ring size and correlate linearly with 1/n, providing a thermodynamic context for the observed ring-size dependence. X-ray crystallography and strain analysis further reveal that oxygen insertion redistributes strain across the ring and lowers molecular symmetry. The resulting CPPoxylenes show markedly altered photophysical properties, with [9]CPP-oxylene reaching ΦF = 0.91. Prolonged photocatalysis of [6]MCPP enables a second, regioselective oxygen insertion at the most highly strained remaining C–C bond of the mono-oxylene framework. The resulting dioxylene adopts a more elongated structure and emits blue fluorescence at 414 nm with ΦF = 0.39; timeresolved measurements show that the higher fluorescence efficiency arises primarily from suppression of nonradiative decay. These results establish direct oxygen insertion as a route to skeletal editing of CPPs and connect sequential editing with changes in strain distribution, molecular geometry, and photophysical behavior.
Source: ChemRxiv
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221634713