Pinning Excited State Self-Trapping with All-Benzene Trefoil Knot.

The synthesis of novel carbon nanostructures with unique topologies expands the landscape of organic molecules, introducing new chemical properties and potential applications. Carbon nanorings, composed of cyclic paraphenylene (CPP) chains, serve as a versatile scaffold for designing materials with unique molecular architectures that impact their optical properties and photoinduced dynamics. These new topologies alter the balance between competing π-conjugation effects, high bending strain energies, and steric hindrances imposed by the rearrangement of their cyclic structures. Here, we explore the photoinduced dynamics of the all-benzene trefoil knot using nonadiabatic excited-state molecular dynamics. We show how its absorption spectra can be modeled by a particle in a box constrained to the trefoil knot geometry, and we analyze the internal conversion process following photoexcitation. Our findings reveal an exciton intraring migration governed by the winding of the paraphenylene chain, ultimately leading to exciton self-trapping at specific high curvature regions of the knot. This behavior contrasts with the nondeterministic exciton self-trapping in the corresponding CPP, where localization occurs randomly across different phenylene units. Our results highlight the ability of molecular knots to control exciton dynamics through curvature, tension, and planarization effects, positioning these materials as promising candidates for future technological applications. This ability to precisely manipulate optical and electronic characteristics is essential for developing more efficient and versatile devices.