Planar π-extended all-armchair edge topological cycloparaphenylenes

It is important to reveal the optical properties and physical mechanisms of electron transitions within planar π-extended cycloparaphenylenes (CPPs) with full armchair edge topology in nanoscience and nanotechnology. The optical properties of the planar π-extended ring stripped from the Au(111) surface are theoretically studied, based on the latest experimental synthesis [Nat. Chem. 2022, 14, 871]. Our calculation results indicate that there is a blue-shift of absorption peaks in non-planar systems compared with planar systems. For non-planar systems, we proved that there is no fluorescence in the closed loop while the open loop exhibits fluorescence, using charge density differences and transition densities as evidence. And we realized the transition from the weak excited state to the strong excited state by the two photon absorption (TPA) method. The resonance Raman spectrum confirmed that the S₁ excited state of the non-planar closed loop is a dark excited state. Moreover, there is a red-shift of absorption peaks in non-planar charged systems compared with non-planar uncharged systems. We also investigated the visualization of charge transfer using absorption and fluorescence spectroscopy. Our results can provide more insights into the optical properties and potential design of optical nanodevices.