Size-dependent optical properties of [6]-, [8]- and [10]Cycloparaphenylene dications: the role of degenerate states

The E \(\otimes\) $\otimes$ e Jahn–Teller (JT) effects associated with the lowest excited degenerate electronic states (S \(_1\) ${}_1$ and S \(_2\) ${}_2$ ) of [6]-, [8]- and [10]cycloparaphenylene dications are studied to unravel their size-dependent optical properties. A model Hamiltonian within the linear vibronic coupling approach is adapted to generate the JT-split potential energy surfaces. Computed JT stabilization energy follows the trend: [6]CPP \(^{2+}\) ${}^{2+}$ < [8]CPP \(^{2+}\) ${}^{2+}$ > [10]CPP \(^{2+}\) ${}^{2+}$ . Theoretical absorption spectral features are generated using the wavepacket simulations within the reduced- and full-dimensional framework. These simulations reproduce the size-dependent absorption spectral broadening where the broadening increases with the increase in CPP ring size. The near-degeneracy of JT-split states (S \(_1\) ${}_1$ and S \(_2\) ${}_2$ ) indicates a possible fluorescence emission from both the states in these molecules.