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

The E ⊗ e Jahn–Teller (JT) effects associated with the lowest excited degenerate electronic states ( S 1 and S 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 + < [8]CPP 2 + > [10]CPP 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 and S 2 ) indicates a possible fluorescence emission from both the states in these molecules.