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

The E \(\otimes\) 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.