Theoretical Studies of the Low-lying Excited Electronic States and Transition Energies of Naphthol Sulfonate Derivatives

Abstract

The low-lying excited states of 2-naphthol and its sulfonate derivatives have been investigated by ab initio and DFT computational methods. The vertical transition energies and oscillator strengths to low-lying singlet excited states of both A′ and A″ symmetries are determined using the EOM-CCSD and MCQDPT2 methods. The energy spacings between the excited states determined by EOM-CCSD are in good agreement with experiment, although absolute transition energies are predicted to be larger than experimental observation. The excited states are characterized based on molecular orbital contributions to each excitation as well as oscillator strengths, and the nature of the two lowest 1A' excited states are discussed in terms of 1La and 1Lb characters. The changes in electronic structure of 2-naphthol by substitution of SO3 – group are also discussed. The TDDFT method using the B3LYP and ωB97X-D functionals is found to have limitations in describing the excited states of 2-naphthol and sulfonate derivatives.