Evidence of structural non-planarity in excited state: New findings provided by vibrational analysis of the guanine–cytosine base pair

Vibrational frequency analysis for the Watson–Crick guanine–cytosine (GC) base pair in the ground and lowest single ππ∗ excited state was performed based on the reference geometry optimized at the HF/6-311G(d,p) and CIS/6-311G(d,p) levels, respectively. It was found that different NH and CH stretching vibrations can be used for the qualitative prediction of excited state geometrical non-planarity and the localization of electronic excitations in the base pair complexes.