2 )-or of Rydberg character-S 5 ( 1 πRy 6 ) and S 7 ( 1 πRy 5 ). When switching from FDA to ESP embedding, the excitation energies and state ordering change to some extent. The 3 ππ * 1 and 3 ππ * 2 , as well as 1 nπ * 1 and 1 ππ * 2 , change their order. The swapped triplet site states are both of ππ * character, making it difficult to rationalize the influence of the embedding to their energy ordering. In contrast, the embeddinginduced swap of the two singlet states can be traced to their different state characters. As seen in the figure, the 1 nπ * 1 state is significantly shifted up in energy by the ESP embedding. This occurs because the 1 nπ * 1 excitation shifts the electron density from the molecular plane to the perpendicular plane around the oxygen atom of guanine (see hole and particle orbitals in Figure ). In G 4 these oxygen atoms participate in hydrogen bonding with neighboring guanine in the molecular-plane configuration (see Figure ). Thus, the 1 nπ * 1 excitation weakens the hydrogen bonds, leading to an overall increase in the energy of 1 nπ * 1 . In Figure at higher energies, we observe some more changes upon switching from the FDA to ESP embedding. While 1 nπ * 2 , 1 ππ * 3 , and 1 πRy 5 do not significantly change in energy, the 1 πRy 6 state character is strongly destabilized and is not found among the seven lowest singlets with ESP embedding. The latter state is destabilized because its particle orbital is lo-cated in front of the NH and NH 2 groups that in G 4 form hydrogen bonds with the oxygen atoms of the neighbouring guanine. Hence, once the negative ESP charges of the neighboring oxygen are included, its repulsion with the Rydberg orbital lead to a strong destabilization of the 1 πRy 6 state. In turn, with ESP embedding a new state character, 1 nπ * 5 , is observed as the S 7 state.