Table 1.

The energies (reference to acetonitrile medium) of HOMO, E_H, and LUMO, E_L, of the berberine cation alone and interacting two cations which were calculated using B3LYP/6-31G(d) with implicit solvation by acetonitrile using the default PCM approach of Gaussian 09.

Sample	EH/eV	EL/eV	∆E(EH–EL)/eV	∆E (Excitation–Ground)/eV, [nm], (Excitation)8
Ber+	– 5.687	− 2.984	2.694	2.725, [455], (S0 → S1)
				2.189, [566], (S0 → T1)
Ber+–Ber+	− 5.902	− 3.113	2.789	2.304, [538], (S0 → S1)
				1.761, [704], (S0 → T1)

Excitation energies at the optimised geometry of the ground state were computed using TD-DFT. Monomeric berberine calculations from ref.⁸.