Interactions and spectroscopic characteristics of propidium dication on soluble graphene oxides

Propidium is widely used as a red-fluorescent nucleic acid stain and universal cell death indicator, and recently experimental understanding of the electron transfer and fluorescence quenching of adsorbed fluorophores on carbon surfaces has attracted intense attention. In this work, the soluble graphene frag-ments were predigested as coronene oxides, and the aromaticity of coronene, a coronene oxide GO and a coronene oxide dianion GO(2- )was measured by HOMA indices and visualized with LOL-pi maps by the M06-2X method. The weak interactions and pi-pi stacking between propidium and coronene, GO or GO(2-) in Complexes 1, 2 and 3 were confirmed by NCI analyses and frontier molecular orbitals. Then the ab-sorption and fluorescence spectra were simulated by the TD-M06-2X method, and hole-electron analyses were employed to characterize electron excitations of these complexes. It is found that the absorption and fluorescence spectra of Complex 1 is much weaker than those of free propidium and Complex 2 . The S-1 -> S-0 transitions (LUMO -> HOMO, pi*->pi) in the fluorescent spectra denote that these complexes can emit fluorescence in the visible-light region. (C) 2022 Elsevier B.V. All rights reserved.