Six crystals of protonated DNA bases, [adenine (N1,N7)H2]Cl2 ([A(N1,N7)H2]Cl2), [adenine(N1)H] PF6 ([A(N1)H]PF6), [cytosine(N7)H]Cl ([C(N7)H]Cl), [cytosine(N3)H]PF6 ([C(N3)H]PF6), [guanine(N10)H]Cl ([G(N10)H]Cl) and [guanine(N7)H]H2PO4 ([G(N7)H]P) were newly prepared by the reaction of DNA bases, where A = adenine, C = cytosine, G = guanine, and P = H2PO4- anion, with concentrated HCl or H3PO4. They were characterized by X-ray analysis and ultraviolet-visible (UV-vis) spectroscopy. Comparison of calculated bond lengths and angles between ground states and singlet excited states for the compounds were examined using density functional theory (DFT). A weak emission in H2O solution was observed in [A(N1,N7)H2]Cl2 due to the formation of hydrogen bond between the protonated base and the Cl- anion.
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