Hetero-ring-expansion design for purine analogs: A theoretical study on the structural, electronic, and excited-state properties

A series of hetero-ring-expanded purine analogs are designed and their structural, electronic and excited-state properties are investigated by DFT calculations. The results indicate that the designed analogs can form stable base pairs with natural counterparts. Compared with natural ones, these size-expanded analogs and corresponding base pairs have smaller ionization potentials and HOMO–LUMO gaps. Furthermore, the A-analogs have ionization potentials even lower than natural G. Finally, the electronic absorption spectra are calculated and the nature of the low-lying excited states is discussed. These observations imply their promising applications as molecular wires and new DNA motifs.