Aromaticity-induced changes in the electronic properties of size-expanded DNA bases: Case of xC

Size-expanded DNA bases are analogues of natural bases that can be described as a synthesis between benzene and a natural base. Size-expanded bases have been combined with natural bases to form xDNA and yDNA, a new class of synthetic nucleic acids. We are interested in xDNA and yDNA because they might function as molecular wires. Recently, we also became intrigued by the possibility of altering the electronic conductivity of xDNA and yDNAby means of structural changes in the constituent bases. This possibility appeared after we noticed that the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap of the base yG can be increased dramatically, ∼0.73 eV, by changing the aromaticity of its benzene ring. Therefore, if one is able to alter the HOMO-LUMO gap of size-expanded bases, it should be possible to change the electronic conductivity of xDNAs and yDNAs as well. In the present work, we extend our study on aromaticity-induced changes on the electronic properties of size-expanded bases by investigating the HOMO-LUMO gap of all possible tautomers of xC. We have found that, as for yG, the HOMO-LUMO gap of xC can be modified by ∼0.74 eV, and that this can be accomplished by changing the aromaticity of its benzene ring.