A comprehensive theoretical study of electronic transitions of naphtho-homologated yyG and its five possible tautomers (yyG-AO7, yyG-AEc, yyG-AEt, yyG-IcO17, and yyG-ItO17) was performed. The nature of the low-lying excited states is discussed, and the results are compared to that of y-bases. Geometry optimizations were performed on the lowest excited singlet ππ* states. Finally, the effects of methanol solution and hydrogen bonding with cytosine on the absorption and emission spectra were examined. The ground state structures were optimized using both the DFT and ab initio HF methods, whereas the excited-state structures were optimized using the CIS method. The methanol solution was found to red-shifts both the absorption and emission maxima of the studied bases except for yyG, for which the absorption and emission maxima were blue-shifted after solvation. In addition, hydrogen bonding with cytosine was found to blue-shifts both the absorption and emission maxima of yyG, yyG-AO7, yyG-IcO17, and yyG-ItO17. © 2013 Wiley Periodicals, Inc.