Benzene expansion Janus GC base analogues: A detailed theoretical study

Density Functional Theory (B3LYP) and Time Dependent Density Functional Theory (TD-B3LYP) computations have been used to investigate the electronic structural and optical properties of the newly designed benzene expansion Janus GC bases (J-GC1, J-GC2 and J-GC3), and the effect of water solution and base pairing also has been considered. The results show that the benzene expansion J-GC bases can pair with G and C simultaneously to form stable H-bonded WC base pairs. The lowest absorption and emission wavelengths of J-GC1¡¢J-GC2 and J-GC3 are red shifted compared with J-GC due to the increase of effective conjugation length with the introduction of benzene. The oscillator strengths of J-GC1¡¢J-GC2 and J-GC3 are similar. The water solution greatly influences the properties of the excited states and the first excitation and emission wavelength changes in the range of 16-65 nm. The water solution can increase the oscillator strengths of the absorption and emission spectra. The TD-B3LYP method predicts that the lowest excitation of J-GC3:C and J-GC2:G are charge transfer states, while the other base pairs present local transitions on the J-GC base moieties. The first excitation wavelengths of these local transition base pairs change in the range of 6-18 nm indicating that H-bonding interaction can influence the first excitation energy.