Computational study of the excited state properties of modified RNA nucleobases

• The absorptive and emissive properties of nucleobase analogues derived from thieno[3,4-d]-pyrimidine investigated using TD-DFT.
• Properties investigated in water and dioxane and compared to experimental measurements.
• Charge-transfer character of low-lying states characterized by considering B3LYP, PBE0, and CAM-B3LYP functionals.
• Properties leading to emission discussed by contrasting to natural RNA nucleobase analogues.

In this work, we present time dependent density functional theory (TD-DFT) computations of the photophysical properties for a recently synthesized family of emissive RNA nucleobases (see: D. Shin, R.W. Sinkeldam, Y. Tor, Journal of the American Chemical Society 133 (2011) 14912–14915). These modified analogues are obtained by replacing the imidazole moiety of the RNA nucleobases with thiopene and represent a complete alphabet of emissive and isomorphic analogues derived from one heterocylic nucleus. An extensive study of absorption and emission wavelengths as well as the excited state charge transfer character for these molecules was conducted at the TD-DFT/6-311++G(2df,2p) level of theory employing the CAM-B3LYP, B3LYP and PBE0 functionals in water and dioxane. The theoretical results reveal good agreement with the reported experimental data. The nature of the low-lying excited states are compared and contrasted with their naturally occurring RNA nucleobase counterparts.