Breaking the blue barrier of nucleobase fluorescence emission with dicyanovinyl-based uracil molecular rotor probes†

Dicyanovinyl-modified uracil produces fluorescent molecular rotors (FMR) that display massively red-shifted emission and huge Stokes shifts. They are exemplified by DCVSU – an intrinsically fluorescent nucleobase analog (IFNA) with the longest emission wavelength of 592 nm (DMSO) reported thus far which also shows strong polarity sensitivity and large Stokes shift (λ = 181 nm). The IFNAs exhibited typical molecular rotor response to solvent viscosity with brightnesses (ε × φ) of up to 8700 cm⁻¹ M⁻¹. ¹H NMR titration confirmed the expected association of the IFNA with the complementary nucleobase adenine-9-ethyl acetate.