Rational design, synthesis, and photophysics of dual-emissive deoxyadenosine analogs

Dual-emissive deoxyadenosine analogs were engineered by compiling 7-deaza-7-ethynyl-2′-deoxyadenosine with two-color dyes, 3-HydroxyChromones (3HC), while electronically conjugating the N9-donor of the nucleobase with the 3HC carbonyl. Their spectroscopic properties were investigated in a set of solvents of different polarities. Several improvements in the 3HC photophysical features were obtained. A significant bathochromic shift moved absorption to the visible range, the extinction coefficient was almost doubled and the fluorescence emission displayed a mega-Stokes shift of the tautomer emission band (>175 nm). The ratio intensity of the dual emission demonstrated high sensitivity to polarity changes, offering a well-resolved green-yellow emission. Considering the strong donating ability of the N9, angular and reversed assemblies were also considered in order to tune the photophysics by weakening the excited-state dipole moment.