Control of intermolecular photoinduced electron transfer in deoxyadenosine‐based fluorescent probes

In this paper, we report on the Photoinduced Electron Transfer ( PET) reaction between a donor (adenine analog) and an acceptor (3-methoxychromone dye, 3MC ) in the context of designing efficient fluorescent probes as DNA sensors. Firstly, Gibbs energy was investigated in disconnected donor-acceptor systems by Rehm-Weller equation. The oxidation potential of the adenine derivative was responsible for exergonicity of the PET reaction in separated combinations. Then, the PET reaction in donor-π-acceptor conjugates was investigated using steady-state fluorescence spectroscopy, acid-mediated PET inhibition and transient absorption techniques. In conjugated systems, PET is a favorable pathway of fluorescent quenching when an electron-rich adenine analog ( d7A ) was connected to the fluorophore ( 3MC ). We found that formation of ground-state complexes even at nM concentration range dominated the dye photophysics and generated poorly emissive species likely through intermolecular PET from d7A to 3MC . On the other hand, solution acidification disrupts complexation and turns on the dye emission. Bridging an electron-poor adenine analog with high oxidation potential ( 8d7A ) to 3MC presenting low reduction potential is another alternative to prevent complex formation and produce highly emissive monomer conjugates.