In this work, we report on the PhotoinducedE lectron Transfer (PET) reactionb etween ad onor (adenine analogue) and an acceptor(3-methoxychromone dye, 3MC)i n the contexto fd esigning efficient fluorescent probesa sD NA sensors. Firstly,G ibbs energy was investigated in disconnected donor-acceptor systems by Rehm-Weller equation. The oxidation potential of the adenined erivativew as responsible for exergonicity of the PET reaction in separated combinations. Then, the PET reactioni nd onor-p-acceptor conjugates was investigated using steady-state fluorescences pectroscopy,a cid-mediated PET inhibition and transient absorption techniques. In conjugateds ystems, PET is af avorable pathway of fluorescent quenching when an electron-rich adenine analogue(d7A)w as connected to the fluorophore (3MC). We found that formation of ground-statec omplexes even at nm concentration range dominated the dye photophysicsa nd generated poorly emissive specieslikely through intermolecular PET from d7A to 3MC.Onthe other hand, solution acidification disrupts complexation and turns on the dye emission. Bridging an electron-poora denine analogue with high oxidation potential (8d7A)t o3MC presenting low reduction potential is another alternative to prevent complex formation andp roduce highly emissive monomer conjugates.