Methylation Induces a Low-energy Emissive State in N6-methyladenine Containing Dinucleotides

Methylation of adenine at the N6 position is a crucial epigenetic modification that profoundly influences gene regulation and expression. Moreover, this modification intricately alters the excited state dynamics of adenine nucleobases. To explore the impact of N6-methyladenine on the excited state dynamics within oligonucleotides, we conducted a comprehensive investigation of two dinucleotides containing N6-methyladenosine, in conjunction with adenosine or guanosine. Using steady-state and time-resolved absorption and fluorescence spectroscopy techniques, we not only observed the customary monomer-like and charge transfer emissive states, as reported in previous dinucleotides, but also identified an additional low-energy emissive state. This unique state exhibits an extraordinary Stokes Shift exceeding 2.3 eV and has a relatively long lifetime of 4–5 ns. We propose that this state corresponds to a bonded exciplex state, governed by ground-state geometries.