The study of the native conformation of nucleic acids and its eventual perturbation induced by the coupling with external perturbation factors is fundamental to better assess the molecular mechanisms underlying their biological role. Indeed, the conformation of nucleic acid may change due to the interaction with small molecules, including potential chemotherapeutic drugs, but also due to the presence of DNA lesions, such as base dimerization or strand breaks, or because of the binding to functional or structural proteins. Furthermore, DNA compaction and the presence of epigenetic markers, such as cytosine methylation, may also lead to significant alteration of the nucleic acid structure. More recently, the even more complex structural landscape of RNA, and specifically the emergence of epitranscriptomic markers significantly influencing the level of protein expression has also been underlined. Because of this complex and dynamic scenario, and of their flexibility, luminescent DNA probes are tools of choice to finely and rapidly evidence the presence of important structural modification of the nucleic acid structure. An efficient DNA probe should possess a bright luminescence, ideally covering the red portion of the electromagnetic spectrum. Additionally, its optical properties should be strongly environmentdependent, thus revealing subtle differences in their surroundings, which may correlate with DNA structural modifications. Different DNA probes have been proposed in the past, yet, and despite their more complicated synthetic procedure, fluorescent nucleosid analogous (FNA); which may be directly incorporated in the nucleotide sequence and maintain the canonical Watson-Crick coupling, represent one of the most suitable solutions. Among FNA, 2-aminopurine has been successfully used in a large variety of studies, despite its relatively low luminescence quantum yield, especially because it minimizes the perturbation to the nucleic acid structure. Indeed, the tuning of 2aminopurine fluorescence by nucleic acid environments, either through Watson and Crick, or Hoogsten hydrogen bond, has attracted considerable interest. to the ribose sugar moiety of a nucleotide leading to its incorporation in the nucleic acid sequence. Furthermore, M is highly fluorescent in hydrophobic environments, such as the helical core of a canonical DNA structure, while its fluorescence is reduced and the intensity ratio of the two emission bands is modified when solvent exposed. This allows, among other, to efficiently studying DNA base flipping and its interactions with different proteins. We have recently shown that the photophysics of M in hydrophobic media may be modulated by its highly efficient intersystem crossing (ISC) rates. Interestingly, a triplet -based emission mechanisms has also been convincingly postulated for 2-amino purine and adenine systems by both experimental, and computational studies. Yet, in the case of M the relatively fast population of the triplet state manifold is also coupled with an excited state intramolecular proton transfer (ESIPT) which leads to the formation of the tautomers (M T , Figure )). Indeed, a singlet triplet crossing (STC) point has been evidenced along the hydrogen transfer coordinate, while the driving force for the process is provided by the increased stability of the lowest excited state, either in singlet or triplet multiplicity, of M T compared to M. These results inferred by the analysis of the excited state potential energy surfaces (PES) are coherent with previous computational studies, and have also been corroborated by performing nonadiabatic surface hopping (SH) dynamics for the gas phase chromophore. Indeed, it has been shown that ISC proceeds with a rate-limiting time constant t of about 4 ps and at 2.0 ps the population of the triplet manifold exceeds 50%. Interestingly, the SH dynamics has also confirmed the ultrafast (sub-ps regime) and dynamic transfer of the proton which takes place mostly in the singlet manifold. Classical MD simulation of the nucleosidic M embedded in a canonical duplex has also confirmed that the chromophore, and more specifically the transferable hydrogen, are residing in a water excluded region. On the contrary, when M is coupled to the sugar base of a nucleoside and incorporated in DNA, the chromophore is exposed to the water environment and the formation of a first solvation shell involving either two or three solvent molecules around the carbonyl and hydroxyl groups. However, while the fundamental reasons, at electronic and molecular level underlying the photophysics of the non-solvated M have been elucidated convincingly, the role of solvation in the quenching of ISC remains rather elusive and should be clarified. To this aim we have considered microhydrated M and its tautomer M T , for which the PES of the lowest lying excited states have been explored with both static approaches and SH dynamics. In particular, we reveal that the ISC mechanisms is strongly delayed by the presence of water molecules. However, the ESPT process is still active but proceeds through a complex network involving multiple transfers through the water bridge. Our results, while showing the non-innocent role of the water molecule network in driving photophysical and photochemical processes, may also pave the way to an enhanced and more optimal design of FNA, in particular concerning their environmentally specific fluorescent response.