The optical spectra of 5-methylcytidine in three different solvents (tetrahydrofuran, acetonitrile, and water) is measured, showing that both the absorption and the emission maximum in water are significantly blue-shifted (0.08 eV). The absorption spectra are simulated based on CAM-B3LYP/TD-DFT calculations but including solvent effects with three different approaches: (i) a hybrid implicit/explicit full quantum mechanical approach, (ii) a mixed QM/MM static approach, and (iii) a QM/MM method exploiting the structures issuing from molecular dynamics classical simulations. Ab-initio Molecular dynamics simulations based on CAM-B3LYP functionals have also been performed. The adopted approaches all reproduce the main features of the experimental spectra, giving insights on the chemical-physical effects responsible for the solvent shifts in the spectra of 5-methylcytidine and providing the basis for discussing advantages and limitations of the adopted solvation models.

*** IBB - CNR ***

Istituto di Biostrutture e Bioimmagini, CNR, Via Mezzocannone 16, I-80134 Napoli, Italy., Dipartimento di Chimica "G. Ciamician", Universita di Bologna , Bologna, Italy., Ecole Normale Superieure de Lyon, CNRS, UMR 5182, Universite de Lyon , 46 Allee d'Italie, F-69364 Lyon Cedex 07, France., LIDYL, CEA, CNRS, Universite Paris-Saclay , F-91191 Gif-sur-Yvette, France.,

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