The effect of protonation on the excited state dynamics of pyrimidine chromophores

F. Kournoutas (1) , I.K. Kalis (1) , M. Fecková (2, 3) , S. Achelle (2) , M. Fakis (1)

1 University of Patras
2 ISCR - Institut des Sciences Chimiques de Rennes
3 University of Pardubice

The effect of protonation on the photophysics and especially on the excited state dynamics of two pyrimidine chromophores, bearing the A-(π-D)2 and A-(π-D)3 structure, is studied by means of fs-ps and ns time resolved fluorescence spectroscopy. Three different acids, namely camphorsulphonic (CSA), acetic (AcOH) and trifluoroacetic acid (TFA) were used. The chromophores bear the pyrimidine electron deficient heterocycle as electron-withdrawing group, used as protonation site, as well as diphenylamino electron donors. Protonation is revealed through the emergence of red-shifted absorption and fluorescence bands accompanied by a quenching of the fluorescence of the neutral molecules. Time-resolved dynamics reveal that protonation with CSA and TFA do not influence the excited state lifetime of the chromophores, pointing to a static quenching process. On the other hand, the lifetime is decreased upon protonation with AcOH. Further investigation based on the Stern-Volmer plots showed that addition of AcOH leads to both dynamic and static quenching.

Keywords: Dynamics; Fluorescence spectroscopy; Protonation; Pyrimidine chromophores

Domains: Chemical Sciences; Theoretical and/or physical chemistry

F. Kournoutas, I.K. Kalis, M. Fecková, S. Achelle, M. Fakis. The effect of protonation on the excited state dynamics of pyrimidine chromophores. Journal of Photochemistry and Photobiology A: Chemistry, 2020, 391, pp.112398. ⟨10.1016/j.jphotochem.2020.112398⟩. ⟨hal-02472929⟩