DNA-mediated charge transfer currently attracts considerable interest because of its relevance for molecular electronics. In this work the fluorescence behavior of the ligand-ligand charge transfer complexes Ni(diimine)(thiol)(2), where diimine = 2,2'-bipiridine and its 4,4' derivatives and thiol = thioaminoacid cisteine and its methyl esther were studied in the presence of DNA components. Substitution of an electron withdrawing group in 4,4' position of 2'2'-bipiridine causes red shift in the absorption spectrum. For all synthesized complex compounds it has been observed a significant increase of fluorescence emission intensity in the presence of DNA nucleobases.