In order to systematically perform an experimental and theoretical study on DNA binding and photocleavage properties of transition metal complexes of the type [M(L)2(L1)](PF6)n x xH2O (where M = Co(III) or Ni(II), L = 1,10-phenanthroline or 2.2' bipryidine, L1 = Thiophene [2,3-b] quinoline (qt), n = 3 or 2 and x = 5 or 2) have been synthesized and characterized by elemental analysis, IR, 1H NMR, UV and magnetic susceptibility data. The DNA-binding properties of these complexes have been investigated with UV-Vis, viscosity measurements, thermal denaturation and cyclic voltametric studies. It is experimentally found that all the complexes are bound to DNA via intercalation in the order [Co(bpy)2(qt)](PF6)3 > [Co(phen)2(qt)](PF6)3 > [Ni(phen)2(qt)](PF6)2 > [Ni(bpy)2(qt)](PF6)2. The photocleavage studies with pUC19 DNA shows that all these complexes promoted the conversion of SC form to NC form in absence of 'inhibitors'.