Using external field effects for elucidating specific features in dye–DNA interaction

We measured the Stark effect of a dye probe covalently attached to a series of different DNA strands. For the first time, we observe a color effect in the permanent dipole moment. This color effect is characteristic for the DNA adduct. We attribute this color effect to a gradual change in the protonation state of the boron fluoride group of the dye probe as the excitation frequency is changed from the blue to the red edge of the inhomogeneous band. Obviously, the local structure plays an important role in the protonation process.