Before revision:  Herea simple theory is proposed that relates the Stokes shift signal to the statistics of Poincar\'e recurrences in the base-pair breathing. This theory can explain the origin of the observed slow non-exponential relaxation in time-resolved Stokes shift data for DNA as well as other complex systems. It turns out that an intercalated coumarin greatly increases the breathing fluctuations in the neighboring base pairs . This motion is qualitatively similar to that in terminal residues, with the same exponent in the power-law relaxation decay.
After revision:  Herea simple theory is proposed that relates the Stokes shift signal to the statistics of Poincar\'e recurrences in the base-pair stack. To this end, the earlier computational approach in combination with an analytical theory is applied to the experimental DNA fragment. It is found that the intensity of breathing dynamics is strongly increased in the internal base pairs that flank the photoprobe, with anomalous relaxation quantitatively close to that in terminal residues, with the same exponent in the power-law relaxation decay.