Low temperature spectroscopy of DNA-intercalator ethidium

Abstract

The flourescence spectrum of ethidium, a well-known dye that binds DNA by intercalation, is interpreted in terms of vibronic components. The role of solvents such as water, ethanol and glycerol together with that of the host DNA is examined and the parameters of the linear electron-vibration interaction are estimated. Hard mode frequencies of 1200–1300 cm−1 and soft mode frequencies of 200–300 cm−1 are obtained. A description of the thermal dependence of the ethidium fluorescence quantum yield in different media between 100 and 350 K is attempted in terms of the thermal activation to a radiationless level.