A pressure tuning hole burning study of resorufin in protic solvents

Resorufin in protic solvents is present in two forms. They have a strongly temperature and solvent dependent equilibrium. The two forms can be interchanged photochemically which seems to be the major hole burning mechanism of this chromophore. We performed pressure tuning hole burning experiments in the long wavelength origins of both forms. In the range where the spectral bands of the two forms overlap, holes split under pressure and a bifurcation of the color effect (frequency dependence of the pressure induced shift) occurs. We could identify two well-defined absorption frequencies with vanishing pressure shift.