Excitation energy transfer between acriflavine and rhodamine 6G as a pH sensor

Excitation energy transfer between acriflavine (donor) to rhodamine 6G (acceptor) molecules in water with varying pH has been studied by using steady state measurements. From absorption and fluorescence spectra of donor and acceptor, overlap integrals for donor fluorescence and donor absorption (ΩDD) as well as donor fluorescence and acceptor absorption (ΩDA) have been calculated. The corresponding critical transfer distances for dipole–dipole Forster mechanism of excitation energy transfer between donor–donor (R0D) and donor–acceptor (R0A), reduced concentration and efficiency of energy transfer have also been calculated. It has been found that the ΩDA change with pH whereas ΩDD remain unchanged, resulting in change in energy transfer from donor to acceptor with pH, but no change in energy migration. The efficiency of excitation energy transfer is maximum for a highly basic solution and it decreases with a decrease in pH. The energy transfer efficiency, reduced concentration, and overlap integrals show a linear dependence on pH. It has been proposed that the system may be used as a wide range (1.4 to 12) pH sensor with an accuracy of 0.01.