In a fluorescence-lifetime experiment, a very short pulse of light is used to excite a sample of dansyl fluorophore. Then the intensity of the fluorescence is recorded as a function of time. Fluorescence intensity Time (ns) 1.1 x 104 4.9 x 103 2.3 x 103 10 1.3x 103 15 5.6 x 102 20 A. What is the observed fluorescence lifetime? B. The fluorescence quantum yield under the same conditions was determined to be 0.7. What is the intrinsic rate constant for the radiative fluorescence decay? C. In a separate experiment, when the dansyl chromophore is 20 away from the 11-cis-retinal chromophore in rhodopsin, the efficiency of fluorescence energy transfer is 50. In a second experiment, rhodopsin is covalently labeled with a dansyl chromophore and the observed fluorescence lifetime for the dansyl-rhodopsin complex is 6 ns. What is the distance between the dansyl lable and the retinal chromophore in rhodopsin? (Tinoco #12, p. 535)