Fluorescence is most commonly found in compounds in which the lowest energy transition is π→π∗π→π∗ (excited singlet state) than n→π∗n→π∗ which suggest that the quantum efficiency is greater for π→π∗π→π∗ transitions. The reason for this is that the molar absorptivity, which measures the probability that a transition will occur, of the π→π∗π→π∗ transition is 100 to 1000 fold greater than n→π∗n→π∗ process. The lifetime of π→π∗π→π∗ (10-7 to 10-9 s) is shorter than the lifetime of n→π∗n→π∗ (10-5 to 10-7).