Fulgide 1-E doped in polystyrene polymer films was heated at various annealing temperatures. Upon irradiation with UV light (366 nm)

fulgide 1-E undergoes a conrotatory ring closure to the pink colored closed form 1-C. The later color was switched back to the original color when the films were irradiated with white light. The kinetics of photocoloration and photobleaching processes were followed spectrophotometrically by monitoring the absorbance of the ring closed product 1-C at its λmax of 525 nm. The first-order plots of photocoloration reaction shows two distinct linear lines. The slopes of which corresponding to the first-order rate constants k1 and k2

where k1 is the rate constant at initial reaction times and k2 is that at late reaction times. These results suggest the plausible presence of two conformers of the ring opened form 1-E which reacts in sequence. On the other hand

photobleaching reaction shows a simple first-order reaction rate. It was found that for photocoloration reaction

the rate constant at initial reaction times is slower than that at late reaction times. Similarly

the photocoloration reaction is slower than the photobleaching reaction and both reactions increases with increasing the annealing temperatures. It was found that there was almost complete loss of photochemical fatigue resistance of fulgide 1 doped in polystyrene polymer film irrespective of the annealing temperature.