and if the applied voltage is reversed the color changes back to dark blue the results are shown in fig6 wherein curves 61 67 are obtained by applying the voltage 0 v 0 2 v 0 4 v 0 6 v 1 0 v 0 1 v and 0 3 v respectively these results also show that when a positive voltage is applied the intensity of u03c0 u03c0 absorption peak at 810 nm decreases and that of the generated broad peak at 1400 nm with increasing the applied voltage when a reversed voltage is applied the absorption spectrum is restored to its original therefore the obtained electrochromic pitn film can be applied for smart windows ecds and observing windows of instruments testing on the electrochromic property of a composite film derived from a pitn derivative dissolve 20 mg poly 1 3 dihydro 5 6 dimethylisothianaphthene and 180 mg pbma in 18 ml anhydride dichloromethane with agitation using an ultrasonic oscillator for about 10 minutes the obtained solution is subject to a dehydrogenation reaction by introducing 2 ml dichloromethane containing 7 5 u03bcl so 2 cl 2 as a dehydrogenation agent and allowing the reaction to proceed for 3 minutes and then terminating the reaction by introducing 0 5 ml pyridine as an inhibitor to obtain a solution of poly 1 3 dihydro 5 6 dimethylisothianaphthene and pbma with the weight ration 1 9 the resulting solution can remain stable for.