The diazotization was carried out by the above-mentioned procedure using PPD–sodium nitrite molar ratio equal to 1:2. Then in order to carry out the azo-coupling reaction, the equivalent amount of PPD was added into the reaction mixture under stirring while the temperature was raised to 268 K. Sodium acetate was then added and the mixture was kept overnight at room temperature. Then the solution was poured into water and the precipitate was collected and dried. Subsequent procedure
was similar to the mentioned above.