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Effect of Secondary Treatments on the Phase Transition of Polydiacetylene LB Films

The photochromic behavior of polydiacetylene LB films has been investigated for samples with different secondary treatments. The monomer film is initially converted to the A-type polydiacetylene LB film showing a pronounced red-shifted band and then to the B-type one, depending on the duration time of UV irradiation. Acid vapor treatments, either before or after the initial UV irradiation, show a tendency to hinder the transition from A-type to B-type on the excessive UV irradiation, with the yield of A-type polymer being enhanced. Further, another type of red-shifted band has been found in the case of a successive process; acid vapor treatment→ heat treatment→UV irradiation, which may be dependent on the degree of polymerization. The relation between these results and the yield of polymerization of the films is explained by assuming an order-disorder scheme of the phase transition.