Molecular Sieve Sensors for Selective Ethanol Detection

changed under ambient condition for at least 40 h, time to which these measurements were carried out. To investigate the absorption behavior as a function of time, the absorption spectrum at 100 OC was taken at regular intervals over 40 h for poled/cured A204/DR1. An absorption peak at A, , = 508 nm existed before poling/curing. After poling/curing &shifta to 493 nm with a decrease of absorbance. During the next 40 h, A, , shifted back toward longer wavelengths with a slight decrease in absorbance (Figure 4). It is important to note that the dye absorption spectrum shape is similar to the spectrum obtained before the curing cycle. This confirms that the azo dye left in the cured film has not degraded during the curing cycle. For A204/ASD, the absorption spectrum was also taken regularly at 100 OC over 40 h. Immediately after poling/curing, a decrease in absorbance was observed. The absorption peak of the disperse orange 3 chromophore (Am, = 480 nm) shifted toward shorter wavelength, A, , = 464 nm (Figure 5). During the next 40 h, the absorption spectrum remained unchanged. This result suggests that the dye/polymer system did not degrade or sublime throughout the whole period of thermal treatment. In conclusion, we have shown that a guest-host system based on cross-linked phenylsiloxane polymer and alkoxysilane dye has excellent room-temperature stability and a slow decay at 100 OC in a period of 40 h. The stability of second-order susceptibility achieved in this work is limited by the NLO chromophore degradation temperature. Curing at higher temperatures is clearly expected to lead to higher stability. However the A204/ASD thin film showed a much more stable second-order response compared to A204/DR1.