In order to further improve the application value of the composite material, the repeatability of the luminescence intensity caused by pH is necessary. However, immersing a red film with pH=13 into a Tris solution with pH=6 did not restore the blue color. We believe that this may be due to the excessive amount of OH- adsorbed in the film and is not completely neutralized. For this reason, the idea of using acids with a lower pH to neutralize excessive alkalis was proposed. However, the acetal structure will undergo hydrolysis in the acid, which clearly damages the film itself. Fortunately, the crosslinking solution itself is strongly acidic and can be happens to neutralize alkali. Putting a red film with pH=13 into the crosslinking solution, the film quickly turned blue in less than a minute, and the morphology of the film did not change significantly. Besides, in the repeatability experiment characterized by fluorescence intensity, the fluorescence intensity of gel film showed good repeatability in pH modulation of pH=13 solution and cross-linking solution (Figure 2c).
Phosphorescence behavior of Y-TCPP/DBCZ PVA mixed gel at different pH values
RTP has a wide range of applications in multi-field. In order to investigate the phosphorescence property of the composite films, the effect of pH value on the yellow-green phosphorescence of DBCZ-MOF PVA composite films were detailed studied. Phosphorescence can hardly be observed in wet films, which is consistent with reports that water can quench phosphorescence.[29] In this case, the films were immersed in Tris solution at pH=6 to 13 for 10 minutes and well dried it at 40 °C subsequently to be tested. As expected, there was no significant change in the phosphorescence of the dried film from pH=6 to pH=12, and exhibited a jump variation in phosphorescence between pH=12 and 13, which is similar to the phenomenon discussed before. When the pH increased to 13, the phosphorescence intensity of the film decreased significantly, and a porphyrin emission peak (650 nm) appeared, which is generally considered delayed fluorescence (Figure 3a). This phenomenon is attributed to energy transfer (Figure 3b).