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).