Chelation ability of spironaphthoxazine with metal ions in silica gel

Reaction of spironaphthoxazine with acid

“…five times greater than that for the SNO-H + system, indicating that the fluorescence quantum yield of MC-Al 3+ is higher than that of MC-H 3 O + . This is a result similar to that observed in the sol-gel reaction system of silicon alkoxide, i.e., the fluorescence quantum yield of MC-M n+ was higher than that of MC-SiOH and depended on the metal ion [18]. The fluorescence process of the metal complex depends on the electron affinity of the metal ion because the metal ion occupies the unshared electron pair on the imine N which quenches the iminonaphtholate fluorescence [8].…”

“…This band can be assigned to a complex of MC with a proton and water molecule, MC-H 3 O + , having a structure similar to the metal chelate complex of MC (MC-M n+ ). The structure of this complex is presumed to be very similar to the MC-SiOH complex observed in the silica xerogel [16][17][18].…”

“…The xerogel system also contained the MC-SiOH complex, like the MC-Zn 2+ , because there were many acidic SiOH groups on the surface of the gel pores in which the organic molecules were encapsulated [16-18,25−28]. The complex formation is expected to depend on the type of metal ions involving a specific electron affinity [18,24]. MC can interact not only with the metal ions, but also with the protons on the silica gel surface.…”

“…In our previous studies, we observed the fluorescence photochromic behavior, that is, the photoinduced interconversion between X s and the MC-Zn 2+ complex in the hydrophobic interlayers of montmorillonite clay modified by organic surfactants [15] and in a xerogel prepared from silicon alkoxide [16][17][18]. The xerogel system also contained the MC-SiOH complex, like the MC-Zn 2+ , because there were many acidic SiOH groups on the surface of the gel pores in which the organic molecules were encapsulated [16-18,25−28].…”