Photophysical properties of hydroxyanthraquinone derivatives (HQAs)-doped SiO2, SiO2–Al2O3 and Al2O3 matrices

Transparent inorganic matrix materials such as SiO2, SiO2–Al2O3 and Al2O3, which were chemically doped with hydroxyanthraquinone derivatives (HAQs) such as 1-HAQ and 1,4-dihydroxyanthraquinone (1,4-DHAQ) were prepared using a sol–gel technique. In SiO2 system, the absorption spectra of 1-HAQ and 1,4-DHAQ were observed to show the absorption maxima around 420 nm by red-shift and blue-shift from those observed in toluene, respectively, whereas those of both HAQs were red-shifted in both SiO2–Al2O3 and Al2O3 matrices. These results indicate that chemical interactions of HAQs in SiO2 system are different from those in Al2O3 and SiO2–Al2O3 matrices, which play important role in electronic structural changes in the intramolecular hydrogen bonding of HAQs. All the HAQs-doped matrix systems showed the markedly Stokes-shifted emission spectra which are originated from the excited-state intramolecular proton transfer (ESIPT) in HAQs. Based on the emission lifetimes of HAQs in each matrix, the ESIPT of HAQs was found to be inhibited by the chemical interaction with Al in the Al2O3-related matrices such as SiO2–Al2O3 and Al2O3.