Optical properties of 1,4-dihydroxyanthraquinone covalently bonded to SiO2-AlO3/2 gel

Transparent SiO2-A1(2)O(3) gels doped with 1,4-dihydroxyanthraquinone (DAQ) were prepared by the sol-gel process (Q/SiO2-AlO3/2 system). The absorption band of DAQ in the SiO2-Al2O3 matrix shifted to longer wavelengths compared to that of DAQ doped SiO2 gel (Q/SiO2 system), and the absorption spectrum of Q/SiO2-AlO3/2 system was similar to the reported fluorescence excitation spectrum of the Q/gamma-Al2O3 system. A binding model for the Q/gamma-Al2O3 system, i.e., one proton of DAQ forming an intramolecular hydrogen bond was replaced by an Al atom has been proposed. It is believed that DAQ in the Q/SiO2-Al2O3/2 system forms a chemical bond with an Al atom. To investigate excited electronic states of the Q/SiO2-Al2O3/2 system, fluorescence lifetimes were measured from 80 to 280 K by means of rime-correlated single photon counting. It was found that the dominant lifetimes of this system were different from those of the gamma-Al2O3 doped systems. This difference indicates that the relaxation process from the excited state of the Q/SiO2-AlO3/2 system differed from that of the gamma-Al2O3O doped system.