Changes in Coordination Number of Co Ion and Fluorescence Spectrum of 1-Naphthol during the Sol-Gel Reaction of TEOS

Changes in coordination number of Co²⁺ and fluorescence spectra of 1-naphthol during the sol-gel transitions of TEOS have been investigated as a function of time. The change in the coordination number of Co²⁺ has been observed as follows. Six-coordinated Co²⁺ decreased quickly within several hours in the first stage of the reaction corresponding to water consumption by initial hydrolysis reaction. Then six-coordinated Co²⁺ increased around gelation due to polycondensation. After the gelation four-coordinated Co²⁺ increased, where isomorphous-replacement of Co²⁺ into the –O–Si–O– networks occurred. In the Co²⁺/1-naphthol mixed system, separate ion pair of 1-naphthol is preferentially coordinated on the six-coordinated Co²⁺ where water molecule(s) plays an important role to geometrical relaxation of excited-state 1-naphthol.