ABSORPTION-SPECTRA OF RHODAMINE-B DIMERS IN DIP-COATED THIN-FILMS PREPARED BY THE SOL-GEL METHOD

Thin films including rhodamine B (RE) which were dip-coated using the sol-gel reaction of tetraethyl orthosilicate (TEOS) have been prepared as a function of time and their absorption spectra observed 72 h after preparation of the thin films. One monomer and two dimers (H- and J-types) are clearly and simultaneously resolved both for RE in the thin films and the water-ethanol mixed solvent. Just after mixing the reaction system, the proportion of the dimers for RE was significant, and the H and J dimer amounts were nearly equal. As the sol-gel reaction proceeded, the relative contribution from the monomer species increased. The relative contribution of the monomer to that of the dimers reached a constant value long before the gelation time. This behavior indicates that the dye molecules are encapsulated in a certain structural region (pores) long before the gelation point of the sol-gel reaction of TEOS.