Silylated Coumarin Dyes in Sol-Gel Hosts. 1. Structure and Environmental Factors on Fluorescent Properties

Several silylated coumarin dyes with different linkages and degrees of functionality have been synthesized and incorporated in both SiO₂ xerogels and various solvent hosts. The absorption and fluorescence spectra were examined to explore selected structural and environmental effects on the optical properties of these dyes. Silylated dyes (also referred to as grafted or functionalized dyes) are dye molecules that have been chemically altered to provide alkoxysilane functionality allowing the active molecule to be covalently bonded to the host. Silylation of dye molecules had little effect on the absorption and fluorescence spectra in neutral solvent environments. The optical spectra of silylated dyes compared to those of their conventional counterpart were less influenced by the local chemical environment (e.g., pH) and thus allow for greater control and stability of the fluorescent properties of the dyes in different host environments. Spectroscopy during the drying/gelling of a derCoum xerogel film containing a silylated coumarin dye illustrate changes in the chemical forms of the dye molecules associated with changes in the local chemical environment of the dye.