Confinement of luminophores in mesostructured sol-gel thin films: Deliberate placement of lanthanides and laser dyes and quantitation of energy transfer.

摘要

The creation of materials that can perform catalysis, store or carry charge, or exhibit photoluminescence and electroluminescence is a major goal of research in sol-gel materials. Doping of sol-gel materials is a popular means of ascribing functionality to them. This dissertation builds upon previous efforts that synthesized mesostructured, sol-gel silicate thin films containing fluorescent molecules. These films contain three chemically distinct regions: the silicate framework, the hydrophobic region of the surfactant micelles and an ionic region at the interface between surfactant and the silicate framework. Luminescent films were synthesized with various laser dyes, a polyparaphenylenevinylene and several lanthanide complexes. Luminescence spectra demonstrate that each lumophore has either a physical or a chemical affinity for a particular region of the mesostructured thin films. Organic dyes associate with the surfactant in the final thin films, and lanthanide complexes containing condensable trialkoxysilane groups are incorporated into the silicate framework of the films during film formation. The spectra also show that two lumophores with affinities for different regions of the thin films are spatially segregated within the thin films during synthesis.; When two dopants with spectral properties adequate for energy transfer are incorporated in the films, energy transfer is observed. Energy transfer is demonstrated between coumarin 540A and rhodamine 6G in the hydrophobic region, between Eu in the silicate framework and rhodamine 700 in the hydrophobic region, and between Tb in the framework and rhodamine 6G in the hydrophobic region. Distance measurements deduced from quantitation of energy transfer between lanthanides and laser dyes verify the segregation of components. Distance between lumophores changes with acceptor concentration, and ranges from 29 A to 65 A. Tb luminescence lifetimes conformed adequately to expressions describing energy transfer in three-dimensional, non-randomly distributed ensembles.; Delayed sensitization of europium in one ligand system is noted and explained in terms of the subtle effects of ligand electronic structure on the relative rates at which Eu 5D0 and 5D 1 atomic states are populated. The exponential time response and signal saturation of luciferase attached to vaults is interpreted as evidence for the enzyme's encapsulation within the vault structure.