Singlet and triplet excitons in organic and organometallic thin films: Diffusion and triplet sensitization.

摘要

Several organic thin films were constructed from optically active organic and organometallic polymers. Using standard photophysical measurement techniques, studies were performed to determine the ability of polymer-based singlet and triplet excitons to diffuse in organic thin films. This work was performed to provide a better understanding of the ability of polymers to efficiently function in organic-based electronic devices.;To study the ability of triplet excitons to diffuse in thin films, a platinum acetylide polymer was spin-coated with varying amounts of molecularly dissolved fullerene or porphryin quenchers. A new model of exciton diffusion was derived where the concentration of acceptor molecules is used to calculate the exciton quenching rate constant; this is further related to the exciton diffusion coefficient through Fick’s Law of Diffusion. The results were validated against time-of-flight experiments, where the same quenchers were thermally deposited onto variable-thickness, pristine films of spin-coated polymer. The effect of film thickness on exciton population was determined. The one dimensional model of exciton diffusion was applied to the results, enabling the calculation of the triplet exciton length of diffusion and diffusion coefficient. These findings validate the new diffusion model and indicate that polymer-based triplet excitons have substantially improved lengths of diffusion compared to small molecules.;The ability of singlet excitons to diffuse within thin organic films was studied using the electrostatic layer-by-layer self assembly technique. Films incorporating water-soluble conjugated polyelectrolytes were constructed. It was found that upon deposition, the polymers in the film aggregate. A mechanism of film aggregation was developed so that ways of preventing film aggregation could be identified. Films built on a quenching substrate enabled the estimation of the singlet exciton length of diffusion using the one dimensional exciton diffusion model. Because the films were aggregated, a decrease in the ability of singlet excitons to diffuse was found. Methods of improving the length of diffusion and avoiding film aggregation were identified.;Finally, a series of iridium-based triplet sensitizers were developed to sensitize the formation of triplets in layer-by-layer self assembled thin films of conjugated polyelectrolytes. This is one way of improving the exciton length of diffusion in layer-by-layer self assembled thin films. Fluorescence and transient absorption titrations of the polyelectrolyte solutions by the iridium sensitizers confirmed their ability to sensitize polyelectrolyte triplets. Methods of incorporating the sensitizers into layer-by-layer self assembled thin films were proposed.