Date: Thursday, Oct 29th
Presenter: Oksana Ostroverkhova, OSU Physics
Organic semiconductors have attracted considerable attention due to low cost, easy fabrication, and tunable properties. Of special technological interest are solution-processable materials that can be cast into thin films. In this presentation, I will present optical, fluorescent, and photoconductive properties of functionalized pentacene and anthradithiophene (ADT) solution- deposited thin films. Fast charge carrier photogeneration and long power-law decays of the transient photocurrent were observed under 100-fs pulsed photoexcitation in all films studied. In ADT films, photoconductive gains of up to 130 were achieved at 532 nm cw photoexcitation. High fluorescence quantum yields were measured in solutions of most molecules and in fluorinated ADT films at room temperature. As the temperature increased, the fluorescence quantum yields decreased in films, but not in solutions, indicative of importance of intermolecular interactions for the fluorescence response in films. Photoconductive and fluorescent properties could be considerably altered by introducing various guest molecules; photocurrent enhancement and different charge carrier dynamics can be achieved, depending on the guest, due to various outcomes of competition between photoinduced charge and energy transfer between host and guest molecules. I will summarize these results from our studies using time-resolved fluorescence and photoconductivity (from 100 ps to >100 µs) techniques to probe the processes responsible. I will also discuss properties of ADT derivatives on a single-molecule level measured using single-molecule fluorescence spectroscopy.