Sterically tuned triarylamines and oligothiophene derivatives as building blocks for novel organic electronic materials : synthesis and characterization

Abstract

Organic electronic thin film devices have gained raising interest due to their variety of applications coincided with an enormous commercial potential. These devices show high energy efficiency, great contrast and the ability to produce flexible lightweight displays at low production costs. Despite these advantages many deficiencies such as short lifetimes, sensitivity to air and humidity, color fidelity and heat generation still need to be conquered. Organic compounds, consisting of electron transporting oligothiophene linker structures combined with hole transporting triarylamine type cap systems incorporate the key features for organic electronic devices and exhibit supreme electroluminescence properties. This contribution reports the impact of sterically tuned and planarized substructures on electro optical properties along with new computational methods for calculating fluorescence characteristics.<br />Synthesis was achieved via Ullman condensations, nucleophilic aromatic substitution and a newly designed C-H activation reaction for the Cap systems and nucleophilic ring closing reactions for the assembly of the anneleated oligothiophene moieties. The key step for the overall pathway is a Suzuki cross coupling reaction applying a NHC allyl-palladium catalyst. When linkers with an increased conjugation length are used a bathochromic shift in the photoluminescence spectra is observed. In contrast, using condensed and planarized Caps results in a hyposochromic shift, probably due to enhanced orbital interactions, as indicated by new DFT calculations.