Aryl-Bridged Thienonaphthalimides: Synthesis, Characterization and Optoelectronic Properties

Three small molecules consisting of thieno-fused naphthalimide units connected via aromatic linkers were synthesized to study the effect of fused thiophene rings on the properties of naphthalimide-based molecules. A protocol for the synthesis of thienonaphthalimide-based molecules without prior preparation and use of thienonaphthalimide precursors and organoelement compounds (organolithium, organotin, or organoboron compounds) was developed. The protocol is based on double thienannulation of bis-alkyne substrates with sodium sulfide. The thin-film morphology, photophysical and electrochemical properties of the obtained small molecules were studied. Single-layer non-doped organic light-emitting diodes based on fluorene-bridged thienonaphthalimide dimer showed yellow emission with luminance of 2200 cd/m2, and current efficiency of 0.35 cd/A. Combination of transient electroluminescence and photo-CELIV methods allowed to estimate electron and hole mobility in the synthesized compounds; both are in order of 10-6 cm2V-1 s-1. A simple protocol with thienannulation at the last step has been developed for the synthesis of aryl-bridged thienonaphthalimides. This unusual approach has significant advantages, namely, thiophene precursors and organolithium reagents are not used to assemble the pi-conjugated molecules. It was found that the aryl-bridged thienonaphthalimides are ambipolar organic semiconductors.image