Synthesis and investigation on processing-depending polarized fluorescence emission in thin-films of 2,2′-([2,2′-bithiophene]-5,5′-diyl)bis(5-octyl-4-phenyl-4H-thieno[2,3-c]pyrrol-6(5H)-one)

Thienopyrrole-dione (TI) end capped materials have recently emerged as polymorphic molecular semiconductors suitable as active layers of ambipolar light emitting transistors, photovoltaic cells and time temperature integrator devices. Here, we report the synthesis of a new derivative, namely 2,2′-([2,2′-bithiophene]-5,5′-diyl)bis(5-octyl-4-phenyl-4H-thieno[2,3-c]pyrrol-6(5H)-one) (R-NT4N), having monoreduced TI moiety (R-TI) end groups. Ring opening of the TI moiety by Grignard reagent addition followed by one-pot reduction/ring closure by triethylsilane afforded the R-TI precursor that was then exploited for the preparation of the target R-NT4N compound. Investigation of the fluorescence properties of thin films, as a function of the processing conditions, showed that different from all the other TI derivatives so far reported, R-NT4N exhibits linearly polarized fluorescent microstructures. Combined micro-Raman and confocal laser-scanning fluorescence microscopies on lithographically controlled wetting (LCW) patterned R-NT4N films allowed us to correlate the emission polarization directions with the microcrystal structures.