Tuning optical, electrochemical, and structural properties of poly(aromatic heterocycles).

Abstract

A series of new conjugated polymers containing 4,4$\sp\prime$-disubstituted-bithiazole moieties and spacers, e.g., phenylene and ethynylene, in the backbone have been synthesized for possible use in light-emitting diodes (LEDs) and thin-film transistors (TFTs). Control of the photoluminescence throughout the visible spectrum was obtained by varying the size of the pendant groups and the degree of conjugation in the mainchain. These polymers are n-dopable to the extent of one electron per bithiazole unit. Further tailoring of the absorption and emission wavelengths is possible via N-methylation with methyl triflate. N-alkylation also makes the reduction potential more positive by up to 750 mV and increases the conductivities by up to 8 orders of magnitude higher than the parent polymers. Three new polymers, regioregular poly(4,4$\sp\prime$-dinonyl-2,2$\sp\prime$-bisoxazole-5,5$\sp \prime$diyl) (PNBO), regioregular, and regiorandom poly(3-octylfuran) (P3OF), were synthesized. The solid state structures, optical and electrochemical behaviors, and thermochromism of these polymers were compared to the corresponding sulfur containing polymers, i.e. poly(nonylbithiazole) (PNBT) and poly(3-octylthiophene) (P3OT) and to a series of oligomers, NBO$\rm\sb{n}$ and NBT$\rm\sb{n}.$ X-ray diffraction patterns indicate that the solid state packing of PNBO and PNBT is identical to that of the corresponding trimers. The morphology of the polymers, PNBO, PNBT, regioregular P3OF, and regioregular P3OT, are similar in that they show strong diffractions corresponding to lamellar spacing and to $\pi$-stacking. Replacement of CH by N in the heteroaromatic ring blue shifts the absorption maximum and increases the reduction potential. Similarly, replacement of sulfur by oxygen also blue shifts the $\rm\lambda\sb{max}.$