Photoluminescence Properties of Polythiophenes

We have characterised two polythiophenes, poly(3-(2,5-octyldiphenyl)-thiophene) (PDOPT) and poly(3-(4-octylphenyl)-2,2′-bithiophene) (PTOPT), with respect to their PL properties both in film and solution. PDOPT is highly regular and has large sidegroups which make the backbone rigid; the PL yield is 0.37 in solution. For thin films, the high regularity makes the polymer partially crystalline. The bulky sidechains efficiently separates the backbones giving the polymer a high PL yield (0.24). PTOPT have a low density of sidechains, and the PL yield reduces from 0.27 to 0.05 going from solution to thin film. Poly(3-methyl-4-octyl-thiophene) (PMOT) is twisted out of planarity by sterical hindrance and shows blueshifted absorption and emission. We show that PMOT have low PL yield in solution due to nonradiative decay with short lifetime.