Abstract
Absolute molecular weight values obtained by gel permeation chromatography with multi angle light scattering of PEDOTF8 were approximately 65% of the relative molecular weight values obtained by gel permeation chromatography using polystyrene standards. Both light absorption and molecular weight measurements showed the effective conjugation lengths (absolute molecular weight <2600, relative molecular weight <4000, number of EDOT-F8 units: n < ca. 5 unit). The low molecular weight polymers showed higher energy absorption and fluorescence bands. Molecular weight also affected the electrochemical process of the polymer films. The high molecular weight PEDOTF8 (number average molecular weight >70000) showed a higher redox stability than the low molecular weight one. The two polymers with number average molecular weights of 70200 and 40000 retained 65% and 25% of the charge storage capacity after 100 electrochemical scans, respectively. Square-wave potential step absorptiometry measurements of the polymers with number average molecular weights of 70200 and 40000 showed that the optical contrasts remain stable after ca. 55 and three cycles, respectively. The high molecular weight polymer has a high electrochemical stability and would be a good material for optoelectronic devices.
Highlights
The optical and electronic properties of π-conjugated polymers are relevant for many applications in the field of semiconductors[1,2,3]
The molecular weights of PEDOTF8 samples were determined by gel permeation chromatography (GPC)
The measurement using GPC and polystyrene standards showed relative molecular weights (Mn and Mw), which are not the true values because rigid segments of π-conjugated polymers imitate a large hydrodynamic radius that does not correspond to the molecular weight of polystyrene, which has coil www.nature.com/scientificreports/
Summary
Direct (C–H) arylation polycondensation of EDOT with 2,7-dibromo-9,9-dioctylfluorene (F8) was performed at previously optimised conditions: 1.0 mol% of Pd catalyst (Pd(OAc)[2], PdCl2, PITS-Cl)[21, 22, 30] mol% of 1-adamantanecarboxylic acid, (1AdCOOH) and 3.0 eq of potassium carbonate (K2CO3) in dry N,N-dimethylacetamide (0.3 M) at 80–120 °C under argon for 5–120 min, giving poly(3,4-ethylenedioxytiophene -2,5-diyl-alt-9,9-dioctylfluorene-2,7-diyl), PEDOTF8, with different molecular weights (Fig. 1). To systematically evaluate the relationship between properties and molecular weights of PEDOTF8 different measurements were performed (Fig. 2 and Table 1). The molecular weights of PEDOTF8 samples were determined by gel permeation chromatography (GPC). The measurement using GPC and polystyrene standards showed relative molecular weights (Mn and Mw), which are not the true (absolute) values because rigid (rod) segments of π-conjugated polymers imitate a large hydrodynamic radius that does not correspond to the molecular weight of polystyrene, which has coil www.nature.com/scientificreports/
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