RESUMO
Side chains play an important role in the photo-oxidation process of low band gap (LBG) polymers. For example, it has been shown that their photostability can be increased by the introduction of aromatic-oxy-alkyl links. We studied the photostability of prototypical LBG polymers with alkyl and oxyalkyl side chains during irradiation with white light (AM 1.5 conditions) in dry air using UV/vis and IR spectroscopy. Though its degradation kinetics were distinctly affected by the presence or absence of oxygen in the structure of the side chains, in particular cases, the stability was more affected by the presence of linear or branched side chains. Moreover, we showed that the exact position of the alkyl/oxyalkyl side chain at the polymer backbone could be crucial. Although minor effects of chemical modifications on the electronic parameters (ionization potential and gap) were observed, the molecular orientation, determined by polarization modulation-infrared reflection-absorption spectroscopy (PMIRRAS), could be affected. The aggregation and crystallinity of these polymers may distinctly affect their stability.
RESUMO
Poly[(2,1,3-benzothiadiazole-4,7-diyl)-alt-4',3''-difluoro-3,3'''-di(2-octyldodecyl)-2,2';5',2'';5'',2'''-quaterthiophene-5,5'''-diyl)] (PBTff4T-2OD) and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-3,3'''-di(2-octyldodecyl)-2,2';5',2'';5'',2'''-quaterthiophene-5,5'''-diyl)] (PffBT4T-2OD) for use as the p-donor component of high-efficiency fullerene-based organic solar cells are usually synthesized in established C-C cross-coupling reactions, preferably using the Stille procedure. This report describes how PBTff4T-2OD and PffBT4T-2OD are generated in a direct arylation polycondensation (DAP) approach with molecular weights up to Mn =19.4â kDa and 21.1â kDa, respectively, and how structural defects in the copolymers (e. g., homocoupling defects) show a strong impact on the pre-aggregation behavior. The optimized reaction conditions allow for a distinct reduction of the amount of such defects in the resulting copolymers. When the Stille-type products are used in the active layer of organic solar cells (OCSs) together with fullerene acceptors, high power-conversion efficiencies (PCEs) in the range of 8.6-10.8 % have been reported. The high PCEs are particularly related to the pre-aggregation of the conjugated copolymers prior to film formation. Despite quite similar characterization data, non-optimized OCSs with the DAP polymers as replacement for the Stille products afforded a relatively low power-conversion efficiency of up to 2.4 %.
RESUMO
Patients with chronic spinal cord injury (SCI) cannot urinate at will and must empty the bladder by self-catheterization. We tested the hypothesis that non-invasive, transcutaneous magnetic spinal cord stimulation (TMSCS) would improve bladder function in individuals with SCI. Five individuals with American Spinal Injury Association Impairment Scale A/B, chronic SCI and detrusor sphincter dyssynergia enrolled in this prospective, interventional study. After a two-week assessment to determine effective stimulation characteristics, each patient received sixteen weekly TMSCS treatments and then received "sham" weekly stimulation for six weeks while bladder function was monitored. Bladder function improved in all five subjects, but only during and after repeated weekly sessions of 1 Hz TMSCS. All subjects achieved volitional urination. The volume of urine produced voluntarily increased from 0 cc/day to 1120 cc/day (p = 0.03); self-catheterization frequency decreased from 6.6/day to 2.4/day (p = 0.04); the capacity of the bladder increased from 244 ml to 404 ml (p = 0.02); and the average quality of life ranking increased significantly (p = 0.007). Volitional bladder function was re-enabled in five individuals with SCI following intermittent, non-invasive TMSCS. We conclude that neuromodulation of spinal micturition circuitry by TMSCS may be used to ameliorate bladder function.