Diyne-Containing PPVs:  Solid-State Properties and Comparison of Their Photophysical and Electrochemical Properties with Those of Their Yne-Containing Counterparts

Abstract

Diyne-containing poly(p-phenylene-vinylene)s, 4a-d, of general chemical structure -(PhCtC-CtC-Ph-CHdCH-Ph-CHdCH-) n, obtained through polycondensation reactions of 1,4-bis(4-formyl-2,5-dioctyloxyphenyl)-buta-1,3-diyne (2) with various 2,5-dialkoxy-p-xylylenebis(diethylphosphonates), 3a-d, are the subject of this report. The polymers exhibit great disparity in their degree of polymerization, n, which might be ascribed to side-chain-related differences in reactivity of the reactive species during the polycondensation process and which led to n-dependent absorption (solution and solid state) and emission (solution) behaviors of the polymers. Polarizing optical microscopy and differential scanning calorimetry are employed to probe their thermal behavior. The structure is investigated by means of wide-angle X-ray diffraction for both isotropic and macroscopically oriented samples. Comparison of photophysical (experimental and theoretical) and electrochemical properties of the polymers with those of their yne-containing counterparts 6a-d [-(Ph-CtC-Ph-CHdCH-Ph-CHdCH-) n] has been carried out. Similar photophysical behavior was observed for both types of polymers despite the difference in backbone conjugation pattern. The introduction of a second yne unit in 4 lowers the HOMO and LUMO levels, thereby enhancing the electron affinity of polymers 4 compared to polymers 6. The "wider opening" introduced by the second yne unit facilitates moreover the movement of charges during the electrochemical processes leading to minimal discrepancy, ∆E g, between the optical and electrochemical band gap energies. Polymers 6, in contrast, show significant side-chain-dependent ∆Eg values. Low turn-on voltages between 2 and 3 V and maximal luminous efficiencies between 0.32 and 1.25 cd/A were obtained from LED devices of configuration ITO/PEDOT:PSS/polymer 4/Ca/Al.

Alkoxy-substituted poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s: synthesis, electroluminescence and photovoltaic applications

“…For instance, higher turnon voltages ($6 V) were obtained from Amherst devices while lower values (2 to 3 V) were obtained from Potsdam and Cologne. 36,37,46,47 However higher EL efficiencies were achieved from Amherst devices. Polymers bearing long linear octadecyloxy or branched 2-ethylhexyloxy side groups exhibited improved OLED performance because of their enhanced solubility, film-forming capability and optimized film morphology.…”

“…46 The chemical structures of the various dialdehydes were confirmed by NMR, IR, elemental analysis and UV-Vis spectroscopy. The same analytical methods were used to confirm the structures of the resulting polymers in addition to gel permeation chromatography (GPC) for the estimation of the molecular weights.…”

“…35,38 The fully substituted polymers of types 30, 31 and 32 are characterized by nearly identical emissive behavior, despite the differences in their phenylene-ethynylene segments, which evidences identical fluorophore systems located around the lower energy alkoxy-substituted phenylene-vinylene segments of the various type of polymers as confirmed by fluorescent kinetics measurements and quantum chemical calculations. 28,40,46 A red shift of the absorption and emission is initiated through the insertion of electron rich anthracene or thiophene units within the conjugated backbone of polymers 36 (AnE-PV) (l a ¼ 550 nm, l f ¼ 580 nm), 37 (l a ¼ 475 nm, l f ¼ 535 nm) and 38 (l a ¼ 490 nm, l f ¼ 540 nm) as compared to polymers 30. 43,45 The position of the thiophene ring in the polymeric backbone has no influence on the spectroscopic properties of the polymers, which can be seen i.e.…”

“…Electroluminescence studies were carried out with polymers of types 29 (Pn/n 0 ), 30, 31, 32, 40 and 41. 28,36,37,40,46,47,[53][54][55] The respective polymers and their EL data are listed in Table 2. EL studies on PPE-PPVs, so far reported, were carried out by Karasz's group in Amherst and Neher's group in Potsdam as well as Meerholz's group in Cologne.…”

Effect of synthesis temperature and alkoxy side chain length on molecular structure and photoelectrochemical properties of terthiophenes

“…The control of intermolecular interactions has been attained mainly through the structural, chemical, and electronic properties of side chains. 14 The alkoxy substituents on the polymer chain induce a low oxidation potential, and if at the α position (involved in the polymerization reaction), they provide fast electropolymerization kinetics. [15][16][17][18] Theoretical studies have been devoted to understanding interchain interactions and their effect on the optical properties of thiophene oligomers.…”