Výsledky projektu Příprava a charakterizace nových konjugovaných polyelektrolytů

The title polymer, PTAA, practically free of ester groups was obtained by oxidative polymerization of methyl thiophen-3-ylacetate and subsequent basic hydrolysis of primary polymer. Poly(thiophen-3-ylacetic acid) has been thoroughly characterized by NMR, IR, Raman, and UV/Vis spectroscopy. The polyacid behavior during neutralization titrations with lithium and sodium hydroxides, carried out under nitrogen atmosphere, has been studied by conductometry and potentiometry. Henderson-Hasselbach plots of Potentiometrie titration curves show a break point at pH around 6, where the curve slope drops from 1.8 (at lower pH) to a value from 1.05 to 1.3 (at higher pH values). The UV/Vis spectra monitored during back titration show: (i) monotonous decrease of both λ, max and ε max as pH decreases, (ii) the presence of the isosbestic point at 401 nm that can be ascribed to conformational transition of PTAA chains, and (iii) absence of the isosbestic point at 392 nm reported previously by other authors.

UV/Vis spectroscopic investigation of aqueous solutions of regio-irregular poly(thiophen-3-ylacetic acid) (PTAA) with and without methyl-ester groups in the presence of sodium and lithium ions as counterions is presented. The samples were carefully purified and characterized with respect to molar mass and the amount of -COOH groups present. We examined how the UV/Vis spectra of solution change with aging of PTAA solution, polymer concentration, addition of low molecular weight salt, temperature, and some other parameters. We show that results crucially depend on whether the spectra are taken for freshly prepared or mature solutions. We demonstrate the validity of the Beer-Lambert law for PTANa, PTAA/Na, and PTAA/Li (aged solution), and violation of this law for PTANa/Me (fresh) solutions in water; the latter system is instead found to exhibit an isosbetic point at 402 nm. We prove that UV/Vis spectra of polythiophene derivatives in water depend on the "age" (time after dissolution) of the solution. The inconsistencies among the spectroscopic data found in literature, as also the discrepancies with our own measurements on PTAA-based systems are discussed.

Aggregated systems of silver (Ag) and gold (Au) nanoparticles coated with cationic polythiophene were prepared, which showed optical properties typical for strongly coupled plasmonic excitations. The procedure allowed tune up the three-dimensional arrangement of nanoparticles assembly for achieving strong SERS effect at the excitation wavelength depending on the polymer concentration. By combination with an anionic derivative of polythiophene thin multilayer films composed of alternating anionic and cationic polythiophene with mutually interacting plasmonic Au nanoparticles were successfully prepared using layer-by-layer deposition.

High-regioregular poly{3-[6-(1-methylimidazolium-3-
yl)hexyl]thiophene-2,5-diyl bromide}, PMHT-Br, has been
prepared by reaction of high-regioregular (above 92%) poly[3-(6-
bromohexyl)thiophene-2,5-diyl] with 1-methylimidazole. PMHTBr
is soluble in water and water miscible solvents such as methanol,
DMSO and shows solvatochromism; kmax (nm): 423 (H2O);
435 (MeOH); 452 (DMSO). Increased absorption band broadening
observed for aqueous solution as well as NMR spectra in D2O suggests
a micelle-like structure of PMHT-Br molecules in these solutions:
poly(3-hexylthiophene) core and 1-methylimidazolium
bromide shell. Despite the disturbing effect of ionic groups, the
solid-state PMHT-Br shows absorption maximum at 520 nm, the
band edge at 660 nm (ca. 1.9 eV), and fluorescence emission with
maximum at 635 nm, in a good agreement with the polymer
regioregularity. Fluorescence emission maxima: kem (nm): 598
(H2O); 562 (MeOH); 574 (DMSO), occur in a vicinity of corresponding
adsorption band edges. Plot of electrical conductivity of PMHTBr
(measured under the dynamic vacuum conditions, 5 ! 10"5 Pa)
versus 1/T shows a break at about 70 #C same as the temperature
dependence of kmax of the solid PMHT-Br. These breaks indicate
an increase in the mobility of polymer segments and ions within
PMHT-Br; however, a thermal analysis did not provide solid evidence
for it.