ESR, raman and conductivity studies on fractionated poly(2-methoxyaniline-5-sulfonic acid)

Synthesis methods used to produce poly(2-methoxyaniline-5-sulfonic acid) (PMAS), a water soluble, self-doped conducting polymer, have been shown to form two distinctly different polymer fractions with molecular weights of approximately 2 kDa and 8 -10 kDa. The low molecular weight (LMWT) PMAS fraction is redox inactive and non-conducting while the high molecular weight (HMWT) PMAS is electro-active with electrical conductivities of 0.94 0.05 S cm-1. Previous investigations have illustrated the different photochemical and electrochemical properties of these fractions, but have not correlated these properties with the structural and electronic interactions that drive them. Incomplete purification of the PMAS mixture, typically via bag dialysis, has been shown to result in a mixture of approximately 50:50 HMWT:LMWT PMAS with electrical conductivity significantly lower at approximately 0.10 to 0.26 S cm-1. The difference between the electrical conductivities of these fractions has been investigated by the controlled addition of the non-conducting LMWT PMAS fraction into the HMWT PMAS composite film with the subsequent electronic properties investigated by solid-state ESR and Raman spectroscopies. These studies illustrate strong electronic intereactions of the insulating LMWT PMAS with the emeraldine salt HMWT PMAS to substantially alter the population of the electronic charge carriers in the conducting polymer. ESR studies on these mixtures, when compared to HMWT PMAS, exhibited a lower level of electron spin in the presence of LMWT PMAS indicative of the the formation of low spin bipolarons without a change the oxidation state of the conducting HMWT fraction

Luminescent metal complexes within polyelectrolyte layers: tuning electron and energy transfer

The electrochemical and photophysical properties or a luminescent metal center, [Os(bPY)(3)](2+), are significantly modified by encapsulation within a conducting polymer composite film. Cyclic voltammetry reveals that the encapsulation in an inherently conducting polymer, polyaniline (Pani) or polypyrrole (PPy), can dramatically influence the charge-transfer rates between the metal centers. The increased electron transport, most likely mediated through the conducting polymer backbone, significantly enhances the electrochemiluminescence (ECL) efficiency. The increased communication between adjacent metal centers can also result in other interesting properties, such as photoinduced electron-transfer processes. In situ electron spin resonance (ESR) spectroscopy has been used to probe the photooxidation of an osmium metal center encapsulated in a PPy composite film. The irradiation of PPy in the presence of the osmium metal center resulted in the photo-oxidation of the Os2+ to Os3+ state and the consequent reduction of the PPy polyelectrolyte. The degree of communication between luminescent metal centers allows the composite properties to be tuned for various applications including ECL sensor devices and light-switching and light-harvesting systems