Fluorescence spectroscopy on a series of aqueous solutions of poly(acrylic acid) containing a luminescent label showed that polymers with molar mass, M_n < 16.5 kDa did not exhibit a pH responsive conformational change, which is typical of higher molar mass poly(acrylic acid). Below this molar mass, polymers remained in an extended conformation, regardless of pH. Above this molar mass, a pH-dependent conformational change was observed. Diffusion-ordered nuclear magnetic resonance spectroscopy confirmed that low molar mass polymers did not undergo a conformational transition, although large molar mass polymers did exhibit pH-dependent diffusion.

The morphology and organic field effect transistor (OFET) properties of two component blends of semi-crystalline 6,13-bis(triisopropylsilylethinyl)pentacene (TIPS-pentacene) with selected amorphous and semi-crystalline side chain aromatic low permittivity insulating binders deposited at room temperature under vacuum from a good solvent are reported. When blended with an amorphous binder there is evidence from X-ray photoelectron spectroscopy (XPS) of a strong interaction between TIPS-pentacene and the binder in the solidified film giving rise to twisted TIPS-pentacene crystals containing dislocations. Due to this strong interaction we see no evidence of segregation of TIPS-pentacene towards the active interface and hence we observe a rapid fall off in saturated hole mobility at an active concentration less than 50 wt%. When blended with a crystalline binder there is no evidence from XPS of any interaction between TIPS-pentacene and the binder in the solidified film. We propose that when a semi-crystalline binder is used, which crystallizes more slowly from solution than TIPS-pentacene, we observe stratification of the active material to both interfaces and as a result retention of saturated hole mobility even down to 10 wt%. The potential applications of the approach are in the formulation of low-cost organic semiconductors whose solution and solid state properties can be fine-tuned by careful binder selection.

The flowing afterglow technique, coupled with laser induced fluorescence (LIF) and vacuum ultraviolet (vuv) absorption spectroscopy, has been used to determine the fractional H-atom contributions, fH, to the product distributions for the dissociative recombination of a series of protonated ions (N2H+, HCO+, HCO+2, N2OH+, OCSH+, H2CN+, H3O+, H3S+, NH+4, and CH+5 ) with electrons. The measurements were made at 300 K in two separate ways in two laboratories by (i) directly determining the H-atom number density using vuv absorption spectroscopy at the Lα (121.6 nm) wavelength and (ii) converting the H atoms to OH radicals using the reaction H+NO2→OH+NO followed by LIF to determine the OH number density. The agreement between the two techniques is excellent and values of fH varying from ∼0.2 (for OCSH+ ) to 1.2 (for CH+5 ) have been obtained showing that in some of the cases recombination can lead to the ejection of two separate H atoms. Comparison of the oxygen/sulphur analogs, HCO+2/OCSH+ and H3O+/H3S+ showed that the fH values were very different. Possible reasons for these differences are discussed. Comparison is also made with the available theory.