Control of the Interchain π−π Interaction and Electron Density Distribution at the Surface of Conjugated Poly(3-hexylthiophene) Thin Films

Interchain interaction, i.e., pi-pi stacking, can benefit the carrier transport in conjugated regio-regular poly(3-hexylthiophene) (P3HT) thin films. However, the existence of the insulating side hexyl chains in the surface region may be detrimental to the charge transfer between the polymer backbone and overlayer molecules. The control of the molecular orientation in the surface region is expected to alter the distribution of the pi electron density at the surface to solve such problems, which can be achieved by controlling the solvent removal rate during solidification. The evidence that the pi-electron density distribution at the outermost surface can be controlled is demonstrated by the investigation using the powerful combination of near edge X-ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, and the most surface-sensitive technique: Penning ionization electron spectroscopy. From the spectroscopic studies, it can be deduced that the slower removal rate of the solvent makes the polymer chains even at the surface have sufficient time to adopt a more nearly equilibrium structure with edge-on conformation. Thus, the side hexyl chains extend outside the surface, which buries the pi-electron density contributed from the polymer backbone. Contrarily, the quench of obtaining a thermo-equilibrium structure in the surface region due to the faster removal of the solvent residual can lead to the surface chain conformation without persisting to the strong bulk orientation preference. Therefore, the face-on conformation of the polymer chain at the surface of thin films coated with high spin coating speed facilitate the electron density of the polymer backbone exposed outside the surface. Finally, thickness dependence of the surface electronic structure of P3HT thin films is also discussed.

Photoactivation mechanism of hyaluronidase by chlorpromazine

A pre-irradiated chlorpromazine (CPZ) in pH 7.2 and aqueous solutions activated hyaluronidase, and it showed the enzyme-activating action even after 7 days of irradiation. This indicates that the stable photoproducts of CPZ activated the enzyme. But promazine and CPZ-5-sulfoxide, which are photoproducts of CPZ, did not activate the enzyme in the presence and absence of UVA. The dimer and higher molecular weight (MW) products of CPZ that were obtained by treating the pre-irradiated CPZ solution with gel permeation chromatography showed the hyaluronidase by activating action without UVA. In addition, photoactivation of hyaluronidase by CPZ was inhibited by radical quenchers. This suggested that the photoproducts with enzyme-activating action were produced via some radicals. On the basis of these findings, a possible mechanism for photoactivation of hyaluronidase by CPZ was proposed.