Pentacene thin-film transistors using different dielectrics including thermal oxide SiO2 and a series of bilayered dielectrics that are polymethyl methacrylate/SiO2, polycarbonate/SiO2, and polystyrene/SiO2 were fabricated. Atomic force microscopic measurements indicated that grain sizes of the submonolayer films were drastically different with the various dielectrics. Dielectrics with lower surface energy lead to larger grain sizes at the first monolayer and consequently higher mobility of the fabricated transistors. The correlation between the mobility and the grain sizes at the first monolayer of the pentacene films could be explained by utilizing a microscopic mobility model relating to the grains and grain boundaries.

We report the electrical characterization of a single layer of an organic semiconductor grown on a dielectric surface. The dynamic response of the charge carriers in the monolayer film of pentacene was characterized through the electrostatic interactions between an electric force microscope (EFM) probe and pentacene islands of various sizes. These islands were formed in situ by segmenting a coalesced pentacene monolayer into separated regions. The size-dependent dielectric responses of the pentacene islands suggest that mobile charges exist in the organic monolayer. Local capacitance spectroscopy revealed that the charge carriers in the p-type pentacene monolayer could be depleted at high bias voltages, enabling a further determination of the charge-carrier concentration in the organic semiconductor ultrathin film.

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A highly selective luminescent chemosensor for Cr(3+) in aqueous solution was assembled by a low-selectivity luminogenic receptor with Cu(2+) as a metal quencher. Three tetranitrogen chelating sites were integrated into the multichannel receptor with a tris(1,10-phenanthroline)ruthenium(II) luminophore at the core. This receptor (2) exhibits chelating affinity for many transition-metal cations, among which Cu(2+) efficiently quenches the emission. The further addition of Cr(3+) into the Cu(2+)-titrated solution of 2 results in a metal-exchange reaction and a sensitive turn-on luminescence response highly selective over other metal cations. The quencher displacement sensing strategy in this design can be a simple but efficient approach for OFF-ON luminescent sensing of metal cations that inherently lack selective ligands.

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