The chemical structures and electronic structures at conjugated polyelectrolyte/Au interfaces demonstrate that conjugated polyelectrolytes with identical backbones but different pendant charges and charge‐compensating ions exhibit different electronic properties. This finding shows that counterions and backbone charges enable control of the electronic and chemical nature of critical device interfaces.

The properties and function of an anionic conjugated polyelectrolyte (CPE)-containing ion-conducting polyethylene oxide pendant (PF(PEO)CO(2)Na) as electron injection layers (EILs) in polymer light-emitting diodes (PLEDs) are investigated. A primary goal was to design a CPE structure that would enable acceleration of the device temporal response through facilitation of ion motion. Pristine PLEDs containing PF(PEO)CO(2)Na exhibit luminance response times on the order of tenths of seconds. This delay is attributed to the formation of ordered structures within the CPE film, as observed by atomic force microscopy. Complementary evidence is provided by electron transport measurements. The ordered structures are believed to slow ion migration within the CPE EIL and hence result in a longer temporal response time. It is possible to accelerate the response by a combination of thermal and voltage treatments that "lock" ions within the interfaces adjacent to PF(PEO)CO(2)Na. PLED devices with luminance response times of microseconds, a 10(5) fold enhancement, can therefore be achieved. Faster luminance response time opens up the application of PLEDs with CPE layers in display technologies.

A new and efficient three-step synthesis of 4H-cyclopenta[2,1-b:3,4-b¢]dithiophen-4-one (CDT) (1) is described. This was achieved by a one-pot, regiospecific synthesis of bis(2-iodo-3-thienyl)methanol (13), its subsequent oxidation to the bis(2-iodo-3thienyl) ketone (14) which after Ullmann coupling yielded the title compound 1.

We examine the influence of halide counteranions on the efficiencies of solution-processed multilayer polymer light-emitting diodes (PLEDs) containing cationic conjugated polyelectrolyte (CPE) electron injection layers (EILs). The parent CPE used in these studies is poly[9,9-bis[6′-(N,N,N-trimethylammonium)hexyl]fluorene-alt-co-1,4-phenylene] bromide. Dialysis was used for exchanging counteranions, while X-ray photoelectron spectroscopy (XPS) provides a convenient technique for evaluating the final polymer composition. The luminous efficiencies of PLEDs with a poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) emissive layer decrease in the order F− > Cl− > Br− > I−. Oxidation of the halide counteranions is likely to occur at the MEH-PPV/CPE interface when the oxidation potential of the counteranion is aligned with the highest occupied molecular orbital of MEH-PPV, that is, Br− and I−. For these heavier halide counteranions, we find that pulsed bias measurements reduce ion migration to the MEH-PPV/CPE interface and result in an increase in the device efficiency. We propose that the oxidation potential of the counterion is a significant factor to consider when selecting CPEs as EILs.

Molecular design: The electronic structure of conjugated polyelectrolytes as a function of ionization potential (IP) and electron affinity (EA) is determined using X-ray absorption and emission spectroscopy (see figure). Different functional groups give rise to dissimilar transport gaps and exciton binding energies.