The function of electronically functional organic materials often originates at an interface, one example being organic electroluminescent devices (the Figure shows a typical energy diagram). Therefore, elucidation of the electronic structure at interfaces will lead to a better understanding of these devices, enabling their performance to be improved. Basic concepts are reexamined and recent progress in the area is reviewed.

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The effect of the method used to clean indium–tin–oxide (ITO) on its work function was investigated by ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy. With only ultrasonic cleaning in the organic solvent, considerable carbon contamination remained on the ITO surface and the work function was low (4.5 eV). In contrast, ultraviolet (UV)–ozone treatment removed significant carbon contamination, with an increase in the work function to 4.75 eV, which improves the hole-injection efficiency into the organic hole-transport layer in organic electroluminescent devices. Although carbon contamination on the ITO surface was also removed by Ar+ sputtering, it was accompanied by the removal of oxygen from ITO, and the work function was reduced (4.3 eV). Three factors, i.e.,: (i) C-containing contaminants, (ii) the O/In ratio, and (iii) the In/Sn ratio on the ITO surface affect the work function. The present results and those of other workers suggest that these three factors affect the work function in the order: (ii)>(i)>(iii), and (i) is the main cause of the increase in the work function in the UV–ozone or O2 plasma treatments.

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Dehalogenation polycondensation of 5,8-dibromoquinoxaline derivatives and 2,6-dibromoquinoxaline with zerovalent nickel complex affords a series of π-conjugated polyquinoxalines with a molecular weight of 6 × 10 3 to 260 × 10 3 . The polymers are electrochemically reduced (or n-doped) with an E°value of -1.75 to -2.35 V Vs Ag/Ag + and converted into electrically conducting materials with a conductivity of 1 × 10 -4 to 7 × 10 -3 S cm -1 by chemical reduction. Poly(quinoxaline-5,8-diyl)s with aromatic substituents give strong fluorescence with emission peaks at 450-520 nm in solutions as well as in cast films. A light-emitting diode (LED), ITO/polymer/Mg(Ag) (polymer ) poly(2,3-diphenylquinoxaline-5,8-diyl)), emits blue-green light (λ max at about 500 nm). Introduction of hole-transporting layers such as vacuum-deposited or spin-coated thin layers of poly(thiophene-2,5-diyl), poly(pphenylene), and poly(N-vinylcarbazole) between ITO and the light-emitting layer enhances electroluminescence efficiency by about 2 orders of magnitude. Polyquinoxalines have an ionization potential of 5.83 ( 0.11 eV and a band gap of 2.56 ( 0.26 eV.

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Many evidences suggest that the central nervous system (CNS) acquires and switches internal models for adaptive control in various environments. However, little is known about the neural mechanisms responsible for the switching. A recent computational model for simultaneous learning and switching of internal models proposes two separate switching mechanisms: a predictive mechanism purely based on contextual information and a postdictive mechanism based on the difference between actual and predicted sensorimotor feedbacks. This model can switch internal models solely based on contextual information in a predictive fashion immediately after alteration of the environment. Here we show that when subjects simultaneously adapted to alternating blocks of opposing visuomotor rotations, explicit contextual information about the rotations improved the initial performance at block alternations and asymptotic levels of performance within each block but not readaptation speeds. Our simulations using separate switching mechanisms duplicated these effects of contextual information on subject performance and suggest that improvement of initial performance was caused by improved accuracy of the predictive switch while adaptation speed corresponds to a switch dependent on sensorimotor feedback. Simulations also suggested that a slow change in output signals from the switching mechanisms causes contamination of motor commands from an internal model used in the previous context (anterograde interference) and partial destruction of internal models (retrograde interference). Explicit contextual information prevents destruction and assists memory retention by improving the changes in output signals. Thus, the asymptotic levels of performance improved.

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