tection in animal models for Parkin­son's. In mice that received MPTP, brain dopamine levels in the area of the brain affected by Parkinson's fell precip­itously to 40% of normal levels. But if the mice were pretreated with the naphtho­quinone compound, their dopamine lev­els remained at least 60% of normal.

The napthoquinone compound is "not a gangbuster" inhibitor, Castagnoli said. "But it's a good inhibitor." Tobacco may contain more potent inhibitors, she suggested, which could be masked by other compounds in the chromatogra­phy fractions that inhibited MAO.

Speaking at the same symposium, Joanna S. Fowler, director of the positron emission tomography (PET) laboratory at Brookhaven National Laboratory, not­ed that PET studies there have shown

that people who smoke have lower levels of MAO in their brains. And lower levels of MAO translate into lower levels of oxi­dative species that damage neurons be­cause MAO produces hydrogen peroxide when it breaks down dopamine and a number of other neurotransmitters, she explained.

This reduction in MAO levels is inde­pendent of nicotine "because we can't block MAO with nicotine," Fowler said. In light of the compound isolated from to­bacco leaves, "we now have an idea of what may be causing this inhibition of MAO." Coupled with nicotinic stimulation of neurotransmitters, the naphthoquinone compound may have something to do with cigarette smokers' reduced risk of developing Parkinson's, she suggested.

Mairin Brennan

'Plastic' Electronics One Step Closer By attaching fluorinated alkyl chains to an electron acceptor, researchers at Lucent Technologies' Bell Laborato­ries in Murray Hill, N.J., have synthe­sized a long-sought molecule: an or­ganic semiconductor with a reason­ably high electron mobility that is also soluble and air-stable [Nature, 4 0 4 , 478(2000)].

The new molecule brings scientists one step closer to "plastic" elec­tronic devices. Such de­vices, based on organic semiconductors, are ex­pected to be simpler and less expensive to make than conventional inor­ganic devices. Organic devices also would lend themselves for use in flexible displays, more durable smart cards, and other low-cost electronic * applications.

To perform well at high speeds and low power levels, the logic elements of such applications will need to be fabricat­ed from η-type and p-type organic semi­conductors, in which the charge carriers are electrons and holes, respectively. Sta­ble p-type organic semiconductors have been developed, but practical η-type or­ganic semiconductors have been elusive until now. A few η-type organic semicon­ductors usable in field-effect transistors (FETs) are known, but these are not con­sidered promising due to their low elec­tron mobility, their poor stability in air,

and/or the demanding processing condi­tions they require.

The Bell Labs researchers, led by

Katz and coworkers developed the organic semiconductor F15.

chemist Howard E. Katz, set out to design a better, more robust organic semi­conductor that could be used as the electron-con­ducting "η-channel" in

FETs. What they came up with is a naph-thalenetetracarboxylic diimide with two highly fluorinated alkyl chains. For sim­plicity, Katz refers to the compound as F15 because each alkyl group has 15 fluo­rine atoms.

From earlier work at Bell Labs, Katz and coworkers knew that a closely relat­ed molecule—a naphthalenetetracar-boxylic dianhydride—can conduct elec­trons, although it does so only under high vacuum. The dianhydride is too air sensitive and too insoluble to be useful in electronics, Katz says.

But by reacting it with a fluorinated amine, his team produced F15, a soluble molecule with several other desirable characteristics. For example, when solu­tions of F15 evaporate, they leave behind a crystalline film so well-ordered that it transports electrons with ease, Katz tells C&EN. The molecules line up side by side, producing isolated layers of the elec­tron-conducting tetracyclic moieties sur­rounded by layers of the fluorinated chains. These chains pack so densely in the crystal that water vapor and oxygen— which would degrade the material's per­formance—are effectively kept away from the electron-conducting layers.

The fluorinated chains also improve the electrical properties of F15, contributing to the material's high electron mobility, as measured in air. Furthermore, F15's on/off ratio—the ratio of the "on" current to the "off' current—is over 100,000, which Katz says is "surely a record" for a thin-film organic η-channel semiconductor.

Using liquid-phase deposition, the Bell Labs scientists fabricated an n-channel FET (incorporating F15) linked to a p-channel FET (incorporating a hole-trans­porting thiophene derivative) on the same substrate. The linked transistors were shown to form an "inverter" circuit that converts a very high input voltage to a very low (or zero) output voltage, or vice versa.

Although more work will need to be done to improve the processing and properties of the new semiconductor, this is clearly a step in the right direction, comments materials scientist Chérie R. Kagan of IBM's Τ J. Watson Research Center in Yorktown Heights, N.Y.

Ron Dagani

From the ACS meeting

Celebrating Chemistry In The 21st Century The American Chemical Society nation­al meeting held last week in San Fran­cisco was a celebration of the chemis­try—and chemists—of the future. And it was a record-breaker with 18,521 at­tendees, just over 8,200 presentations in 786 technical sessions, and 289 compa­nies represented in a 488-booth exposi­tion. The National Employment Clear­ing House boasted 165 employers, 1,053 candidates, 723 positions posted, and 1,049 potential hires, with more than 3,000 interviews conducted.

ACS members had many reasons to

12 APRIL 3, 2000 C&EN

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