Organic crystal lattices for blue lasers

MINNEAPOLIS, Nov. 29 (UPI) -- New organic crystal lattices -- able to internally arrange themselves -- may someday open the door to high energy blue lasers for use in advanced cutting tools and telecommunications. The research may also one day lead to better, safer pharmaceuticals.

"This research may have lots of implications in numerous areas," said lead researcher Michael Ward, a chemist at the University of Minnesota in Minneapolis. "The work represents an advance in crystal engineering, in which we control how organic crystals are assembled in space. If you can control that, you can control many of the key properties of organic crystals."

On the molecular level, the lattice is like a building -- a series of chambers where the floors, ceilings and pillars are made of crystal and held in place by weak chemical attractions. Inside the chambers are "guest" molecules that perform some function. In the case of this lattice, the guests can perform the trick of changing red light to green or blue light.

"You actually upgrade the energy of the light, although the intensity is much weaker," Ward said in an interview with UPI. "People want blue lasers for telecommunications, because with higher energy you have shorter wavelengths, so you can deliver more information in a shorter time. Blue lasers have been hard to fabricate, save for some made with inorganic materials, but red lasers are relatively inexpensive."

The lattice is capable of this light-changing behavior because it exhibits polarity -- all the electric charges of the guest molecules are lined up with all the negative poles pointing one way and the positive poles the other. Polar crystals are known for color changing by doubling light's frequency.

"It's usually difficult to get molecules to go the way you want because the forces pulling them into position are so weak," Ward explained. "If some of the guests are pointing the wrong way when the lattice is formed, they remain stuck that way and the lattice as a whole will not be polar."

In order for all the guest molecules to line up right in this lattice, the researchers used organic crystal pillars shaped like bananas. The guests can only fit if they line up in one direction. This in turn forces all the molecules inside the lattice to align in the same direction, causing the material to exhibit polarity. The lattice is made simply by mixing three organic components in water or methanol at room temperature and waiting about a day.

Related crystal lattices may one day be used to separate molecules with the same chemical makeup but different structure.The need for this kind of purification is exemplified by the notorious drug thalidomide -- one form of the chemical alleviates morning sickness, while the other causes birth defects.

"Now that we know how to do this, we can try other 'pillar' molecules and other 'guests' with the same basic framework," said Ward. "What makes this unique is that it's so amenable to modifications."

The researchers reported their findings in the journal Science.

(Reported by Charles Choi in New York)