Researchers create novel molecules that serve as ziplines for energy


Date:
November 16, 2021
Source:
University of Bonn
Summary:
Researchers have moved packets of energy along a molecular ladder
made of hundreds of benzene rings. Such polymers can potentially be
used to design new displays based on organic light-emitting diodes,
or for solar cells.



FULL STORY ==========================================================================
In the 19th century, the scientific community puzzled over how the atoms
in the mysterious compound benzene were arranged. This "aromatic" molecule
soon proved to have a surprisingly simple structure: It consisted of six
carbon and six hydrogen atoms. But how could these twelve atoms arrange themselves in space to form a chemically stable object? The chemist
Friedrich August Kekule', later professor at the University of Bonn,
brought light into the darkness. Legend has it that he sat dozing by
the fireplace in the winter of 1861. Kekule' suddenly had a vision of
a snake devouring its own tail. He realized that the carbon atoms of
benzene must be organized in a circle, similar to a small wagon wheel.


========================================================================== "This dream ultimately laid the foundation for the massive expansion
of the chemical industry toward the end of the 19th century," says
Prof. Sigurd Ho"ger of the Kekule' Institute of Organic Chemistry
and Biochemistry at the University of Bonn, who is a member of the Transdisciplinary Research Area "Building Blocks of Matter and Fundamental Interactions" at the University of Bonn. Benzene is an important building
block for paints, pharmaceuticals and plastics, for example.

Hundreds of benzene rings in the shape of a ladder Although the wheel
is often touted as humankind's oldest invention, the ladder is actually
quite a bit older. Kekule''s successors at the University of Bonn had
long been dreaming of molecules in the shape of a ladder, consisting of hundreds of benzene rings. The researchers from the Kekule' Institute
and the Mulliken Center for Theoretical Chemistry at the University of
Bonn, together with a team led by Prof. John Lupton from the Institute
of Experimental and Applied Physics at the University of Regensburg,
have now constructed such a molecular ladder. This is a molecule with
two tracks of so-called "conjugated polymers," in which double and single
bonds alternate between the carbon atoms.

They make up the rails that you hold on to when climbing up an ordinary
ladder.

The researchers first designed a precursor compound that contained only
a single polymer chain and attached polymerizable groups -- a flexible
"snake." For some of the material, the second rail of the ladder was
then formed in a subsequent step by means of a zipper reaction, much
like when close an anorak.

In this way, in addition to the polymer with a single conjugated rail,
the team obtained a polymer with two conjugated rails -- the stiff
"ladder." Both polymers were of equal length and could now be compared
to each other: How would turning a snake into a ladder affect the
material's properties? The researchers examined the structure using a
scanning tunneling microscope.

The tiny molecular ladder is one nanometer (a millionth of a millimeter)
high, two nanometers wide and one hundred nanometers long. The chemists
also confirmed the shape and extraordinary rigidity of the ladders --
compared to the snakes -- through extensive computer simulations using
a novel theory that predicts the individual motions of all atoms within
the molecule.

Potential building block for electronics "The ladder structure is
retained not only when the molecules are placed on a surface, but also
when they are dissolved in a liquid," says Prof. Lupton of the University
of Regensburg. This feature, he adds, allows energy to move along the
molecule in space, providing a potential building block for optical
networks, circuits and sensors.

In principle, such polymers conduct electrical currents and can be used
to make new displays based on organic light-emitting diodes (OLEDs), or
to convert light into electricity in a solar cell. When light falls onto
such a molecule, it is absorbed and produces a small packet of energy. The researchers were able to observe how these packages moved along the ladder virtually unimpeded, as if on a zipline. The open snake-like polymers,
on the other hand, do not show this effect. Their properties are similar
to those of conventional polymer molecules: the packages slide along the "snakes" and lose energy.

Kekule''s shattered dream "While old Kekule' 'saw' the single molecule
as a ring, he certainly never dreamed that there would one day be giant molecules of such rigidity that they are unable to bite their own tails,"
says Ho"ger, summarizing the result with a wink.

Video of computer simulation of molecules:
https://www.youtube.com/ watch?v=PgBQ4pOKlE0 ========================================================================== Story Source: Materials provided by University_of_Bonn. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Stefanie A. Meissner, Theresa Eder, Tristan J. Keller, David A.

Hofmeister, Sebastian Spicher, Stefan-S. Jester, Jan Vogelsang,
Stefan Grimme, John M. Lupton, Sigurd Ho"ger. Nanoscale p-conjugated
ladders.

Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-26688-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211116111342.htm

--- up 5 days, 2 hours, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)