The future will be dominated by organic electronics, as opposed to current silicon-based technology. In the journal Angewandte Chemie,
an international team of researchers has now introduced a new
luminescent organic liquid that can be applied like ink. When two
additional dyes are dissolved in this liquid, it forms a white
luminescent paste that may offer a new way to make devices like large
displays and white light-emitting diodes.            

   

Current
approaches to organic electronics mainly involve plastic film supports
with conducting paths and components made of organic molecules
inexpensively printed or glued on. Organic electronics are interesting
as potential “disposable electronics” for applications like electronic
price tags. Even more intriguing are devices that cannot be produced
with standard electronics, such as flexible films with integrated
circuits for use as novel flat-panel displays or “electronic paper”. A
third area of interest involves applications such as photovoltaics that
are dependent on economical mass production in order to be profitable.

The
development of large components like displays requires organic coatings
that emit white light and are inexpensive to produce. Previous gel- or
solvent-based liquid “dyes” are easy to apply, but are often not
colorfast or are barely luminescent after drying. For solids, on the
other hand, processing is often too complex.

A
team led by Takashi Nakanishi at the National Institute for Materials
Science in Tsukaba (Japan) has taken a different approach: they use
uncharged organic substances that are luminescent liquids at room
temperature and require no solvent. The electronically active parts of
the molecules consist of linear chains of carbon atoms linked by
?-conjugated double bonds. This means that electrons can move freely
over a large portion of the molecule. The core is shielded by
low-viscosity organic side chains that ensure that the core areas do not
interact with each other and that the substance remains liquid.

The
researchers were able to prepare a liquid that fluoresces blue under UV
light. They then dissolved green- and orange-emitting dyes in this
solvent-free liquid. This results in a durable, stable white-emitting
paste whose glow can be adjusted from a “cool” bluish white to a “warm”
yellowish white by changing the ratio of the dyes. It is possible to use
this ink directly in a roller-ball pen for writing, or to apply it with
a brush on a wide variety of surfaces. Application to a commercially
available UV-LED allowed the researchers to produce white light-emitting
diodes.

Solvent-Free Luminescent Organic Liquids

Source: Wiley