What is it about?
A yellow compound crystallizes to make an orange-red substance. The color change is from an unusual stacking pattern in the crystal, which facilitates a type of light absorption due to charge transfer. The strong dipole moment of the compound makes it possible for photons to excite an electron from one portion of the crystal to another. The crystals are similar to some colored inorganic semiconductors, whose band gap (the energy needed to excite the electron) also gives rise to an orange-red color.
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Why is it important?
Color can be an important clue about what is going on in solids. In the case of semiconductors, color provides information about basic information such as band gap. Some solids have what are called non-linear optical properties, which are important in applications involving laser optics. But most semiconductors and non-linear optics materials are inorganic. This work may help in the development of organic semiconductors and non-linear optics. Organic materials can be cheaper and easier to work with.
Perspectives
As a chemist, it is amazing and entertaining to find interesting material properties in simple and mundane compounds which are chosen for one purpose, and end up being the star of the show for a completely different purpose. In the present case, the orange-red substance was originally selected as a starting material for an organic synthesis project, with no particular attention paid to its color. But once its color became the focus, other potential applications became evident.
Jonathan Filley
Oligometrics, Inc.
Read the Original
This page is a summary of: Color center creation by dipole stacking in crystals of 2-methoxy-5-nitroaniline, Acta Crystallographica Section E Crystallographic Communications, September 2024, International Union of Crystallography,
DOI: 10.1107/s2056989024008739.
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