In a previous article, I wrote about an accidental discovery made by a student that led to a new, more efficient synthetic route to producing a chemical compound. Historically, accidental discoveries have resulted in some of our greatest scientific advances. This week we have been reminded of another such discovery with a huge amount of potential in a range of applications.
Back in 2009, Professor Mas Subramaniun from the Department of Chemistry at Oregon State University created a pigment which had a new and vibrant shade of blue. Formed by heating black manganese oxide and other chemicals in a furnace to 2,000 degrees Fahrenheit, the intention of Subramaniun and his research group was not to create new pigments, but to create new materials for applications in solid state electronics. Instead, by pure chance, a graduate student of Subramaniun happened to notice the blue color of the compound in the furnace that is now known as YInMn Blue, a nod to its composition that includes Yttrium, Indium and Manganese. Now, I know what you’re thinking. How can we have a ‘new’ color? We know that white light contain all the colors of the rainbow. Presumably, this means that every conceivable color has been discovered? Well, not quite. While this may mean that we know of a full spectrum of possible colors, many of these have not been created or observed in real life.
The rainbow of colors of light that we see fall within a range of wavelengths, from shorter wavelength blue light to longer wavelength red light. Each and every color pigment has a spectral profile, which shows the wavelengths of this light that are absorbed and reflected by it. Generally speaking, a pigment is the color of the wavelength of light that is most reflected. One example of this is found in plants. Chlorophyll-containing plants look green because more green light is reflected than any of the other colors of the rainbow. The other colours are absorbed. Similarly, plants that contain carotenoid pigments such as tomatoes reflect yellow and red light, and absorb blue and green light, and so look red and orange. This can be seen in the following image, showing the wavelengths of light absorbed by three different pigments; chlorophyll a, chlorophyll b, and carotenoids.
Currently we do not have pigments to match every color in the rainbow, and some colors have always been notoriously difficult to find in nature, particularly those blue and indigo colors; indeed, indigo was originally found in small quantities in India, extracted from the plant Indigofera tinctoria, and exported in small quantities for vast sums of money. These days, blue dyes are reasonably commonplace, but are prone to rapidly losing their vibrancy.
So what makes this new blue pigment so special? To find out we need to once again consult the spectral profile of the pigment, and also at the crystal structure of the compound. The intense blue color of the pigment is a result of the strong reflection of blue light, and blue light alone. It absorbs green and blue light, making the blue color incredibly vibrant. This is down to the arrangement of the atoms that have trigonal bipyramidal coordination (they are arranged to form a shape like two triangular based pyramids with their bases stuck together). The pigment is very durable, even in both water and oil, and resistant to acids and fading over time, and it also reflects around 40% of long wavelength infra-red light, which we can’t see as it doesn’t fall within the rainbow range of wavelengths, but results in a warming effect. By applying this pigment as a paint to roofs, it could keep homes cooler, and saving energy.
While YInMn has sat on the shelf for seven years, it has now been commercialized as a paint, owing to the low toxicity and high durability of the pigment. Given its applications in energy efficient paint, this beautiful new shade of blue could be coming to a roof or wall near you some time soon.