New Blue Chromophore

Mn³⁺ in Trigonal Bipyramidal Coordination

"The researchers were trying to make compounds with novel electronic properties, mixing manganese oxide, which is black, with other chemicals and heating them to high temperatures.

Then Mas Subramanian, a professor of material sciences, noticed that one of the samples that a graduate student had just taken out of the furnace was blue."

FULL TEXT

-New York Times: Kenneth Chang

"We show that trivalent manganese, Mn³⁺, imparts an intense blue color to oxides when it is introduced at dilution in trigonal bipyramidal coordination. Our optical measurements and first-principles density functional theory calculations indicate that the blue color results from an intense absorption in the red/green region. This absorption is due in turn to a symmetry-allowed optical transition between the valence-band maximum, composed of Mn 3d_x²−y²,xy states strongly hybridized with O 2p_x,y states, and the narrow Mn 3d_z²-based conduction-band minimum. We begin by demonstrating and explaining the effect using a well-defined prototype system: the hexagonal YMnO₃−YInO₃ solid solution. We then show that the behavior is a general feature of diluted Mn³⁺ in this coordination environment."

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-Journal of the American Chemical Society