When MOED is dissolved in various liquids, its colour will vary, depending on the solvent and its polarity. In general, the more polar the solvent, the shorter the
wavelengths of the light absorbed will be, this is referred to as a
hypsochromic shift. When light of a certain colour (wavelength) is absorbed, the solution will appear in the complementary colour of the one absorbed. Therefore, in water, a highly polar solvent, MOED appears yellow (corresponding to absorbed blue light of wavelengths 435–480 nm), but is purple or blue (corresponding to absorbed green to yellow light of wavelengths 560–595 nm) in
acetone, a less polar solvent. The effect stems in part from the stabilization of the
ground state of the merocyanine molecule in polar solvents, which increases the energy gap between the ground state and
excited states, which corresponds to shorter wavelengths (increased energy) of the absorbed light. Similarly, protic and aprotic solvents also affect MOED in solution differently. Solvents that are hydrogen donors (i.e. water, acids), will affect the visible absorption spectra by engaging in hydrogen bonding or donating the hydrogen outright, making the molecule favor the zwitterionic resonance form; an example of this may be seen in the picture where acetic acid, though less polar than water, was able to produce a more yellow solution. ==Uses==