How the solvent changes the colour of dyes

Conjugated organic molecules such as used in photovoltaics cells and LED's are often dissolved in polar solvents. The same physics that allows solvation of the molecule (due to the polarity of the solvent) can also cause significant shifts in the absorption and emission spectrum of the molecule. Much of the physics is also applicable in amorphous thin films.

Last year, I gave a talk on this topic at the thursday COPE science meeting. I discussed how it is possible to quantify these spectral shifts in terms of the static dielectric constant of the solvent. It was based on a nice PRL, Solid State Solvation in Amorphous Organic Thin Films.

Such a quantitative analysis should be the starting point for any claims about the origin and cause of solvatochromatic shifts in complex molecular materials.