The lippert-mataga equation is typically used to determine the difference in the dipole moments, it does not really deal with the specific solvent effects that can influence the relative energy levels (and hence the emission wavelength). The blue/red shifts observed can be the result of conformational changes that give rise to new bands (TICT states).

take a look at this review: Z. Grabowski, K. Rotkiewicz, W. Rettig, Chem. Rev. 2003, 103, 3899–4031.

The lippert-mataga equation is typically used to determine the difference in the dipole moments, it does not really deal with the specific solvent effects that can influence the relative energy levels (and hence the emission wavelength). The blue/red shifts observed can be the result of conformational changes that give rise to new bands (TICT states).

take a look at this review: Z. Grabowski, K. Rotkiewicz, W. Rettig, Chem. Rev. 2003, 103, 3899–4031.

As said above, the lippert-mataga equation is an approximation and only works if specific interaction are not present. Specific interaction can be of any kind, as for example conformational changes, as said by Vazquez, or only a reorganization of the electronic levels that can result in different LUMO (Lowest Unoccupied Molecular Orbital) for different solvents. Even if you have hydrogen bonds between solute-solvent the lipper-mataga equation can not be used.

For instance, a DFT study of the hydration of Mg++ at the level BPW91/6-311++G(3d3p) , shows a red shift, for the stretching vibration Mg-O , when going from 2 to 6 H2O around Mg++ .

See our article in Theochem,728,p231(2005) in whic this result is not related.

Best regards

Dan Vasilescu

Perhaps I should be more specific; yes for fluorophores in the liquid state there are many possible interactions that can cause the Lippert Mataga equation to be wrong. These Solvatochromic shifts can be due to conformational change, exciplex formation, H-bonds etc.

What I'm particularly interested in is the influence of the host media's relative permittivity (be it liquid or solid) on a fluorophore doped into it. If you take DCM as an example fluorophore it has a large change in dipole moment upon excitation and this causes the surrounding medium (liquid or solid) to respond and give rise to a reaction field which subsequently relaxes the excited state, redshifting it relative to the absorption spectrum. This is a pure OLM theory response with no extra processes and can be shown to produce a very good fit to the Lippert-Mataga equation, particularly in the solid state where rigidity stops most unwanted bonding/conformational change.

Now I've heard tell of a converse blue-shifting response and I'm wondering how can that even be possible? There must be some energy transfer involved or some resonance with the dipole to enhance it by constructive interference? I think it has something to do with the sign of the change in dipole moment, but in the LM equation this is squared and so the -ve sign cancels; hence it seems that what I was told, i.e. that a blueshift is possible, isn't described by the LM equation. Obviously any theory has its limitations...

Adam,

solvatochromic blue shifts with increasing solvent-polarity occur almost exclusively due to geometric effects. Although it is in general possible to have it without the latter, I dont know a single example of a non-geometric blue shift. The Lippert-Mataga does not include such geometric effects and hence, will never predict a blueshift.

Brooker's merocyanine is a good example for a hyposochromic (blue)-shift. The polar, zwitterionic ground-state structure is apparently stabilized in polar solvents, causing the respective bond-length alternation pattern (C-O becomes more of a single-bond and so on). As a result,  the energy of the S1, whose electronic structure resembles the uncharged lewis structure, increases with solvent polarity. Eventually, the excitation wavelength increases in with solvent polarity.

I hope it still helps two years later.