Friday, April 23, 2010

A simple model for solvent effects in chemically complex charge transfer dyes

Anna Painelli (Parma, Italy) gave a really nice talk,
How molecular functional materials respond to the environment: from solvation to cooperativity.

She illustrated how simple model Hamiltonians can capture essential photophysical properties of complex molecular systems. The first system was a donor-acceptor (D-A) molecule in a solvent.

The simple model describes two electronic states (D-A and D+-A-), one vibrational mode, and the solvent which is described by one classical co-ordinate and a key parameter (the polarisability).

This nice paper from J. Phys. Chem A. in 2002 shows how this model gives a good quantitative description of the absorption and emission spectra for several different dyes in three different polar solvents.

This 2006 JACS paper extends the model to describing "quadrupolar" molecule, which has the structure DAD . The model involves 3 electronic states, 2 vibrations, plus the solvent polarisation.
I am keen to apply this model for solvent effects to methine dyes, such as the Green Flourescent Protein chromophore, which Seth Olsen and I have argued is nicely described by a three state model.

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