Why vibrational structures in absorption and fluorescence spectra of chromophoric dyes change with solvent polarity? Is possible to quantify these changes in terms of polarity change or any other physical parameter of the solvent/dye?
Hi Haridas, I guess that different solvent polarity leads to different structures of the dyes. The solvent molecules can stabilize some structures more than others. Dyes often contain free electron pairs or pi-electron clouds and maybe some structures show interactions between these electrons and other structures show no interactions. In case of interactions there will be additional energy levels which can absorb spectral energy.
Response to Prof. Harry ten Brink,
Please find the attached file reference and the observed spectral changes for two styryl dyes studied by us. Vibrational structures gradually disappear on increasing solvent polarity. Can one quantify these changes in the Vibrational structures in the electronic absorption and emission spectra? There are theories to correlate spectral shifts with solvent polarities. Can similar theoretical basis be given for the changes in the Vibrational structures?
Dear Haridas,
There are two aspects to this problem. 1. The structure of the absorption and emission spectra changes with increasing polarity of the solvent due to the inhomogeneous broadening of the bands of the vibronic spectra:
as the polarity of the medium increases, the spectra lose signs of the vibrational structure and become diffuse. These effects are associated with fluctuations in the interaction of the dye with the internal electric field acting on the solute molecule from the side of the nearest environment. For more than 30 years the first problem was developed by me and found a generalization in the mini-review.
Article Solvatochromism and Nonradiative Decay of Intramolecular Cha...
2. However, this is not the only reason for the structural change - with the polarity of the medium changing, the Franck-Condon factor also changes. This problem is more complicated and does not have a simple analytical solution. It is briefly discussed for peridinin in my work, the link to which is given below.Article Gas-phase energy of the S-2
@mr Pal
I do not see a definite vibrational progression in your example
Dear Prof. Pavlovich,
Many thanks for your kind response. I will go through you papers and try to understand and correlate my results.
With best regards,
Haridas
dr Pal
I refer to wikipedia for
.Franck-Condon factors
.progression in a vibronic transition
Dear Prof. Brink,
Many thanks for your kind response. I will definitely go through your suggestions and try to understand and correlate my results.
With best regards,
Haridas
Dear Prof. Markus Christ,
Many thanks for your kind response. I will certainly look into this possibility of different structures in the solutions.
With best regards,
Haridas
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