Hello,
I am studying the photophysical properties of a molecular rotor which unexcpectedly, shows a lambda(max, absorption) = 565 nm in toluene, but a lambda (max, absorption) = 540 nm in MeOH and EtOH.
I have recorded its absorption spectrum in other solvents: DCM, CHCl3, DMF, and H2O showing the expected shifting. l(max, Toluene) < l (max, DCM) < l(max, CHCl3) < l(max, DMF) < l(max, PBS and H2O) .
Any idea why in those alcoholic solvents I observed a weird situation, since the polarity is larger?
Thank you in advance
Eduardo Cueto Diaz The shifts are due to different intermolecular interactions between your molecular rotor and the solvent. With toluene there can be pi-pi bonding, dispersive interaction, with alcohols, hydrogen bond, dipole-dipole interaction is possible. For a more specific assessment, you need to know the chemical structure of your molecule.
Yuri Mirgorod Thank you for your answer. Yes, I understand that there is a charge re-distribution along the molecule (TICT) associated to the solvent environment. But I was wondering why it is behaving so weird in MeOH and EtOH. What you mentioned could be a solution, but then, why is in water (also a polar protic solvent) behaving normally.
Eduardo Cueto Diaz For example, TICT in
https://pubmed.ncbi.nlm.nih.gov/17520133/
rotors (dyes) have a carboxyl group. It enters into a hydrogen bond well. Reversible intramolecular transitions in TICT, apparently, occur with the participation of a solvent. Therefore, along with intramolecular interaction with the solvent, the sizes of water molecules and alcohols are important. The solvophobic interaction contributes to alcohol, in contrast to the hydrophobic interaction in water.
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