Firstly, it is important to measure absorbance and emission in dilute solution, to ensure that any apparent shifts are really to changes in the electronic states. The Stokes shift is largely due to relaxation of the molecule in the excited state. If the molecule becomes more rigid, then the Stokes shift can be reduced.

"Structure Property Relationships for Electron-Vibrational Coupling in Conjugated Organic Oligomeric Systems",

L. O'Neill and H.J. Byrne,

Journal of Physical Chemistry B, 109 (26): 12685-12690 (2005)

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