What is solvatochromism?

Solvatochromism refers to the phenomenon where the color of a compound changes in response to variations in the solvent in which it is dissolved. This effect occurs due to alterations in the electronic environment of the solute, primarily influenced by the solvent's dielectric properties and polarity.

When a solute is placed in a solvent, the solvent molecules can interact with the solute through various intermolecular forces, causing the energy levels of the electronic transitions to shift. These shifts can lead to changes in absorption and emission spectra, effectively altering the wavelengths of light that the compound absorbs or emits.

In this context, the statement about variation in the transition frequency with change in solvent permittivity captures the essence of how solvatochromism works, as solvent permittivity is closely related to the solvent's ability to stabilize different electronic states of the solute.

The other options describe different phenomena or processes that do not align with the specific definition of solvatochromism. For instance, ligand exchange involves changing the ligands coordinating to a central atom in a complex, which is a different type of chemical interaction. Temperature effects on electronic transitions pertain to how thermal energy influences the behavior of electrons but do not encapsulate the nuances of solvatochromism.