This is a quote from Anslyn's Physical Organic Chemistry:
[...] One way to think of these systems is that the ground state is a weak, intermolecular complex, (D • A). Often such molecules are polar and / or quite polarizable, facilitating complex formation. Because one partner is intrinsically a good electron donor (low ionization potential) and the other is a good acceptor (high electron affinity), the excited state will have a large contribution from states such as (D+• A-) that involve electron transfer, a configuration not possible for either isolated molecule. This preferentially stabilizes the excited state, leading to a lower energy (longer wavelength) absorption. Because of this highly polar character, charge-transfer absorptions are extremely sensitive to solvent polarity, moving to longer wavelengths as the solvent polarity increases.
Earlier I read about Franck-Condon principle but I lack QM-mathematical background behind, so that's why this principle still leave me at unease, and hence my question. How is it possible that absorption wavelength is so sensitive to solvent polarity, when significant charge develops not until the complex is excited? I mean how the excited state of the molecule "knows" there is solvent ready to solvate it, since according to Frank-Condon principle solvent rearrangement is much slower than absorption.