# UV Absorption of iodine with some solvent

$$I_2$$ in solution is typically absorbing around $$525 \; nm$$ this is why it appear to be magenta, I recently learn that with some solvent :

• Benzene
• Toluene
• $$o$$-Xylene
• $$p$$-Xylene

The coordination complex between the solvent and $$I_2$$ is also absorbing around $$300 \; nm$$ I guess there is some explanation with the MO diagram ?

Iodine is highly polarisable and will form a (Mulliken) charge-transfer complex with many aromatics. Very many pairs of donor - acceptor pairs do this and have been studied for approx $$100$$ years, see for example tetracyanoethylene–pyrene (J. Chem. Phys. 105,1996 p2287) for an ultrafast time resolved study. In absorbing a photon the ground state complex DA transfers an electron directly to a charge transfer state $$DA \overset{h\nu} \to \mathrm D^+A^-$$. The interaction is thus that of all the orbitals in one molecule with all those in another.