Optical properties of bis-(2,4,6-trimethylpyridine)iodine(I) cation: absorption and emission

With regard to its electronic structure, the cation Icoll2+ (coll = collidine or 2,4,6-trimethylpyridine) is viewed as a coordination compound of iodine(I) with a p4 electron configuration. The lowest-energy excited state of Icoll2+ is suggested to be a ππ* collidine intraligand (IL) triplet which appears in absorption (λmax=332 nm, ε=250) and emission (λmax=405 nm, φ=0.001, τ∼90 ns). Owing to the heavy-atom effect of iodine this phosphorescence occurs at r.t. The longest-wavelength pp absorption is apparently obscured by the intense spin-allowed IL band at λmax=268 nm.