title: Thioindigo dyes: highly accurate visible spectra with TD-DFT.
abstract: The structure and visible spectra of a large panel of thioindigo dyes and derivatives have been evaluated using a TD-PBE0/6-311+G(2d,p)//PBE0/6-311G(d,p) approach explicitly taking bulk solvent effects into account by means of the polarizable continuum model. The influence of the solvent characteristics, the trans-cis isomerization, and the chemical substitution on the benzene rings have been investigated. In addition, hemi-thioindigo dyes, thiazine-indigo, chromophore-like molecules, and selenoindigo have been considered. Though the relative oscillator strengths of the two allowed visible transitions in the nonplanar cis isomers are not always correctly reproduced by theory, the agreement between theoretical and experimental results is far above expectations. For the 170 cases studied, we obtained a mean unsigned error on the predicted lambda(max) limited to 6.9 nm or 0.03 eV, with only 6 (4) cases for which the difference exceeds 20 nm (0.10 eV). These errors are 1 order of magnitude smaller than what has previously been reported for indigoids. A linear correlation between the central double bond length and the lambda(max) has been established, while the bond length and vibrational frequency of the carbonyl groups do not correlate with the thioindigo color. The higher excitation energies of the cis conformers, compared to the trans structures, result from a less stabilized LUMO in the former case. Indeed, for cis thioindigo, the two electron-rich (in the excited state) carbonyl units lie close to each other.
authors.affiliation: Laboratoire de Chimie Théorique Appliquée, Facultés Universitaires Notre-Dame de la Paix, rue de Bruxelles 61, B-5000 Namur, Belgium. denis.jacquemin@fundp.ac.be
authors.forename: Denis
authors.initials: D
authors.lastname: Jacquemin
authors.forename: Julien
authors.initials: J
authors.lastname: Preat
authors.forename: Valérie
authors.initials: V
authors.lastname: Wathelet
authors.forename: Michèle
authors.initials: M
authors.lastname: Fontaine
authors.forename: Eric A
authors.initials: EA
authors.lastname: Perpète
mesh_terms: D004396:Coloring Agents / Q000737:chemistry*; D007203:Indigo Carmine; D007211:Indoles / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D013843:Thiazines / Q000737:chemistry*
chemical_list: D004396:Coloring Agents; D007211:Indoles; D013843:Thiazines; D007203:Indigo Carmine