title: 3,5,7,9-Substituted hexaazaacridines: toward structures with nearly degenerate singlet-triplet energy separations.
abstract: Toward the goal of preparing stable, neutral open-shell systems, we synthesized a novel series of p-phenyl-substituted 3,5,7,9-hexaazaacridine and 3,5,7,9-hexaazaanthracene derivatives. The effects of substitution on the molecular electronic properties were probed both experimentally and computationally [B3LYP/6-311G(d,p)//B3LYP/6-31G(d,p)]. While the experimentally prepared structures already have small (20-25 kcal/mol) singlet-triplet energy gaps, systems with even smaller (<9 kcal/mol) singlet-triplet energy separations can be realized through systematic variation of the substituent numbers, types, and patterns. Hexaazaanthracenes show generally smaller singlet-triplet energy gaps than hexaazaacridines. Nitrogen-bonded sigma- and pi-acceptor substituents that cause positive inductive and mesomeric effects as well as carbon-bonded sigma-donor substituents make substituted hexaazaanthracenes promising candidates for purely organic high-spin systems.
authors.affiliation: Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, D-18059 Rostock, Germany. peter.langer@uni-rostock.de
authors.forename: Peter
authors.initials: P
authors.lastname: Langer
authors.forename: Shadi
authors.initials: S
authors.lastname: Amiri
authors.forename: Anja
authors.initials: A
authors.lastname: Bodtke
authors.forename: Nehad N R
authors.initials: NN
authors.lastname: Saleh
authors.forename: Klaus
authors.initials: K
authors.lastname: Weisz
authors.forename: Helmar
authors.initials: H
authors.lastname: Görls
authors.forename: Peter R
authors.initials: PR
authors.lastname: Schreiner
mesh_terms: D000166:Acridines / Q000138:chemical synthesis*; D000873:Anthracenes / Q000138:chemical synthesis; D015394:Molecular Structure
chemical_list: D000166:Acridines; D000873:Anthracenes