title: Electronically tunable anion-π interactions in pyrylium complexes: experimental and theoretical studies.
abstract: Noncovalent interactions of anions with electron-deficient aromatic rings that have been studied so far involve non-heteroaromatic or nitrogen-based heteroaromatic systems. Here we report the first case of an organic oxygenated aromatic system, in particular the tri-aryl-pyrylium tetrafluoroborate system, for which noncovalent anion-π interactions of the pyrylium cation with the tetrafluoroborate anion have been experimentally detected and demonstrated by means of (19)F NMR spectroscopy in solution. A series of pyrylium tetrafluoroborate salts were synthesized in the presence of BF3·Et2O, by direct reaction of 4-substituted benzaldehydes with 4-substituted acetophenones or via the previously obtained chalcone of the less reactive ketone. Correlations of (19)F NMR chemical shifts of tetrafluoroborate anion for most of the synthesized tri-arylpyrylium tetrafluoroborate complexes with both the pyrylium cation molecular weight and the standard substituent Hammett constants, demonstrate anion-π(+) interaction to act between the polyatomic anion BF4(-) and the pyrylium aromatic system. DFT calculations reveal that an additional (C-H)(+)-anion hydrogen bond involving the H(5) of pyrylium ring exists for these fluorescent dyes that show a tunable cup-to-cap shape cavity. The strong fluorescence emission observed for some representative pyrylium tetrafluoroborates described herein, makes them a promising class of tunable emission wavelength dyes for laser technology applications.
authors: Departamento de Química Orgánica, Facultad de Química, Universidad de Sevilla, C/ Profesor García González 1, 41012 Sevilla, Spain. fcabrera@us.es.
authors: Antonio
authors: A
authors: Franconetti
authors: Lidia
authors: L
authors: Contreras-Bernal
authors: Sorel
authors: S
authors: Jatunov
authors: Manuel
authors: M
authors: Gómez-Guillén
authors: Manuel
authors: M
authors: Angulo
authors: Rafael
authors: R
authors: Prado-Gotor
authors: Francisca
authors: F
authors: Cabrera-Escribano
mesh_terms: D000838:Anions / Q000737:chemistry; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006575:Heterocyclic Compounds, 3-Ring / Q000737:chemistry* / Q000528:radiation effects; D008422:Materials Testing; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation
chemical_list: D000838:Anions; D006575:Heterocyclic Compounds, 3-Ring