title: Role of counteranions in acid-induced aggregation of isomeric tetrapyridylporphyrins in organic solvents.
abstract: The effect of adding various kinds of acids HX (X = Cl, Br, I, CF(3)COO, CF(3)SO(3), TFPB ((3,5-(CF(3))(2)C(6)H(3))(4)B) to isomeric tetra(2-pyridyl)porphyrin, tetra(3-pyridyl)porphyrin, and tetra(4-pyridyl)porphyrin (TpyP(2), TpyP(3), and TpyP(4)) in dichloromethane solution has been investigated through the combined use of UV/vis absorption, fluorescence emission, and resonance light scattering (RLS) techniques. The experimental evidence points to a marked dependence of the protonation and aggregation behavior on the nature of both acids and porphyrins. In general, three different trends can be recognized: (i) formation of a fully protonated species, followed by aggregation; (ii) formation of a tetraprotonated species, which aggregates and, on further addition of acid, disaggregates; and (iii) protonation of the four pyridyl moieties, leading to a tetraprotonated ion pair, in the unique case of the bulky TFPB(-) anion. In all cases, the protonated species and the resulting aggregates exhibit spectroscopic features that are markedly influenced by the nature of the counteranions. A model for J-aggregation has been proposed on the basis of an interplay of hydrogen bonding, electrostatic interactions, and dispersive interactions. Kinetic control of the aggregation process allows for a fine-tuning of the spectroscopic properties of the final aggregated species.
authors.affiliation: Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Salita Sperone 31, 98166 Vill. S. Agata, Messina, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: De Luca
authors.forename: Andrea
authors.initials: A
authors.lastname: Romeo
authors.forename: Luigi Monsù
authors.initials: LM
authors.lastname: Scolaro
mesh_terms: D000143:Acids / Q000737:chemistry*; D000838:Anions; D002625:Chemistry, Organic / Q000379:methods*; D007477:Ions; D007700:Kinetics; D008027:Light; D008752:Methylene Chloride / Q000737:chemistry; D008956:Models, Chemical; D011166:Porphyrins / Q000737:chemistry*; D011522:Protons; D012542:Scattering, Radiation; D012997:Solvents / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
chemical_list: D000143:Acids; D000838:Anions; D007477:Ions; D011166:Porphyrins; D011522:Protons; D012997:Solvents; D008752:Methylene Chloride