Probing Surface Basicity of Solid Acids with an Aminobenzodifurandione Dye as the Solvatochromic Probe

Abstract

Solvatochromism and sorptiochromism of the dye 3-(4-amino-3-methylphenyl)-7-phenyl-benzo1,2b:4,5b‘difuran-2,6-dione (1) are studied with an extended set of solvents and various solid acids including silicas, aluminas, and alumosilicates. 1 shows a positive solvatochromism with increasing basicity and dipolarity/polarizability of the solvent; its solvent-induced bathochromic UV−vis absorption band shift ranges from formic acid (υmax = 21 630 cm-1) to hexamethylphosphoric acid triamide (υmax = 14 200 cm-1). Multiple square analyses of υmax of the solvent-dependent solvatochromic UV−vis absorption band of 1 with several empirical solvent polarity parameters prove that a composite of basicity, acidity, and dipolarity/polarizability of the environment must be taken into account. For the analysis of the solvent-dependent UV−vis shift of 1, the Kamlet−Taft and Catalán solvent parameters have been evaluated. It could be shown that the Catalán solvent parameter set is more suitable to reflect multiple solvation processes involving both strong basic and strong acidic solvents. Quantum chemical calculations indicate that an interaction of the silanol oxygen atom with the protons of the amino group is clearly favored over various acidic attacks of silanol groups upon 1. Accordingly, surface basicity of silica, alumina, and alumosilicates can be determined using the linear solvation energy relationship derived from the solvent-dependent UV−vis band of 1. An unambiguous interpretation of the UV−vis spectroscopic data of 1 adsorbed on surfaces containing Lewis-acid sites is sometimes difficult. UV−vis monitoring of 1-loaded solid acids during surface titration with 2,6-di-tert-butyl pyridine allows the discrimination of whether Brønsted- or Lewis-acid sites interfere with 1. Additionally, adsorbed water has an important influence on the actual surface basicity of solid acids. 1 is recommended as a sensitive probe for checking both basicity and acidity when directly compared with solvatochromism of the established hydrogen-bond-donating indicator (cis-dicyano)bis(1,10-phenanthroline)iron(II) (2).

Dipolarity versus Polarizability and Acidity versus Basicity of Ionic Liquids as a Function of Their Molecular Structures

“…In earlier work we could determine the HBA ability b by means of the solvatochromic dye 3-(4-amino-3-methylphenyl)-7-phenylbenzo[1,2-b:4,5-b']difuran-2,6-dione (ABF). [19] However, the long-wavelength UV/Vis absorption band of this dye is not solely sensitive to b; a and especially p* have a small influence. The reason for using the single-parameter equation was that the significance ofñ max (ABF) as function of b is excellent.…”

Titanium Dioxide/Graphene and Titanium Dioxide/Graphene Oxide Nanocomposites: Synthesis, Characterization and Photocatalytic Applications for Water Decontamination

“…Determining the surface properties on the microscopic level of a catalytic material is relevant to its application because these surface properties have a significant impact on the adsorption/desorption processes on the catalyst surface, and on the physico-chemical processes taking place therein. In this respect, surface properties, such as the number, location, and strength of acidic and basic sites on the catalytic surface, as well as surface polarity and surface polarizability play a key role in the catalytic activity of the catalyst and hence its applications [172][173][174]. Surface free energy, determined by inverse gas chromatography, is used to determine the acidic and basic properties of solid surfaces accurately over a wide range of temperature [175,176].…”

Employing perichromism for probing the properties of carboxymethyl cellulose films: an expedient, accurate method for the determination of the degree of substitution of the biopolymer derivative

“…Probes have been employed in order to study the properties of inorganic solid surfaces, e.g., silica, alumina, and titanium dioxide Fidale et al 2010;Khristenko et al 2006;Spange et al 2000Spange et al , 2005Zimmermann et al 2002). They have also been employed in order to probe the surface properties of: Untreated and treated celluloses and other carbohydrates (microcrystalline cellulose; bacterial cellulose; cotton linters; regenerated cellulose; sulfite kraft pulp; starch; chitin, chitosane) (Fidale et al 2010;Fischer and Spange 2000;Fischer et al 2002;Spange et al 2003 Fig.…”