Internal and External Acidity of Faujasites As Measured by a Solvatochromic Spiropyran

Abstract

The adsorption of the photochromic 1,3,3-trimethyl-6′-nitroindoline-2-spiro-2′-benzopyran (SP) on Y-zeolites from dichloromethane solution and the ship in the bottle reaction (SIBOR) of SP have been studied by measuring the UV/vis absorption of the resulting materials to achieve information on polarity of the internal and external surface environments. The acidity and α values (hydrogen bond donating ability) of the faujasites significantly differ whether the probe is located at the external surface or inside the Y-zeolite. Additionally, dicyanobis(1,10-phenanthroline)iron(II) [Fe(phen)2(CN)2] (1) and 4-tert-butyl-2-(dicyanomethylene)-5-[4-(diethylamino)benylidene]-Δ3-thiazoline (2) were used as solvatochromic probes for the external surface. The empirical Kamlet−Taft polarity parameter α (hydrogen bond donating (HBD) ability) and π* (dipolarity/polarizability) have been determined for the faujasites surfaces using the linear solvation energy relationship (LSER).