Fluorescence Probing of Solvent Accessibility and Micropolarity on Silica and Alkylated Silica Surfaces

Abstract

The highly solvatochromic probe “Fluoroprobe”, which fluoresces in a wide range of the visible spectrum, was covalently attached to silica and alkylated silica particles to study solvent accessibility and surface micropolarity. A two step attachment method was used which was found to lead to a quite homogeneous distribution of the probes without extensive local clustering. On silica the probe experiences a local dielectric constant of ϵ = 6, while its solvent accessibility is ca. 30%. On alkylated silica this reduces to ϵ = 3.4 and ca. 23% respectively.

Dansylated Aminopropyl Controlled Pore Glass: A Model for Silica−Liquid Solvation

“…The current work focuses on determining the effects of a probe molecule's loading, solvent dipolarity, and surface-residue end capping on the cybotactic region that surrounds a covalently attached organic probe molecule on aminopropyl CPG. In previous work, researchers have typically investigated the effects of a covalently attached probe molecule when the probe molecule loading ranged from 0.13 to 1.10 μmol/g. − In previous studies where the fluorescent probe is covalently attached to pre-aminated silica, a typical probe-to-amine ratio was on the order of 0.5:1. , In the current work, the probe-to-amine ratio spans 5 orders of magnitude; a much larger range in comparison to those investigated previously. − …”

“…The use of fluorescence to characterize silica surfaces is well documented, especially silica-based materials that have importance to chromatography. Specifically, fluorescence-based experiments on either covalently attached − or physiosorbed probe molecules − have been carried out to gain a better understanding of the orientation, distribution, mobility, and accessibility of surface-bound ligands.…”

“…41,42 In the current work, the probe-to-amine ratio spans 5 orders of magnitude; a much larger range in comparison to those investigated previously. [41][42][43][44][45][46][47][48][49][50][51][52][53] Dansyl was chosen as our probe molecule because an amine-selective analogue (dansyl-SO 2 Cl) is commercially available, it is reasonably fluorescent, and its emission spectrum is solvatochromic. Thus, changes in the physicochemical properties surrounding the dansyl probe are reflected in its emission spectrum.…”

Comparison of Dansylated Aminopropyl Controlled Pore Glass Solvated by Molecular and Ionic Liquids

“…The use of fluorescence to characterize silica surfaces is well-documented, especially for silica-based materials in chromatography. Specifically, fluorescence-based experiments on covalently attached [42][43][44][45][46][47][48][49][50][51][52][53][54] or physiosorbed probes [55][56][57][58][59][60][61][62][63] have been carried out to gain a better understanding of the accessibility, distribution, mobility, and orientation of surface-bound molecules (e.g., catalysts, ligands, reagents, and recognition elements).…”

Temperature Dependence of Charge-Transfer Fluorescence from Extended and U-shaped Donor−Bridge−Acceptor Systems in Glass-Forming Solvents

“…In these systems, an aniline type donor and an arylethylene acceptor are held in a rod-shaped conformation by a piperidine bridge. The extremely solvatochromic CT fluorescence of 1 and related systems has been studied in liquid solution, ,,− in polymeric matrixes, − on solid surfaces, and even in the gas phase under supersonic jet cooled conditions . Because of the very large dipole moment of the CT fluorescent state inferred from various measurements, ,, it has been assumed that the extended geometry of these molecules is maintained after charge separation and does not give way to the “crunch” of the electrostatic attraction that is known to lead to large conformational changes in more flexibly bridged systems …”