Novel acridone-modified MCM-41 type silica: Synthesis, characterization and fluorescence tuning

Abstract

A Mobil Composition of Matter (MCM)-41 type mesoporous silica material containing N-propylacridone groups has been successfully prepared by co-condensation of an appropriate organic precursor with tetraethyl orthosilicate (TEOS) under alkaline sol-gel conditions. The resulting material was fully characterized by means of X-ray diffraction (XRD), N(2)-adsorption-desorption, transmission electron microscopy (TEM), IR and UV-vis spectroscopy, as well as (29)Si and (13)C CP-MAS NMR techniques. The material features a high inner surface area and a highly ordered two-dimensional hexagonal pore structure. The fluorescence properties of the organic chromophore can be tuned via complexation of its carbonyl group with scandium triflate, which makes the material a good candidate for solid state sensors and optics. The successful synthesis of highly ordered MCM materials through co-condensation was found to be dependent on the chemical interaction of the different precursors.

Keywords: MCM-41; acridone; co-condensation; fluorescence; scandium.

Scheme 1

Synthesis of the sol–gel precursor 1.

Figure 1

Infrared spectra of compound 1 (A), MCM-ACR (B) and MCM-ACR + Sc(OTf)₃ (C). The box marks the section given in Figure 2 (resolution ±2 cm⁻¹).

Figure 2

C=O vibrational band section of the infrared spectra of compound 1 (A), MCM-ACR (B) and MCM-ACR + Sc(OTf)₃ (C).

Figure 3

TEM images showing the mesoporous structure of MCM-ACR (left: frontal, right: lateral), inset in left image: Electron diffraction pattern.

Figure 4

Sorption isotherm (left) and pore size distribution (BJH plot) (right) of MCM-ACR.

Figure 5

XRD pattern of MCM-ACR.

Figure 6

¹³C CP-MAS NMR spectrum of MCM-ACR overlaid with the high resolution ¹³C NMR spectrum of precursor 1 (recorded in CDCl₃).

Figure 7

²⁹Si CP-MAS NMR spectrum of MCM-ACR.

Figure 8

Visual appearance of MCM-ACR and MCM-ACR + Sc(OTf)₃ under normal (a) and UV light (b).

Figure 9

Overlay of the solid state UV-vis (top) and fluorescence (bottom) spectra of MCM-ACR, MCM-ACR + Sc(OTf)₃ and pure Sc(OTf)₃ (fluorescence excitation wavelength λ_ex. = 400 nm). UV–vis-absorption intensities are not normalized to a given value; fluorescence has been normalized to an intensity of 1.0. Sc(OTf)₃ shows no significant fluorescence and therefore was omitted in the second diagram.