Molecular Organization Induced Anisotropic Properties of Perylene - Silica Hybrid Nanoparticles

Abstract

Optically active silica nanoparticles are interesting owing to high stability and easy accessibility. Unlike previous reports on dye loaded silica particles, here we address an important question on how optical properties are dependent on the aggregation-induced segregation of perylene molecules inside and outside the silica nanoparticles. Three differentially functionalized fluorescent perylene - silica hybrid nanoparticles are prepared from appropriate ratios of perylene derivatives and tetraethyl orthosilicate (TEOS) and investigated the structure property correlation (P-ST, P-NP and P-SF). The particles differ from each other on the distribution, organization and intermolecular interaction of perylene inside or outside the silica matrix. Structure and morphology of all hybrid nanoparticles were characterized using a range of techniques such as electron microscope, optical spectroscopic measurements and thermal analysis. The organizations of perylene in three different silica nanoparticles were explored using steady-state fluorescence, fluorescence anisotropy, lifetime measurements and solid state polarized spectroscopic studies. The interactions and changes in optical properties of the silica nanoparticles in presence of different amines were tested and quantified both in solution and in vapor phase using fluorescence quenching studies. The synthesized materials can be regenerated after washing with water and reused for sensing of amines.

Figure 1

Three models of perylene incorporated silica nanoparticles with different organization of perylene molecules and the molecular structure of perylene silanes used for the synthesis.

Figure 2

SEM morphologies of P-ST (a), P-NP (b) and P-SF (c). Polymerization of PDI-1 (d) to form perylene rich region and silica region. FTIR spectra (e) of unmodified silica NPs, P-ST1, P-ST2, P-SF and P-NP. TGA traces (f) of P-ST1 (■), P-ST2 (), P-SF (), and P-NP () particles in air.

Figure 3

Absorbance (a,c) and emission spectra (b,d) of (■) PDI silane monomer, P-ST1(), P-ST2(), P-SF () dispersed in THF and P-NP () dispersed in water. Excitation wavelength was 350 nm.

Figure 4

Fluorescence anisotropy (r) of PDI molecule, P-SF, P-ST1, P-ST2 nanoparticles dispersed in THF and P-NP nanoparticles in water.

Figure 5

Polarized UV/Vis absorption spectra of perylene silica nanoparticles (a) P-ST2, (b) P-SF and (c) P-NP with the samples set parallel (||, ■) and perpendicular (⊥, ) to the polarizer.

Figure 6

Percentage quenching efficiency of P-ST2, P-SF and P-NP nanoparticles in sensing (a) butylamine, diisopropylamine, triethylamine, aniline and biogenic amines such as phenylethylamine, diaminopropane and diethylenetriamine in solution. (b) P-SF nanoparticles sensing biogenic amines both in solution (~1 mins) and vapor phase (24 hr). (c) Reusability of P-ST2 particles for sensing amines in THF solution. Excitation wavelength was 350 nm.

Figure 7

Schematic representation of solid state absorption anisotropy setup.