Organic nanocrystals grown in sol-gel matrices: new hybrid organic-inorganic materials for optics

Abstract

We have developed a simple and generic preparation of stable organic nanocrystals grown in gel-glass matrices. The synthesis of these hybrid organic-inorganic materials is based on the confined nucleation and growth of organic phases in the pores of dense gels. For bulk nanocomposite samples, narrow size distributions of particles (10-20 nm in diameter) are obtained. We have extended this method to the preparation of organic nanocrystals embedded in sol-gel thin films prepared by spin-coating. For all these nanocomposite materials, we have significantly increased the dye stability and obtained promising optical properties: luminescence, non-linear optical properties or photochromism. Moreover, we have also demonstrated basic working principles of a new type of fluorescent nanosensor through the preparation of organic luminescent nanocrystals grown in silicate films.

New core–shell hybrid nanoparticles for biophotonics: fluorescent organic nanocrystals confined in organosilicate spheres

“…To produce linear silicate chains, weakly interconnected, the alkoxides were hydrolyzed under acid-catalyzed conditions (pH z 1, HCl) associated with the hydrolysis molar ratio h ¼ 1. On the other hand, based on previous works related to organic nanocrystals grown in sol-gel thin films, 36,[44][45][46][47][48] we used high solvent amounts: 50 # s # 500. These high amounts of solvent led to a better control of the hydrolysis and polycondensation reactions of the silicon alkoxides and to nanometre-sized particles after the solvent evaporation.…”

“…On the other hand, as ethylenyl is a bridging group between two trialkoxysilyl functions, the hydrophobic character of the resulting surface may be decreased, compared to the methyl groups of MTMOS. 36,46,47 With equimolar 0.5 TMOS + 0.5 TMSE mixtures (S 0.5TMSE ), the CMONS dye appeared correctly embedded (Fig. 3c) in the resulting NPs.…”

“…This equimolar mixture of TMOS + MTMOS was chosen on the basis of previously optimized conditions of the confined nucleation and growth of organic nanocrystals in sol-gel thin films. 36,46,47 Involving this sol, three main physical parameters of the spray-drying process were first optimized: the drying temperature in the horizontal furnace (Scheme 2-( 4)), the N 2 pressure involved in the sol atomization (Scheme 2-( 2)) and the flow of vector gas (Scheme 2-(3)). The N 2 pressure and gas vector flow were initially fixed respectively at 2 bars and 2 L min À1 , referring to previous spraydrying works done with similar equipment.…”

“…This phenomenon can strongly disturb the formation of the silicate crust at the initial step of the droplet drying and the following confined nucleation and growth of CMONS nanocrystals (Scheme 1) as previously observed for the confined growths of molecular nanocrystals in different sol-gel matrices, bulk and thin films. 36,[44][45][46][47][48] Thus, S xMTMOS compositions were tested to decrease the dye-silicate interactions. In this case, MTMOS was added to TMOS, to screen the dye-silicate hydrogen bondings by the non-bridging methyl groups coming from this alkoxide.…”

Hybrid materials for optics and photonics

“…Optical properties such as luminescence, nonlinear optical properties and photochromism have been observed. 11,12 Another interesting approach has been developed by the group of D. Levy and consists in the dispersion of liquid crystal droplets within a sol-gel matrix 13 for electro-optical applications.…”