Smartly designed photoreactive silica nanoparticles and their reactivity

Monodisperse, colloidal silica nanoparticles (NPs) are being widely investigated due to a variety of applications in various fields of chemistry. Many works utilize incorporation of various functional groups to silica NPs for their further modifications. However, at present no benzophenone (BPh) or phenyl azide (PA) containing silica NPs exist. Upon UV irradiation BPh and PA form highly reactive species that react with any organic material. Here we present a convenient method for the preparation of novel hybrid photoreactive silica NPs (denoted as SiO₂@photoreactive group) prepared by co-condensation of photoreactive organosilanes and tetraethyl orthosilicate (TEOS) to obtain SiO₂@PA and SiO₂@BPh NPs. The reactivity of these two types of silica NPs is compared to that of perfluorinated phenyl azide (PFPA) based SiO₂ NPs. The reactivity evaluation is carried out by the reaction of the three types of SiO₂ NPs with highly inert poly(2-chloro-paraxylelene) films. It is found that, in contrast to what is stated in the literature, PA is much more reactive than PFPA, when dealing with solid state photochemical reactions. Next, photoreactive silica NPs on polymer films are used as an intermediate functional phase for a second modification step using silane-based chemistry. A successful incorporation of amine functionality onto silica NPs is achieved by their reaction with 3-aminopropyltriethoxysilane (APTES) and is verified by fluorescence microscopy. This strategy provides a general and versatile route to efficient functionalization of silica by light.