the systems described so far require UV-Vis light which limits their applications. Two-Photon Excitation (TPE) in the near-infrared region is a promising alternative to UV-vis light due to the many advantages TPE provides such as three dimensional spatial resolution, lower scattering losses, and deeper penetration in tissues.[ 16 ] Very few TPE-triggered MSN-based drug delivery systems have been described in the literature, [ 17,18 ] and only two very recent examples were reported with cytotoxic drug delivery in cancer cells. The fi rst example is based on coumarin cleavage and needed very high material concentration (1 mg mL −1 ) in cells and long time of irradiation (1 h) to observe a cancer cell killing effect.[ 19 ] The second was described by us and concerned nanoimpellers reconfi gured for TPE.[ 20 ] The system was effi cient in inducing cancer cell death under TPE. In this communication, we report an alternative MSN-azobenzene-based system with a high specifi c surface area and pore volume for TPE-triggered drug delivery in cancer cells. Furthermore, two-photon fl uorescence imaging in vitro was also performed (see Scheme 1 ). First of all, a novel two-photon paracyclophane-based fl uorophore (CF) possessing a high two-photon absorption cross-section was designed and fully characterized. (see the Supporting Information). The maximum emission of the fl uorophore was 415 nm in THF, with a quantum yield of 68% suitable for FRET with azobenzene ( Figure 1 ).The silylated fl uorophore (CF) was co-condensed with tetraethoxysilane (TEOS) and cetyltrimethylammonium bromide (CTAB) in basic media to lead to the two-photon fl uorescent MSN (MCF NPs). Mono-triethoxysilylated azobenzene was then grafted on the surface of the nanoparticles (MCF-AZO NPs). Then, the cargo was loaded in the pores of the MCF-AZO NPs. The supramolecular complexation of β-cyclodextrin was performed in ice-cooled conditions, in order to cap the porous surface to lead to the nanovalve (MCF-AZO@βCD NPs). As a control MCM-41 type MSN NPs were functionalized with azobenzene (MSN-AZO NPs) and β-cyclodextrin MSN-AZO@βCD NPs using the same procedure.The characterizations of the MCF NPs after surfactant removal confi rmed the monodispersity and mesoporosity of Drug Delivery

Porous silicon nanoparticles (pSiNPs) act as a sensitizer for the 2-photon excitation of a pendant porphyrin using NIR laser light, for imaging and photodynamic therapy. Mannose-functionalized pSiNPs can be vectorized to MCF-7 human breast cancer cells through a mannose receptor-mediated endocytosis mechanism to provide a 3-fold enhancement of the 2-photon PDT effect.