Organic nanodots for multiphotonics: synthesis and photophysical studies

Organic nanodots based on the gathering of an exponentially increasing number of two-photon fluorophores on a dendritic platform of controlled size and symmetry represent a promising nontoxic alternative to quantum dots for (bio)imaging purposes. This modular route offers a number of advantages in terms of versatility but also raise a number of questions to be addressed. In particular, possible interactions between fluorophores, due to confinement effects, have to be taken into account. With this aim in mind we have investigated and compared the photophysical and two-photon absorption (TPA) properties of two series of organic nanodots of different geometries: spherical-like organic nanodots derived from a dendritic scaffold built from a cyclotriphosphazene core and dumbbell-like organic nanodots derived from a dendritic scaffold built from an elongated rod-like chromophore. The study provides evidence that the different topology and nature of the dendritic architecture lead to significant changes in photoluminescence characteristics as well as to subtle variations of the TPA efficiency. As a result, the dumbbell-like nanodots although less promising in terms of two-photon induced fluorescence (due to partial quenching of fluorescence efficiency) also demonstrate that improvement of the TPA efficiency can be achieved by playing on the nature and topology of the dendritic scaffold of the nanodots.