In this paper we show how to easily obtain multicomponent fluorescent organic nanoparticles displaying an excitation energy-transfer cascade between the different molecular components. The use of an optically neutral polymer as dopant helps to increase the colloidal stability of the water suspensions and to slow down luminescence loss over time. In particular, core@shell@shell ternary nanoparticles are designed and investigated, providing a strongly increased luminescence in the red spectral region. The two-photon brightness of the ternary nanoparticles is greatly enhanced with respect to that of the single-component nanoparticles. In addition, these ternary nanoparticles can be two-photon excited over a broad spectral range (from 600 to 1200 nm) inside the biological transparency window. This property, together with the good colloidal stability in water suspension, suggests these fully organic multicomponent nanosystems to be very promising nanoprobes for bioimaging applications.
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