Aggregation induced enhanced emission of conjugated dendrimers with a large intrinsic two-photon absorption cross-section

Organic nonlinear optical materials combining high luminescence quantum yields and large two-photon absorption cross-sections are attractive for both fundamental research and practical applications, such as up-converted lasers and two-photon fluorescence microscopy. Herein, we reported a series of conjugated dendrimers (AnG0, AnG1, and AnG2) which showed weak emissions in dilute solution due to the twisted intramolecular charge transfer (TICT) and free intramolecular rotational motion. On the contrary, high luminescence quantum yields (up to 0.85) have been observed in the nanoaggregated and solid-state because of the restriction of intramolecular rotation (RIR) and the more planar conformation, which has been demonstrated by experimental and theoretical investigations. These dendrimers possess an obviously large intrinsic two-photon absorption cross-section (up to 5180 GM), which is enhanced with the increase of the generation number. Due to the high solid-state luminescence quantum yields, an intense two-photon excited fluorescence with a larger Stokes shift can be obtained from these dendrimers as nanoaggregates and thin films. Thus, these dendrimers successfully provide large two-photon action cross-sections in the nanoaggregated or solid-state and have the potential for nonlinear optical applications.