Reported here is a successful strategy for the design of ultrabright red luminogens with aggregation-induced emission (AIE) features, donor-acceptor structures, and intense charge transfer effects. These luminogens show no aggregation caused emission quenching in the solid state and have high quantum efficiency. They can be fabricated into AIE dots by a simple nanoprecipitation procedure. The AIE dots exhibit high brightness, a large Stokes shift, good biocompatibility, satisfactory photostability, and a high two-photon absorption cross section. The AIE dots can be utilized as highly efficient fluorescent probes for in vivo deep-tissue imaging by a two-photon technique, which outperforms the one-photon technique under the same experimental conditions, in terms of penetration depth and image contrast. This is the first report of using highly emissive AIE dots for the accurate measurement of capillary diameters in mouse ears. Such a strategy sheds light on the development of efficient solid state red/NIR emitters for biological applications.