Trifunctional uniform nanoparticles comprising a manganese nanocrystal core and a functionalized mesoporous silica shell (MnO@mSiO(2)(Ir)@PEG, where Ir is an emissive iridium complex and PEG is polyethylene glycol) have been strategically designed and synthesized. The T(1) signal can be optimized by forming hollow core (H-MnO@mSiO(2)(Ir)@PEG) via a novel and facile etching process, for which the mechanism has been discussed in detail. Systematic investigation on correlation for longitudinal relaxation (T(1)) versus core shapes and shell silica porosity of the nanocomposites (MnO, H-MnO, MnO@SiO(2), MnO@mSiO(2), H-MnO@mSiO(2)) has been carried out. The results show that the worm-like nanochannels in the mesoporous silica shell not only increase water permeability to the interior hollow manganese oxide core for T(1) signal but also enhance photodynamic therapy (PDT) efficacy by enabling the free diffusion of oxygen. Notably, the H-MnO@mSiO(2)(Ir)@PEG nanocomposite with promising r(1) relaxivity demonstrates its versatility, in which the magnetic core provides the capability for magnetic resonance imaging, while the simultaneous red phosphorescence and singlet oxygen generation from the Ir complex are capable of providing optical imaging and inducing apoptosis, respectively.