Three new trinuclear lantharide-based compounds: [Ln3(dbm)5(L)2(CH3OH)]·CH2Cl2 (LnIII = Nd(1), Sm(2), and Tb(3), dbm− = diphthaloylmethae) have been synthesized via the solvothermal method by using a polydentate Schiff base ligand (H2L = (E)-6-(hydroxymethyl)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide) reacting with Ln(dbm)3·2H2O. X-ray diffraction study reveals that all compounds 1–3 belong to monoclinic crystal system with space group C2/c, and compounds 1–3 are isostructural and possess a broken-line Ln3 core. The solid-state luminescence properties measurements indicate that compound 3 displays the characteristic lanthanide luminescence at room temperature. Moreover, photoluminescence properties study show that 1 and 2 display typical NIR luminescence of Nd(III) and Sm(III) ions at room temperature. Furthermore, biological activities research reveals that compounds 1–3 have greater antibacterial activity than the ligand H2L and Ln(dbm)3·2H2O (LnIII = Nd (1), Sm (2), and Tb (3)). The interaction between compounds 1–3 and calf thymus DNA was studied and the results revealed that the compounds were mainly intercalated with calf thymus DNA.