Two new trinuclear Mn complexes containing naphthalene moieties, [Mn 3 (μ 3 -O)(μ-O 2 CCH 2 -1-naph) 6 (py) 3 ] (1) and [Mn 3 (μ 3 -O)(μ-O 2 CCH 2 -2-naph) 6 (py) 3 ] (2) (naph-1-CH 2 CO 2 H=1-naphthylacetic acid, naph-2-CH 2 CO 2 H=2-naphthylacetic acid, py=pyridine), were synthesized. The X-ray crystallography of 1, the EXAFS analyses of 1 and 2, and the magnetic susceptibility data for these complexes showed that they are trinuclear complexes containing a [Mn 3 (μ 3 -O)(μ-O 2 CR) 6 ] core with mixed-valence Mn 3 (II, III, III) centers. CVs exhibited an oxidation peak ascribed to Mn III 3 /Mn II Mn III 2 and a reduction peak ascribed to Mn II Mn III 2 /Mn II 2 Mn III in CH 2 Cl 2 . In the fluorescence spectra, the fluorescence intensities of 1 and 2 were smaller than those of the naphthylacetic acids and depended on the dielectric constant of solvent. These results suggested that there is electron transfer between the manganese centers and the naphthyl moieties. The fluorescence decays of 1 and 2 in CH 3 CN were also faster than the decays in the toluene solutions; this result parallels the lower intensity of the static fluorescence spectra in solvents with a higher dielectric constant. The fluorescence decay curves of 1 and 2 were fitted by two lifetimes, τ 1 and τ 2 , suggesting that electron transfer occurs from the monomer (τ 1 ) and the excimer (τ 2 ) of the naphthyl moieties to the manganese center.