A new non-aggregating and electrochromic manganese(3 +) phthalocyanine, (acetato)[2(3),9(10),16(17),23(24)-tetrakis(4-(1-naphthoxy-4-sulfonic acid sodium salt))phthalocyaninato]manganese(3 +) [NhtMn(3 +)PcL] (where Nht and L indicate naphthoxy-4-sulfonic acid sodium salt and acetate ion, respectively), was synthesized by reaction of the metal-free phthalocyanine (NhtH(2)Pc) and manganese(2 +) acetate (Mn(OAC)(2)) in methanol. The formation of the complex was monitored by both in situ UV-Vis and fluorescence techniques based on the change of the symmetry and the quenching of the fluorescence-probe molecule as a result of the insertion of the metal into the cavity of the macrocycle. The electro-spectrochemical behavior of [NhtMn(3 +)PcL] was investigated with thin-layer UV-Vis and fluorescence spectroelectrochemical methods in DMSO solution. The electrochemical studies revealed that [NhtMn(3 +)PcL] exhibited two reversible one-electron reductions which were assigned to Mn(2 +)Pc(2-)/Mn(3 +)Pc(2-) and Mn(2 +)Pc(3-)/Mn(2 +)Pc(2-) reversible couples based on the metal and phthalocyanine ring reductions, respectively. All redox processes were accompanied with a change of color from dark green to green and purple which are clearly monitored on the surface of the light transparent platinum gauze working electrode in the thin-layer cell. In situ UV-Vis and fluorescence spectroelectrochemical methods were also applied to determine the E-1/2 (half-wave potential) and n (number of electrons) of the first reduction process, both of which confirmed the reversible one-electron [Mn(3 +)Pc(2-)L] + e [Mn(2 +)Pc(2-)L]- reduction process.