Lanthanide(III) Bis(phthalocyaninato)-[60]Fullerene Dyads: Synthesis, Characterization, and Photophysical Properties

A novel series of double-decker lanthanide(III) bis(phthalocyaninato)-C-60 dyads [Ln(III)(Pc)(Pc')]-C-60 (M = Sm, Eu, Lu; Pc = phthalocyanine) (1a-c) have been synthesized from unsymmetrically functionalized heteroleptic sandwich complexes [Ln(III)(Pc)(Pc')] (Ln=Sm, Eu, Lu) 3a-c and fulleropyrrolidine carboxylic acid 2. The sandwich complexes 3a-c were obtained by means of a stepwise procedure from unsymmetrically substituted free-base phthalocyanine 5, which was first transformed into the monophthalocyaninato intermediate [Ln(III)(acac)(Pc)] and further reacted with 1,2-dicyanobenzene in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). H-1 NMR spectra of the bis(phthalocyaninato) complexes 3a-c and dyads 1a-c were obtained by adding hydrazine hydrate to solutions of the complexes in [D-7]DMF. a treatment that converts the free radical double-deckers into the protonated species, that is, [Ln(III)(Pc)(Pc')H] and [Ln(III)(Pc)(Pc')H]-C-60. The electronic absorption spectra of 3a-c and la-c in THF exhibit typical transitions of free-radical sandwich complexes. In the case of dyads 1a-c, the spectra display the absorption bands of both constituents, but no evidence of ground-state interactions could be appreciated. When the UV/Vis spectra of 3a-c and la-c were recorded in DMF, typical features of the reduced forms were observed. Cyclic voltammetry studies for 3a-c and 1a-c were performed in THE The electrochemical behavior of dyads 1a-c is almost the exact sum of the behavior of the components, namely the double-decker [Ln(III)(Pc)(Pc')] and the C-60 fullerene, thus confirming the lack of groundstate interactions between the electroactive units. Photophysical studies on dyads 1a-c indicate that only after irradiation at 387 nm, which excites both C-60 and [Ln(III)(Pc)(Pc')] components, a photoinduced electron transfer from the [Ln(III)(Pc)(Pc')] to C-60 occurs.