Optically active mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complexes. Synthesis, spectroscopy, and effective chiral information transfer

With the view to creating novel sandwich-type tetrapyrrole rare earth complexes toward potential applications in material science and chiral catalysis, two new optically active mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complexes with both (R)-and (S)-enantiomers [M ₂(Pc)₂(TCBP)] {TCBP = Meso-tetrakis [3,4-(11,12:13, 14-di(1′,2′-naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11, 13-triene)-phenyl] porphyrinate; M = Eu (1), Y (2)} have been designed and prepared by treating optically active metal free porphyrin (R)-/(S)-H ₂TCBP with M(Pc)₂ in the presence of corresponding M(acac)₃ · nH₂O (acac = acetylacetonate) in refluxing 1,2,4-trichlorobenzene (TCB). These novel mixed ring rare earth triple-decker compounds were characterized by a wide range of spectroscopic methods including MS, ¹H NMR, IR, electronic absorption, and magnetic circular-dichroism (MCD) spectroscopic measurements in addition to elemental analysis. Perfect mirror image relationship was observed in the Soret and Q absorption regions in the circular-dichroism (CD) spectra of the (R)-and (S)-enantiomers, indicating the optically active nature of these two mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complexes. This result reveals the effective chiral information transfer from the peripheral chiral binaphthyl units to the porphyrin and phthalocyanine chromophores in the triple-decker molecule because of the intense π-π interaction between porphyrin and phthalocyanine rings. In addition, their electrochemical properties have also been investigated by cyclic voltammetry (CV).