No abstract

'Axial-bonding'-type hetero trimers have been constructed by employing a simple 'inorganic' reaction such as axial bond formation of main group element containing phosphorus corrole. The approach is simple and modular in nature. The architecture of these hetero trimers such that, while a phosphorus(V)corrole forms the basal scaffolding unit, either two free-base porphyrins [(H 2 ) 2 -PCor] or Zn(II) porphyrins [(Zn) 2 -PCor] occupy the two axial sites via an aryloxy bridge. Both hetero trimeric species have been completely characterized by mass (FAB), UV/Vis, proton nuclear magnetic resonance spectroscopies and also by the differential pulse voltammetric method. Comparison of their spectroscopic and electrochemical data of these trimers with those of the corresponding reference compounds reveal that there is no apparent ring-to-ring interactions in these 'vertically' linked hetero trimers. Reduced fluorescence quantum yields were observed for [(H 2 ) 2 -PCor] and [(Zn) 2 -PCor] when compared to corresponding monomeric chromophores. Finally, a comparison is made between the presently reported phosphorus(V)corrole based hetero arrays and the previously reported analogous arrays based on Ge(IV)corrole with regard to their spectroscopic properties and photochemical activities.

Two new nonconjugated porphyrin-coumarin dyads with different orientations with respect to donor-acceptor entities and their zinc complexes were synthesized. Single-crystal structures of the free-base porphyrin-coumarin dyads were successfully resolved. The absorption spectra of the dyads were linear combinations of the spectra of their corresponding monomers, indicating a negligible electronic communication between the coumarin and porphyrin moieties. However, the fluorescence emission of the coumarin entity in all of the dyads was quenched significantly compared to that of pristine coumarin, and this effect was attributed to intramolecular energy transfer from the coumarin to the porphyrin. The energy transfer kinetics from the coumarin to the porphyrin was shown to be fast ( k = 1.13 × 10 s for the ortho-isomer and 5.13 × 10 s for the para-isomer in DMF) and efficient (transfer efficiency ca. 96-97%). Transient absorption studies showed that the excited state decay process (S → S*, S* → S, S → S, and S → T) of the para-isomer was faster than that of the ortho-isomer in DMF. All of the synthesized dyads were tested for their interactions with ct-DNA and photocleavage activity toward PBR322-DNA. The results revealed that all of the dyads interacted with ct-DNA via only an external groove-binding mode; the binding constants were calculated to be 3.24 × 10 (3a), 3.05 × 10 (3b), 3.04 × 10 (4a), and 4.88 × 10 (4b), and the photocleavage activity was in the order 4b < 3b < 4a < 3a. Furthermore, only the zinc complexes of the porphyrin-coumarin dyads could be absorbed by tumor cells (A549). These complexes were mainly localized in the cytoplasm, exhibited red fluorescence, and showed low cytotoxicity toward all of the tumor cell lines tested. The results showed that these zinc complexes of the porphyrin-coumarin dyads have potential applications in fluorescence imaging.

No abstract

No abstract