Through-space electronic communication of zinc phthalocyanine with substituted [60]Fullerene bearing O2Nxaza-crown macrocyclic ligands

• Two new O2N3-donor aza-crowns anchored to [60]Fullerene were synthesized.
• The steady-state and time resolved fluorescence quenching properties of L1–L4 were studied.
• The correlated decrease in both F0/F and τ0/τ suggested a static quenching for L1–L3/ZnPc.
• The quenching was attributed to involvement of a static π–π* charge transfer process.
• DFT calculations showed the relation between structural features and the observed KSV values.

Two new macrocyclic ligands containing 17- and 19-membered O2N3-donor aza-crowns anchored to [60]Fullerene were synthesized and characterized by employing HPLC, electrospray ionization mass (ESI-MS), 1H and 13C NMR, UV–vis, IR spectroscopies, as well as powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) in solid state. TGA measurements revealed that upon linking each of these macrocycle rings to [60]Fullerene, the decomposition point measured for [60]Fullerene moiety was increased, indicating on the promoted stability of [60]Fullerene backbone during binding to these macrocyclic ligands. Moreover, the ground state non-covalent interactions of [60]Fullerene derivatives of O2Nx (x = 2, and 3) aza-crown macrocyclic ligands namely, L1–L4 with zinc phthalocyanine (ZnPc) were also investigated by UV–vis absorption, steady state and time resolved fluorescence spectrophotometry in N-methyl-2-pyrrolidone (NMP). The calculation of Stern-Volmer constants (KSV) indicated on existence of an efficient quenching mechanism comprising of the excited singlet state of ZnPc in the presence of L1–L4. The observation of an appropriate correlation between decrease in fluorescence intensity and lifetime parameters led us to propose the occurrence of a static mechanism for the fluorescence quenching of ZnPc in the presence of L1–L3. The binding constants (KBH) of L1–L4/ZnPc were also determined applying the fluorescence quenching experiments. Meanwhile, the incompatibility of both KSV and KBH values found for L4 was also described in terms of structural features using DFT calculations using the B3LYP functional and 6-31G* basis set.

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