Supramolecular architecture of tetrathiafulvalene-bridged bis(β-cyclodextrin) with porphyrin and its electron transfer behaviors

Abstract

A bridged bis(β-cyclodextrin) 3 with a tetrathiafulvalene (TTF) linker was synthesized by an electrophilic reaction of mono-6-deoxy-6-iodo-β-cyclodextrin 1 with 6,7-bis(methylsulfanyl)-2,3- bis(2-cycanoethylsulfanyl)tetrathiafulvalene 2 under the alkaline condition. Benefiting from the good solubilizing ability of the β-cyclodextrin unit, the solubility limit of 3 in water could reach 1.0 × 10⁻³ M, i.e. 0.4 mg mL⁻¹ calculated as TTF residue. The conformational changes during the inclusion complexation process of 3 with 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin 4 were investigated by UV/Vis and 2D NMR spectroscopy. Significantly, the photo-induced electron transfer (PET) process between the TTF moiety in 3 and the porphyrin unit in 4 would take place within the 3/4 supramolecular complex under the light irradiation, leading to the highly efficient quenching of the fluorescence of 4, and could then be recovered by the formation of TTF cations in the presence of H₂O₂. Furthermore, taking advantage of the high affinity between 3 and 4, the linear nanoarchitectures were achieved and comprehensively characterized by using transmission electron microscopy (TEM) and atomic force microscopy (AFM). These observations indicated that the strong complexation was a crucial and basic factor to achieve the PET process in the non-covalently constructed assemblies.