Functional Nanoassemblies with Mirror-Image Chiroptical Properties Templated by a Single Homochiral DNA Strand

For the supramolecular chemistry of self-assembly systems, a major goal is to achieve the level of control of the assembly process equal to the capabilities of classical asymmetric organic synthesis, such as high stereospecificity, regiospecificity, and reproducibility. Herein we report the stereoselective porphyrin-driven formation of left- and right-handed, chiral functional supramolecular nanoassemblies with mirror image chiroptical properties templated by a single homochiral ssDNA by changing the cooling rate, DMSO, and salt concentration. Upon dialysis and annealing that caused the porphyrin units to relax into their preferred slipped cofacial stacking geometry, the nanoassemblies displayed near ideal mirror-image chiroptical properties, as well as unusually high thermal and acid-base structural stability. ssDNA-porphyrin nanoassemblies preserved their photocatalytic activity in the visible spectral range as demonstrated by iodide oxidation. ssDNA-porphyrin nanoassemblies formed higher order fluorescent nano- and microstructures as evidenced by TEM and confocal microscopy. We propose a plausible mechanism for the formation of nanoassemblies and induction of helicity based on our molecular dynamics (MD) simulations, time-dependent density functional theory (TD DFT) computations, and experimental spectroscopic data. We suggest that the ssDNA templates interact with preformed achiral porphyrin columnar nanostacks. These results provide further insight into the stereoselective synthesis of chiroptical nanostructures and control of supramolecular helicity.