Self-assembly of a new class of rhenium(I)-based double stranded dinuclear monohelicates with their photophysical and electrochemical studies.

A new class of double stranded dinuclear monohelicates, -[{Re(CO)-(μ-L)-Re(CO)}L] (1-4), were self-assembled from Re(CO), a rigid bischelating donor (H-L: 1,4-dihydroxybenzoquinone (H-dhbq) for 1 and 3; 2,5-pyrazine dicarboxylic acid (H-pydc) for 2 and 4) and a flexible bis(monodentate) pyrazolyl N donor L (L = bis(4-((pyrazolyl)methyl)phenyl)methane for 1 and 2; L = bis(4-((pyrazolyl)methyl)phenyl)methanone for 3 and 4) in mesitylene. Metallomacrocycle 1 was confirmed by single crystal X-ray crystallography. Although these helicates contain two organic ligand strands, only one strand is arranged in a helical fashion, which is an unprecedented form in the helicate architecture. The molecular structures of 1-4 as helicates and mesocates were optimized using DFT methods. The dynamic interconversion of the metallomacrocycles in solution was studied by H NMR studies. The photophysical properties of 1-4 were studied experimentally and the nature of electronic transitions was determined by TD-DFT analysis. Quinonoid motif-based complexes 1 and 3 displayed strong visible light absorption. The redox properties of 1-4 were studied using cyclic voltammetry.