Electrochemical test of flexibility of pyridine terminated molecular rods

A family of seven symmetrical molecular rods, which are sharing 4-ethynylpyridyl terminal groups and differ in the structure of the linker have been investigated. Although structurally related they show unique electrochemical behavior, which clearly correlates with their conformational flexibility. Two flexible compounds are reduced by two electrons. Their reduction yields intensive charge transfer UV-vis absorption bands and is accompanied by characteristic EPR spectra. In contrast, all conformationally rigid structures are reduced by four electrons and do not yield neither charge transfer bands nor distinct EPR signals. Simple irreversible voltammetry of all derivatives is similar to the reduction of 4-ethynylpyridine at -2.1 V. The experimental observations were supported by the extensive DFT calculations. Electrochemical techniques proved to be valuable in distinction between molecular rigidity and flexibility. [Display omitted]