Two double helical modes of bidipyrrin–ZnII complexes

This paper reports the formation and properties of covalently strapped double helices of bidipyrrin–ZnII complexes, where four dipyrrin chromophores interact with one another by strong exciton coupling. Thorough experimental examination, UV/vis, CD and 1H NMR spectra, and theoretical studies suggest the existence of two modes of the double helix depending on the dihedral angles between two of the dipyrrin units at the pyrrole α–α bond. In fact, the changes of the modes were observed according to the lengths of straps as well as the temperatures.