Two double helical modes of bidipyrrin-ZnII complexes

This paper reports the formation and properties of covalently strapped double helices of bidipyrrin-Zn-II complexes, where four dipyrrin chromophores interact with one another by strong exciton coupling. Thorough experimental examination, UV/vis, CD and H-1 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 alpha-alpha bond. In fact, the changes of the modes were observed according to the lengths of straps as well as the temperatures.