Self-assembly and chiroptical properties of chiral dendrimers consisting of a Hamilton receptor substituted porphyrin and depsipeptide cyanurates

The synthesis and characterisation of a new type of porphyrin-based tetrakis (Hamilton receptor) 1 is presented and the complexation of 1 with the chiral depsipeptide dendrons 7-12, with cyanuric acid functionalities as their focal points, is reported. The resulting first- to third-generation chiral supramolecular dendrimers 13-18 were characterised by NMR, UV/Vis and CD spectroscopy. Chirality transfer from the depsipeptide dendrons to the porphyrin core was demonstrated by CD spectroscopy in the case of the second- and third-generation complexes 15-18, whereas no chirality transfer and hence no diastereoselective formation of a chiral superstructure could be determined in the case of the first-generation systems. The intensities of the complexes' CD absorptions in the porphyrin region are inversely proportional to the size of the dendrons, pointing to a size-dependent cooperativity of the fourfold complexation of the dendrons with the more effective binding of the second-generation dendrons 9 and 10 relative to their bulkier third-generation counterparts 11 and 12. Pronounced cooperativity during the formation of the second-generation 1:L-4 complexes (L = 9, 10) is considered to be the reason for the diastereoselective formation of a preferred chiral conformation of the Hamilton receptor 1 in the complexes 15 and 16. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)