Influence of supramolecular organization on energy transfer properties in chiral oligo(p-phenylene vinylene) porphyrin assemblies

A comparative study on oligo(p-phenylene vinylene) (OPV)-appended porphyrins contg. all trans-vinylene (either hydrophilic or lipophilic) or amide linkages (lipophilic) is presented. The type of supramol. arrangement obtained in org. solvents proves to be strongly dependent on the nature of the covalent connection. In the case of all trans-vinylene linkages, a J-type intermol. packing is obtained and the assemblies are only of moderate stability. Conversely, the supramol. structures obtained from the amide-linked system display an H-type stacking arrangement of enhanced stability and chirality as a consequence of intermol. hydrogen bonding along the stack direction, favorably interlocking the stacked building blocks. Interestingly, the obsd. differences in stability and organization are qual. illustrated by monitoring the sequential energy transfer process in both types of assemblies. Efficient intramol. energy transfer from the OPVs (donors) to the resp. porphyrin cores is followed by energy transfer from Zn-porphyrin (donor) to free-base porphyrin (acceptor) in both systems. However, the improved intermol. organization for the amide-linked system increases the energy transfer efficiency along the stack direction. In addn., the water-sol. (OPV)-appended porphyrin system forms highly stable assemblies in an aq. environment. Nevertheless, the poor energy transfer efficiency along the stack direction reveals a relative lack of organization in these assemblies.