Photoinitiated charge transport in supramolecular assemblies of a 1,7,N,N′-tetrakis(zinc porphyrin)-perylene-3,4:9,10-bis(dicarboximide)

We report the synthesis and photophysical characterization of a multichromophore array, (Z3PN)₄PDI, consisting of four zinc 5-phenyl-10,15,20-tri(n-pentyl)porphyrins (Z3PN) attached to the 1,7,N,N′-positions of perylene-3,4:9,10-bis(dicarboximide) (PDI). The dynamics of energy and charge transport within this system were compared to those of two model compounds, N,N′-(Z3PN)₂PDI and 1,7-(Z3PN)₂PDI. The symmetry of the lowest unoccupied and highest occupied molecular orbitale of PDI results in significantly different electronic couplings between Z3PN and PDI when they are connected at the 1,7-positions vs the N,N′-positions of PDI. This results in two distinct pathways for electron transfer in (Z3PN)₄PDI. Using a combination of metal-ligand binding with the bidentate ligand 1,4-diazabicyclo[2.2.2.]-octane (DABCO) and π-π stacking, (Z3PN₄)PDI forms a supramolecular assembly, [[(Z3PN)₄PDI]₂-DABCO₄]₂, in toluene solution. The structure of this hierarchical assembly is characterized with the use of solution-phase X-ray scattering techniques and demonstrates both efficient light harvesting and facile charge separation and transport using multiple pathways.