Energy Migration in a Self‐Assembled Nonameric Porphyrinic Molecular Box

Abstract

We describe the construction of self-assembled double-decker porphyrin arrays built up from two covalently connected trimeric Zn-porphyrin units that are joined together by metal-coordination bonds with diamine ligands. We used three different types of diamine ligands: 1,4-diaza[2.2.2]bicyclooctane (DABCO), 4,4'-bipyridine (BIPY), and 5,15-bis(4-pyridyl)-10,20-diphenylporphyrin (DPYP). The ligands act as pillars, through two axial coordination bonds with the porphyrinic Zn(II) ions, to block the planes of the porphyrin units in an almost cofacial orientation and inducing the formation of a trigonal prismatic structure. The spectroscopic and photophysical properties of the Zn-trisporphyrin component were determined as well as those of the resulting multimolecular cagelike assemblies. The double-decker assembly with DPYP as the pillars constitutes a nonameric porphyrin aggregate. Although this assembly is thermodynamically less stable than those containing DABCO or BIPY, efficient photoinduced energy transfer occurs (96% yield) from the trisporphyrin base units to the DPYP side walls. The rate of the energy-transfer process is in good agreement with that calculated for a dipole-dipole (Förster) mechanism corrected for the unfavorable orientation geometry of the donor and the axially bound acceptor.

Supramolecular Coordination: Self-Assembly of Finite Two- and Three-Dimensional Ensembles

“…These ligands act as pillars via two axial coordination bonds with the porphyrinic Zn(II) ions, locking the planes of the porphyrin units in an almost cofacial orientation. 514,515 For example, treatment of Zn(II)-trisporphyrin ( 458 ) with DABCO in a 2:3 ratio led to the formation coordination cage ( 459 ; Scheme 120). Measurement of stability constants using UV-vis and 1 H NMR spectroscopic studies revealed that in presence of an excess of the ditopic N-donor ligand, these coordinations cages fall apart to give open species.…”

“…Photophysical studies on self-assembled Zn(II)-trisporphyrin prisms having 1,4-diazabicyclo[2.2.2]octane (DABCO), 4,4′-bipyridine and 5,15-(4-pyridyl)-10,20-phenyl-porphyrin (4′- trans -DPyP) as pillars have shown efficient photoinduced energy transfer from the triporphyrin unit to the pillars upon excitation of both components within the assemblies. 515 Luminescence experiments showed that when 4′- trans -DPyP was used as a pillar, a highly efficient photoinduced electron transfer (96% efficiency) from the trisporphyrin units to the 4′- trans -DPyP pillars occurred. The analogous trigonal prisms having ditopic N-donor ligands based on perylene tetracarboxylic acid bisimide also showed efficient photoinduced electron transfer from the Zn porphyrin units to the axially coordinated bisimide pillars, occuring from the singlet excited states localized on both chromophores.…”

Investigation of the biological and anti-cancer properties of ellagic acid-encapsulated nano-sized metalla-cages

“…Since the past decade, there has been an increasing amount of interest in the design and synthesis of discrete 3D metallo-supramolecular architectures, as well as in their potential applications ranging from host-guest chemistry, 1,2 catalysis, [3][4][5][6] and light harvesting [7][8][9] to biology. [10][11][12][13][14][15][16][17][18][19] Three-dimensional cages, engineered via coordinationdriven self-assembly paradigms, have distinct advantages over conventional covalentcontainer molecules, owing to the synthetic ease with which the coordination cages can be assembled, the availability of a large library of building blocks, and the ability to design selective guest encapsulations.…”

Energy Transfer Followed by Electron Transfer in a Porphyrin Macrocycle and Central Acceptor Ligand: A Model for a Photosynthetic Composite of the Light‐Harvesting Complex and Reaction Center

“…A number of researchers have attempted to construct various synthetic models of LH, [6][7][8] RC, [9,10] and their combined architectures [11] by using porphyrins. Although covalently linked cyclic porphyrin arrays accommodating an energy acceptor by multipoint coordination bonds have been constructed, [11a,c,e] a synthetic model performing energy transfer from the cyclic porphyrin arrays to the reaction center followed by charge separation, to the best of our knowledge, has not been reported so far.…”