Porphyrin Assemblies and Their Scaffolds

Abstract

The chlorophyll and heme molecules of chloroplasts and mitochondria are brought to life by "the global fold of the protein scaffolds". Proteins in hydrophobic cell regions touch the dye platelets from both sides, pushing and orienting them according to their life-spending activities in light and electron transfers. The conjugated π-electron systems or planarity of the porphyrin macrocycles are never disturbed. Most artificial porphyrin assemblies contain meso-tetraphenylporphyrins (TPPs), because the four phenyl groups rotate freely and carry their substituents above or below the macrocycle. A single porphyrin molecule can, for example, be attached to an anionic surface with ammonium groups on its 2,3-carbons, be located within a hydrophobic membrane with its alkyl chains on the 4-position, and then fixate a cationic polymer with 4,5-sulphonates. Charged TPPs also show unique spectroscopic changes at different pH values and a reversible loss of the macrocycle's planarity. On smooth silicate, graphite, or gold scaffolds TPPs have been attached irreversibly as single molecules, as extended non-covalent H or J aggregates as well as acetylene or thiophene-linked polymers. Soft, mobile porphyrin ladders conduct excited electrons ("excitons") better than rigid porphyrin wires ("polarons").

Surface chemistry of porphyrins and phthalocyanines

“…In some cases, electronic decoupling from the (metal) substrate was desired, for example to avoid quenching of excited states by substrate influences in the context of photochemistry. Covalent tethering with suffiently long anchor/spacer groups or scaffolds [454] or the perpendicular mounting of the porphyrins on triphenylmethane-type platforms [439,455] have been proposed for this and related purposes.…”

Bottom-Up Hierarchical Self-Assembly of Chiral Porphyrins through Coordination and Hydrogen Bonds

“…24,25 The coordination of zinc porphyrins with axial nitrogen derivative ligands, such as imidazolyl or pyridyl groups afford the formation of well-organized macromolecules in the form of cyclic structures, [26][27][28][29] or linear polymers 30,31 and oligomers. [32][33][34] The coordination between zinc(II) and pyridyl ligands has a relatively large association constant (~10 3 M -1 ) 35,36 and usually does not disturb the photoexcited state of the metalloporphyrin. 37,38 Zinc (II) porphyrins have a strong tendency to form pentacoordinate aggregates with a square pyramidal geometry, although the hexacoordination of this class of metalloporphyrins have also been reported in solid state structures.…”

Tautomerism and Atropisomerism in Free‐Base (meso)‐Strapped Porphyrins: Static and Dynamic Aspects

“…Besides their exceptional optical, photophysical and electrochemical properties extensively exploited for decades in donor-acceptor systems [1] and molecular photovoltaics, [2][3][4] porphyrins (Pors) have also proved to be extraordinary supramolecular scaffolds in the design of sophisticated 1D-, 2D-and 3D-dimensional architectures, [5][6][7][8][9] covalently or self-assembled, [10][11][12][13][14] including chiral materials [15][16][17] or sensors, [18] molecular cages, [19][20][21][22][23] turnstiles, [24] tweezers [25,26] and dendrimer cores. [9] Since the first reported example in 1969, [27] atropisomerism in porphyrins has been a concept widely exploited in these kinds of architectures (and, in particular, in tetra-meso-arylporphyrins).…”