Aggregation of Tetraaryl-Substituted Porphyrins in Homogeneous Solution

Abstract

Electronic absorption, fluorescence and fluorescence excitation spectra, and vibrational Raman spectra of selected homogeneous solution phase, free-base tetraaryl-substituted porphyrinsspecifically, tetraphenylporphine (TPPH2), tetra(p-pyridyl)porphine (TPyPH2), tetra(p-N-methylpyridyl)porphine (TMPyPH2), tetra(p-carboxylphenyl)porphine (TCPPH2), and tetra(p-sulfonatophenyl)porphine (TSPPH2)as well as their protonated diacids are acquired and analyzed. N-protonation induces a structural change in which the free-base porphyrin is converted from a configuration in which the aryl moiety is twisted relative to the macrocycle plane to one in which it is nearly coplanar, thus promoting aggregation. However, spectroscopic investigations of the tetraaryl-substituted porphyrins reveal that coplanarity, although necessary, is insufficient for aggregation to occur. Also required is that the doubly protonated porphyrin have a net zero charge, i.e., be zwitterionic. The structural alignments of monomers in tetraaryl-substituted porphine aggregates are suggested to be similar to those of J-aggregates of cyanine dyes.

meso-Aryl-substituted free-base porphyrins: formation, structure and photostability of diprotonated species

“…1) undergoes protonation at one or both of the pyrrole nitrogen atoms, which results in formation of either a monocation or dication, respectively [6][7][8][9][10][11][12][13][14][15][16][17][18]. Although the existence of the mono-protonated cation was reported elsewhere, the diprotonated porphyrin form was practically the only stable product found in acidic media [9][10][11][12][13][14][15][16][17]. The dication, H 4 Por 2?…”

Exciton Spectra and the Microscopic Structure of Self-Assembled Porphyrin Nanotubes

“…As a result, the formation of threadlike or planar structures of a tiled nature for these aggregates has been suggested. [24][25][26] Two different zwitterionic forms of TPPS 4 monomers can occur, i.e. with the charged side groups on either adjacent or opposite sides of the porphyrin ring.…”

“…For the zwitterion with oppositely placed SO 3 -groups, a threadlike structure can easily be envisaged. [24][25][26] There is no trivial way to extend this to a higher-dimensional aggregate, however, the experimental evidence shows that large tubular aggregates are formed. 16,17 The adjacent form of the zwitterion, on the other hand, does support a planar stacking straightforwardly and can thus result in the creation of tubular aggregates.…”

Spectral properties of tetraanionic porphyrin in formamide colloids of layered double hydroxides

“…J-aggregates, which are generally less frequent, are built from headto-tail associates and absorb light of lower energies [19]. Although, TPPS is known to form the J-aggregates [20], especially in acidic solutions, this is not the case for the colloids with LDH. No Soret band component or enhanced absorption at longer wavelengths typical of J-type assemblies was observed.…”

“…No J-aggregates were formed, which would be otherwise detected as a sharp band at longer wavelengths of the Soret band edge (~ 490 nm) [20]. The J-aggregates of TPPS are mostly formed in acidic solutions, which convert the TPPS anion to a zwitterion by protonation of the imino nitrogens in the molecule.…”