Rotation of phenyl rings in metal complexes of substituted tetraphenylporphyrins

Illustrating atropisomerism in the porphyrin series using NMR spectroscopy

“…1B) by visual comparison of the areas of the six types of methyl group resonances [11]. According to other studies on porphyrins (see references [3][4][5] and [12][13][14][15][16][17][18][19] for a representative list of examples), the existence of atropisomers is usually revealed in NMR spectroscopy by multiplets with rather broad peaks mainly due to extensive overlap of signals.To clearly illustrate atropisomerism, we discuss the wellresolved 250 MHz 1 H NMR spectrum of meso-tetrakis(3-sulfonatomesityl)porphyrin tetrasodium salt (Fig. 3), a porphyrin prepared (note 1) as a potential antiviral agent [20] Illustrating atropisomerism in the porphyrin series using NMR spectroscopy -the mesityl ring introduced in the meso positions of the porphyrin has methyl substituents in both ortho positions of the phenyl group, which greatly increases the activation energy of the rotation barrier around the C-C bond diminishing the possibility of thermal isomerization [12].…”

“…3) are macrocycles consisting of four pyrroles linked by four methine bridges. Carbons 5,10, 15 and 20 are designated meso and carbons 2,3,7,8,12,13, 17 and 18 are the β pyrrole positions (Fisher's convention [8]). Porphyrins with four identical aryl groups in the meso position are derivatives with restricted rotation about the aryl-porphyrin bond due to interactions of the β-CH groups with the ortho-substituents of the meso-aryl groups (R or R' ≠ H, R and R' magnetically nonequivalent, Fig.…”

Excavations at the Alamo Shrine (Mission San Antonio de Valero)

“…It seems possible that the footing had been installed some years prior to the construction of the foundation and might be the footing which supported the original stone church that subsequently collapsed. The construction of the foundation footing is remarkably similar to the technique recorded at Missions San Juan Bautista and San Bernardo (Eaton 1975(Eaton ,1976.…”

Spectral-Luminescent Properties of meso-Tetraarylporphyrins Revisited: The Role of Aryl Type, Substitution Pattern and Macrocycle Core Protonation

“…[36] Structural changes in porphyrins and porphyrin-based supramolecular assemblies related to the meso-aryl substitution pattern are frequently observed. [19][20][21][22][31][32][36][37][38] The synthesis and properties of different series of porphyrin compounds with sequential attachment of meso-aryl groups or the exchange of aryl groups of one type with those of another type have been widely reported. It was shown that the changes of numerous photophysical and physico-chemical properties of the studied meso-arylporphyrins, including the nonlinear two-photon absorption cross section, [39] the molecular contraction upon triplet state formation, [40] the fluorescence quantum yield from the lowest and higher excited states, [36,[41][42] the shift of the bands in the absorption spectra, [41][42][43] and the rates of radiative and nonradiative excitation energy deactivation pathways, [36,[41][42][43] can be interpreted as being "additive" with respect to the number of attached/replaced aryl groups.…”

“…

Both the ground (S 0 ) and the lowest singlet excited states (S 1 ) for a series of 5,10,15,20-rotation, and the accessible range for the dihedral angle q between the mean macrocycle and meso-aryl ring planes decreases drastically, [21,22] leading to the formation of atropoisomers for sterically hindered meso-arylporphyrin derivatives. However, even in such a case, non-zero electronic communication between the macrocycle and meso-periphery exists.

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