Expanded Porphyrins and Their Heterologs

Extroverted Confusion—Linus Pauling, Melvin Calvin, and Porphyrin Isomers

“…[43] Next to synthetic studies areas of current interest included the metal coordination chemistry due to the ability of these systems to form carbon-metal bonds, their anion sensing abilities, and their utility as photosensitizers, to name only a few. The whole field of macrocycle modified porphyrins has evolved to include isomeric expanded systems, [44] heteroatom substituted and carbaporphyrins, [45] Möbius aromatics, [46] cyclic oligopyrroles, [18] calixphyrins and -pyrroles, [47] and more. Even the chemical interconversion, i.e.…”

“To Twist or Not to Twist”: Figure‐of‐Eight and Planar Structures of Octaphyrins

“…Peculiarly,t he thiophene units adopted ap arallel orientation and the protons on their b-carbon atoms were engulfed by the diatropic ring current of the macrocycle. 1 HNMR analysisc onfirmed this orientation,w ith two upfield doubletsi nt he region d = 4-6 ppm. These values supposedly reflected as ubdued diatropic ring current in comparison to that in 34 p octaphyrin 43.I nc ontrast, the addition of ap rotic acid induced ad rastic upfield shift by more than Dd = 6ppm for the inverted ring protons of compound 48.S uch as ubtle change conveyed complete inversion of the heterocyclic rings upon protonation, in comparison to its native form.…”

“…Structuralanalysisofthis macrocycle revealed abimetallic complex of the octaphyrin, albeit with af igure-of-eight conformation, that had ac lose resemblance to the earlier report by Vogel et al, [14b] except for meso-phenyl substituents rather than the b-alkyl groups on the pyrrole rings. 1 HNMR characterization revealed minor paratropic ring-current effects, which could be attributed to an onplanar structure of the macrocycle. The small positive values that were estimated from Nucleus Independent Chemical Shift (NICS) calculations further supported this observation.…”

A density functional theory study on the porphyrin isomers: Effect of meso-bridge length, relative stabilities, cis-trans isomerism

“…1,2,3 Porphyrins with their extended π-electron networks and exhibit high stability and have displayed applications in advanced materials as components in organic metals and in photodynamic therapy in the treatment of cancer and dermotological The different types of isomers are possible by varying methine bridges in addition to the parent porphyrin moiety. Considering all the possible geometric isomers, a total of 46 structures of 1,3 (anti) and 1,2 (syn) tautomers were considered in the present study, are given in Schemes 1 and 2.…”

“…The B3LYP/6-31G optimized geometries of anti tautomeric structures and the relative energies with enthalpy correction are given in Figure 1. The variation in relative energies of anti (1,3) and syn (1,2) tautomeric porphyrin isomers obtained at B3LYP/6-31G and 6-311+G** levels of theory are given in Figure 3. Considering all the possible cis-trans isomers of 1,3 (anti) and 1,2 (syn) tautomers totally 46 porphyrin isomers are resulted.…”