Directly meso−meso Linked Porphyrin Rings:  Synthesis, Characterization, and Efficient Excitation Energy Hopping

Abstract

Directly meso-meso linked porphyrin rings CZ4, CZ6, and CZ8 that respectively comprise four, six, and eight porphyrins have been synthesized in a stepwise manner from a 5,10-diaryl zinc(II) porphyrin building block. Symmetric cyclic structures have been indicated by their very simple (1)H NMR spectra that exhibit only a single set of porphyrin and their absorption spectra that display a characteristic broad nonsplit Soret band around 460 nm. Energy minimized structures calculated at the B3LYP/6-31G* level indicate that a dihedral angle between neighboring porphyrins decreases in order of CZ6 > CZ8 > CZ4, which is consistent with the (1)H NMR data. Photophysical properties of these molecules have been examined by the steady-state absorption, fluorescence, fluorescence lifetime, fluorescence anisotropy decay, and transient absorption measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly related with the excitation energy migration processes within the porphyrin rings, where the exciton-exciton annihilation time and the polarization anisotropy rise time are well described in terms of the Forster-type incoherent energy hopping model. Consequently, the excitation energy hopping rates have been estimated for CZ4 (119 +/- 2 fs)(-)(1), CZ6 (342 +/- 59 fs)(-)(1), and CZ8 (236 +/- 31 fs)(-)(1), which reflect the magnitude of the electronic coupling between the neighboring porphyrins. Overall, these porphyrin rings serve as a well-defined wheel-shaped light harvesting antenna model in light of very efficient excitation energy hopping along the ring.

Modification of Supramolecular Binding Motifs Induced By Substrate Registry: Formation of Self‐Assembled Macrocycles and Chain‐Like Patterns

“…[15] Suzuki-Miyaura cross-coupling of 6 with pinacolborane afforded bis(boronic ester) 7 in quantitative yield. A second Suzuki-Miyaura cross-coupling of 7 with commercially available 4-bromo-1-iodobenzene afforded cisbis(4-bromophenyl)porphyrin 8.…”

“…All reactions were performed under an inert atmosphere by applying a positive pressure of N 2 . Compounds 5, [15] 9, [16] and 10 [17] were synthesized according to literature procedures. Adsorption chromatography columns and plug filtrations were carried out with SiO 2 60 (particle size 0.040-0.063 mm, 230-400 mesh ASTM; Fluka) or SiO 2 60 (particle size 0.063-0.200 mm, 70-230 mesh ASTM; Merck).…”

Supramolecular Chirality in Porphyrin Chemistry

“…For example, a direct C-C bond between two porphyrins at the corresponding meso-or beta-positions may be a suitable target for this approach if the rotation around the bond is blocked, for example, by bulky substituents or an additional linkage. Hence, a simple meso-meso linked bis-porphyrin, 33, was optically separated into two enantiomers through chiral high performance liquid chromatography (HPLC) ( Figure 12) [39]. However, whilst the 180° rotation around the binding axis was prohibited, the overall geometry was not completely fixed, leaving room for several existing conformers, resulting in a rather moderate CD outcome (within ±20 cm…”

Meso-Linked Multiporphyrins as Model for Light Harvesting Systems: Review

“…A variety of porphyrin arrays has been reported by Osuka et al by the use of coupling reactions in the presence of Ag (I) salts [74]. On treating the zinc porphyrin possessing unsubstituted meso positions with Ag (I) salt, the meso-meso linked diporphyrins and oligomeric porphyrins have been formed.…”