Hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1): A Dual Site Ligand That Supports Thermal Conformational Changes

Abstract

A new expanded porphyrin, hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1), is reported. It was obtained via the condensation of a hexapyrrolic derivative prepared in turn from a bipyrrole dialdehyde and a stable quaterpyrrole precursor. This hexadecaphyrin contains eight direct α-pyrrole-to-α-pyrrole linkages in its structure. It supports the formation of bimetallic complexes of both zinc and cobalt that are characterized by different conformational structures. Furthermore, a mixed zinc/cobalt macrocycle has been prepared. The cobalt bimetallic complex shows two stable conformations with the same oxidation state that are in equilibrium. All compounds have been characterized by common spectroscopic means, and single crystal X-ray diffraction structures were obtained for all macrocyclic compounds. DFT calculations and transient absorption spectra were used to study the electronic features of the complexes and the effect of conformational changes. This system shows promise as an accumulated heat sensor.

Synthesis of Imidazole-Based [30]Heptaphyrin and Stable Figure-Eight [60]Tetradecaphyrins via [5 + 2] Condensations in One Pot

“…By the development of relatively rigid and π-conjugated polyheteroaryl units, more targeting syntheses are realized, providing [54]dodecaphyrin 5 and [64]hexadecaphyrin. 6 Except classical pyrrole, other heteroarenes including thiophene, furan, and pyridine have been widely utilized to construct novel expanded porphyrins to tune their properties. In contrast, azoles are rarely employed.…”

“…Expanded porphyrins have gained much attention in recent years due to their unique optical and electronic properties and promising applications in near-infrared dyes, nonlinear optical materials, photodynamic therapy, and metal-ion binding . As substantial progress has been made for medium-sized porphyrinoids in regard to their syntheses, conformations, aromaticity, coordination behaviors, and radical characters, expanded porhyrins bearing over 10 heteroarenes are still rare because of their synthetic challenges, more complicated geometry, and lower stability along with the added heteroaryl subunits. − The groups of Setsune and Osuka have isolated multisized macrocycles (from [18]­porphyrin up to [96]­tetracosaphyrin) in ring-closure reactions of bipyrrole or di/tripyrrane derivatives. By the development of relatively rigid and π-conjugated polyheteroaryl units, more targeting syntheses are realized, providing [54]­dodecaphyrin and [64]­hexa­deca­phyrin …”

Excitonically Coupled Cyclic BF2 Arrays of Calix[8]‐ and Calix[16]phyrin as Near‐IR‐Chromophores

“…Theg oal of the present study was to create large oligopyrrolic frameworks containing multiple BODIPY-like fluorogenic centers.T oavoid possible complexities associated with post-synthetic functionalization, we elected to use the bis-naphthobipyrrolylmethene-BF 2 complex 3 as the key precursor.Afurther incentive for this particular choice of building blocks was the thinking that the relatively large size of this chosen building block might limit the number of possible products formed during macrocyclization. [13] In this context, we note the growing interest in using BODIPY-based precursors to construct novel expanded porphyrins. [6b,e,f,14] Previously,the Panda group reported a meso-free,tetra-balkylated version of 3 with impressive photophysical properties.…”

Functionalized 2,2’-Bipyrroles: Building Blocks for Pyrrolic Macrocycles

“…Recent efforts devoted to expansion of the porphyrin core have led Sessler and co-workers to prepare one of the largest expanded porphyrin yet reported, namely hexadecaphyrin ( 160 ) (Scheme 37). [110] This compound contains eight direct α-pyrrole-to-α-pyrrole linkages and was obtained via the condensation 2,2’-bipyrrole dialdehyde 141 with the hexapyrrolic derivative 159 . This expanded porphyrin was shown to support the formation of different metal complexes that interconvert between different conformations as temperature is applied to the solution.…”