Ion-pairing π-electronic systems: ordered arrangement and noncovalent interactions of negatively charged porphyrins.

In this study, charged π-electronic species are observed to develop stacking structures based on electrostatic and dispersion forces. i π- i π Interaction, defined herein, functions for the stacking structures consisting of charged π-electronic species and is in contrast to conventional π-π interaction, which mainly exhibits dispersion force, for electronically neutral π-electronic species. Establishing the concept of i π- i π interaction requires the evaluation of interionic interactions for π-electronic ion pairs. Free base (metal-free) and diamagnetic metal complexes of 5-hydroxy-10,15,20-tris(pentafluorophenyl)porphyrin were synthesized, producing π-electronic anions upon the deprotonation of the hydroxy unit. Coexisting cations in the ion pairs with porphyrin anions were introduced as the counter species of the hydroxy anion as a base for commercially available cations and as ion-exchanged species, via Na+ in the intermediate ion pairs, for synthesized π-electronic cations. Solid-state ion-pairing assemblies were constructed for the porphyrin anions in combination with aliphatic tetrabutylammonium (TBA+) and π-electronic 4,8,12-tripropyl-4,8,12-triazatriangulenium (TATA+) cations. The ordered arrangements of charged species, with the contributions of the charge-by-charge and charge-segregated modes, were observed according to the constituent charged building units. The energy decomposition analysis (EDA) of single-crystal packing structures revealed that electrostatic and dispersion forces are important factors in stabilizing the stacking of π-electronic ions. Furthermore, crystal-state absorption spectra of the ion pairs were correlated with the assembling modes. Transient absorption spectroscopy of the single crystals revealed the occurrence of photoinduced electron transfer from the π-electronic anion in the charge-segregated mode.

Liquid Crystals Comprising π-Electronic Ions from Porphyrin-AuIII Complexes.

Porphyrin-AuIII complexes were found to act as π-electronic cations, which can combine with various counteranions, including π-electronic anions. Single-crystal X-ray analyses revealed the formation of assemblies with contributions of charge-by-charge and charge-segregated assemblies, depending on the geometry and electronic state of the counteranions. Porphyrin-AuIII complexes possessing aliphatic alkyl chains formed dimension-controlled ion-pairing assemblies as thermotropic liquid crystals, whose ionic components were highly organized by π-π stacking and electrostatic interactions.

Peripheral Modifications of meso-Hydroxyporphyrins: Formation of π-Electronic Anions and Ion-Pairing Assemblies.

Phenyl groups were introduced at the ß-positions proximal to the meso-hydroxy moiety in hydroxyporphyrin NiII complexes by oxidized BINAP PdII complexes. Ion-pairing assemblies of deprotonated π-electronic anions, anionic site of which was stabilized by the introduced phenyl moieties with a bulky cation, were formed. They showed charge-by-charge assemblies, assembly modes of which were modulated by the anionic building units.

H-Aggregated π-Systems Based on Disulfide-Linked Dimers of Dipyrrolyldiketone Boron Complexes.

Dipyrrolyldiketone boron complexes linked by a disulfide bond were synthesized, forming H-aggregated dimers assisted by intramolecular π-π and hydrogen-bonding interactions. The conformations of the dimers, with small C-S-S-C dihedral angles, were examined by UV-vis absorption and 1H NMR spectra as well as single-crystal X-ray analysis and theoretical studies.

Deprotonated meso-hydroxyporphyrin as a stable π-electronic anion: the building unit of an ion-pairing assembly.

The NiII complex of 5-hydroxy-10,15,20-tris(pentafluorophenyl)-porphyrin was synthesized as the precursor of a negatively charged π-electronic system. Deprotonation, which was examined through UV/vis and 1H NMR spectra, provided an anionic species as the building unit of an ion-pairing assembly in combination with an aliphatic cation.

Negatively Charged π-Electronic Systems by Deprotonation of Hydroxy-Substituted Dipyrrolyldiketone Boron Complexes.

Boron complexes of meso-hydroxy-substituted dipyrrolyldiketones, as the precursors of negatively charged π-electronic systems, were synthesized via the oxidative introduction of an acetoxy unit at the meso position of dipyrrolyldiketones and subsequent hydrolysis. The anionic site formed upon deprotonation was moderately stabilized by hydrogen-bond-donating pyrrole NH, generating non-complexing anionic species.