Charged Porphyrins: π-Electronic Systems That Form Ion-Pairing Assembled Structures

Abstract

Noncovalent interactions are important for determining the assembling modes of materials. Electronically neutral π-systems form stacking structures based on π–π interactions, which are mainly derived from dispersion forces. Introducing charges into π-systems would affect the interaction, owing to the increased contribution from electrostatic forces. This unique interaction, which we have proposed as iπ–iπ interaction, can provide ion pairs that form assembled structures. The number of possible combinations of ion pairs can be obtained as the product of the number of components being paired. As π-electronic ions, especially anions, are more reactive than electronically neutral π-systems, their stabilization is required. We have recently focused on porphyrins as platforms to stabilize π-electronic ions by charge delocalization over their large π-systems. In addition, the facile structural modifications of porphyrins enable tuning of the assembly modes and functionalization of the ion-pairing assemblies. In this account, progress of charged porphyrin derivatives and their ion-pairing assembly behaviors is summarized.

π-Stacked Ion Pairs: Tightly Associated Charged Porphyrins in Ordered Arrangement Enabling Radical-Pair Formation

“…The combination of oppositely charged species achieved by the HSAB theory can be considered as a new synthetic method for functional materials. This strategy, which introduces complementary species at stoichiometric ratios, has been limited to selected combinations of opposite ions . In particular, various charged π-systems are included as building units by stabilization via ion pairing.…”

“…Thus, investigating the properties of ion pairs as discrete chemical species is crucial for developing functional materials. In particular, π-electronic ion pairs are of interest for fabricating electronic materials that use intermolecular interactions based on electrostatic and dispersion forces, defined as i π– i π interactions, to provide dimension-controlled assemblies. , The i π– i π interactions induce stacking between cations and anions, forming contact ion pairs as π-stacked ion pairs (π- sips ). Controlling the electronic states can provide π-stacked radical pairs (π- srps ) (Figure b).…”

Ionic supramolecular polymerization of water-soluble porphyrins: balancing ionic attraction and steric repulsion to govern stacking

“…Among the various p-conjugated molecules, porphyrin derivatives are attractive because they have a characteristic absorption band in the visible region, making their supramolecular polymers fascinating candidates for practical electro-optical materials. [1][2][3][4][5][6][7] Over the years, many porphyrin-based supramolecular polymers have been created by tuning the structures of their monomers, especially by varying the peripheral groups attached to the porphyrin cores. [8][9][10][11] Similar to the general supramolecular polymerization strategies of p-conjugated monomers, selfassembly of porphyrin monomers is commonly driven primarily by strong p-stacking, with the assistance of other noncovalent interactions (e.g., hydrogen bonding).…”

Biomimetic and Biological Nanoarchitectonics

“…In general, the creation of functional materials has been pursued using the more orthodox methodologies of organic chemistry [ 7 , 8 , 9 ], inorganic chemistry [ 10 , 11 , 12 ], supramolecular chemistry [ 13 , 14 , 15 ], coordination chemistry [ 16 , 17 , 18 ], polymer chemistry [ 19 , 20 , 21 ], and other material sciences [ 22 , 23 ]. It has gradually become clear that functionality depends not only on the properties of the substance itself, but also on how its structure is controlled and how its components are arranged.…”