Do Anionic π Molecules Aggregate in Solution? A Case Study with Multi‐interactive Ligands and Network Formation

Abstract

An anionic π molecule can form an aggregate when a multi‐interactivity is introduced, in sharp contrast to common anionic molecules that are generally difficult to stack on each other. We found that a multi‐interactive ligand, 2,5,8‐tri(4′‐pyridyl)‐1,3,4,6,7,9‐hexaazaphenalenate (TPHAP−) exhibited a large Stokes shift and an intramolecular charge transfer, both of which were sensitive to hydrogen‐bonding media. An anionic potassium salt of TPHAP− in methanol formed various aggregation states depending on the concentration examined; this was revealed by steady‐state spectroscopic and fluorescence lifetime measurements. Self‐assembling cadmium ions and the ligands can create several morphological crystals that are controlled by the ligand concentration, among which three new structures were determined by single‐crystal analysis. The X‐ray structures obtained suggest that the aggregation states of the ligand in solution can be transferred to the solid system of the porous coordination networks.

Multi-interactive Coordination Network Featuring a Ligand with Topologically Isolated p Orbitals

“…3-TPHAP – was prepared as a potassium salt, K­(3-TPHAP), from 3-amidinopyridine hydrochloride and potassium tricyanomethanide in moderate yield (9%) using a modified procedure for the synthesis of K­(4-TPHAP) (Scheme ). The molecule displays several interactive sites, including nine nitrogen atoms, which can be involved in H-bond or coordination bond formation, a large aromatic plane capable of π–π interaction, and delocalized negative charge (Figure a) . The basic characterization of 3-TPHAP – is detailed in the Supporting Information, which revealed that its properties closely resemble those of 4-TPHAP – (Figures S4 and S5).…”

“…7 The molecule displays several interactive sites, including nine nitrogen atoms, which can be involved in H-bond or coordination bond formation, a large aromatic plane capable of π−π interaction, and delocalized negative charge (Figure 1a). 9 The basic characterization of 3-TPHAP − is detailed in the Supporting Information, which revealed that its properties closely resemble those of 4-TPHAP − (Figures S4 and S5). 10 Attempts to form coordination networks using the K(3-TPHAP) ligand alone proved challenging.…”

Photoactive Hexaazaphenalene‐based Coordination Network as a Two‐Pathway Photosensitizer for Oxidation of Alkanes

“…The UV-Vis spectra exhibited an absorption band at 335 nm (ɛ = 11114 M À 1 cm À 1 ) similar to previously reported results, which were obtained in different solvents and in the presence of different counter cations. [40,41] This band was assigned to an intramolecular charge transfer (ICT) transition from the HAP core to the three peripheral pyridyl groups. In addition, TPHAP compounds were shown to display photoluminescence at 25 °C.…”

“…[42][43][44] Due to the intramolecular charge transfer nature of this transition, the excitation energy and extinction coefficient could be modulated by modifying the substituent groups. [40,41,45] The possibility of formation of singlet oxygen ( 1 O 2 ) via the energy transfer pathway was considered. The existence of 1 O 2 was confirmed by photooxidation of 1,5-dihydroxynaphthalene (1,5-DHN), which is typically used as a selective trap (Scheme 2).…”

“…[38,39] Moreover, TPHAP displayed interesting electronic and electrochemical properties defined by an intramolecular charge transfer (ICT) from hexaazaphenalene skeleton (HAP) to terminal pyridine substituents and a stable redox couple at À 1.45 V vs Fc 0/ + . [40,41] This anionic specie contains a phenalene-type fused tricyclic core. Related phenalene-based analogues were used to generate singlet oxygen upon light irradiation.…”