Recent Advances in Subporphyrins and Triphyrin Analogues: Contracted Porphyrins Comprising Three Pyrrole Rings

Abstract

Subporphyrinato boron (subporphyrin) was elusive until the syntheses of tribenzosubporphine in 2006 and meso-aryl-substituted subporphyrin in 2007. These novel contracted analogues possess a 14π-electron conjugated system embedded in a bowl-shaped structure. They exhibit absorption and fluorescence in the UV/vis region and nonlinear optical properties due to their octupolar structures. The unique coordination geometry around the central boron atom in the structure of subporphyrin enabled investigation of rare boron species, such as borenium cations, boron hydrides, and boron peroxides. Along with the burgeoning development of the chemistry of subporphyrins, analogous triphyrin systems have also emerged. Their rich coordination chemistry as a result of their free-base structures, which are different from the boron-coordinating structure of subporphyrins, has been intensively investigated. On the basis of the unique structures and reactivities of subporphyrins and their related triphyrin analogues, supramolecular architectures and covalently linked multicomponent systems have also been actively pursued. This Review provides an overview of the development of subporphyrin and triphyrin chemistry in the past decade and future prospects in this field, which may inspire molecular design toward applications based on their unique properties.

Synthesis of novel dimeric subphthalocyanines via azide-alkyne Huisgen 1,3-dipolar cycloaddition and palladiumcatalyzed Glaser–Hay coupling reactions

“…The MALDI-TOF mass spectra also confirmed the proposed structures of the studied subphthalocyanines (2)(3)(4)(5) + for 5 ( Fig. 1).…”

“…On the other hand, the dimeric subphthalocyanine 5 was also synthesized by the homo coupling reaction of two axially substituted terminal ethynyl subphthalocyanines 3 by "Glaser-Hay" coupling reaction in the presence of PdCl 2 (PPh 3 ) 2 and CuI as catalysts in THF/trimethylamine (3:1) mixture (Scheme 1).…”

“…The synthesized subphthalocyanines (2)(3)(4)(5) were characterized by elemental analysis and general spectroscopic methods including FT-IR, 1 H-NMR, UV-vis and MALDI-TOF. In the FT-IR spectra of these subphthalocyanines (2-5), the aromatic CH stretching vibrations were observed at around 3060 cm -1 .…”

“…The triplet state of a photosensitizer transfers its energy to ground state molecular oxygen to produce singlet oxygen, which could destroy tumor cells. The Φ D values of the studied subphthalocyanines (2)(3)(4)(5) were determined by a chemical method using 1,3-diisobenzofuran (DPBF) as a quencher in ethanol solution (Fig. 4).…”

“…The most important common feature of the chlorosubphthalocyanines, the lowest homolog of phthalocyanine molecule, is they possess a 14 π-electron aromatic core [2]. These compounds are formed by a macrocyclic ring, arranged by three isoindole subunits that are bound together by three aza bridges [3].…”