New aspects in bis and tris(dipyrrinato)metal complexes: bright luminescence, self-assembled nanoarchitectures, and materials applications

Abstract

Dipyrrins serve as monovalent bidentate ligand molecules that coordinate to various cations. Their BF 2 complexes, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene and its derivatives (BODIPYs), exhibit excellent photostability, strong light absorption, and high fluorescence quantum yield, thereby encouraging their application in various fields, e.g., as biological and biomedical fluorescent markers. Dipyrrin may also accept a wide variety of metal ions spontaneously. However, dipyrrin metal complexes have been disregarded from materials science research. This review article summarizes recent progress in bis(dipyrrinato)metal(II) and tris(dipyrrinato)metal(III) complexes from the viewpoint of materials chemistry. Section 2 describes a series of efforts aimed to realize intense luminescence superior to or comparable with that of BODIPYs. The spontaneous coordination of these complexes enables them to construct self-assembled nanoarchitectures, such as supramolecules and coordination polymers that form one-dimensional nanowires, two-dimensional nanosheets, and metal-organic frameworks. Section 3 describes such alluring molecular superstructures. Section 4 discusses potential applications based on these nanoarchitectures, such as thermoelectric and photoelectric conversion. aimed to realize intense luminescence superior to or comparable with that of BODIPYs. Section 3 discusses the selfassembly of bis and tris(dipyrrinato)metal complexes, which results in the formation of alluring nanoarchitectures, such as supramolecules and coordination polymers giving rise to onedimensional nanowires, two-dimensional nanosheets, and metal-organic frameworks (MOFs) and porous coordination polymers (PCPs). Section 4 describes potential applications based on these nanoarchitectures. Pursuit of bright luminescenceA plain BODIPY shows intense absorption and bright fluorescence at approximately 500 nm, which are derived from the 1 π-π * transition of the dipyrrinato ligand. 5-16 The absorption and fluorescence may be redshifted upon the introduction of substituents on the dipyrrinato ligand, covering the region 500-900 nm. BODIPYs are good fluorophores even in polar solvents such as water. In sharp contrast, dipyrrin metal complexes have long been believed to be non-luminescent or weakly luminescent. This drawback seriously reduces the value of dipyrrinato-metal complexes in applications in which they serve, for example, as photosensitizers. In this section, the authors concentrate on efforts to improve the luminescent ability of bis and tris(bisdipyrrinato)metal complexes. For comprehensive knowledge on the whole types of luminescent dipyrrinato-metal complexes (i.e. mono(dipyrrinato)metal complexes with ancillary ligands other than dipyrrins), please see a comprehensive review article contributed by Baudron. 2

Makroskopische kristalline 2D‐Polymere

“…2D-Polymere sind dementsprechend topologisch planare,t rennbare Monolagen mit interner Fernordnung, zusammengehalten durch starke (kovalente) Bindungen. [97,98,107,[99][100][101][102][103][104][105][106] Besonders die Bedeutung interner Fernordnung und der Isolierbarkeit einzelner Lagen wird oft als gering eingestuft. [97,98,107,[99][100][101][102][103][104][105][106] Besonders die Bedeutung interner Fernordnung und der Isolierbarkeit einzelner Lagen wird oft als gering eingestuft.…”

“…Wiedas Beispiel der Herstellung von Graphen aus Graphit zeigt, sind die Ausbeuten von Flüssigexfolierungen meist sehr gering und nur eine sehr kleine Massenfraktion ausgedehnter Monolagen kann mit solchen Methoden isoliert werden. [70,107] Abbildung 1a zeigt repräsentativ die Struktur eines 2D-Polymers,d ie regelmäßig angeordnete hexagonale Poren aufweist. Von einer quantitativen Exfolierung zu den gewünschten Monolagen ist man aber auch hier noch weit entfernt.…”

“…[94][95][96] Diese Beschreibung findet vermehrt Akzeptanz, aber es gibt auch anderslautende Definitionen. [97,98,107,[99][100][101][102][103][104][105][106] Bis vor wenigen Jahren war es nicht mçglich, 2D-Polymere nach der oben erwähnten Definition herzustellen; [108][109][110][111] das erste Beispiel eines synthetischen 2D-Polymers,d as obiger Definition entspricht, wurde 2012 publiziert. [ [57,[112][113][114][115] Der in Abbildung 1d argestellte Fall eines synthetischen 2D-Polymers basierend auf einer [2+ +2]-Cycloadditionsreaktion [116] ermçglicht bereits hçhere Ausbeuten brauchbarer Monolagen.…”

“…Mosaizitätd es Einkristalls [117] und Zerreißen während der Exfolierung senken die erreichbare Grçße der isolierbaren Monolagen weiter ab,s odass sich die grçßten erreichten Flächen fürM onolagen im Bereich einiger mm 2 bewegen. [70,107] Abbildung 1a zeigt repräsentativ die Struktur eines 2D-Polymers,d ie regelmäßig angeordnete hexagonale Poren aufweist. In der Vergrçßerung sind außerdem stereochemische Details der Struktur um die Pore herum dargestellt sowie die kurzen (1.6 nm) und langen (2.8 nm) Distanzen innerhalb der Pore eingezeichnet.…”

Pyrrole‐Based π‐System–PtII Complexes: Chiroptical Properties and Excited‐State Dynamics with Microsecond Triplet Lifetimes

“…Among metal complexes, cyclometalated Pt II complexesh ave gained much attention due to their photophysical properties, and show high tripletq uantum yields, long-lived triplet excitons, and photocatalytic activities. [4] Previously,a variety of dipyrrin-based metal-coordinationo ligomers and polymers were investigated for the fabrication of organized structures. Thus,i ti sc rucial to investigate the dynamics, whichi ncludes radiative and non-radiative processes, as well as the reactivity of excited states because highly efficient photofunctional materials can be fabricated.…”