Intriguing Heteroleptic ZnII bis(dipyrrinato) Emitters in the Far-Red Region With Large Pseudo-Stokes Shift for Bioimaging

Abstract

Novel heteroleptic ZnII bis(dipyrrinato) complexes were prepared as intriguing emitters. With our tailor-made design, we achieved far-red emissive complexes with a photoluminescence quantum yield up to 45% in dimethylsulfoxide and 70% in toluene. This means that heteroleptic ZnII bis(dipyrrinato) complexes retain very intense emission also in polar solvents, in contrast to their homoleptic counterparts, which we prepared for comparing the photophysical properties. It is evident from the absorption and excitation spectra that heteroleptic complexes present the characteristic features of both ligands: the plain dipyrrin (Lp) and the π-extended dipyrrin (Lπ). On the contrary, the emission comes exclusively from the π-extended dipyrrin Lπ, suggesting an interligand nonradiative transition that causes a large pseudo-Stokes shift (up to 4,600 cm−1). The large pseudo-Stokes shifts and the emissive spectral region of these novel heteroleptic ZnII bis(dipyrrinato) complexes are of great interest for bioimaging applications. Thus, their high biocompatibiliy with four different cell lines make them appealing as new fluorophores for cell imaging.

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

“…The application potential of charge-transfer excited states in Zn II complexes has so far remained underexplored in comparison to isoelectronic copper­(I) coordination compounds. , Here, we demonstrate that intraligand charge-transfer (ILCT) excited states in tetrahedral Zn II complexes can display similar reactivity as metal-to-ligand charge-transfer (MLCT) excited states in four-coordinate Cu I compounds. In the latter, the photoactive MLCT excited states are typically strongly distorted due to the transient formation of a Jahn–Teller susceptible Cu II d 9 metal species, , opening up unwanted nonradiative excited-state relaxation pathways.…”

“…The most frequently observed emission type in Zn II complexes until now is ligand-based fluorescence, for example, in many dipyrrin-based compounds, − complexes with benzothiazole ligands, − as well as with other nitrogen and oxygen donor ligands, , or phosphines . Possible applications of fluorescent Zn II compounds in electroluminescence, ,− including organic light-emitting diodes (OLEDs), − circularly polarized luminescence, sensing, or cell imaging, have attracted interest .…”

Trendbericht: Photochemie

“…Bizzarris Gruppe hat mit dieser Strategie Rotlichtemitter (Abbildung 4c) hergestellt, die für bildgebende Verfahren in biologischen Systemen interessant sein könnten. 34) Neuerdings rücken Triplettzustände mit Ladungstransfer-Charakter in Zn II -Komplexen vermehrt in den Fokus, und so hat das Team um Steffen Zn II -Verbindungen hergestellt, die im festen Zustand langlebige Phosphoreszenz zeigen (Abbildung 4d). 35) Roeskys Team beobachtete thermisch aktivierte verzögerte Fluoreszenz aus einem Zn II -Komplex mit Iminophosphonamid-Liganden im festen Zustand (Abbildung 4e).…”

Pd and Pt Complexes of Benzo-Fused Dipyrrins: Synthesis, Structure, Electrochemical, and Optical Properties

“…Benzo-fused dipyrrins, in which each of two conjugated pyrrole units is fused with the benzene ring, possess a bathochromic shift in absorption spectra due to extended π-conjugation and therefore can be particularly interesting for biomedical ,, and material science applications, such as solar cell technology, , circularly polarized luminescence materials, and optical power limiting (OPL) filters . However, in contrast to regular dipyrrins, there is limited information available regarding complexes of benzo-fused dipyrrins with transition metals.…”