Azadipyrromethene Complexes of d8 Metal Centers: Rhodium(I), Iridium(I), Palladium(II), and Platinum(II)

Anion-selective "Turn-on" two color phosphorescent probes based on "Pd-Pd" interaction of a series of cyclometallated Palladium (II) complexes induced by a self-assembly in aqueous solution

Herein, three pairs of cationic cyclometallated palladium (II) complexes with different types of C^N ligands, which is non-phosphorescent in aqueous solution, interestingly, they can be utilized as turn-on blue phosphorescent probes selectively for ClO^-, HSO₃^- and CO₃^2-, and turn-on green phosphorescent probe for HSO₃^- in aqueous solution. These different phosphorescent turn-on responses of Pd(II) complexes could be attributed to the degree of coordination and electrostatic interaction between them with specific anion. It suggests that the selectivity towards specific anion of these cyclometallated Pd(II) complexes can be further improved by rationally tuning the structure and enhancing aromaticity of C^N ligand. Our study reveals that these specific species of anions can effectively induce self-assembly of Pd(II) compounds with different C^N ligand based on PdPd interaction, the aggregation and morphology of palladium complex with anion in aqueous media was also investigated by various means of ¹H NMR, UV/Vis, fluorescence spectra, and dynamic light scattering (DLS) analysis. Moreover, transmission electron microscopy (TEM) reveals that nanowires with increased length of diameters of Pd complexes can form in aqueous solution in presence of anions with different high concentration. Furthermore, the cellular uptake and location of Pd2a was also investigated by confocal imaging for the first time. DFT calculation of monomer and dimer of Pd2a was also performed, which is helpful to explain the turn on phosphorescent effect during self-assembly process.

Al(III) and Ga(III) Bisphenolate Azadipyrromethene-Based “N2O2” Complexes as Efficient NIR-Fluorophores

Aza-boron-dipyrromethenes (Aza-BODIPYs) are an increasingly studied class of fluorophores. They can be seen as an azadipyrromethene ("aza-DIPY") ligand rigidified by a metalloid, a boron atom. Based on this idea, a series of complexes of group 13 metals (aluminum and gallium) have been synthesized and characterized. The impact of the metal and of the nature of the substituents of aza-DIPY core were investigated. The photophysical and electrochemical properties were determined, and an X-ray structure of an azaGaDIPY was obtained. These data reveal that azaGaDIPY and azaAlDIPY exhibit significant red-shifted fluorescence compared to their analogue aza-BODIPY. Their emission can go up to 800 nm for the maximum emission length and up to NIR-II for the emission tail. This, associated with their electrochemical stability (no metal release whether oxidized or reduced) makes them a promising class of fluorophores for optical medical imaging. Moreover, X-ray structure and molecular modeling studies have shown that this redshift seems to be more due to the geometry around the boron/metal than to the nature of the metal.

Synthetic Exploration of Bis(phenolate) Aza-BODIPYs and Heavier Group 13 Chelates

A series of boron, aluminum, gallium, and indium chelates containing the underexplored bis(phenolate) aza-dipyrromethene (aza-DIPY) core were prepared. These compounds were found to possess near-infrared absorption and emission profiles in the 710 to 770 nm domain and exhibit quantum yield values up to 14%. X-ray diffraction analysis revealed that heavier group 13 bis(phenolate) aza-DIPY chelates possessed octahedral geometries with either THF or pyridine groups occupying the axial positions as opposed to the tetrahedral geometry of the boron chelate.

Rational Design of Near-Infrared-Absorbing Pt(II)-Chelated Azadipyrromethene Dyes as a New Generation of Photosensitizers for Synergistic Phototherapy

Pt(II) photosensitizers are emerging as novel Pt anticancer agents for cancer photodynamic therapy (PDT) to avoid uncontrollable toxicity of cisplatin. However, the application of Pt(II) photosensitizers is limited by tumor hypoxia and the poor penetration depth of excitation light. To overcome these drawbacks, exploiting the next generation of Pt anticancer agents is of urgent need. According to theoretical calculations, novel near-infrared (NIR)-absorbing Pt(II)-chelated azadipyrromethene dyes (PtDP-X, where X = N, C, and S) were designed. Importantly, spin-orbit coupling of the Pt atom could promote the intersystem crossing of a singlet-to-triplet transition for converting oxygen to singlet oxygen (¹O₂), and the azadipyrromethene skeleton could provide a strong photothermal effect. As expected, PtDP-X exhibited intense NIR absorption and synergistic PDT and photothermal effects with low dark cytotoxicity. Furthermore, water-soluble and biocompatible PtDP-N nanoparticles (PtDP-N NPs) were prepared that achieved effective tumor cell elimination with low side effects under 730 nm light irradiation in vitro and in vivo. This pioneering work could push the exploitation of NIR-absorbing metal-chelated azadipyrromethene dyes, so as to promote the positive evolution of phototherapy agents.

Classifying donor strengths of dipyrrinato/aza-dipyrrinato ligands

A parameter is reported by which to use ¹³C NMR chemical shifts to measure and predict the donor capabilities of N^N dipyrrinato and aza-dipyrrinato ligands chelating in L^X fashion. The results enable the rationalisation of the properties of these ligands and their complexes, as well as enable rational design incorporating both steric and electronic considerations when tuning to effect desired applications. Complexes containing these ligands are prevalent due to their desirable photophysical properties such as high chemical stability, resistance to photodegradation, strong absorbance, and ease of chemical modifiability.

Synthesis and reactivity of aza-dipyrrin alkali metal salts

Reaction of aza-dipyrrins with alkali bases provides alkali salts of the anionic aza-dipyrrinato ligand. This anionic ligand source demonstrates complementary reactivity to the traditionally-used neutral pre-ligand.

Heck functionalization of an asymmetric aza-BODIPY core: synthesis of far-red infrared probes for bioimaging applications

Heck functionalization of azadipyrromethenes (aza-DIPY) allows the introduction of suitable functional groups to convert aza-BODIPY in bioconjugate complexes.

Azadipyrromethenes: from traditional dye chemistry to leading edge applications

The journey of azadipyrromethenes from accidental dye chemistry to a compound class with widely applicable near infrared photophysical properties is documented.

Azadipyrromethene cyclometalation in neutral RuII complexes: photosensitizers with extended near-infrared absorption for solar energy conversion applications

In the on-going quest to harvest near-infrared (NIR) photons for energy conversion applications, a novel family of neutral ruthenium(ii) sensitizers has been developed by cyclometalation of an azadipyrromethene chromophore.

Twofac-tricarbonylrhenium(I) azadipyrromethene (ADPM) complexes: ligand-substitution effect on crystal structure

The crystal structures offac-(acetonitrile-κN)(2-{[3,5-bis(4-methoxyphenyl)-2H-pyrrol-2-ylidene-κN1]amino}-3,5-bis(4-<!?tlsb=0.2pt>methoxyphenyl)-1H-pyrrol-1-ido-κN1)tricarbonylrhenium(I)–hexane–acetonitrile (2/1/2), [Re(C36H30N3O4)(CH3CN)(CO)3]·0.5C6H14·CH3CN, (2), andfac-(2-{[3,5-bis(4-methoxyphenyl)-2H-pyrrol-2-ylidene-κN1]amino}-3,5-bis(4-methoxyphenyl)-1H-pyrrol-1-ido-κN1)tricarbonyl(dimethyl sulfoxide-κO)rhenium(I), [Re(C36H30N3O4)(C2H6OS)(CO)3], (3), at 150 K are reported. Both complexes display a distorted octahedral geometry, with afac-Re(CO)3arrangement and one azadipyrromethene (ADPM) chelating ligand in the equatorial position. One solvent molecule completes the coordination sphere of the ReIcentre in the remaining axial position. The ADPM ligand shows high flexibility upon coordination, while retaining its π-delocalized nature. Bond length and angle analyses indicate that the differences in the geometry around the ReIcentre in (2) and (3), and those found in three reportedfac-Re(CO)3–ADPM complexes, are dictated mainly by steric factors and crystal packing. Both structures display intramolecular C—H...N hydrogen bonding. Intermolecular interactions of the Csp2—H...π and Csp2—H...O(carbonyl) types link the discrete monomers into extended chains.

Introducing asymmetry in tetradentate azadipyrromethene chromophores: a systematic study of the impact on electronic and photophysical properties

As analogues of the porphyrinoid and dipyrromethene families of dye, azadipyrromethene (ADPM) derivatives exhibit exciting photophysical properties.

Molecular excitons in a copper azadipyrrin complex

Exciton coupling is applied for the first time to successfully explain the excited-state structure of metalloazadipyrrins.