Radical Complexes of Nickel(II)/Copper(II) and Redox Non-innocent MB-DIPY Ligands: Unusual Stability and Strong Near-Infrared Absorption at λmax ∼1300†nm.

The preparation of radicals with intense and redox-switchable absorption beyond 1000 nm is a long-standing challenge in the chemistry of functional dyes. Here we report the preparation of a series of unprecedented stable neutral nickel(II) and copper(II) complexes of "Manitoba dipyrromethenes" (MB-DIPYs) in which the organic chromophore is present in the radical-anion state. The new stable radicals have an intense absorption at λmax ∼1300 nm and can be either oxidized to regular [MII (MB-DIPY)]+ (M=Cu or Ni) or reduced to [MII (MB-DIPY)]- compounds. The radical nature of the stable [MII (MB-DIPY)] complexes was confirmed by EPR spectroscopy with additional insight into their electronic structure obtained by UV-Vis spectroscopy, electro- and spectroelectrochemistry, magnetic measurements, and X-ray crystallography. The electronic structures and spectroscopic properties of the radical-based chromophores were also probed by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. These nickel(II) and copper(II) complexes represent the first stable radical compounds with a MB-DIPY ligand.

Environmentally Benign Route for Scalable Preparation of 1-Imino-3-thioisoindolines-The Key Building Blocks for the Synthesis of Dithio- and Diamino-ß-isoindigo Derivatives.

A one-step, gram-scale protocol for the preparation of 1-imino-3-thioisoindolines and a novel one-pot two-step methodology of the synthesis of dithio- or diamino-ß-isoindigo derivatives starting from phthalonitriles and sodium hydrosulfide in an aprotic dipolar solvent have been developed. It was demonstrated that the electronic properties of the substituent(s) in the phthalonitrile core play a critical role in ß-isoindigo synthesis resulting either in the selective formation of dithio- or diamino-ß-isoindigo chromophores. The N-acylated 1-imino-3-thioisoindolines can be used for the direct, easily scalable, and chromatography-free procedure for the preparation of a new class of N,N'-diacylamino-ß-isoindigoid compounds. Properties of the monomeric as well as J-aggregated forms of dithio- and diamino-ß-isoindigo were probed by the absorption and fluorescence spectroscopies. It was demonstrated that the tetracyano-diamino-ß-isoindigo 3f can form a J-aggregate that absorbs at 793 nm and fluoresces at 824 nm. This aggregate is stable in N,N-dimethylformamide solution; however, it slowly dissociates in tetrahydrofuran or under sonication conditions. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were employed to elucidate the electronic structures, spectroscopic properties, and aggregation of new dithio- and diamino-ß-isoindigo derivatives.

ß-Isoindigo-azaDIPYs: Fully Conjugated Hybrid Systems with Broad Absorption in the Visible Region.

A one-step synthetic pathway for the preparation of fully conjugated ß-isoindigo-azaDIPY hybrid chromophores comprised of ß-isoindigo and azadipyrromethene moieties is reported. The target compounds were characterized by spectroscopic, crystallographic, and theoretical methods and show unprecedented broad absorption across the visible region of the electromagnetic spectrum. The X-ray crystal structure of the octa(n-butyl)-ß-isoindigo-azaDIPY derivative revealed that a trans-configuration of the ß-isoindigo fragment accompanies a planar conjugated core.

Synthesis pathways for the preparation of the BODIPY analogues: aza-BODIPYs, BOPHYs and some other pyrrole-based acyclic chromophores.

This mini-review summarizes the synthesis strategies for the preparation and post-functionalization of aza-BODIPYs, BOPHYs, "half-Pcs", biliazines, MB-DIPYs, semihemiporphyrazines, BOIMPYs, BOPPYs, BOPYPYs, BOAHYs, and BOAPYs.

Probing Electronic Communication and Excited-State Dynamics in the Unprecedented Ferrocene-Containing Zinc MB-DIPY.

The electronic communication between two ferrocene groups in the electron-deficient expanded aza-BODIPY analogue of zinc manitoba-dipyrromethene (MB-DIPY) was probed by spectroscopic, electrochemical, spectroelectrochemical, and theoretical methods. The excited-state dynamics involved sub-ps formation of the charge-separated state in the organometallic zinc MB-DIPYs, followed by recovery of the ground state via charge recombination in 12 ps. The excited-state behavior was contrasted with that observed in the parent complex that lacked the ferrocene electron donors and has a much longer excited-state lifetime (670 ps for the singlet state). Much longer decay times observed for the parent complex without ferrocene confirm that the main quenching mechanism in the ferrocene-containing 4 is reflective of the ultrafast ferrocene-to-MB-DIPY core charge transfer (CT).

Rigid, yet flexible: formation of unprecedented silver MB-DIPY dimers with orthogonal chromophore geometry.

The reaction between MB-DIPY sodium salts and Ag(i) ions results in the formation of unprecedented MB-DIPY2Ag2 dimers in both solution and the solid state. These dimers have a short Ag-Ag contact (∼2.9 Å) and orthogonal twist in each of the MB-DIPY chromophores. The electronic structure of the unique dimers was probed by spectroscopic and theoretical methods.

Development of a Class of Easily Scalable, Electron-Deficient, Core-Extended Benzo-Fused Azadipyrromethene Derivatives ("MB-DIPY").

We have developed a new synthetic strategy for the preparation of a series of isoindolin-1-imines and isoindolin-1-ones from aromatic ketones and phthalonitrile. Self-condensation reactions of these isoindolin-1-imines led to the formation of a novel class of benzo-fused, highly electron-deficient core-extended azadipyrromethene chromophores ("MB-DIPY"). The influence of temperature, catalyst, and the template ions on the self-condensation reaction rate, yield, and stereoselectivity was examined in detail. New chromophores (sodium, zinc, and metal-free compounds) were characterized by NMR, UV-vis, fluorescence, high-resolution mass spectroscopies, and in many cases, X-ray crystallography. Their redox properties were probed by electrochemical and spectroelectrochemical approaches that revealed the remarkable electron-accepting nature of the new systems. Stepwise one- and two-electron reduction of the new MB-DIPYs and their zinc complexes was investigated by spectroscopic and spectroelectrochemical methods. Both one- and two-electron reduced forms of all zinc complexes studied have strong absorption in the near-infrared region up to ∼1200 nm. Unusual spectroscopic and electrochemical properties of these dyes were correlated with their electronic structures and excited-state natures predicted by density functional theory (DFT) and time-dependent DFT calculations. Despite some structural similarities with well-known aza-BODIPYs, the new MB-DIPYs differ remarkably from them in spectroscopic and redox properties.

Modeling K+ and Ag+ complexation by thiacalix[4]arene amides using DFT: the role of intramolecular hydrogen bonding.

Complexation of methyl-glycine-amide functionalized thiacalix[4]arene with K(+) and Ag(+) has been studied using density functional theory (DFT) in the gas phase. To account for the conformational possibilities of the ligand, the free ligand and its potassium complexes were subjected to global minima searches on the molecular mechanics (MM) level of theory with the OPLS (optimized potentials for liquid simulations) force field. For the free ligand, the order of the energies and geometries of the ligand conformers is in agreement between MM and DFT; however, the position of K(+) in the ligand's cavity was predicted differently by these methods. Hydrogen bonding of amide hydrogens in the ligands' podand arms was found to take place predominantly with the ether oxygens of the same arm rather than the other arms' carbonyls. According to DFT calculations, the silver cation preferred to coordinate with one sulfur bridge and three carbonyl groups, whereas potassium cation favored interaction with the four carbonyl oxygens of the podand amide arms. Neither cation preferred the N-mode of coordination. For all obtained conformers, intramolecular hydrogen bonds disfavor complexation, increasing the preorganizational energy to be paid.