Yuriy V. Zatsikha

The excited state dynamics in two fully characterized pyridoneBODIPY-fullerene complexes were investigated using time-resolved spectroscopy. Photoexcitation was initially localized on the pyridoneBODIPY chromophore. The energy was rapidly transferred to the fullerene, which subsequently underwent ISC to form a triplet state and returned the energy to the pyridoneBODIPY via triplet-triplet energy transfer. This ping-pong energy transfer mechanism resulted in efficient (>85%) overall conversion of the excited state pyridoneBODIPY constituent despite a complete lack of ISC in the pyridoneBODIPY in the absence of the fullerene partner. The small difference in attachment chemistry for the fullerene did not impact the initial singlet energy transfer. However, the N-methylpyrrolidine bridge did slow both the triplet-triplet energy transfer and the ultimate relaxation rate of the final triplet state when compared to an isoxazole-based bridge. The rates of each step were quantified, and computational predictions were used to complement the proposed mechanism and energetics. The result demonstrated efficient triplet sensitization of a strong chromophore that lacks significant spin-orbit coupling.

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 λ_max∼1300 nm and can be either oxidized to regular [M^II(MB‐DIPY)]⁺ (M=Cu or Ni) or reduced to [M^II(MB‐DIPY)]⁻ compounds. The radical nature of the stable [M^II(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.

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-β-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 β-isoindigo synthesis resulting either in the selective formation of dithio- or diamino-β-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-β-isoindigoid compounds. Properties of the monomeric as well as J-aggregated forms of dithio- and diamino-β-isoindigo were probed by the absorption and fluorescence spectroscopies. It was demonstrated that the tetracyano-diamino-β-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-β-isoindigo derivatives.

A one‐step synthetic pathway for the preparation of fully conjugated β‐isoindigo‐azaDIPY hybrid chromophores comprised of β‐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)‐β‐isoindigo‐azaDIPY derivative revealed that a trans‐configuration of the β‐isoindigo fragment accompanies a planar conjugated core.

A one‐step synthetic pathway for the preparation of fully conjugated β‐isoindigo‐azaDIPY hybrid chromophores comprised of β‐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)‐β‐isoindigo‐azaDIPY derivative revealed that a trans‐configuration of the β‐isoindigo fragment accompanies a planar conjugated core.

Several pyrene–boron-dipyrromethene (BODIPY) and pyrene–BODIPY–ferrocene derivatives with a fully conjugated pyrene fragment appended to the α-position(s) of the BODIPY core have been prepared by Knoevenagel condensation reaction and characterized by one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR), UV–vis, fluorescence spectroscopy, high-resolution mass spectrometry as well as X-ray crystallography. The redox properties of new donor–acceptor BODIPY dyads and triads were studied by electrochemical (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)) and spectroelectrochemical approaches. Formation of weakly bonded noncovalent complexes between the new pyrene–BODIPYs and nanocarbon materials (C₆₀, C₇₀, single-walled carbon nanotube (SWCNT), and graphene) was studied by UV–vis, steady-state fluorescent, and time-resolved transient absorption spectroscopy. UV–vis and fluorescent spectroscopy are indicative of the much stronger and selective interaction between new dyes and (6,5)-SWCNT as well as graphene compared to that of C₆₀ and C₇₀ fullerenes. In agreement with these data, transient absorption spectroscopy provided no evidence for any significant change in excited-state lifetime or photoinduced charge transfer between pyrene–BODIPYs and C₆₀ or C₇₀ fullerenes when the pyrene–BODIPY chromophores were excited into the lowest-energy singlet excited state. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations suggest that the pyrene fragments are fully conjugated into the π-system of BODIPY core, which correlates well with the experimental data.

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.

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).