Use of Unprecedented Intramolecular 1, 3-Dipolar Cycloaddition Reaction in meso-Nitrile Oxide-Containing BODIPYs as a New Pathway for the Preparation of Fused NIR Platforms.

Meso-nitrile oxide group in 1,7-Diphenyl-containing BODIPYs can be involved in highly unusual [3+2] intramolecular cycloaddition reaction with the formation of the dihydrobenzo[d]isoxazole-containing BODIPYs. Oxidation of these compounds results in the formation of unprecedented either benzisoxazole- or benzo[b]azepine-fused fully conjugated NIR absorbing BODIPYs. The photophysical properties and electronic structures of the target compounds were studied by an array of experimental and theoretical methods.

Electronic Structures of an Annulated meso-Tetraphenylchlorin and a Related Chlorin Analogue Incorporating an 8-Membered Ring through MCD Spectroscopy and DFT Calculations.

Herein, we compare the electronic structures of the metal-free and nickel(II) derivatives of an annulated meso-tetraphenyldihydroxychlorin with those of the (metallo)chlorin analogues derived by pyrroline ß,ß'-ring cleavage of the annulated (metallo)chlorins. These (metallo)chlorin analogues incorporate 8-membered heterocycles in place of the pyrroline, carry oxo-functionalities on the former pyrroline ß-carbon atoms, and were previously shown to possess drastically ruffled (twisted) nonplanar conformations. The magnetic circular dichroism spectra of all chromophores investigated feature chlorin-like UV-vis spectra and correspondingly reversed (positive-to-negative in ascending energy) sign sequences in the Q-band region, indicative of ΔHOMO < ΔLUMO relationships. Density functional theory (DFT) calculations indicate that the HOMOs in all compounds are a1u-type molecular orbitals (in traditional for the porphyrin spectroscopy D4h point group). Time-dependent DFT calculations correlate well with the experimental spectra and indicate that Gouterman's four-orbital model can be applied to these chromophores. This work highlights to which degree synthetic chlorin analogues can deviate from the structural parameters of natural chlorins without losing their electronic chlorin characteristics.

Role of MCD and Mössbauer Spectroscopy in the Explanation of the Properties of a Highly Soluble (µ-Oxo)bis[tetra(tert-butyl)(phthalocyaninato)iron(III)] Complex, Its Pyridine Adduct, and Redox Forms Oxidized under Anaerobic Conditions in Non-Coordinating Solvents.

Solid-state Mössbauer spectra of a highly soluble (µ-oxo)bis[tetra(tert-butyl)(phthalocyaninato)iron(III)] complex 1 ((PctBuFe)2O) consist of two doublets that represent bent geometry in µ-oxo(1) (1a, ΔEQ = 0.43 mm/s, T = 10 K) and linear geometry in µ-oxo(2) (1b, ΔEQ = 1.40 mm/s, T = 10 K) isomers with the ratio between two isomers depending on the purification method. Both isomers were found to be diamagnetic and transform entirely to the 1a isomer in solution. The room- and low-temperature magnetic circular dichroism (MCD) spectra of 1a µ-oxo(1) show one Faraday A- and one B-term between 670 and 720 nm, which correlate with the 690 nm band and 709 nm shoulder observed in the UV-vis spectrum of this compound. UV-vis and MCD spectra of 1a are almost independent of the temperature. Both 1a and 1b are diamagnetic between room temperature and 4 K. Electrochemical experiments show up to three oxidations and up to four reduction processes in 1a. Its oxidation under spectroelectrochemical or chemical (in the absence of oxygen-containing oxidants) conditions in non-coordinating solvents results in the formation of broad NIR bands around 1195 nm (first oxidation) and 1264 nm (second oxidation). The MCD spectra of the redox-active species show a Faraday B-term signal with negative amplitude in this region and are very different from those in the monomeric PctBu(1-)FeIIIX2 complexes 5X (X = Cl- or CF3CO2-). The pyridine adduct of 1a ((PyPctBuFe)2O; 2Py) is paramagnetic (µB = 2.19, g = 2.11, and J = -6.1 cm-1) and has a major peak at 627 nm of its UV-vis spectrum, which is associated with a MCD pseudo A-term. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, along with the exciton coupling theory, were used to explain the unusually red-shifted intense transitions in 1a as well as the H-aggregate-like spectra of the pyridine adduct 2Py.

Photophysical Exploration of Two Isomers of Octaethyltrioxopyrrocorphin.

The introduction of three ß-oxosubstituents to octaethylporphyrin by means of an oxidation/rearrangement reaction generates the trioxopyrrocorphin chromophore. Pyrrocorphins (hexahydroporphyrins) are generally nonaromatic, but we recently demonstrated trioxopyrrocorphins to possess considerable aromatic character. This contribution explores the photophysical characteristics of these unusual chromophores. In agreement with density functional theory modeling, the UV-vis and magnetic circular dichroism spectra of the two─out of the four possible─triketone regioisomers investigated conform to the Gouterman model of porphyrinoid optical spectra, in alignment with their aromaticity. Their excited-state dynamics shed further light on the degree to which ß-oxo substitutions tune the photophysical properties of porphyrinoids. Introduction of ß-oxo functionalities increases the rate and yield of intersystem crossing and shortens the triplet state lifetime. Unexpectedly, the singlet oxygen generation yield of both pyrrocorphins remains relatively high, with modes of distortion from planarity likely enhancing triplet energy transfer. This work thus expands our understanding of a rare class of porphyrinoids and further characterizes them as sustaining aromatic porphyrinic π-systems. Our findings suggest triple ß-oxo substitution as a viable route toward the development of novel, high-singlet oxygen yield porphyrinic photosensitizers.

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.

Meso-Carbon Atom Nucleophilic Attack Susceptibility in the Sterically Strained Antiaromatic Bis-BODIPY Macrocycle and Extended Electron-Deficient BODIPY Precursor.

A sterically strained 32π-electron antiaromatic bis-BODIPY macrocycle in which two BODIPY fragments are linked by p-divinylbenzene groups was prepared and characterized. Unlike regular BODIPYs, the fluorescence in this macrocycle is quenched. The broad signals in the NMR spectra of the macrocycle were explained by the vibronic freedom of the p-divinylbenzene fragments. The possible diradicaloid nature of the macrocycle was excluded on the basis of variable-temperature EPR spectra in solution and in solid state, which is indicative of its closed-shell quinoidal structure. The meso-C-H bond in the macrocycle and its precursor BODIPY dialdehyde 3 forms a weak hydrogen bond with THF and is susceptible for the nucleophilic attack by organic amines and cyanide anion. The reaction products of such a nucleophilic attack have meso-sp3 carbon atoms and were characterized by NMR, mass spectrometry and, in one case, X-ray crystallography. Unlike the initial bis-BODIPY macrocycle, the adducts have strong fluorescence in the 400 nm region. The electronic structure and spectroscopic properties of new chromophores were probed by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations and correlate well with the experimental data.

Charge-Transfer Spectroscopy of Bisaxially Coordinated Iron(II) Phthalocyanines through the Prism of the Lever's EL Parameters Scale, MCD Spectroscopy, and TDDFT Calculations.

The position of the experimentally observed (in the UV-vis and magnetic circular dichroism (MCD) spectra) low-energy metal-to-ligand charge-transfer (MLCT) band in low-spin iron(II) phthalocyanine complexes of general formula PcFeL2, PcFeL'L″, and [PcFeX2]2- (L, L', or L″ are neutral and X- is an anionic axial ligand) was correlated with the Lever's electrochemical EL scale values for the axial ligands. The time-dependent density functional theory (TDDFT)-predicted UV-vis spectra are in very good agreement with the experimental data for all complexes. In the majority of compounds, TDDFT predicts that the first degenerate MLCT band that correlates with the MCD A-term observed between 360 and 480 nm is dominated by an eg (Fe, dπ) → b1u (Pc, π*) single-electron excitation (in traditional D4h point group notation) and agrees well with the previous assignment discussed by Stillman and co-workers[ Inorg. Chem. 1994, 33, 573-583]. The TDDFT calculations also suggest a small energy gap for b1u/b2u (Pc, π*) orbital splitting and closeness of the MLCT1 eg (Fe, dπ) → b1u (Pc, π*) and MLCT2 eg (Fe, dπ) → b2u (Pc, π*) transitions. In the case of the PcFeL2 complexes with phosphines as the axial ligands, additional degenerate charge-transfer transitions were observed between 450 and 500 nm. These transitions are dominated by a2u (Pc + L, π) → eg (Pc, π*) single-electron excitations and are unique for the PcFe(PR3)2 complexes. The energy of the phthalocyanine-based a2u orbital has large axial ligand dependency and is the reason for a large energy deviation for B1 a2u (Pc + L, π) → eg (Pc, π*) transition. The energies of the axial ligand-to-iron, axial ligand-to-phthalocyanine, iron-to-axial ligand, and phthalocyanine-to-axial ligand charge-transfer transitions were discussed on the basis of TDDFT calculations.

Resolving a Half-Century-Long Controversy between (Magneto)optical and EPR Spectra of Single-Electron-Reduced [PcFe]-, [PcFeL]-, and [PcFeX]2- Complexes: Story of a Double Flip.

The reduction of iron(II) phthalocyanine (Pc(2-)FeII) or its bisaxially coordinated complexes results in the formation of the purple/red [PcFe]-, [PcFeL]-, and [PcFeX]2- (L is neutral and X is anionic ligand) species. The X-ray structure of the [K(DME)4][PcFe] complex exhibits a square-planar [PcFe]- anion. 1H NMR spectra of the reduced species have one or two phthalocyanine broad peaks between 15 and 17 ppm. Solution magnetic moments are consistent with the presence of a single unpaired electron. A solid-state Mössbauer spectrum of [K(DME)4][PcFe] is consistent with an early report [Taube, R. Pure Appl. Chem.1974, 38, 427-438]. The solid-state EPR spectrum of the [PcFe]- anion is close to that recorded by Konarev et al. [ Dalton Trans.2012, 41, 13841-13847]. Solution EPR spectra of reduced species have axial symmetry (g⊥ ∼ 2.08-2.17 and g|| ∼ 1.95-1.96) and correlate well with spectra reported by Lever and Wilshire in 1978 [ Inorg. Chem.1978, 17, 1145-1151]. The UV-vis spectra of pentacoordinated [PcFeL]- and [PcFeX]2- anions consist of the characteristic bands around 810, 690, and 515 nm. These bands correlate well with the set of MCD pseudo A-terms and resemble transitions in the [Pc(3-)M]- and [Pc(3-)ML]- compounds. The UV-vis and MCD spectra of [PcFeL]- and [PcFeX]2- complexes are in stark contrast to the crystallographically characterized reference [Pc(2-)CoI]- anion, which is EPR silent, has a regular diamagnetic 1H NMR spectrum, and has an intense Q-band at 699 nm, which correlates well with the strong MCD A-term. The DFT and TDDFT calculations are suggestive of the iron(II) center in a (dxy)2(dxz,yz)3(dz2)1 (s = 1) electronic configuration that is antiferromagnetically coupled with the one-electron-reduced Pc(3-) ligand (i.e., [Pc(3-)FeII]-, [Pc(3-)FeIIL]-, and [Pc(3-)FeIIX]2-). The calculated EPR, Mössbauer, and UV-vis spectra of [PcFe]-, [PcFeL]-, and [PcFeX]2- complexes are in excellent agreement with the experimental data, thus resolving the controversy between axial s = 1/2 like EPR and Pc(3-)-like UV-vis spectra of these compounds.

Unveiling KuQuinone Redox Species: An Electrochemical and Computational Cross Study.

The study of the electrochemical properties of variegated quinones is a fascinating topic in chemistry. In fact, redox reactions occurring with quinoid scaffolds are essential for most of their applications in biological systems, in photoelectrochemical devices, and in many other fields. In this paper, a detailed investigation of KuQuinones' redox behavior is presented. The distinctiveness of such molecules is the presence in the structure of two condensed naphthoquinone units, which implies the possibility to undergo multiple one-electron reduction processes. Solvent, supporting electrolyte, and hydrogen bond donor species effects have been elucidated. Changing the experimental parameters provoked significant shift of the redox potential for each reduction process. In particular, additions of 2,2,2-trifluoroethanol as a hydrogen bond donor in solution as well as Lewis acid coordination were crucial to obtain important shifts of the redox potentials toward more favorable values. UV-vis-NIR spectroelectrochemical experiments and DFT calculations are also presented to clarify the nature of the reduced species in solution.

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.

Application of Lever's EL Parameter Scale toward Fe(II)/Fe(III) versus Pc(2-)/Pc(1-) Oxidation Process Crossover Point in Axially Coordinated Iron(II) Phthalocyanine Complexes.

The electronic structures and, particularly, the nature of the HOMO in a series of PcFeL2, PcFeL'L″, and [PcFeX2]2- complexes (Pc = phthalocyaninato(2-) ligand; L = NH3, n-BuNH2, imidazole (Im), pyridine (Py), PMe3, PBu3, t-BuNC, P(OBu)3, and DMSO; L' = CO; L″ = NH3 or n-BuNH2; X = NCO-, NCS-, CN-, imidazolate (Im-), or 1,2,4-triazolate(Tz-)) were probed by electrochemical, spectroelectrochemical, and chemical oxidation as well as theoretical (density functional theory, DFT) studies. In general, energies of the metal-centered occupied orbitals in various six-coordinate iron phthalocyanine complexes correlate well with Lever Electrochemical Parameter EL and intercross the phthalocyanine-centered a1u orbital in several compounds with moderate-to-strong π-accepting axial ligands. In these cases, an oxidation of the phthalocyanine macrocycle (Pc(2-)/Pc(1-)) rather than the central metal ion (Fe(II)/Fe(III)) was theoretically predicted and experimentally confirmed.

Similar, Yet Different: Long-Range Metal-Metal Coupling and Electron-Transfer Processes in Metal-Free 5,10,15,20-Tetra(ruthenocenyl)porphyrin.

The electronic structure, redox properties, and long-range metal-metal coupling in metal-free 5,10,15,20-tetra(ruthenocenyl)porphyrin (H2TRcP) were probed by spectroscopic (NMR, UV-vis, magnetic circular dichroism (MCD), and atmospheric pressure chemical ionization (APCI)), electrochemical (cyclic voltammetry, CV, and differential pulse voltammetry, DPV), spectroelectrochemical, and chemical oxidation methods, as well as theoretical (density functional theory, DFT, and time-dependent DFT, TDDFT) approaches. It was demonstrated that the spectroscopic properties of H2TRcP are significantly different from those in H2TFcP (metal-free 5,10,15,20-tetra(ferrocenyl)porphyrin). Ruthenocenyl fragments in H2TRcP have higher oxidation potentials than the ferrocene groups in the H2TFcP complex. Similar to H2TFcP, we were able to access and spectroscopically characterize the one- and two-electron oxidized mixed-valence states in the H2TRcP system. DFT predicts that the porphyrin π-system stabilizes the [H2TRcP]+ mixed-valence cation and prevents its dimerization, which is characteristic for ruthenocenyl systems. However, formation of the mixed-valence [H2TRcP]2+ is significantly less reproducible than the formation of [H2TRcP]+. DFT and TDDFT calculations suggest the ruthenocenyl fragment dominance in the highest occupied molecular orbital (HOMO) energy region and the presence of the low-energy MLCT (Rc → porphyrin (π*)) transitions in the visible region with energies higher than the predominantly porphyrin-centered Q-bands.

Accurate Prediction of Mössbauer Hyperfine Parameters in Bis-Axially Coordinated Iron(II) Phthalocyanines Using Density Functional Theory Calculations: A Story of a Single Orbital Revealed by Natural Bond Orbital Analysis.

Density Functional Theory (DFT) calculations coupled with several exchange-correlation functionals were used for the prediction of Mössbauer hyperfine parameters of 36 bis-axially coordinated iron(II) phthalocyanine complexes with the general formulas PcFeL2, PcFeL'L″, and [PcFeX2]2-, including four new compounds. Both gas-phase and PCM calculations using BPW91 and MN12L exchange-correlation functionals were found to accurately predict both Mössbauer quadrupole splittings and the correct trends in experimentally observed isomer shifts. In comparison, hybrid exchange-correlation functionals underestimated quadrupole splittings, while still accurately predicted isomer shifts. Out of ∼40 exchange-correlation functionals tested, only MN12L was found to correctly reproduce quadrupole splitting trends in the PcFeL2 complexes coordinated with phosphorus-donor axial ligands (i.e., P(OnBu)3 ≈ P(OEt)3 < PMe3 < P[(CH2O)2CH2]-p-C6H4NO2 < PEt3 ≈ PnBu3). Natural Bond Orbital (NBO) analysis was successfully used to explain the general trends in the observed quadrupole splitting for all compounds of interest. In particular, the general trends in the quadrupole splitting correlate well with the axial ligand dependent, NBO-predicted population of the 3dz2 orbital of the Fe ion and are reflective of the hypothesis proposed by Ohya and co-workers ( Inorg. Chem., 1984, 23, 1303) on the adaptability of the phthalocyanine's π-system toward Fe-Lax interactions. The first X-ray crystal structure of a PcFeL2 complex with axial phosphine ligands is also reported.

Accurate Prediction of the Excited States in the Fully Conjugated Porphyrin Tapes across the Full Spectral Range: A Story of the Interplay between π-π* and Intramolecular Charge-Transfer Transitions in Soft Chromophores.

The ability of density functional theory (DFT) and time-dependent DFT (TDDFT) methods for the accurate prediction of the energies and oscillator strengths of the excited states in a series of fully conjugated meso-meso ß-ß ß-ß triple-linked porphyrin oligomers (porphyrin tapes 2-12) was probed in the gas phase and solution using several exchange-correlation functionals. It was demonstrated that the use of the hybrid B3LYP functional provides a good compromise for the accurate prediction of the localized π-π* and intramolecular charge-transfer transitions, thus allowing confident interpretation of the UV-vis-NIR spectra of porphyrin oligomers. The TDDFT-based sum-over-state (SOS) calculations for the porphyrin tape dimer 2 and trimer 3 as well as parent monomer 1 correctly predicted the signs and shapes of the magnetic circular dichroism (MCD) signals in the low-energy region of the spectra.

Binding a Meridional Ligand in a Facial Geometry: A Square Peg in a Round Hole.

The bis(pyridylimino)isoindoline (BPI) ligand is a tridentate chelate that binds to metals via a meridional coordination mode. However, when this ligand forms a complex with Re(CO)3, an almost exclusively facial moiety, the BPI ligand deforms to coordinate in a facial mode. We have in-vestigated this deformation via structural and theoretical means, and the non-planar binding mode of the ligand bathochromically shifts the metal to ligand charge transfer (MLCT) transition.

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.

Siamese-Twin Porphyrin Goes Platinum: Group 10 Monometallic, Homobimetallic, and Heterobimetallic Complexes.

A series of PtII-based monometallic (H2PtL), homobimetallic (Pt2L), and heterobimetallic (NiPtL and PdPtL) group 10 complexes of the previously established expanded twin porphyrin (H4L) were prepared. Structural characterization of the bimetallic PtII series (Pt2L, NiPtL, and PdPtL) revealed their similar general structures, with slight differences correlated to the ion size. An improvement of the metal-ion insertion process also allowed efficient preparation of the known Pd2L complex, and the novel heterobimetallic NiPdL complex was also structurally characterized. UV-vis spectroscopy, NMR spectroscopy, magnetic circular dichroism (MCD), and (spectro)electrochemistry were used to characterize the complexes; the electronic properties followed largely established lines for metal complexes of the twin porphyrin, except that the PtII-based systems exhibited more complex UV-vis spectral signatures. MCD spectra accompanied by density functional theory (DFT)/time-dependent DFT computations (TDDFT) rationalize the origins of the optical features of the twin porphyrin. The presence of the nonplanar, nonaromatic macrocyclic π system with conjugation pathways confined to each half of the molecule could be visualized. Significant pyrazole(π) → pyrrole(π*) charge-transfer character was predicted for several transitions in the visible region. This study adds to our fundamental understanding of the formation, structure, and electronic structure of bimetallic complexes of this class of expanded metalloporphyrins containing nonpyrrolic moieties.

Synthesis, Characterization, and Electron-Transfer Properties of Ferrocene-BODIPY-Fullerene Near-Infrared-Absorbing Triads: Are Catecholopyrrolidine-Linked Fullerenes a Good Architecture to Facilitate Electron-Transfer?

A series of covalent ferrocene-BODIPY-fullerene triads with the ferrocene groups conjugated to the BODIPY π-system and the fullerene acceptor linked at the boron hub by a common catecholpyrrolidine bridge were prepared and characterized by 1D and 2D NMR, UV/Vis, steady-state fluorescence spectroscopy, high-resolution mass spectrometry, and, for one of the derivatives, X-ray crystallography. Redox processes of the new compounds were investigated by electrochemical (CV and DPV) methods and spectroelectrochemistry. DFT calculations indicate that the HOMO in all triads was delocalized between ferrocene and BODIPY π-system, the LUMO was always fullerene-centered, and the catechol-centered occupied orbital was close in energy to the HOMO. TDDFT calculations were indicative of the low-energy, low-intensity charge-transfer bands originated from the ferrocene-BODIPY core to fullerene excitation, which explained the similarity of the UV/Vis spectra of the ferrocene-BODIPY dyads and ferrocene-BODIPY-fullerene triads. Photophysical properties of the new triads as well as reference BODIPY-fullerene and ferrocene-BODIPY dyads were investigated by pump-probe spectroscopy in the UV/Vis and NIR spectral regions following selective excitation of the BODIPY-based antenna. Initial charge transfer from the ferrocene to the BODIPY core was shown to outcompete sub-100 fs deactivation of the excited state mediated by the catechol bridge. However, no subsequent electron transfer to the fullerene acceptor was observed. The initial charge separated state relaxes by recombination with a time constant of 150-380 ps.

1,3-Diylideneisoindolines: Synthesis, Structure, Redox, and Optical Properties.

Diiminoisoindoline (DII) is a crucial reagent for the synthesis of phthalocyanine as well as related macrocycles and chelates such as hemiporphyrazine and bis(iminopyridyl)isoindoline. In this report, we present the synthesis and characterization of four 1,3-diylideneisoindolines prepared via the reaction of several organic CH acids and DII. These orange or red compounds exhibit intense π → π* transitions in the UV-visible region. The redox properties and electronic structures of all new compounds were investigated using cyclic voltammetry and density functional theory (DFT). The observed electrochemistry and UV-visible transitions are in good agreement with the DFT and time-dependent DFT calculations, which indicate that the HOMO is largely centered at the O═C-C-C═O fragments, and the lowest unoccupied molecular orbital is more extended onto the isoindoline unit.

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.