Environmental impacts of continued CO2 production have led to an increased need for new methods of CO2 removal and energy development. Nanomaterials are of special interest for these applications, because of their unique chemical and physical properties that allow for highly active surfaces. Here, we successfully synthesize AgPd nanodendrite-modified Au nanoprisms in various shapes (nanoprisms, hexagonal nanoplates, and octahedral nanoparticles) by selective metal deposition. This strategy involves coupling galvanic replacement between Ag layers in Au@Ag core–shell nanoprisms and H2PdCl4 with a coreduction process of silver and palladium ions. Synthesis of AgPd nanodendrite-tipped (4.14–11.47 wt % Pd) and -edged (25.25–31.01 wt % Pd) Au nanoparticles can be controlled simply by tuning the concentration of H2PdCl4. More importantly, these multicomponent AgPd nanodendrite-modified Au nanoparticles show exceptional electrocatalytic performance for CO2 reduction. AgPd nanodendrite-edged Au nanoprisms show more favorable potentials (−0.18 V vs RHE) than previously reported nanocatalysts for the reduction of CO2 to formate, and exhibit higher faradaic efficiencies (49%) than Au, Au@Ag, and AgPd nanodendrite-tipped Au nanoprisms in aqueous electrolytes. Moreover, AgPd nanodendrite-modified Au nanoprisms show much higher selectivity and faradaic efficiency for CO2 reduction to CO (85–87%) than Au and Au@Ag nanoprisms (43–64%) in organic electrolytes. The high performance of these particles for CO2 reduction is attributed to the unique structure of AgPd nanodendrite-modified Au nanoprisms and the synergistic effect of Ag having an affinity for CO2, efficient binding of hydrogen at Pd, and Au as a stable, conductive support. In addition, AgPd nanodendrite-edged Au nanoprisms show highly stable catalytic activity during long-term electrolyses (up to 12 h) and repetitive use. These exciting results indicate that AgPd nanodendrite-modified Au nanoparticles are promising for application in CO2 conversion into useful fuels.

Developing facile synthetic routes to multifunctional nanoparticles combining the magnetic properties of iron oxides with the optical and catalytic utility of noble metal particles remains an important goal in realizing the potential of hybrid nanomaterials. To this end, we have developed a single route to noble metal-decorated magnetic nanoparticles (Fe3O4@SiO2–M; M = Au, Pd, Ag, and PtAg) and characterized them by HRTEM and STEM/EDX imaging to reveal their nanometer size (16 nm Fe3O4 and 1–5 nm M seeds) and uniformity. This represents one of the few examples of genuine multifunctional particles on the nanoscale. We show that these hybrid structures have excellent catalytic activity for the reduction of 4-nitrophenol (knorm = 2 × 107 s−1 mol(Pd)−1; 5 × 106 s−1 mol(Au)−1; 5 × 105 s−1 mol(PtAg)−1; 7 × 105 s−1 mol(Ag)−1). These rates are the highest reported for nano-sized comparables, and are competitive with mesoparticles of similar composition. Due to their magnetic response, the particles are also suitable for magnetic recovery and maintain >99% conversion for at least four cycles. Using this synthetic route, Fe3O4@SiO2–M particles show great promise for further development as a precursor to complicated anisotropic materials or for applications ranging from nanocatalysis to biomedical sensing.

Herein we adhere gold nanorods (Au NRs) to glass coverslips through electrostatic interactions by treating the glass coverslips with (3-aminopropyl)trimethoxysilane (APTMS) and polystyrene sulfonate (PSS). These Au NR-functionalized coverslips were used to demonstrate the sustainable, catalytic reduction of 4-nitroaniline by sodium borohydride. Au NRs in solution were compared to the Au NR coverslips and were found to have pseudo-first-order observed rate constants of 1.35 × 10−2 min−1 (2.79 × 106 min−1 per Au) and 4.12 × 10−2 min−1 (4.26 × 105 min−1 per Au), respectively. The same catalytic reaction was executed under photolysis (1000 W Xe lamp); free NRs and Au NR-functionalized coverslips demonstrate pseudo-first-order observed rate constants of 2.15 × 10−2 min−1 (4.44 × 106 min−1 per Au) and 6.28 × 10−2 min−1 (6.48 × 105 min−1 per Au), respectively, which are two orders of magnitude faster than the only other affixed catalyst, Au NP in polymer. In addition to being scalable in Au-NR layers, a representative Au NR-functionalized coverslip was re-used for three consecutive catalysis reactions before decrease in rate, and had a rate ∼65% of the original reaction after the fifth cycle. Thus, we have demonstrated an efficient and reusable, thermal and photochemical gold nanorod catalyst assembly that does not require a complex synthetic protocol or the use of specialized equipment.

One of the key concerns with the development of radical-generating reactive therapeutics is the ability to control the activation event within a biological environment. To that end, a series of quinoline–metalloenediynes of the form M(QuiED)·2Cl (M = Cu(II), Fe(II), Mg(II), or Zn(II)) and their independently synthesized cyclized analogs have been prepared in an effort to elucidate Bergman cyclization (BC) reactivity differences in solution. HRMS(ESI) establishes a solution stoichiometry of 1:1 metal to ligand with coordination of one chloride counter ion to the metal center. EPR spectroscopy of Cu(QuiED)·2Cl and Cu(QuiBD)·2Cl denotes an axially-elongated tetragonal octahedron (g|| > g⊥ > 2.0023) with a dx2-y2dx2-y2 ground state, while the electronic absorption spectrum reveals a pπ Cl→Cu(II) LMCT feature at 19,000 cm−1, indicating a solution structure with three nitrogens and a chloride in the equatorial plane with the remaining quinoline nitrogen and solvent in the axial positions. Investigations into the BC activity reveal formation of the cyclized product from the Cu(II) and Fe(II) complexes after 12 h at 45 °C in solution, while no product is observed for the Mg(II) or Zn(II) complexes under identical conditions. The basis of this reactivity difference has been found to be a steric effect leading to metal–ligand bond elongation and thus, a retardation of solution reactivity. These results demonstrate how careful consideration of ligand and complex structure may allow for a degree of control and selective activation of these reactive agents.A series of metalloenediynes containing Fe(II), Cu(II), Zn(II), or Mg(II) have been prepared which demonstrate differing solution Bergman cyclization relativities. EPR and UV–Vis spectroscopic investigations reveal an interesting binding mode of the tetradentate ligand. Our results demonstrate how complex structure may allow for selective activation of these reactive agents.

Halting cancer progression by altering the tumor microenvironment is an exciting new frontier in oncology. One target for new therapies is the structural support provided by the extracellular matrix, which for cancer cells is often abnormal and undergoes drastic modification during angiogenesis, tumor proliferation, and metastasis. We have developed a new magnetic nanoparticle-based agent, Fe3O4–PEG–EDDA (EDDA: (Z)-octa-4-en-2,6-diyne-1,8-diamine), that is capable of generating radicals via Bergman cyclization of the pendant enediyne during mild hyperthermia treatment using an alternating magnetic field. We observe formation of a cyclized aromatic product in the Raman spectra of the thermally excited material and can detect polymeric product after periods of induction. When mixed with the basement membrane extract Matrigel, the nanoparticles do not interfere with normal biopolymer network formation. Applying the same hyperthermia conditions as in solution samples, Fe3O4–PEG–EDDA causes structural collapse of the matrix, visible by electron microscopy, in contrast to the nonradical-forming thermal control Fe3O4–PEG–BD (BD: o-xylylenediamine). Localized damage to the extracellular matrix by nanoparticle-induced molecular transformations represent a conceptual new tool in tumor microenvironment modification.

Current approaches toward modulation of metal-induced Aβ aggregation pathways involve the development of small molecules that bind metal ions, such as Cu(II) and Zn(II), and interact with Aβ. For this effort, we present the enediyne-containing ligand (Z)-N,N′-bis[1-pyridin-2-yl-meth(E)-ylidene]oct-4-ene-2,6-diyne-1,8-diamine (PyED), which upon chelation of Cu(II) and Zn(II) undergoes Bergman-cyclization to yield diradical formation. The ability of this chelation-triggered diradical to modulate Aβ aggregation is evaluated relative to the non-radical generating control pyridine-2-ylmethyl-(2-{[(pyridine-2-ylmethylene)-amino]-methyl}-benzyl)-amine (PyBD). Variable-pH, ligand UV-vis titrations reveal pKa = 3.81(2) for PyBD, indicating it exists mainly in the neutral form at experimental pH. Lipinski's rule parameters and evaluation of blood–brain barrier (BBB) penetration potential by the PAMPA–BBB assay suggest that PyED may be CNS+ and penetrate the BBB. Both PyED and PyBD bind Zn(II) and Cu(II) as illustrated by bathochromic shifts of their UV-vis features. Speciation diagrams indicate that Cu(II)–PyBD is the major species at pH 6.6 with a nanomolar Kd, suggesting the ligand may be capable of interacting with Cu(II)–Aβ species. In the presence of Aβ40/42 under hyperthermic conditions (43 °C), the radical-generating PyED demonstrates markedly enhanced activity (2–24 h) toward the modulation of Aβ species as determined by gel electrophoresis. Correspondingly, transmission electron microscopy images of these samples show distinct morphological changes to the fibril structure that are most prominent for Cu(II)–Aβ cases. The loss of CO2 from the metal binding region of Aβ in MALDI-TOF mass spectra further suggests that metal–ligand–Aβ interaction with subsequent radical formation may play a role in the aggregation pathway modulation.

Thrombosis is a hallmark of several chronic diseases leading to potentially fatal heart attacks and strokes. Frontline interventions include intravenous delivery of potent, enzymatic fibrinolytics that possess a high risk for inducing systemic bleeding. As a conceptual countermeasure, we have developed a water-soluble PEGylated gold nanoparticle appended with the enediyne diamine (Z)-octa-4-en-2,6-diyne-1,8-diamine that is capable of photothermally generating 1,4-diradical species under visible excitation (λ = 514 nm, 100 mW, 2–6 h). In the absence of biopolymer substrate, photothermal excitation of these particles leads to self-quenching polymer coating formation in water. When these radical-generating nanoparticles are intrinsically applied toward the blood clot structural protein assembly fibrin, as well as its nonpolymerized precursor protein fibrinogen, scanning electron microscopy images reveal significantly modified fibrin clot morphology, as evidenced by larger void spaces and collapsed fiber regions. Quantitatively, laser confocal microscopy images of Alexa Fluor 488-labeled fibrin clots extrinsically treated with nanoparticles at the clot/solution interface show that photothermal radical formation by these particles leads to marked increase in the number of larger pore sizes (>2.0 μm) within the fibrin matrix, which derive from a corresponding decrease in the histogram of smaller pore sizes (1.5–2.0 μm). These larger pore sizes ultimately result in total perfusion of solution through the entire clot volume. The chemical manifestation of this is that radical-induced modifications occur mainly at the protein level but lead to morphological changes at the micron scale. Overall, this technology could have significant impact for disease states such as deep vein thrombosis via a localized, catheter-delivered approach.

Reaction of 2 equiv of 1,2-bis((diphenylphosphino)ethynyl)benzene (dppeb, 1) with Pt(cod)Cl2 followed by treatment with N2H4 yields the reduced Pt(0) metalloenediyne, Pt(dppeb)2, 2. This complex is stable to both air oxidation and metal-mediated Bergman cyclization under ambient conditions due to the nearly idealized tetrahedral geometry. Reaction of 2 with 1 equiv of I2 in the presence of excess 1,4-cyclohexadiene (1,4-CHD) radical trap rapidly and near-quantitatively generates the cis-Bergman-cyclized, diiodo product 3 (31P: δ = 41 ppm, JPt–P = 3346 Hz) with concomitant loss of 1 equiv of uncyclized phosphine chelate (31P: δ = −33 ppm). In contrast, addition of 2 equiv of I2 in the absence of additional radical trap instantaneously forms a metastable Pt(dppeb)22+ intermediate species, 4, that is characterized by δ = 51 ppm in the 31P NMR (JPt–P = 3171 Hz) and νC≡C = 2169 cm–1 in the Raman profile, indicating that it is an uncyclized, bis-ligated complex. Over 24 h, 4 undergoes ligand exchange to form a neutral, square planar complex that spontaneously Bergman cyclizes at ambient temperature to give the crystalline product Pt(dppnap-I2)I2 (dppnap-I2 = (1,4-diiodonaphthalene-2,3-diyl)bis(diphenylphosphine)), 5, in 52% isolated yield. Computational analysis of the oxidation reaction proposes two plausible flattened tetrahedral structures for intermediate 4: one where the phosphine core has migrated to a trans-spanning chelate geometry, and a second, higher energy structure (3.3 kcal/mol) with two cis-chelating phosphine ligands (41° dihedral angle) via a restricted alkyne-terminal starting point. While the energies are disparate, the common theme in both structures is the elongated Pt–P bond lengths (>2.4 Å), indicating that nucleophilic ligand substitution by I– is on the reaction trajectory to the cyclized product 5. The efficiency of the redox-mediated Bergman cyclization reaction of this stable Pt(0) metalloenediyne prodrug and resulting cisplatin-like byproduct represents an intriguing new strategy for potential dual-threat metalloenediyne therapeutics.

Porphyrins have remarkable utility in optical and materials applications due to their extensive π-network and the corresponding electronic properties associated with this delocalization. Recent strategies have focused on methods to modulate these properties by chemically extending the conjugation. Our approach to periphery modification has centered on the application of diradicals generated through unique diyne-ene and diazo-keto functionalization at the β,β′-position of the macrocycle. In the former case, Bergman cyclization of the enediyne motif generates a new aromatic ring via a 1,4-phenyl diradical intermediate. In the absence of bimolecular quenchers in very high concentrations, the diradical adds across the adjacent phenyl rings of the meso-positions to extend the aromaticity across three rings. In the second case, dione or diazo-keto functionalization and subsequent reaction with nucleophiles in the presence of Ag+ generates acetals that lead to modified chemical properties and potentially, additional reactivity at the periphery. Diazoketochlorin photolysis on the other hand, leads to rapid N2 extrusion and initial carbene formation. The carbene is short lived and cannot be trapped even at extremely low temperatures (2 K). The subsequent Wolff ring-contracted ketene, however, is detectable, demonstrating that the out-of-plane electronic configuration is initially generated and reacts to give the nucleophile-quenched species, as well as relaxing to form exocyclic ring addition and other radical-based products. In addition to generating unique infrared and electronic spectral properties, together these strategies offer unusual synthetic opportunities, to markedly modulate macrocycle electronic structure in a highly asymmetric manner to form truly distinct porphyrinoid constructs.Graphical abstractHighlights► Approach to periphery modification centered on the application of diradicals generated through unique diyne-ene and diazo-keto functionalization at the β,β′-position of the macrocycle. ► Diradical adds across the adjacent phenyl rings of the meso-positions to extend the aromaticity across three rings. ► Dione or diazo-keto functionalization and subsequent reaction with nucleophiles in the presence of Ag+, generates acetals that lead to modified chemical properties additional reactivity potential at the periphery – diazoketochlorin photolysis leads to rapid N2 extrusion and initial carbene formation. ► Wolff ring-contracted ketene, is detectable, demonstrating that the out-of-plane electronic configuration is initially generated and reacts to give the nucleophile-quenched species, as well as relaxing to form exocyclic ring addition and other radical-based products. ► Synthetic opportunities to markedly modulate macrocycle electronic structure in a highly asymmetric manner to form truly distinct porphyrinoid constructs.

Thermal Bergman cyclization of Pt(II) dialkynylporphyrins reveals a marked reduction in the cyclization temperature relative to the free base and Zn(II) derivatives. In contrast, photogenerated 3ππ* population produces no detectable Bergman photocyclization, suggesting that the photoreactivities of the related free base and Zn(II) derivatives occurs via the 1ππ* state.

Photolysis of metalated (Cu and Ni) and free base 2-diazo-3-oxochlorins within a frozen matrix (λ = 457.9 nm, toluene, 80 K) generates a single photointermediate with a hypsochromically shifted electronic absorption spectrum relative to the starting diazochlorins. The appearance of ketene (∼2131 cm–1) and azete (∼1670 cm–1) vibrations in infrared absorption and Raman spectra, respectively, identifies this intermediate as resulting from the Wolff rearrangement of the diazochlorins upon N2 loss. Computational modeling of the vibrational spectra and TDDFT simulation of the electronic transitions of potential photointermediates corroborate this assignment. Isolation and analysis of photoproducts of these diazochlorins formed within n-butanol-doped frozen toluene matrices indicate near exclusive formation of azeteoporphyrins. In sharp contrast, room temperature laser photolysis of these materials yields a mixture of photoproducts deriving from the presence of both carbene and ketene intermediates. Computational modeling of the intramolecular reactivity of the proposed sp2 carbene intermediate shows exclusive bond insertion to the adjacent phenyl group, and no evidence of Wolff rearrangement. Computational reaction profile analyses reveal that the barrierless Wolff rearrangement proceeds via an out-of-plane carbene electronic configuration that is generated directly during the loss of N2. The formation of out-of-plane carbene, resulting in the exclusive formation of the observed ketene photointermediate at low temperatures, is consistent with orbital symmetry considerations and by the geometric constraints imposed by the frozen matrix. Combined, this leads to a model showing that azeteoporphyrin formation via the Wolff rearrangement is dependent upon the structural disposition of the adjacent framework, and the specific reaction intermediate formed is very sensitive to this feature.

Gold nanoparticle theranostic agents have dramatic potential in the fight against disease, particularly cancer, as multifunctional platforms combining biocompatibility, unique optical properties for detection/activation, and heat generation. In this vein, a new thiol-functionalized enediyne surfactant ligand was synthesized and coordinated to gold nanoparticles, as confirmed by the red-shift in the optical spectrum from λ = 520 to 529 nm upon ligand exchange. Raman spectra of the nanoparticle conjugate material show characteristic vibrations at 2192 (alkyne), 1582 (alkene), and 670 cm–1 (C–S). The photoreactivity of the material is explored under two sets of photolysis conditions: solution, λexc = 514 nm, RT, t = 8 h; solid aggregate, λexc = 785 nm, T = −190 °C, t = 4 h. Under these conditions, exciting into the surface plasmon of the Au nanoparticle substrate transfers heat to the organic ligand layer, initiating enediyne cyclization and generating surface radicals that lead to subsequent polymerization. New vibrational signatures arise in the alkyne (2170–1900 cm–1) and aromatic (1520–1200 cm–1) spectral regions, indicating the formation of highly conjugated species in the initial stages of the photoreaction. Prolonged irradiation results in the observation of a dense polymer coating in the TEM images, complete loss of observable molecular vibrations in the Raman spectra as a result of strong fluorescence, and a red-shift and broadening of the surface plasmon band in the electronic spectrum. Translation of this approach to nanorods and other architectures is also possible with carbon coatings clearly visible by TEM. The reported nanomaterial design represents a new approach to developing reactive biomedical agents for phototherapy applications, as well as a novel method toward carbonaceous coatings of nanoarchitectures.Keywords: (Au nanoparticles; photothermal activation; radical polymerization); surface functionalization;

The spectroscopic, electronic, and DNA-binding characteristics of two novel ruthenium complexes based on the dialkynyl ligands 2,3-bis(phenylethynyl)-1,4,8,9-tetraaza-triphenylene (bptt, 1) and 2,3-bis(4-tert-butyl-phenylethynyl)-1,4,8,9-tetraaza-triphenylene (tbptt, 2) have been investigated. Electronic structure calculations of bptt reveal that the frontier molecular orbitals are localized on the pyrazine-dialkynyl portion of the free ligand, a property that is reflected in a red shift of the lowest energy electronic transition (1: λmax = 393 nm) upon substitution at the terminal phenyl groups (2: λmax = 398 nm). Upon coordination to ruthenium, the low-energy ligand-centered transitions of 1 and 2 are retained, and metal-to-ligand charge transfer transitions (MLCT) centered at λmax = 450 nm are observed for [Ru(phen)2bptt]2+(3) and [Ru(phen)2tbptt]2+(4). The photophysical characteristics of 3 and 4 in ethanol closely parallel those observed for [Ru(bpy)3]2+ and [Ru(phen)3]2+, indicating that the MLCT excited state is primarily localized within the [Ru(phen)3]2+ manifold of 3 and 4, and is only sparingly affected by the extended conjugation of the bptt framework. In an aqueous environment, 3 and 4 possess notably small luminescence quantum yields (3: ϕH2O = 0.005, 4: ϕH2O = 0.011) and biexponential decay kinetics (3: τ1 = 40 ns, τ2 = 230 ns; 4: τ1 ∼ 26 ns, τ2 = 150 ns). Addition of CT-DNA to an aqueous solution of 3 causes a significant increase in the luminescence quantum yield (ϕDNA = 0.045), while the quantum yield of 4 is relatively unaffected (ϕDNA = 0.013). The differential behavior demonstrates that tert-butyl substitution on the terminal phenyl groups inhibits the ability of 4 to intercalate with DNA. Such changes in intrinsic luminescence demonstrate that 3 binds to DNA via intercalation (Kb = 3.3 × 104 M−1). The origin of this light switch behavior involves two competing 3MLCT states similar to that of the extensively studied light switch molecule [Ru(phen)2dppz]2+. The solvent- and temperature-dependence of the luminescence of 3 reveal that the extended ligand aromaticity lowers the energy of the 3ππ* excited state into competition with the emitting 3MLCT state. Interconversion between these two states plays a significant role in the observed photophysics and is responsible for the dual emission in aqueous environments.

The synthesis of novel metalloendiyne complexes MLRX2 (where L = 1,4-dibenzyl/diethyl-1,4-diaza-cyclododec-8-ene-6,10-diyne, X = halogen) are reported with their X-ray crystal structures and thermal Bergman cyclization temperatures. Two distinct types of constructs are obtained; the Zn(II) compounds are tetrahedral, while the Cu(II) and the Pd(II) compounds are all distorted- or square-planar. Each possesses structurally similar enediyne conformations and critical distances (3.75−3.88 Å). The tetragonal Cu(II) species all exhibit Bergman cyclization temperatures between 140 and 150 °C in the solid state, while the square-planar Pd(II) analogues possess similar critical distances but cyclize at significantly higher temperatures (205−220 °C). In contrast, the Zn(II) derivatives show a marked halogen dependence, with X = Cl having the highest Bergman cyclization temperature, which is comparable to the Pd(II) square-planar set, while the ZnLX2 compound with X = I shows the lowest Bergman cyclization temperature (144 °C), similar to the Cu(II) derivatives. Moreover, for the planar constructs, the R group has little influence on the cyclization temperatures; however, for the tetrahedral ZnLX2 compounds, the steric influence of the R group plays a more significant role in the cyclization reaction coordinate by influencing the stability of the precyclized intermediate. This complex set of results is best interpreted by a combination of steric contributions and electronic interactions between the halogen through space (in the case of Zn(II)) and through bonds (in the case of Pd(II)) and the π orbitals of the endiyne fragment. In contrast, for Cu(II) systems, the distorted square-planar geometry permits neither direct through space nor symmetry-allowed through bond communication between the orbital partners, and thus little variation in Bergman cyclization reactivity is observed.

Density functional theory (DFT) has been used to study electronic perturbations induced by ancillary halogen ligation within metalloenediyne constructs, and the subsequent affect upon thermal Bergman cyclization temperatures. To isolate electronic from geometric components of Bergman cyclization thermodynamics, model diamine- and diphosphine-enediynes (L = 1,6-diamino- or 1,6-diphosphino-cis-1,5-hexadiyne-3-ene) of Mn(II), Cu(II), Zn(II), and Pd(II) with ancillary chloride ligands have been examined computationally and compared to more complex ethylenediamine-based metalloenediyne frameworks of the form MLX2 (X = Cl, Br, I; L = 1,4-dibenzyl-1,4-diaza-cyclododec-8-ene-6,10-diyne) with distorted square-planar (Cu(II)), Td (Zn(II)), and D4h (Pd(II)) geometries. In the latter systems, the ethylenediamine linkage restricts the conformation of the enediyne backbone, causing the alkyne termini separation to be nearly independent of metal geometry (3.75−3.82 Å). Within the Zn(II) family, steric effects are shown to induce conformational changes on the cyclization potential energy surface (PES) prior to the Bergman transition state, introducing distinct electron−electron repulsive interactions. Multiple metal and ligand conformations are also observed on the Cu(II) metalloenediyne cyclization PES. In contrast, square-planar Pd(II) compounds exhibit overlap between the out-of-plane halogen lone pairs and metal d orbitals, as well as the enediyne π system, reminiscent of an organometallic “push−pull” reaction mechanism. These systems have significantly higher predicted activation barriers toward cycloaromatization due to enhanced electron repulsion.

The electronic and vibrational Raman spectra of octa-substituted (R = –SC10H21) Co- and Cu-porphyrazines are reported in their solid-state, mesophase, and isotropic liquid forms, as well as in THF solution. Their electronic spectra are composed of traditional Soret (CuS10 = 355 nm, CoS10 = 347 nm) and lower energy Q-bands (CuS10 = 669 nm, CoS10 = 639 nm), as well as a weaker, functionality-specific sulfur n → porphyrin π∗ feature (CuS10 = 500 nm; CoS10 = 447 nm). In contrast to the broad Q-band for CoS10 in all three neat phases, the lower energy analogue for CuS10 is markedly sharper in the microcrystalline state, but similarly broadens in the mesophase, indicative of long range macrocycle π–π interactions that persist even into the liquid state. The resonance (λ = 647 nm) and off-resonance (λ = 785 nm) Raman spectra of these materials in each phase exhibit four diagnostic vibrations; the Cα–Nm stretch (∼1540–1553) cm−1, Cβ–Cβ stretch (∼1450 cm−1), Cα–Cβ–Np stretch (∼1300–1315 cm−1), and Cα–Cβ stretch (∼1070 cm−1). For CoS10, these vibrations systematically shift to lower energy upon melting, while those for CuS10 collapse to degenerate sets. The differences in the electronic and vibrational profiles as a function of temperature suggest that the mesophase structure is governed by strong axial Co–S interactions for CoS10 which template macrocycle π–π stacking, while for CuS10 the same contacts exist, but they are phase dependent and markedly weaker. These inter-porphyrazine interactions are, therefore, responsible for the distinct differences in the melting and clearing temperatures of their respective mesophases. Finally, based on these diagnostic spectroscopic signatures, a photo-thermal, phase-switching mechanism is demonstrated with λ = 785 nm excitation at reduced temperatures, leading to the ability to spectrally monitor and phase change with a single photon source.Electronic and Raman spectroscopy of Co- and Cu-porphyrazine liquid crystals in all three phases reveal subtle, inter-macrocycle structural detail regarding metal–sulfur and π–π association within the layers. Photo-thermal laser excitation can disrupt this association and phase transition these materials, simultaneously monitoring their in situ state by Raman spectroscopy.

Reaction of 2,3-dioxochlorins with benzeneselenic anhydride (BSA) results in the formation of unusual ring-contracted azetine derivatives that further react with BSA to afford porpholactones.

Photolysis of the Ni(II), Cu(II), and Zn(II) 2-diazo-3-oxochlorins generates 4-membered rings containing azeteoporphyrins.

Tetradentate metalloenediynes with strong imine and weaker thioether coordination serve as a geometrically non-rigid switch to drive thermal Bergman cyclization.

Time-dependent density functional theory shows that the photoreactivities of copper and zinc metalloenediynes derive from multi-configurational excited states involving the enediyne and pyridine π systems.

The Bergman cyclization of simple diethynylporphyrinic-enediynes exhibits a double activation barrier to the formation of Bergman cyclized product. Addition of H-atom acceptor accelerates the formation of the picenoporphyrin, indicating that the second barrier is rate limiting.

Isostructural d10 metalloenediynes of Cu(I), Pd(0) and Ag(I) exhibit metal-dependent variations in their thermal Bergman cyclization temperatures which correlate with differences in their alkyne termini separations.

The photochemical reactivities of 3-hydroxy-1,2,3-benzotriazine-4(3H)-one (1a) and tris[3-hydroxy-1,2,3-benzotriazine-4(3H)-one]iron(III) (1b) have been studied in solution and low temperature (5–77 K) glasses. Photoexcitation (λ345 nm) of 1a and 1b ultimately results in population of a ligand-centered excited state that releases N2. Electron paramagnetic resonance reveals the presence of S  = 1 and S  = 0 diradical intermediates upon photolysis of 1a and 1b, respectively, at 4 K. These species convert to an S  = 1/2, nitrogen-centered monoradical species (aN  = 23 G) upon warming to 77 K ia H-atom abstraction from the matrix. In solution, the first intermediates observed upon photolyses (λ  = 355 nm) of 1a and 1b are oxime ketenes (5: λ  = 385, 440 nm; 9: λ  = 390, 430, 740 nm) that are formed from collapse of the diradical to generate a 4-membered β-lactam ring. The decay kinetics for the oxime ketene 5 decay can be fitted to a biexponential expression representing a parallel reaction mechanism with an element of reversibility. Thus, the data proposes the existence of an equilibrium between the oxime ketene and the spectroscopically silent β-lactam intermediate, as well as a first or pseudo first-order solvent-dependent pathway for the oxime ketene. The kinetics for formation and decay of the ketene are strongly influenced by the presence of the Fe(III) center, which leads to an increase in the lifetime of the diradical in solution, and a retarded rate of formation for the oxime ketene 9. The solution lifetimes suggest that the diradical intermediates only persist sufficiently long to react with bound solution substrates, whereas the ketene intermediates have suitable kinetic viabilities to react bimolecularly in solution.

The steric influences of the functional groups at the termini of acyclic enediynes can dramatically affect the Bergman cyclization temperatures of the resulting compounds.

Visible wavelength ligand-to-metal (LMCT) activated N2 release from tris(3-hydroxy-1,2,3-benzotriazine-4(3H)-one]iron(III) produces localized ligand radical intermediates capable of cleaving DNA and represents a new chemical approach to photonuclease design for biological applications.

Thermal Bergman cyclization of Pt(II) dialkynylporphyrins reveals a marked reduction in the cyclization temperature relative to the free base and Zn(II) derivatives. In contrast, photogenerated 3ππ* population produces no detectable Bergman photocyclization, suggesting that the photoreactivities of the related free base and Zn(II) derivatives occurs via the 1ππ* state.

Current approaches toward modulation of metal-induced Aβ aggregation pathways involve the development of small molecules that bind metal ions, such as Cu(II) and Zn(II), and interact with Aβ. For this effort, we present the enediyne-containing ligand (Z)-N,N′-bis[1-pyridin-2-yl-meth(E)-ylidene]oct-4-ene-2,6-diyne-1,8-diamine (PyED), which upon chelation of Cu(II) and Zn(II) undergoes Bergman-cyclization to yield diradical formation. The ability of this chelation-triggered diradical to modulate Aβ aggregation is evaluated relative to the non-radical generating control pyridine-2-ylmethyl-(2-{[(pyridine-2-ylmethylene)-amino]-methyl}-benzyl)-amine (PyBD). Variable-pH, ligand UV-vis titrations reveal pKa = 3.81(2) for PyBD, indicating it exists mainly in the neutral form at experimental pH. Lipinski's rule parameters and evaluation of blood–brain barrier (BBB) penetration potential by the PAMPA–BBB assay suggest that PyED may be CNS+ and penetrate the BBB. Both PyED and PyBD bind Zn(II) and Cu(II) as illustrated by bathochromic shifts of their UV-vis features. Speciation diagrams indicate that Cu(II)–PyBD is the major species at pH 6.6 with a nanomolar Kd, suggesting the ligand may be capable of interacting with Cu(II)–Aβ species. In the presence of Aβ40/42 under hyperthermic conditions (43 °C), the radical-generating PyED demonstrates markedly enhanced activity (2–24 h) toward the modulation of Aβ species as determined by gel electrophoresis. Correspondingly, transmission electron microscopy images of these samples show distinct morphological changes to the fibril structure that are most prominent for Cu(II)–Aβ cases. The loss of CO2 from the metal binding region of Aβ in MALDI-TOF mass spectra further suggests that metal–ligand–Aβ interaction with subsequent radical formation may play a role in the aggregation pathway modulation.