Effect of β-Substitution and β,β'-Fusion on the Formation of Boron Complexes of Porphycenes.

Boron(III) complexation was investigated in a series of β-substituted porphycenes. Unlike -arylporphycenes, these macrocycles undergo a facile complexation reaction. Upon fusion of the β,β'-positions of the porphycene ligand, the complexation resulted in fast insertion of boron, forming the -BOF complex.

Toward combined photobiological-photochemical formation of kerosene-type biofuels: which small 1,3-diene photodimerizes most efficiently?

A transition from fossil- to bio-based hydrocarbon fuels is required to reduce greenhouse gas emissions; yet, traditional biomass cultivation for biofuel production competes with food production and impacts negatively on biodiversity. Recently, we reported a proof-of-principle study of a two-step photobiological-photochemical approach to kerosene biofuels in which a volatile hydrocarbon (isoprene) is produced by photosynthetic cyanobacteria, followed by its photochemical dimerization into C hydrocarbons. Both steps can utilize solar irradiation.

3,6,13,16-Tetrasubstituted Porphycene: The Missing Link in Porphycene Chemistry.

We have introduced the first 3,6,13,16-tetrasubstituted porphycene as its tetramethoxy analogue. This substitution pattern is one of the most general patterns yet missing in this isomeric porphyrin chemistry. This porphycene exhibits intense fluorescence along with the ability to coordinate with divalent metal ions; in particular, it forms the first stable Zn(II) complex among the tetrasubstituted porphycenes.

Reactivity of the Major Product of C5'-Oxidative DNA Damage in Nucleosome Core Particles.

The major pathway for DNA damage following hydrogen atom abstraction from the C5'-position results in direct strand scission and concomitant formation of a 5'-aldehyde-containing nucleotide (e.g., T-al).

Stable Expanded Porphycene-Based Diradicaloid and Tetraradicaloid.

The synthesis of a bithiophene-bridged 34π conjugated aromatic expanded porphycene 1 and a cyclopentabithiophene bridged 32π conjugated anti-aromatic expanded porphycene 2 by a McMurry coupling strategy is presented. Magnetic measurements and theoretical calculations reveal that both 1 and 2 exhibit an open-shell singlet ground state with significant radical character (y =0.63 for 1; y =0.

Versatile Approach for Reliable Determination of Both High and Low Values of Luminescence Quantum Yields.

The determination of luminescence quantum yields by means of relative methods requires setting identical experimental conditions for both sample and reference compounds. This requirement has a critical impact on the applicability of these protocols, as it does not allow for the precise determination of low quantum-yield values using well-characterized high-quantum-yield standards. We show that using the simultaneous absorption and fluorescence-emission measurement (SAFE) approach [ Nawara and Waluk.

Fragmentation of a dioxolanyl radical via nonstatistical reaction dynamics: characterization of the vinyloxy radical by ns time-resolved laser flash photolysis.

The photochemistry of two Barton esters, one derived from a dioxolane carboxylic acid and the other from pivalic acid, was investigated by product analysis and nanosecond laser flash photolysis (LFP). As expected, photolysis of the pivalate ester resulted in formation of the pyridine-2-thiyl and the t-butyl radical. Photolysis of the Barton ester of 2,2-dimethyl-1,3-dioxolane-4-carboxylic acid, on the other hand, revealed a complex multi-step fragmentation.

Four-component zinc-porphyrin/zinc-salphen nanorotor.

An off-axis supramolecular rotor was composed of four components: a zinc-porphyrin based stator with four phenanthroline stations and a zinc-salphen based rotator were self-assembled with DABCO and four copper(i) ions to furnish the rotor ROT-2 in quantitative yield. The DABCO serves as a connecting axle between the rotator and the stator, while the rotator is additionally connected to two copper(i)-loaded phenanthroline stations of the stator via its two pyridine terminals (N → [Cu(phen)]). For the thermally activated rotation both N → [Cu(phen)] interactions have to be cleaved.

Influence of Rotator Design on the Speed of Self-Assembled Four-Component Nanorotors: Coordinative Versus Dispersive Interactions.

Four-component nanorotors are prepared by the self-assembly of stator [Cu(4)] with its four copper(I)-loaded phenanthroline stations and various rotators carrying one, two, or three pyridine terminals. The fourth component, 1,4-diazabicyclo[2.2.

Solving the puzzling competition of the thermal C(2)-C(6) vs Myers-Saito cyclization of enyne-carbodiimides.

The mechanism of the thermal cyclization of enyne-carbodiimides 7a-c has been studied computationally by applying the DFT method. The results indicate that enyne-carbodiimides preferentially follow the C(2)-C(6) (Schmittel) cyclization pathway in a concerted fashion although the Myers-Saito diradical formation is kinetically preferred. The experimentally verified preference of the C(2)-C(6) over the Myers-Saito pathway is guided by the inability of the Myers-Saito diradical to kinetically compete in the rate-determining trapping reactions, either inter- or intramolecular, with the concerted C(2)-C(6) cyclization.

Conformational Slippage Determines Rotational Frequency in Five-Component Nanorotors.

Several five-component nanorotors ROT-3 that rotate at different rates were prepared by adding phenanthrolines of distinct lateral size as brake blocks to the four-component nanorotor ROT-2. The brake blocks interfere with the 180° rotor causing the rotational frequency to drop from 97 kHz to 5 kHz. The effect of the rotating brake blocks on the rotational frequency in ROT-3 is accurately predicted by a nanomechanical model called "conformational slippage".

Mechanistic Information from Nonstationary Points.

The thermal cyclization of enyne-carbodiimides substituted at both the alkyne and carbodiimide terminus showed two curved Hammett correlations (log k/k0 against σp) that were fully reproduced by DFT (density functional theory) computational results. The latter suggest a concerted mechanism, but the transition state (TS) analysis failed to reveal any mechanistic insight about the reason for a curved Hammett correlation. Instead a preTS inspection, i.

β-Octamethoxy-Substituted 22π and 26π Stretched Porphycenes: Synthesis, Characterization, Photodynamics, and Nonlinear Optical Studies.

Three meso-expanded tetrapyrrolic aromatic macrocycles, including 22π and 26π acetylene-cumulene bridged stretched octamethoxyporphycenes and octamethoxy[22]porphyrin-(2.2.2.

β-Tetrachlorotetramethoxyporphycenes: positional effect of substituents on structure and photophysical properties.

We report the regiospecific synthesis of the first chloro-substituted porphycenes as two positional isomers of β-tetrachlorotetramethoxyporphycene. The positional effect of the substituents on these isomers could be clearly distinguished in their structure and photophysical properties.

β-Decamethoxysapphyrin and Its N-Benzyl Analogue.

The synthesis of a highly electron-rich decamethoxysapphyrin and its 27-N-benzyl analogue is reported for the first time. The effects of β-methoxy and 27-N-benzyl substitution on structure, anion binding, absorption, and electrochemical properties were explored in detail. Upon 27-N-benzyl substitution, counteranion-induced structural deformation arises in the diprotonated state, which could be clearly noticed both in solution (1)H NMR study and solid-state structural analysis.

β-Octakis(methylthio)porphycenes: synthesis, characterisation and third order nonlinear optical studies.

A novel electron deficient β-octakis(methylthio)porphycene, along with its Zn(ii) and Ni(ii) derivatives, was synthesized for the first time. The macrocyclic structure exhibits core ruffling with a largely red shifted absorption band (∼750 nm) and also a large enhancement in the third order nonlinear optical response.

A one-pot multistep cyclization yielding thiadiazoloimidazole derivatives.

A versatile synthetic procedure is described to prepare the benzimidazole-fused 1,2,4-thiadiazoles 2a-c via a methanesulfonyl chloride initiated multistep cyclization involving the intramolecular reaction of an in-situ generated carbodiimide with a thiourea unit. The structure of the intricate heterocycle 2a was confirmed by single-crystal X-ray analysis and its mechanism of formation supported by DFT computations.

Nonstatistical dynamics in the thermal C2-C6/diels-alder cyclization of enyne-allenes: effect of topology.

The thermal C(2)-C(6) (Schmittel) cyclization of an enyne-allene with two aryl rings at the allene terminus experimentally leads to three formal Diels-Alder (DA) cycloaddition products, two of which (involving the dimethylamino phenyl unit) are shown to form in a nonstatistical process. DFT computations on the reaction paths reveal that the two aryl rings (Ph vs PhNMe2) do not interact in a dynamic manner as their minimum energy pathways (MEPs) are separated by a large barrier. The preferential formation of the more-hindered DA product 8 (ortho to the dimethylamino group) over the less-hindered product 9 (para to the dimethylamino group), despite the higher energy TS for 8, suggests the occurrence of nonstatistical dynamics in the cyclization onto the dimethylamino phenyl unit, though.

Nonstatistical dynamics in the thermal Garratt-Braverman/[1,5]-H shift of one ene-diallene: an experimental and computational study.

A mechanistic study of the thermal Garratt-Braverman/[1,5]-H shift of ene-diallene 6 leading to alkenes (E)-8 and (Z)-8 is reported. The product ratio was found to be temperature-independent and does not agree with the computed energy barriers (i.e.

Reversible cargo shipping between orthogonal stations of a nanoscaffold upon redox input.

The sterically shielded terpyridine was prepared, both as a new ligand and as part of the four-station nanoscaffold . Mixing of terpyridine , the parent phenanthroline and the shielded phenanthroline in the presence of Zn(2+) (1 : 1 : 1 : 1) furnished quantitatively the inverse HETTAP complex [Zn()()](2+) by self-sorting, while in the presence of Cu(+) the HETPHEN complex [Cu()()](+) was preferred (89%). Due to the akin coordination preferences of Cu(2+) and Zn(2+), the above self-sorting was implemented for Cu(+)/Cu(2+) on nanoscaffold , the latter equipped with the binding motifs of (PhenAr2) and (TerpyAr2).

Quantification of nonstatistical dynamics in an intramolecular Diels-Alder cyclization without trajectory computation.

Experimental and computational (DFT) investigations reveal that enyne-allenes with an aryl group as probe at the allene terminus follow a dynamic non-IRC Diels-Alder cyclization pathway. Starting from two separate C(2)-C(6) (Schmittel) transition states (TS), two distinct reaction paths originate that share a common diradical intermediate, however, without mixing! Because the momentum of the initial TS is transmitted into product formation, we suggest a simple protocol without trajectory computations to estimate the fraction of molecules that follow nonstatistical dynamics: It was calculated from the partitioning at the TSs, as derived from DFT computations, and the experimental ratio. The thus-determined percentage of dynamically reacting molecules only slightly depends on the depth of the intermediate well but rather on ΔΔG(‡) of the initial and the follow-up transition states.

β-Octamethoxyporphycenes.

Porphycene with eight methoxy substituents at its β-positions was synthesized for the first time in three steps from 3,4-dimethoxypyrrole. The presence of methoxy groups increases its hydrophilicity as evident from their increased solubility in methanol. Among its metallo-derivatives, the Pd(II)-complex displays efficient singlet oxygen quantum yield (73%) and hence can be a potentially good photosensitizer for photo-oxidation, DNA cleavage, and photodynamic therapy (PDT).

Microwave-vacuum drying of flax fiber for biocomposite production.

Flax fiber is one of the important bast fiber available in North America which has low density and good mechanical properties for reinforcing various polymers to develop industrial biocomposite. But the hydrophilic nature of the fiber leads to poor adhesion between the fiber and the polymer matrices which, in turn, leads to poor dimensional stability. To enhance the adhesion between polymer matrix and fiber, chemical treatments of the fiber are necessary.